Author: Daniel

Figure 1. The Ebola virus (source CDC).

This is a good question. The current outbreak Ebola is happening in a part of the world (west Africa) where death is unfortunately all too common and where diseases like Malaria or HIV are killing many more people. Why should we care more about Ebola than HIV? Wouldn’t the resources required to stop Ebola be better spent controlling mosquitos (Malaria), or providing antiretroviral drugs to HIV patients? While I think these diseases are very important, and I wish the world did put more money into all infectious diseases, Ebola is different.

Speed

Ebola is spreading at a very rapid rate with the new case numbers doubling every 20 days or so. Diseases like Malaria and HIV are not spreading at anywhere near this rate, and while very serious, are not a threat that must be stopped today. The speed at which Ebola is spreading gives us very little time to develop control measures — we just don’t have the time to develop new drugs or vaccines (they are needed). Any delay makes the problem much, much bigger. Ebola is a problem that you can’t put off for tomorrow.

Ebola is not (yet) a human disease

This is a really important difference and one we should be most concerned about. Diseases like Malaria and HIV are human diseases, while Ebola is still a zoonotic disease caused by a virus picked up from an animal. Human diseases are adapted to infecting humans and being passed efficiently from person to person. How efficient a disease is passed from person to person is described by scientists using the term R0. This term tells you how many new people a person infected with the disease will on average infect. For example, a human disease like Polio has a R0 of between 5 and 7 (i.e. each person that gets infected with Polio will infect between 5 and 7 new people in an unvaccinated population). The R0 for Ebola in this outbreak is unknown (it ranges between under 1 to over 20 depending on the conditions), but the best estimate across the region is it is in the range of 1.3 to 1.8. This is quite low for an human disease and reflects that Ebola is not very good at being passed from person to person. This is not surprising when you remember that Ebola is a virus that normally infects flying foxes (fruit bats).

The major reason Ebola is not good at getting passed from person to person is that it kills you so quickly. Once you have symptoms you are normally dead (or hopefully on the way to recovery) within 7 to 10 days and before you have symptoms you are normally not infectious. This leaves very little time for Ebola to infect the next person, in fact Ebola is about as quick at killing humans as any disease can be and still be able to spread. If Ebola killed people any quicker (say within 3 days) then its R0 would be below 1 and the virus would have died out in humans on its own and never become a problem.

The fact that Ebola is infecting and killing thousands of people despite not being very good at it is worrying. Each person that gets infected produces hundreds of trillion of new viral particles. Many of these viral particles will have mutations (mistakes) in their genome (Ebola has a genome made up of RNA not DNA like in our own genome). Almost all of these mutated viruses are losers in the sense that the changes don’t improve Ebola’s ability to spread in humans, but just like with a lottery, the more tickets you buy the greater the chance you have of winning. By letting this outbreak run wild we are effectively buying trillions of tickets in a lottery we do not want to win — the human adapted Ebola lottery. Each person infected is making it a little more likely that a new mutant Ebola strain will arise with a much higher R0.

How would a such a mutated Ebola viral strain act? This is hard to say as we don’t know how well adapted Ebola can become to humans (we are in a way running a massive uncontrolled natural experiment to see how well adapted Ebola can become to infecting humans), but do we really want to find the answer to this question? Would it be wise to let a new strain arise that say took a month to kill you (thus allowing you to infect many more people), or one where you are infectious for a couple of weeks before the normal deadly symptoms arise? If such a strain arose then all our plans for containment of Ebola in western countries would be worthless.

We know how to stop Ebola

Unlike most human disease we actually know how to stop Ebola. All we need to do is get 70% of the infected people into simple treatment facilities where they can be cared for and where they can stop infecting new people. We have done this dozen of times with previous Ebola outbreaks and it has always worked. If we do this now we won’t have to worry about Ebola as future problem beyond being vigilant if any new zoonotic outbreaks occur. If we don’t stop this outbreak then we risk letting Ebola becoming entrenched in the human population like HIV or Polio. It is rare to have the ability to stop a new disease before it gets too big to control – let’s not let this opportunity go to waste.

Economics

One area that has received relatively little attention is the economics of Ebola. Even if the case numbers stay relatively low (say under 100,000), Ebola has the ability to cause major economic damage. As we have seen in recent weeks in the USA and other western countries, even a single imported case can cause mass concern (hysteria) leading to counterproductive proposals like travel bans and stopping flights. There is a real risk that politicians will overreact to the fears of an ill informed public and introduce policies that will disrupt international trade. The world economy is very weak; Europe is in or near to recession, China’s growth is slowing, Japan’s economy is running out of steam on the back of large VAT increases, and the resource-rich countries like Australia are slowing as commodity prices fall. With global interest rates at or near zero levels there is little that the world’s central banks can do to protect the world economy from even a small slow down in trade. With a fragile world economy we don’t want to be taking risks allowing anything that could derail growth and trade to run wild. Time to get serious.

I am a scientist with a background in Microbiology and Virology and what is happening (or more importantly what is not happening) with the current Ebola outbreak is very worrying. Rather than just scare my family I thought I should do a write up about what needs to be done.

Figure 1. Scale of the Ebola outbreak October 2014 (source WHO).

Where are we right now?

Ebola is completely out of control and the case numbers are doubling every 20 days or so. It does not look like Ebola had changed (it certainly could), it has just overwhelmed the containment systems we had in place in west Africa. The hospitals in the affected areas have reached (exceed) capacity and are not able to take in any new patients so the virus is running wild (this point seems to have been reached around August). A consequence of this is we really have a very poor idea of the number of cases since no-one is recording the cases that don’t make it to hospital.

What is going to happen?

Ebola is actually a very well studied virus from an epidemiological perspective so we can model its spread quite accurately. Here is what is going to happen according to the CDC.

Figure 2. Estimated impact of delaying intervention* on daily number of Ebola cases, with and without correction for underreporting† — EbolaResponse modeling tool, Liberia, 2014–2015 (source CDC).

* Intervention: Starting on September 23, 2014 (day 181 in model), and for the next 30 days, the percentage of all patients in Ebola treatment units was increased from 10% to 13%. This percentage was again increased on October 23, 2014 (day 211 in model) to 25%, on November 22, 2014 (day 241 in model) to 40%, and finally on December 22, 2014 (day 271 in model) to 70%. Day 1 in model is March 3, 2014. The impact of a delay of starting the increase in interventions was then estimated by twice repeating the above scenario but setting the start day on either October 23, 2014, or November 22, 2014.
† Corrected for potential underreporting by multiplying reported cases by a factor of 2.5 (Table 4).
§ New Ebola patients at peak of each start date. (Note that when the intervention is started on November 22, 2014, the peak is not reached by January 20, 2014, which is the last date included in the model.)

The only thing missing from this modelling is the “do nothing” option since the CDC has assumed that we will start doing something by November 22nd (unlikely). They have also been too scared to model past January 2015.

This modelling also assumes that the virus does not become better adapted to spread in humans which could, and may even be likely, to happen. The most probable adaption would not be for Ebola to become airborne (this is only slightly less likely than pigs becoming airborne), but for the virus to slow down in the speed in which it kills people so they stay infectious for a longer period of time. A strain could arise that takes a month to kill you (rather than a week) and where you are asymptomatic, but infectious, for a couple of weeks. Such a strain would allow each patient to infect many more people before they died or recovered. One of the reasons that Ebola has not caused major outbreaks in the past is that it kills so rapidly that there is little time for each patient to infect new people. The selection pressure on Ebola to slow the speed in which it kills is extremely strong and the more people infected the more likely it becomes that such a mutation will occur.

Why did this Ebola outbreak get so bad?

This is a good question as it is not the first Ebola outbreak. The best explanation I have seen is from the discoverer of Ebola, Professor Piot, as quoted in De Spiegel.

SPIEGEL: Why did WHO react so late?

Piot: On the one hand, it was because their African regional office isn’t staffed with the most capable people but with political appointees. And the headquarters in Geneva suffered large budget cuts that had been agreed to by member states. The department for hemorrhagic fever and the one responsible for the management of epidemic emergencies were hit hard. But since August, WHO has regained a leadership role.

What do we need to do to stop Ebola?

We need to get the R0 below 1. This means each infected person needs to infects less than one new person. Right now the R0 is somewhere between 2 and 10 (i.e. each infected person is infecting between 2 to 10 new people). To get the R0 of Ebola below 1 we need to move at least 70% of infected people into properly functioning infection control hospitals. Sounds easy doesn’t it?

How do we actually do this?

This outbreak is now beyond the ability of the governments in the affected areas, the WHO, or any NGO to bring under control (the head of MSF has stated that the outbreak is now beyond their ability to deal with). There is only one option left which is full-scale military mobilisation. In practicable terms this is what needs to happen:

• The UN Security Council needs to authorise the use of all available resources to control and contain the outbreak in the affected countries and surrounding regions including the use of international military force. This needs to be done as soon as possible (days not weeks).
• Those countries with the ability to do this (the USA mostly) need to move to full-scale military mobilisation (i.e. war level)*. This may require conscription of the required healthcare workers, but if we are lucky and act soon we might be able to get by with just volunteers.
• Start an outside-in Ebola containment/infection control process in the region. This will require putting large numbers of troops and medical personnel on the ground in the surrounding countries and then moving into the worst affected areas as more hospitalisation capacity is brought online. The key is to fight Ebola where it can be controlled so that it does not spread further and not waste our resources fighting it in those areas where we can’t get the R0 below 1 (i.e. where we can’t achieve the required 70% hospitalisation rate).

*Why do we need mobilisation? In theory we don’t, but politics in the USA is so toxic that unless this is treated as war it won’t be possible to get the required resource on the ground quickly enough. An example of this is the 3000 troops announced a couple of weeks back that were going to be sent to Liberia to help have still not left as they are being held up by congress as politics is played.

What do I think will actually happen?

A lot of dithering and token efforts from the UN and the rest of the world until January 2015 when wholesale panic sets in and we then move to full-scale mobilisation. If we are lucky the virus won’t have mutated and will only destroy west Africa. By the end of 2015 a 100 million people could be dead and the world in a massive recession as international trade grinds to a halt. Of course I could be wrong (I certainly hope I am), but based on what I know and what I see happening (or more importantly not happening) I am not that hopeful. Time to get serious.