Why is the current Ebola outbreak different from previous outbreaks?

Question

I don't know if this question has an answer at this time, but I would like to know if there is some biological reason why the current Ebola outbreak is so much more complicated and widespread than in the past. Traditionally it has been initially very virulent and has then has rapidly waned. I hope what I am saying is accurate, and if so why dont we see the same pattern now ?

Answer 1

This is too long for a comment, so I put this in here: The main reasons are sociological. From the data I have read so far, this outbreak (actually these are two independent outbreaks, one in West-Africa and another one -not connected- in the Democratic Republic of Congo) is not exceptionally deadly in terms of Ebola. The death rate is about 60% which is extremely high compared to other diseases, but Ebola had reached up to 90%...

I think the main differences are that this outbreak struck in a much more populated area which has a very poor health care system (if you can call it like this at all). Then it happened in a border region, I recall reports about a traditional funeral of a Ebola victim which infected visitors, some of them crossed the border afterwards.

Then it was completely underestimated in the beginning, because a lot of cases stayed unknown. This led to a wider spreading as people who got sick infected relatives and medical personnel subsequently. And although the reaction has been powered up a lot since then, it is still not adequate to contain the outbreak.

Former outbreaks happened in rural areas which where easier to contain with a smaller number of personal, which is not possible this time. If you want to read further about this, I recommend the blog of Tara C. Smith which has been doing research about Ebola for some time and also worked in crisis response teams. Especially interesting are these two:

• A historical perspective on Ebola response and prevention
• Addressing more Ebola myths

Answer 2

For some background, it is essential to know that Ebola is actually a group (genus) of ebolaviruses, each with different fatality rates. There are five known species of Ebola, and four are known to cause disease humans (WHO: Ebola virus disease; wikipedia).

The known species of Ebola includes:

• Zaire ebolavirus (or just ebolavirus)
• Sudan ebolavirus
• Bundibugyo ebolavirus
• Tai ebolavirus (only one known human case)
• Reston ebolavirus (can infect but does not seem to cause disease in humans)

Zaire ebolavirus is the deadliest strain (with Sudan second), and also the one that is causing the current outbreak. A table of all known ebola outbreaks can be found in the WHO report (WHO: Ebola virus disease), which shows that the historical fatality of the Zaire strain has been between 44% and above 90%.

From my limited understanding, when dealing with ebola it is essential for infected individuals to be identified early so that they can get intensive care (most importantly intravenous fluids because of dehydration), but also to prevent further spread. This is probably what has failed during this outbreak, but another problem is also that the size of the outbreak has put tremendous strain on an already weak healthcare system. These outbreaks have also occurred in well populated areas in countries with very weak governments, that also lacked experience in dealing with ebola (both in the administration and among the population).

In many former outbreaks, the initial death rate is very high since early victims are found at late stages of the disease, but when the outbreak is more controlled the death rate drops due to supporting care of infected individuals. I don't know to what extent this has been the case during the current west african outbreak. However, the overall fatality rate of the current outbreak is 52% (tabulated Aug. 28 2014), with 44% in Sierra Leone and 66% in Guinnea (WHO: Ebola virus disease update - west Africa), and this lies well within the normal fatality rate of the Zaire ebolavirus.