Category Archives: Africa

Has #Ebola Death Toll Surpassed Malaria in West Africa?

In the earlier days of the West African Ebola outbreak, it was not uncommon to hear people note that we should not panic about Ebola because, after all, far more people are killed from Malaria than Ebola. This is of course an irrelevant argument. That is like telling a person who has lost their family in a tragic airplane accident that it isn’t so bad because, after all, far more people die in car crashes than aircraft crashes. For example, on August 5th, James Bell write in the Guardian, in a piece called Concerned about Ebola? You’re worrying about the wrong disease:

Since the Ebola outbreak began in February, around 300,000 people have died from malaria, while tuberculosis has likely claimed over 600,000 lives. Ebola might have our attention, but it’s not even close to being the biggest problem in Africa right now. Even Lassa fever, which shares many of the terrifying symptoms of Ebola (including bleeding from the eyelids), kills many more than Ebola – and frequently finds its way to the US.

I’m not picking on James Bell here. A lot of people said things like this, and the facts are true, though as I said, there is almost always (actually, in exactly N-1 scenarios within a given domain of scenarios) an argument that goes like this, and it really isn’t particularly relevant unless one is tasked with dividing up a fixed set of resources that will be used for a fixed set of problems. Resources rarely come that way and problems are rarely solved that way. As I pointed out earlier, consider the thought experiment where you have $10,000,000 that you want to give to either developing an Ebola vaccine, or a Malaria vaccine. Since billions have been spent on developing a Malaria vaccine and there still isn’t one, your donation would be a drop in the bucket. Retrospectively, it would be equivalent to something like the combined costs of couriers and mail by researchers working on a Malaria vaccine over the last few decades. Or the cost of coffee and donuts in the break room. Or conference travel fees. Or something like that. The point is, a bunch of millions of dollars might actually produce an Ebola vaccine given the starting point we have now, or at least, move us a good deal in that direction.

But now, we can ask if Ebola in the countries that are heavily affected right now is still “minor” compared to Malaria.

This is a matter of numbers and the numbers are hard to come by. James Bell notes that between February and July, inclusively, there had been over 300,000 malaria deaths, I assume world wide. So the comparison is not really relevant; we should be looking at what is happening specifically in, for instance, Liberia, Guinea, and Sierra Leone (or the three combined perhaps). Comparing world wide figures to a regional outbreak is a bit like reducing the Malaria death rate by shifting from numbers from countries that have endemic Malaria to include the global population.

It is hard to know how many people die of malaria every year, and the quality of the data varies considerably from country to country. A fairly recent study (here’s a discussion of it) suggests that an older estimate of 600,000 deaths per year should be doubles to 1,200,000 deaths per years. Having worked and lived in a region with some of the worst malaria (measured numerous ways) for several years, I can easily accept a doubling of numbers. If we assume that 1.2 million is right, by the way, Bell’s number of 300,000 is actually conservative.

Using data from that malaria study and WHO’s Ebola data, we can make some comparisons. I’m including all the information so you can check my work.

Here we have data from Liberia, Guinea, and Sierra Leone. The population number and malaria deaths per year are both from the aforementioned study and pertain to 2012. Then I divided malaria deaths per year by 12 to get a monthly value. I’m more comfortable working in months than years because an Ebola outbreak is normally short lived, and the number of deaths changes dramatically from month to month.

Following this we have the total number of Ebola deaths per country (summed in the right hand column as are the above mentioned data) and the approximate number of months of the outbreak. Then, the total deaths divided by the number of months. This constitutes a low-ball estimate of deaths per month from Ebola for the given expanding outbreak. Here we can see that in the comparison between Malaria and Ebola, it is not clear that one is a greater threat than the other (142:92, 49:67, 145:144).

Then we have the August-only monthly number of deaths. Here we dee that Ebola is huge compared to Malaria. So, back when people were saying “Malaria is worse,” in late July and early August, Ebola was starting to prove them wrong.

The last two numbers are calculated for all three countries combined. Here we are going out on a limb, and it is better statistically to crawl out on a thicker limb than a thinner limb. I made some estimates here, and those numbers conform to what is being talked about by WHO and others. If Ebola continues to spread at its current rate the daily number of new cases could be between 150 and 300 by the beginning of January. I state these as low vs high estimates, but actually, they are both conservative. Multiplying this by 30 days in a month, and dividing by 2 to approximate the ca 50% mortality rate, we have conservative numbers for Ebola that leave Malaria in the dust. Even if the doubling of estimated Malaria death rates should be doubled again, Ebola will be a bigger factor than Malaria.

Liberia Guinea Sierra Leone Total
Population 3,954,977 10,068,721 5,696,471 19,720,169
Malaria Deaths Per Year 1706 586 1734 4,026
Malaria Deaths Per Month 142 49 145 336
Ebola Deaths Total 508 400 461 1,369
Months of outbreak 6 6 3
Monthly average Ebola deaths 92 67 144 303
August Ebola Deaths 644 148 224 1,016
Estimated Janurary Ebola Deaths (low) 4,500
Estimated Janurary Ebola Deaths (high) 9,000

So that is why we should stop saying that Ebola is not Malaria, so relax about Ebola.

More on Ebola:

Update on West Africa's #Ebola Outbreak: Getting worse

The news is bleak. I don’t have a lot of confidence in the reported numbers. At one time it was said that on a nice Saturday in the summer, four out of five cars driving around in downtown Boston were looking for a parking place. This is somewhat like the situation in Liberia and possibly other affected areas. There may be as many Ebola victims driving around in taxis looking for a clinic as there are in clinics. Or maybe a fewer. Or, maybe more. Maybe a lot more.

But, we have to work with the data we have. There are two charts based on the information provided by WHO for up through September 6th. I’ve projected each data set out 90 days. Since there is no abatement in frequency of new cases, and in fact the number continues to increase on average, and since WHO is claiming that the situation in the worst hit areas is pretty much out of control, a 90 day projection seems reasonable. In other words, there is no reason to think that the relative rate of new infections is going to change because of any outside intervention or internal change in the situation.

The first chart shows the number of new cases. This varies a great deal from report to report. Some of that variation over time is probably real, reflecting the internal complexities of disease spread. But I suspect it is mostly administrative. If a bunch of cases don’t get into one report, the get into the next report. This explains a nearly perfect alternation between increase and decrease between successive reports.

Screen Shot 2014-09-10 at 1.03.44 PM
The second chart shows the number of cases over time, accumulated. This Projected outwards, we can guess that by around the beginning of 2015, there will have been over 10,000 people who have been infected by Ebola in West Africa (including Nigeria and Senegal as well as the main area of the outbreak), and over 5,000 deaths. Since I know you are curious, if this is projected out over a year or so, the number of infected people goes to between 60,000 and 70,000. I have no idea if this is realistic.

Screen Shot 2014-09-10 at 1.02.24 PM

The situation is bad and getting worse.

#Ebola in West Africa: Update

WHO has put out very few updates in the last several days. The most current update is August 28th, and it pertains to information from August 26th and before. Based on that update, the total number of cases (confirmed, suspected, etc.) is ow 3069 with 1552 deaths. The number of new cases per day may be increasing, may be decreasing; hard to say at this point. Here’s the new cases per day since the second week of July:

Screen Shot 2014-09-02 at 11.08.33 AM

Senegal now has one case, a person who traveled there from Guinea. He had contact with a lot of people including health workers and family before it was figured he may have Ebola. There is no word from the Congo since I last wrote about it, at least from WHO.

I’m sure Murphy’s Law will apply and WHO will issue new information soon after this post goes up, so expect an update very soon.

DR Congo #Ebola Outbreak

We can now be pretty sure that the Ebola outbreak in the DR Congo is not an extension of the West African outbreak. The index case seems to have gotten the disease from a mammal she butchered, and the numerous other cases seem to stem from contact with her primary as health care workers and family members. I don’t think we have enough information yet to assess this outbreak vis-a-vis the genetics of the Ebola itself.

From WHO:

On 26 August 2014, the Ministry of Health, Democratic Republic of the Congo (DRC) notified the World Health Organization (WHO) of an outbreak of Ebola virus disease (EVD) in Equateur Province.

The index case was a pregnant woman from Ikanamongo Village who butchered a bush animal that had been killed and given to her by her husband. She became ill with symptoms of EVD and reported to a private clinic in Isaka Village. On 11 August 2014, she died of a then-unidentified haemorrhagic fever. Local customs and rituals associated with death meant that several health-care workers were exposed and presented with similar symptoms in the following week.

Between 28 July and 18 August 2014, a total of 24 suspected cases of haemorrhagic fever, including 13 deaths, have been identified. Human-to-human transmission has been established and includes the health-care personnel who were exposed to the deceased pregnant woman during surgery (one doctor and two nurses) in addition to the hygienist and a ward boy, all of whom developed symptoms and died. Other deaths have been recorded among the relatives who attended the index case, individuals who were in contact with the clinic staff, and those who handled the bodies of the deceased during funerals. The other 11 cases are currently being treated in isolation centres.

#Ebola: Second, possibly third outbreak, West African outbreak growing

The number of people known or suspected to be infected with Ebola in the West African outbreak is increasing, and the rate at which it is increasing is increasing. About 40 new cases are being reported per day on average, but the number of new cases has been going up by a few a day.

However, it is still unclear that these numbers represent what is actually happening on the ground. There is little confidence that the WHO has a good idea of who is currently stricken with the disease, and efforts to contain those who are have had mixed results.

A second outbreak is now occurring in the DR Congo (formerly Zaire). This is a second separate outbreak. So, it is NOT correct to say that Ebola has spread into the Congo. It didn’t. It emerged there independently.

What are the chances of that happening? I have long maintained that the conditions for Ebola spreading into human populations include factors that make the overall chance of that happening, for a large region, go up enough for multiple simultaneous epidemics to be more likely than chance might suggest. Perhaps I’ll discuss my reasoning for that another time. In any event, the DR Congo outbreak, about which we know very little so far, appears to be a different strain of Ebola, so this is not the Wester African Ebola spreading to Central Africa.

There are reports of a third outbreak of an unknown disease that might be Ebola also in the DR Congo. But that could be a lot of things. Including Ebola… so we shall see.

Also, there is one new case in Nigeria, after a period of several days with no new cases.

#Ebola UPDATE-Rate Of New Cases Rises, Note to Laurie Garrett, is there a case in South Africa?

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h2>New for August 16th

I will try to keep new information and updates in the same post for a while until I have a chance to do a comprehensive re-overview of everything.

The 16 August update from WHO indicates a large uptick in the daily number of cases. Over the two days of the most recent reporting period an average of 76 cases per day have been identified as confirmed, probable, or suspect, with a total of 76 deaths over that period of time.

Good news is that the situation in Nigeria doesn’t seem to be developing. There were no new cases over the this reporting period, and one death. The last new cases in Nigeria were reported on August 6th for the period between August 2 and august 4. So over ten days without a new case in Nigeria probably means that the “outbreak” is burned out.

Meanwhile, there is another suspected/possible case in another country. This has happened a number of times, where a suspected Ebola case is identified. Hong Kong, the Philippines, the US, etc. have had these, and of all of the cases none have been shown to be Ebola except possibly one, and that is in Saudi Arabia did not work out either, the Saudi case was not Ebola. The new possible case is in South Africa.

The updated graph showing the increase in daily cases is inserted below as before.

And now, a personal note to Laurie Garrett. Laurie wrote this post, and I wanted to comment on it but the commenting system there did not work for me. (Perhaps one has to be subscriber.)

Laurie,

I love you work. It was your book, based on your Thesis at the Kennedy School, that got me interested in tropical diseases. Well, that and at the same time going to the tropics, running a makeshift health clinic there, and getting some of the diseases. I often point people to your earlier writing on influenza to find out about the true pre-Wakefield anti-vax movement, to see how the US handling of Swine Flu made it very difficult if not impossible to have a sensible national vaccine program that was not byzantium (which is what we have now)

But I think your article on not being scared enough about Ebola has some problems. I agree that this outbreak has not been taken seriously. I nave noted in my own writing that WHO and CDC, even, are coddling the public about some of this. I also noted, which I don’t think you did, that Ebola “in Africa” is Ebola in America already. One of my neighbors died of Ebola, and one of his relatives in Liberia did as well, and some of my other neighbors lost relatives, I’ve heard. This is because Liberians and other Africans live in communities with one foot in Africa and one foot here. Those who died of Ebola did so in West Africa, but they are still neighbors who live here part time or African-based relatives of neighbors who live here full or part time.

So yes, for many reasons, be concerned.

Here’s where I don’t agree with you.

First, while the cures and vaccines are truly not deployed as you point out, you are more negative than necessary. In fact you are hyperskeptical. A common phrase in hyperskepticism is “there is not a shred of evidence of…” Well, there is not a shred of evidence that my four year old is upstairs eating a peanut butter and jelly sandwich instead of the nice dinner I made my family, but that does not mean it is anywhere near impossible. In fact, he’s probably eating a peanut butter and jelly sandwich, though I can produce not a shred of evidence from here in my basement that he is. There is in fact good scientific reasons to think that the cures that have been brought to the brink of testing are likely to work, and Ebola is not like Malaria (not even close) or even viral cousins such as Influenza when it comes to vaccine prospects. The prospects are good, if only someone would work on them.

Next problem: No, Saudi has not Ebola. No, there have not been a number of actual, non-panic-based cases of Ebola outside of the affected area other than my neighbor and those he infected, in Nigeria.

Next:No, Nigeria does not actually seem to be having an outbreak. No new cases in ten days is good news. It may be over there.

We’ll see about South Africa.

But yes, I do agree with you on two other points. First, all of the health care molecules have moved to one corner of the proverbial room suffocating other health care efforts in the affected countries. This is a big deal. Second, yes, it really is possible despite major media and major organizations insisting it is highly unlikely for this outbreak to seed an outbreak pretty much anywhere in the world. Not that likely. But I won’t say that there is not a shred of evidence that it could happen (citing that every single case outside the zone for which confirmation was completed has not worked out). I’ll just say that we have no freakin’ clue how likely it is, but it is not zero and the consequences would be dire.

So, I don’t want to tone-troll your article. You went for breathless, and you got to breathless, and that’s probably a good choice, you have the credibility to pull it off and people need to hear much of what you said. But no, Ebola is not leaking out of the zone now, and yes, there is better hope I think for the existing (as in on the table, not deployed or even tested) cures and vaccines (and by the way, the “ethical considerations” are a red herring, that is true for all drug development, but seems only mentioned frequently with respect to Ebola).

End of rant. Again, love your work.

Cheers,

Greg

<

h2>End of August 16th update

Probably.

Yesterday I made the optimistic statement that the number of new cases a day may be leveling off, as for two reporting periods in a row, representing five days, the new cases were about half of the previous reporting period, normalized to a per-day estimate.

Today’s report from WHO covers two days and indicates 128 more cases, so the number of new cases per day for the latest known period is actually higher than at any previous time during this outbreak. Pursuant to this I’ve replaced the pertinent graphic below. I was optimistic, but I also provided caveats. The caveats won.

Is the current Ebola Outbreak subsiding?

At some point, the Ebola Outbreak in West Africa has to slow down and stop. The disease is too hot to not burn itself out, and it has no human reservoir. Ebola accidentally broke into the human population earlier this year or late last year, probably once (see below), and despite the regular increase in daily reported cases over the last several weeks, the disease must at some point begin to level off.

The latest two updates from WHO indicate that the Ebola outbreak may be leveling off now, tough it is too early to be certain. The following graph shows the approximate number of new cases reported per day by WHO. This is calculated by taking the number of new cases in a report and dividing by the number of days covered by that report. A given estimate of daily new cases may be quite off for a number of reasons. First, even if there is a long term upward or downward trend, there is likely to be a lot of randomness in the data. Second, this is the number of cases reported in that time period, not the number of cases that manifest. It is likely that some cases manifest during the reporting period are not recorded yet, and cases manifest for the prior reporting period are included in the current reporting period. Over several reporting periods this would, obviously, even out, but a given number of days in a reporting period may be off by a day or so. So, these caveats mean that we should be very cautious in interpreting this graph.

NEWER GRAPH:
Ebola_2014_outbreak_cases_per_day_Aug_15Update

Note that what appears to have been a fairly steady increase in number of cases, with about the same number of ups as downs but with the ups adding to a higher sum, since late June, has been followed by two reporting periods with decreases in numbers of new cases. Note also, however, that in late May the number of new cases per day went up fairly quickly then dropped again before a new steady rise occurred. If we use a moving average of 3 data points, which would combine sets of 2-4 days each to obtain something close to a 10 day effective moving average, the upward trend is more evident than any recent downward trend:

Screen Shot 2014-08-12 at 2.44.43 PM

The next two WHO reports may clarify this trend.

Mortality Rate Is Decreasing

The mortality rate for this outbreak continues to decrease slightly, which is probably a result of increase effectiveness of the response to the outbreak, despite all the news stories about how things seem out of control.

EbolaOutbreak_2014_MortalityRate_Aug_11_update

The current mortality rate is dropping below 55% given confirmed, probable, and suspected cases and deaths. But the rate varies across different categories. The outbreak-long rate for all cases and all deaths is currently 55%, and looking only at confirmed cases and deaths, it is 56%. The mortality rate for all previous African Ebola outbreaks, taking total reported cases and total reported deaths, is 66%.

This is the largest outbreak ever, and then some

Currently there are over 1,800 confirmed, probable, or suspected cases reported in the West African outbreak, and 1176 confirmed cases. Using just the confirmed cases, to be conservative, the present outbreak is 277% larger than the next largest outbreak, which was in 2000 in the Gulu, Masindi, and Mbarara districts of Uganda, with 425 cases. The total number of confirmed cases for the present outbreak represents about 49% of all of the prior African Ebola outbreaks combined.

Patient Zero Identified?

Patient Zero, who we assume is the person to whom the disease jumped from its usual animal reservoir, directly or indirectly, may have been a toddler in Guinea. The two year old child died in December 2013, which is quite a bit before this outbreak came on everyone’s radar screen, and after which it was fairly low level for a while.

I’ve long maintained that a likely way for Ebola to get into other species is from ground dwelling mammals, such as chimps, gorillas, or forest antelopes and duikers, ingesting or mouthing the discarded wadges of fruit previously handled by Ebola-carrying fruit bats. From such non-human animals the Ebola would then enter human populations from people butchering bush meat. In this case though, I wonder if the toddler may have been a direct recipient, picking up and mouthing fruit-bat spit covered fragments of fruit found on the ground. A parent’s worse nightmare, apocalypse style, to be sure.

The Famous Untested Drug

There has been a bit of complaining about my use of the term “drug” or “cure” for ZMapp, a drug that was developed to fight Ebola but not used until just now. Some have said it is not a drug until it is tested and deployed, and until then, it is a possible cure and not a real cure.

This is wrong. A “possible cure” is when you take an existing compound or substance, apply it to a pathogen or an affected animal model, and get a hopeful result. This possible cure can then be further developed to make, most of the time, nothing because these things generally don’t work out. Or, to make a cure. Which can then be tested.

In the case of the treatment now given to three patients (two survived one died), the cure was developed for Ebola based on some pretty solid science and prior experience with similar type cures working for similar diseases, successfully, in the past. The cure was not in “hopeful” or “possible” phase, but rather in developed but untested phase. The WHO convened an emergency panel of experts, yesterday, which decided that the cure should be used in the field under certain circumstances. So now there is an untested but developed cure for Ebola being deployed in West Africa. The WHO discussion on this is here.

Ebola Outbreak Continues, Probably Worsens, Perhaps Spreads

The WHO came out with a new report today with the latest figures on Ebola. These numbers take us to the end of July. There are two bits of bad news.

First, the number of new cases is high, as high as any prior report (but keep in mind that these reports cover uneven time periods). There are 163 new cases and 61 new deaths, bringing the total number of confirmed cases and deaths to 1009 and 574, with the total number of confirmed, probable, and suspected to 1,603 cases and 887 deaths.

Second, Nigeria is now in the mix. There was previously only one case in Nigeria, a Liberian man who contracted Ebola in Liberia and died in Nigeria. But now there are three probable new cases in Nigeria and one probable Death (none confirmed). According to WHO, of the Nigerian cases, “…one is a health-care worker and one is a Nigerian who travelled to Guinea — and a suspected case in a nurse.” I’m not sure if four cases (if confirmed) is an outbreak yet. If all the cases have quirky explanations having to do with other countries, than this not be anything new. But this could also be the beginning of the spread of the disease into Nigeria.

Here’s a graphic of the cumulative number of caeses by country (not counting Nigeria) and the total so far. These are all cases (confirmed, probable, suspected). You will notice that Sierra Leone is contributing the largest number of cases, but Liberia is contributing the strongest uptick in what seems to be an increase in rate of new cases (more on that below).

Ebola2014_Aug4_update_cases_by_country

This graphic shows the number of cases over time and the number of deaths over time (totals). Note that the gap between the two is widening, suggesting a lowering of the mortality rate.

Ebola_2014_total_cases_and_deaths_Aug4_update

To try to get a better idea of mortality rate over time, here’s a graph of the an estimate mortality rate based on the total number of cases and the total number of deaths for each of the WHO reports (which come out every few days) over time. There is no sense in calculating a simple correlation coefficient or R-squared value for these data because each data point is based on the adjoining data point plus or minus (they are not independent) but one suspects a proper time series analysis would suggest a decrease.

Ebola_2014_mortality_rate_over_time_per_report_August_4_update

Keep in mind that as the number of cases or deaths shifts along the confirmed-probable-suspected axis, the morality rate can change quite a bit. One might expect that the least certain category would have the lowest mortality rate because one is more likely to incorrectly assign a patient to having the illness than one is to attribute a death to the disease. Here’s the behavior of mortality rate across the different categories of available data. Note that the rate for “new” is probably going to be biased downwards if the rate of new cases is going up (because the number of people who have not died yet, but will, is greater than if the rate is going down); that 37% figure, therefore, is nothing to get excited about. Also keep in mind that “Total” is a combination of the other three categories. Given the vagueness of some of the data, one could say that a good estimate of mortality is 55%, but a large number of cases have been added in the last several days, so it might be better to say that the mortality rate in this outbreak is at least 55%.

Ebola_2014_Mortalit_Rate_Across_Categories_Aug_4_update

It seems that the number of new cases is going up but this is hard to count. The WHO reports cover different time periods, and I’ll wager that even within that constraint the data are a bit funky given the on the ground situation. Over the large scale of time it is clear that the number of new cases is rising. This graph shows the number of new cases per month, but keep in mind that the dates of the various reports do not match the ends of the months cleanly so there is room for error her. These are all cases.

Ebola_2014_New_Cases_Per_Month_Aug_4_Update

Since the rate of infection can go up or down over a matter of days, or a least, more rapidly than would be reflected in a month by month accounting, here’s the same data by half-month:

Ebola_2014_New_Cases_Per_Half_Month_Aug_4Update

And, because that does not capture important detail here’s the data again by WHO report, keeping in mind that the length of time covered by each report varies.
Ebola_2014_Rate_New_Cases_Per_Report_Aug_4_update

Actual epidemiologists use much more sophisticated methods for analyzing this sort of data, but this should give you the idea that while the rate of new cases varies a lot from report to report, there is a general upward trend in the number of new cases.

This Ebola outbreak is not going away soon, it seems.

Other posts on Ebola:

<li><a href="http://scienceblogs.com/gregladen/2014/08/04/there-is-a-cure-for-ebola-we-have-it-we-just-dont-let-anyone-use-it/">There is a cure for Ebola, we have it, we just don’t let anyone use it.</a>

<li><a href="http://scienceblogs.com/gregladen/2014/08/04/ebola-outbreak-continues-probably-worsens-perhaps-spreads/">Ebola Outbreak Continues, Probably Worsens, Perhaps Spreads</a></li>
  • Ebola Perspective: Risks of spread to the US and elsewhere
  • <li><a href="http://scienceblogs.com/gregladen/2014/07/27/ebola-outbreak-in-west-africa-some-basic-information/">Ebola Outbreak in West Africa: Some basic information (Updated)</a></li>
    

    Ebola Perspective: Risks of spread to the US and elsewhere

    LATEST UPDATE HERE

    It is true that this particular outbreak of Ebola has taken health officials somewhat by surprise. It is impossible to know, but I suspect that if you had asked a few ebola experts, a year ago, if there could be an epidemic that would spread across three or four countries, infect a couple thousand people, and last with no sign of letting up for a few months (that is the current situation, more or less), most would say no, probably not, though it is within the range of possibilities. Does the fact (assuming it is true) that this particular Ebola outbreak is unprecedented and kinda over the top even for an over the top disease like Ebola mean that there is something different about this Ebola or this outbreak? That is a question that may be on your mind.

    Another concern is the possibility that since this outbreak involves populations with more mobility including via aircraft than previous outbreaks that the Hollywood Scary Fiction scenario could happen. Here’s how that goes. Someone infected with Ebola, but not symptomatic, gets on a long plane flight, maybe with a few legs and layovers. They start to get sick on the first flight, and after changing planes twice and being very sick for the last leg, they get off the plane and collapse, are taken to a local hospital very far form the Ebola epidemic where no one is expecting Ebola, spend a little quality time in the waiting room, and are finally put in an in-patient unit in a room with two or three other people. Hundreds of people have been near this person. The patient threw up in the bathroom of each of the airplanes he was on, and later someone filled the sink in the same bathroom and used the water in the basin to wash his or her face. He drooled on his pillow while sleeping in his seat, and somehow the person next to him ended up with that pillow and slept on it for an hour. He threw up on some nurses and some orderlies had to clean up his diarrhea in the hospital a few times. And so on. By the end of all of this, a half dozen people are infected with Ebola, including a personal trainer, a grade school teacher, and four nurses. That’s just the first scene in the movie, long before the character played by Morgan Freeman is on the scene, and when the character played by Morgan Freeman shows up, you know things are getting serious.

    A variant of that concern is this: Two aid workers helping with the Ebola epidemic, Americans, catch Ebola and are very ill. It is decided to fly them back to the United States for treatment. This brings Ebola into the US, where it could spread to other people because, well, because Ebola! But is this a realistic concern or just a Hollywood studio’s wet dream?

    At this point in the epidemic we are seeing the usual bifurcation of reaction among the general public, sciency bloggers, and the press. On one had there is growing panic, people either being very scared, for real, or people or press outlets shopping fear on the market because it sells. On the other hand there is the stern corrective statement that all your fears are invalid, Ebola isn’t going to get out of hand, isn’t going to get to the US, there is nothing to worry about.

    At the same time there is a parallel and equally bifurcated rhetoric about the bigger picture, about dealing with Ebola as a public health problem. On one hand you have people asking for a vaccine, or some sort of cure, to address this thus far orphaned disease, because they are worried about it. On the other hand you have people noting that Malaria kills millions a year, and most years, Ebola kills no one, and when there is an outbreak, it only kills dozens or hundreds, except this last time which is still only many hundreds dead and the very low three figures sickened.

    Every one of the above mentioned concerns is valid and invalid at the same time, and every one of the reactions to the current Ebola crisis is both correct and incorrect at the same time. Let me explain.

    What is the meaning of the bigness and badness of the Ebola 2014 outbreak?

    There may be new things to learn about Ebola from this outbreak, but that won’t be until after the dust has settled and scientists have had a chance to look more closely at the data, and the virus, and everything else. But there does not seem to be anything new or unusual about the disease, and I don’t think there is any major difference in how the outbreak is being handled. But there are two differences from earlier outbreaks, one of which is certainly relevant to the large size of this event, the other perhaps important but as yet unclear.

    <li>Most, really all, prior outbreaks occurred in areas where the affected population was relatively thinly scattered on the landscape and the movement of people in and out of the area was minimal and slow. This outbreak is happening where there are much larger concentrations of population and a lot of movement of people.  This has simply upped the chance of transmission in close quarters (higher density) and made for opportunities for spread to previously unaffected settlements.</li>
    
    
    <li>There has been resistance to health workers coming into some villages.  This story is spreading around as though it was a major thing, that large areas were becoming dangerous or difficult for health workers to enter or work in.  We need to be cautious in drawing conclusions from the news.  It is very easy for westerners to slip into blaming the natives for their own difficulties and contrasting native ignorance with Great White Smartness.  There may well be areas where this is happening or important but until there is some actual unbiased carefully collected and evaluated information on this, please don't draw conclusions.  If you hear about something that looks like a great story, there is a good chance that it is a great story.  Emphasis on "story." </li>
    

    This particular Ebola outbreak is really like all the others, but jumbo size.

    Could sick aid workers being brought to the US spread the disease here?

    No.

    You can stand in a room with a person infected with Ebola ten feet across the room from you, and stand there for hours, without a mask, and you will not, can not, get Ebola. It simply isn’t transferred that way. Clean up Ebola vomit, Ebola diarrhea, physically move Ebola victims from bed to bed, give them a sponge bath, tend wounds or other injuries, insert and remove IV’s, handle the bodies of recently deceased Ebola victims, and especially, give traditional treatment to those bodies which, as is done in many cultures, which may involve cleaning and even internal cleaning or handling of organs, etc. etc., and you’ve got a reasonable chance of getting Ebola. Even then, the number of health care workers who actually get Ebola is probably very small. Tragic and horrible when it happens, but a few out of thousands most directly exposed and at risk for months is a small number.

    The people who are being transported to the US are isolated, in negative pressure facilities, and are being handled with kid gloves. Well, latex gloves, actually. They can not infect anybody but their immediate caretakers, and those individuals are very well protected.

    There is a risk of a different sort, though. While these particular patients are being handled with great care, there are healthy helpers, medical workers or others, who have been working with Ebola patients and seem to have not contracted the disease, who are occasionally wandering off to their respective homes and, I’m pretty sure, not being quarantined. I am not sure if all the people involved in helping in West Africa are being tested or properly watched. They may be, but there is some evidence that this is not the case. I’d like to learn more about that, and I hope we don’t learn anything the hard way.

    One US based doctor has returned to the United States and decided to quarantine himself. Alan Jamison will keep himself separate from society for 21 days since his last potential exposure to Ebola.

    If he is doing this on his own, there is the implication that doctors or others who were working with Ebola victims are being allowed two wander off and commune with the rest of us with the prospect that they are infected and eventually could spread the disease. However, I’m not sure that this is true. I don’t know that Dr. Jamison was not tested, I don’t know how much exposure he had and I don’t know what the procedure is for managing this potential problem. This is one guy who may be making hay where there is no grass. Worst case scenario, though, is that a health worker gets sick, the beginnings of Ebola like symptoms emerge, and the health worker gets treated. Nobody who has been working with Ebola patient is going to get a head ache, feel like throwing up, and say to themselves, “Hmm. I wonder if I’ve got allergies or something?”

    We should be worried about people wandering off, leaving the sites of the outbreak, generally. That’s clearly how this has spread to begin with. This applies to health workers and regular people. It applies to journalists in the field. We should not assume, but we can reasonably hope, that people are doing the right thing. But even when they don’t, remember, this is not measles, which is highly contagious.

    (Also, in case you didn’t know, Ebola is of course already in the United States. See this.)

    Can the scary hollywood scenario happen?

    Yes, of course it can. There is nothing in that scenario, taken on its own, that can’t happen. Bodily fluids get around. People are confined on aircraft, share a bathroom, and occasionally eat each other’s cookies by mistake. I don’t think there is any scientifically valid way to suggest that people who are symptomatic with Ebola are anything but a nightmare on a regular airplane flight, hanging around in airports, sharing cabs, et. When I hear international health experts saying that the chance of Ebola transmission on an airplane is pretty much non existent, I want to ask them: Ok, so, you’ll be entering and leaving the sick rooms of Ebola patients, maybe taking your kids along because it’s Follow Your Parents to Work Day, and maybe even have your kid sit next to the patient in bed and read them a story, without any protective gear at all. Right? No, absurd.

    However, the crazy scenario I gave you above, with the vomit and the pillow and the bathroom, requires a lot of things to go wrong in sequence, which is pretty unlikely. Also, the worst case scenario is that a few people end up with Ebola. It would be very hard for that to spread in the US. We’re too good on our health care, even when it seems we are not. On the other hand, if an air route with a symptomatic Ebola patient is sending people to any of many other places, with high population density, little education or information about things like Ebola (or even a belief that it is not a disease you get from other people) and no monitoring, I’d worry that smaller outbreaks could show up in other countries or other cities, in West Africa, elsewhere in Africa, or beyond. You can say that chances are it won’t happen. But it did happen. Ebola is in multiple countries spreading from multiple sites in West Africa.

    I’m pretty sure the people who deal with Ebola, though, try to not take chances. Rhetoric to the contrary is to avoid panic. Avoiding panic is good, and in fact, panic is unnecessary. Ebola is not that contagious. But somewhere between being concerned and avoiding panic by making it sound like Ebola refuses to pass from person to person on air planes, there is clearly something lost in translation.

    Who cares about Ebola, it is not Malaria!

    To me this is one of the most insidious problems we have and it doesn’t just apply to Ebola vs. Malaria. Let me give you an example from an entirely different area.

    How much money have spent on the science of subatomic physics, say, just in the US. And, what are the benefits? More importantly, what were the benefits that were specified at the outset of various research projects, and which of those have been realized?

    The answer to that second question is probably zero, zero. No benefits were specified, and thus, any gained don’t count. You are probably thinking, “No, wait, what about the knowledge, and all that stuff!?? That was surely specified in the grant proposals!” No doubt, but simply advancing knowledge is not a benefit. How do I know that? Malaria! Those physicists may have advanced our knowledge, and as a side effect invented the DVD and stuff, but nobody cured Malaria. Therefore it doesn’t count.

    Sounds like an incredibly stupid argument, doesn’t it?

    Now, side step over to Ebola. Is creating, say, a vaccine to address Ebola worth it? No! Why? Because Malaria! Malaria is way bigger, kills more people, is a truly serious public health problem, Ebola is rare. So if you’ve got some research money don’t spend it on Ebola, spend it on Malaria.

    That would be the smart thing to do!

    This is also an incredibly stupid argument, for a few reasons. The only reason you can compare Ebola and Malaria is because they are both diseases. They aren’t even the same kind of disease, they don’t have the same geographical spread (though it is overlapping). But they are diseases, so when we consider spending resources on research in one, it is natural to compare to the others. But they are also two different things. If I had a million dollars in the bank of my Malaria Vaccine Research Institute and gathered all the scientists together and said, “OK, folks, until we’ve spent this one million dollars, I want you all working on Ebola instead of Malaria, K?” they would look at me funny for a while and then call my wife to take me home. Ebola is a virus, Malaria is a cellular organism. They are very different things. The expertise and lab equipment would not be in my Institute. I might as well tell my scientists to spend a million dollars working on the next generation of high definition TV. That would be cool! And, suggesting that we compare the costs and benefits of that project to working on Malaria or Ebola would be dumb.

    One of the benefits of working on a vaccine for ANY virus is advancing knowledge of vaccines for viral disease generally, and we have a lot of work to do on vaccines for viral diseases. Perhaps work on Ebola would have some great side benefits. Indeed, money spent on a vaccine for Ebola would very likely produce … wait for it … a vaccine! Money spent working on a vaccine for Malaria has thus far failed to produce squat.

    A vaccine for Ebola is probably relatively easy to develop. Ebola is not a human disease. It comes from an animal reservoir. Ebola, if hit with a vaccine in human populations, can’t evolve resistance to that vaccine (or other treatment). Humans have little or no history of immune response to Ebola, and a very long (in essence, multi million year long) history of immune response to Malaria and its cousins. Developing an Ebola vaccine would be like putting up a childproof gate in your house, where the 2 year old is Ebola and the childproof gate is the Vaccine. Developing a vaccine for Malaria is like trying to stop a squadron of Navy Seals from penetrating a drive-in theater at a date and time of their choosing.

    This is why literally billions of dollars has been spent … billions, seriously … on developing a Malaria vaccine and there isn’t one. I would venture to say that if we looked at the part of the money spent on Malaria research in general (including vaccines) that covered just couriers and postage over the years, we’d have enough to fund a full on Ebola vaccine development program. Maybe not. Maybe you’d have to add in a few percent of the money spent on conferences (which are very important, I’m not saying they are not) by Malaria scientists. There is probably more money being spent right now on retirement payments to retired scientists who spent most of their time working on Malaria than needed to build an Ebola Research Center that could get a vaccine out there in a few years. Seriously. Please don’t compare Malaria to Ebola and use that to suggest that we should ignore Ebola. The crumbs that fall off the pieces of Malaria cake at the Malaria birthday party would be enough to handle Ebola. (Bonfire of the Vanities Reference.)

    But still, why should we bother with Ebola?

    Why bother with any disease? Why not figure out which one disease causes the most mortality or morbidity, and disallow any research on anything else? Then, when that is solved, move on to the next one. There are several reasons to not do this. First, it might not be possible to solve the big bad disease quickly, or ever, so the entire research program would spin its wheels forever. Second, the second and third and way down to the tenth or twentieth diseases are all real disease people really get and that really cause suffering. While the argument that spending excessively on a rare disease is a poor choice, spending a modest amount on a very addressable problem that is also small is exactly what we should be doing. Third, you can and should think of some of this as pure research. Pure research is where scientists seek out the answers to questions in a special category of question: Questions that scientists ask. No other criteria need apply. Scientist tend to ask questions that are at the edge of knowledge, or perhaps that are hanging around this or that water hole of ignorance. Scientists ask the questions they ask because they have two characteristics: There is something unknown, and there is something about that unknown thing that is knowable. With research. Usually.

    Now go back to Ebola again. Doesn’t somebody want to know about Ebola? Of course they do. Ebola is one of a family of viruses, the Filovirus family, that includes some pretty benign viruses and a handful of nasty ones (Ebola isn’t the only one). In the past there was a lot of research interest in the filovirus family for use as a biological weapon. Imagine making an Ebola like virus that spread though the air! You could really kick ass, militaristically speaking, with such a weapons. But, fortunately, we as a species have recently decided to not view biological weapons as legitimate. Research on biological weapons continued, of course, long after they were outlawed because we assumed we needed to “understand them” (make them and test them on rats) in case the other guys were making them, so we could deal with them. But I’m pretty sure most of that research has gone by the wayside as well. I would not be surprised, and I’m not much of a conspiracy theorist so I don’t want to emphasize this too much, if a lot of the work to make an Ebola vaccine was in a file drawer somewhere.

    Also, there is the simple stark reality of Ebola. If you are a typical American you may not care about Ebola because it is in a different country and won’t get here and there are other problems. But say you are like my neighbor here in Coon Rapids, Minnesota, Decontee. Decontee is Liberian. She is part of a large Liberian community here in the Twin Cities. Many Liberians are American Citizens with strong ties to Liberia. There is constant travel back and forth. I asked a Liberian guy I know where he gets his sombe (a wonderful traditional West and Central African dish) and he said “From my grandmother.” “Does she grow it?” “Yes. In Liberia. I get it when I go there.” The point is, there is a lot of back and forth. To be an American who is Liberian is to be a member of a community of people who is currently, at this very moment, threatened with Ebola. People in your community, in your family, can get Ebola. Decontee’s husband and her sister in law both got Ebola and died of it last week. Ebola is a problem that affects communities that are Diaspora that include our very neighbors and friends. It should not be an orphan disease.

    So wait, there was way too much nuance and possibly contradiction here, what am I supposed to think?

    I don’t want to tell you what to think.

    But in this case I’ll make a suggestion.

    Do not be worried about the health workers being brought back to the US. Indeed, at this point, openly worrying about this can do little more than make you look a bit dumb and a bit insensitive.

    Yes, worry about the possibility of Ebola getting “out” to pretty much anywhere, elsewhere in Africa, to the US, etc., because it can. But don’t worry too much. The chances are low. Forget about this “Oh, Ebola is not transmitted between people on airplanes” magical thinking. Of course it is. But Ebola is always hard to transmit, even on airplanes. In other words, be realistic.

    Forget about this comparison between Ebola and Malaria. When the Malaria people turn up a vaccine after spending billions of dollars of research money we can make a comparison. At the moment, Ebola is probably a vaccine-ready disease, and Malaria is not. You are comparing apples and oranges. No, worse than that. They’re both fruit. You are trying to compare, in a cost benefit analysis, the efficacy of spending money on a new car vs. working out whether or not it is worth clipping coupons when you go to the grocery store. Why are you doing that?

    But, if you are a member of a community like the various African communities in the US, then you do indeed have more of a concern. Not so much that travelers will bring Ebola to your doorstep, though that is a tiny bit more likely for you than for some others, maybe. But because your community is being directly affected because your community lives in two worlds, and one of those worlds is being invaded by a monster.

    Ebola Outbreak in West Africa: Some basic information (Updated)

    LATEST UPDATE HERE

    UPDATE: The latest numbers do not indicate a weakening of the outbreak. (See list of new cases below. Several graphs have been updated as well)
    UPDATE: More detailed discussion of transmission of Ebola
    UPDATE: I note with sadness the death of my neighbor (though I did not know him) of Patrick Sawyer, of the Liberian Ministry of Finance, who died in Nigeria of Ebola contracted in Liberia. He was on his way home to Minnesota at the time.

    There is an Ebola Outbreak currently underway in several West African countries, mainly Sierra Leone, Liberia, and Guinea. This is the most extreme known Ebola outbreak to date. The first known outbreak of this virus was in 1976, and there have been several instances since then ranging from single cases (which by definition are not outbreaks) to 425 confirmed cases (with 224 deaths in that instance, in Uganda, 2000-2001). The current outbreak is significantly larger with about double that number or more.

    There is some confusion in the press (most notably in CNN) about the nature of Ebola and perhaps about some of the details of this outbreak. Here, I want to provide some basic data to help clear some of this up. CNN reported at one point that you can get Ebola only after a person is symptomatic, and (in the same story) at any time a person is infected even if they are not symptomatic. It is probably the case that as long as Ebola is in a person’s system, they can spread it. It is only spread through contact with bodily fluids, but that is not such a hard thing to do; mucus membranes can absorb the virus, as well as cuts or other injuries. It is probably sexually transmittable. It does not appear to be airborne, but bodily fluids that are in or on needles, hospital equipment, etc. can carry the disease to another person.

    Another issue with reporting is the difference between suspected cases, likely cases, and confirmed cases. Even within the health community these numbers are all over the place because they are always changing as cases go from suspected to either eliminated or confirmed. Wikipedia and CNN both recently stated that there have been 1,093 human cases with 660 deaths so far. However, this includes both confirmed and suspected cases. There is a good chance that the total number of cases is in fact close to this, but the data are of lower than ideal quality. If we want to look at mortality rates and changes over time in this outbreak, it is better to look at a smaller subset of the better confirmed data. That’s what I’ll do here. But, when looking at the numbers, keep in mind that although most of the data I show in graphics below show several hundred fewer cases than being widely reported, the actual number of people affected by the disease over the last four months or so is probably not only higher than the cleaned up data set but also, likely higher than the reported 1,093. Furthermore, the data I’m using here only go up to July 24th.

    One of the most egregious errors at CNN is the frequent statement that Ebola has a 90% death rate, but that the current outbreak has a much lower death rate. This is rubbish. Ebola simply does not have a 90% mortality rate, and stating that the current outbreak is much lower in mortality gives the impression that this particular form of Ebola, or this particular outbreak of the disease, is somehow not as bad as usual. In fact, this outbreak is worse than any previous outbreak for several reasons. For one, it is larger. Also, it seems to be not burning itself out like most previous outbreaks did. Ebola outbreaks in the past have tended to happen in relatively isolated areas, because the population that includes victims is in close proximity to the presumed reservoir of the disease (probably fruit bats) and interacts directly with the intermediate hosts (eg. primates or other mammals that picked up the disease from fruit bats*). But there is plenty of reservoir and intermediate reservoir in some areas near major population areas. Apparently, Ebola broke into the human population in one or more areas of high population density, and this density together with relatively high mobility is allowing the disease to persist.

    The following graphs are based on data I collected from the WHO reports. For March, I use only very likely cases, for April through July, I use only confirmed cases (not available for March). And, July does not include the last week for that month (a few more days have been added to this information bringing us to July 23rd, added on July 30th).

    The following charts show the total number of cumulative cases conservatively estimated, and total number of cumulative deaths. When the outbreak starts to weaken, we would see a leveling off, but that is not indicated here (UPDATED).

    UPDATED_EbolaCumulativeCases2014

    The last several reports from WHO (including confirmed, probable, and suspect cases) are as follows:

    July 21st through July 23rd: 108 NEW
    July 18th through July 20th: 45
    July 15th through July 17th: 67
    July 13th through July 14th: 18
    July 08th through July 12th: 85
    July 06th through July 08th: 44
    July 03rd through July 06th: 50

    The exact time spans for each of these reports may not be the same, but I believe the number of cases do not overlap; each listing is a separate set of new cases. Clearly, for the last several days of available information, there is variation in, but no let up in, the number of new cases.

    Looking at the number of new cases reported (and for the most part confirmed) and the number of deaths (the same data as used to make the cumulative graphic above, but by month) we have this (Updated):

    EbolaConfirmedCasesAndDeaths2014

    Keep in mind that the data for July are short by several days.

    Another area where MSM, and for that matter, Wikipedia, could do a better job is in reporting the mortality rate for the disease. Wikipedia states that “The disease has a high death rate: often between 50% and 90%.” This is misleading because the outbreaks with 90% mortality rates are not typical, and the statement seems to be based on a set of data that includes a lot of data points one would do better to ignore. I assume CNN is taking this information (from Wikipedia or elsewhere, which perhaps repeats the Wikipedia claim) and exaggerating slightly when they say that Ebola normally has a 90% mortality rate.

    The Ebola affecting people right now in Africa is one of a handful of similar viruses known over a larger geographical range. Some of the deaths found in the larger data set of all known outbreaks are from individuals who showed up in a hospital nowhere near where they got the disease, or laboratory workers. The best way to estimate mortality rates related to the present outbreak in West Africa is to take only field cases — actual outbreaks in normal populations — in Africa only, and to not count “outbreaks” that are not outbreaks because only one person is in the sample.

    The following chart compares mortality rates for all of the “outbreaks” listed in Wikipedia page regardless of size of sample, geography, or circumstances, with only those that are African Ebola in the field. The latter set also excludes the present outbreak.

    Ebola_Mortality_Rates

    Notice that the clean data are bimodal; some outbreaks have mortality rates between 0 and 90%, others between 40 and 60%, and not much in between. Also, there are several in the all-data set that have a mortality rate of zero. This bimodality is not necessarily a persistent statistical characteristic of the sample; I could make it go away by changing the histogram intervals. But it is a convenient place to break the sample into “more severe” and “less severe” outbreaks.

    The zero cases in the full data set are all odd cases. Seven are not in Africa and include in some cases lab workers or animal handlers, and most are not African (Zaire type) Ebola. One is a scientist who caught the disease from doing a necropsy on a chimp in the Ivory Coast, examining an outbreak among the non-human primates there. There is one case where the fatality rate is 100%, but this was only one person, and the case was discovered post hoc. We don’t know if anyone else there had the disease. A 90% mortality rate occurred in a remote part of the Congo, with 143 people affected including health care workers. It appears that several individuals contracted the disease butchering non-human primates. This occurred during suboptimal conditions during the Second Congo War. One case of 88% mortality occurred early on in the history of the disease (the second known outbreak) also under very poor conditions. Although the data are too sparse to draw firm conclusions, it seems that the more severe outbreaks in terms of mortality tend to have occurred under more difficult conditions.

    Ebola probably has a very high mortality rate when an infected person gets no medical treatment, and a mortality rate closer to 50% when a person quickly gets medical attention. There is no cure, but when a patient is given IV solutions in a hospital setting the chance of survival goes way up. This might suggest that smaller outbreaks that run their course before intervention would have a higher mortality rate, or that the mortality rate would be higher near the beginning of the event. Similarly, one might expect mortality rates to be higher in the early years of Ebola than later, as treatment methods developed.

    There is some, but not much, evidence for these effects.

    The following chart shows mortality over size of the outbreak, using only the cleaned up data set:

    Ebola_Mortality_Rate_Over_Size_Of_Outbreak

    There is not a relationship between size of outbreak and mortality rate.

    This chart shows the mortality rate over time, for the cleaned up data:

    Ebola_Mortality_Rate_Over_Time

    This seems to show that lower mortality has been achieved in recent outbreaks, though the statistical significance of this is non existent. But, the data set is small. The above chart also indicates the average morality rate across all of these events, which is 64% across 18 outbreaks. Not “usually 90%” as CNN states.

    The following chart shows the approximate mortality rate for the current outbreak by month.

    Ebola_Outbrak_2014_Mortality_Rate_By_Month

    This is calculated from confirmed or highly likely cases. This is not a true mortality rate because people who got the disease in one month may have died the next month. But it does give an approximate indication of change over time in rates. The rate at the beginning of the outbreak could be high, or this large percentage could be a function of how cases were counted. In any event, this is an indication of higher mortality rates calculated at the beginning of an outbreak, and there are likely two reasons for that high rate, either or both applying in a particular case.

    <li>Early in an outbreak a number of people are affected, but live, and don't make it into the data  base because they are not identified; they got sick, got better, and went on their way. Those who died were all or almost all counted. </li>
    
    
    <li>Early in an outbreak a number of infected people are not treated with the maximum available medical attention, so more of them die.</li>
    

    The current outbreak is settling in at about 60% mortality rate. There is no indication from WHO that the epidemic is slowing down.

    UPDATE: Is Ebola Only Transmitted By Symptomatic Individuals?

    According to the usual sources (WHO and CDC for example) the following is probably true. When someone gets Ebola, typically, after a while they get sick. This means they show symptoms. If they did not show symptoms they would not be “sick” even if the virus was in them and even if the virus is multiplying in them. Presumably people are infected with a sufficient number of viroids that they become a host for the disease, the virus starts to multiply above some level that makes the person sick, and we can say at that point that they “have Ebola.” This is when the infected person is able to transmit the disease to others through bodily fluids that might come into contact with wounds or mucous surfaces in the downstream patient.

    This is what the WHO and CDC literature on Ebola says, and this has lead bloggers and news outlets to state incorrectly that Ebola is only transmitted to others when the person shows symptoms. Unfortunately this is not true in one or possibly two ways.

    It appears that people who have had Ebola, live, and get “better” (i.e., their symptoms go away) can still carry Ebola for a period of time, and in this state, they can still transmit it. What has probably happened is their immune system has started to fight the virus enough that it is attenuated in its effects, but it isn’t’ entirely gone yet. Medical personnel like to send someone home only after the virus has cleared. Even so, men who are supposedly virus free by that standard, when sent home after surviving Ebola, are told to avoid sex for several weeks because there is still the possibility of sexual transmission of the virus. Meaning, of course, that the virus is still knocking around in some individuals at this point, and still transmittable. It is not clear how likely that is to happen.

    This is very important. Most people would interpret “only transmitted by people showing symptoms” (or words to that effect) when they read it in a news outlet as meaning – well, as meaning exactly what it says. But post-symptomatic patients may still transmit the disease.

    Is it possible that pre-symptomatic people can transmit the disease too? Personally I think it is possible even if it is generally unlikely. In a disease that kills over half of those who get it, “unlikely” is not comforting. A small percentage of people who never seemed to have had Ebola, or to have been exposed to it, seem to have antibodies that would probably only develop if exposed to Ebola. Some studies have shown immune reactions to Ebola in those known to have been exposed but also known to not have gotten sick. This is important but not shocking. There are a number of different situations where a normally icky disease that makes you really sick seems to have infected a certain percentage of people asymptomatically. Are these people carriers at some point, i.e., people who have the virus in them, can transmit it to others, but don’t get sick themselves? There is no evidence to suggest that this is the case with Ebola, but the total number of known human cases of Ebola is very small and the conditions for study of the disease in the field very poor, so the safest thing to conclude is that we simply don’t know, but it is also reasonable to say that asymptomatic carriers don’t seem to be a problem, or this would likely be noticed.

    The important point here is that there is not a perfect correspondence to being infected and having symptoms, and transmission post-treatment and survival is possible and of sufficient concern that WHO and CDC assume it, so it would be unwise to make too many assumptions about pre-symptomatic transmission.

    Imagine you are a health care person addressing an Ebola epidemic. An jet liner flies over a very long flight, say 10 hours long, on Monday. On Friday five people who were on the plane come down with Ebola and you have reason to believe that they were all infected before the flight. Would you determine that it was impossible for the nearly 300 people stuck on a tube with five pre-symptomatic Ebola carriers to become infected? No. You would watch those people and test them.

    An additional point to underscore; it has been touched on but not emphasized. The symptoms of Ebola include vomiting and bleeding from places one normally does not bleed. Put another way, the symptoms of Ebola include spreading around bodily fluids. This is often how diseases spread. The disease results in a bodily reaction that spreads the disease (look up “virulence”). So, no matter what, the most likely transmission by far is during the period of symptomatic reaction to the disease, or for some time after death while the virus is still viable. That does not mean that there is no transmission before or after, but it does mean that the most obvious transmission will be from symptomatic patients or recently diseased symptomatic patients.


    • Fruit bats will drop fragments, or stones, of fruit they feed on, sometimes in discrete piles. It is almost impossible to imagine a ground dwelling frugivore, such as a chimp or a duiker, not stopping to munch on this detritus. Since Ebola is spread through bodily fluid contact and can be spread via mucous membranes, and fruit bat spit counts as a bodily fluid, I’m personally of the opinion that this is how Ebola may often transfer from its natural reservoir, where it seems to exist without harm, to other animals. Of course, I figured this out after having discovered and handled several such piles of fruit bad wadge.