Thursday, 5 February 2015

Cases of Ebola virus infection can be exported any old time...

I'm adding my two cents on the issues around remaining vigilant about Ebola virus disease (EVD) cases. 

There are far fewer weekly EVD cases than there used to be but it remains absolutely essential to "kill off" this particular highly-passaged Zaire ebolavirus variant. In other words, push new cases down to zero per day in all three countries, keep it there for 42-days, and thus declare all three nations free of Ebola virus transmission.

Apart from the obvious desire to see these countries rid of this horrible and deadly pestilence, another, less likely thing to consider is that more spillovers to other countries can still happen at any time. And apart from the costs, the reaction from a certain country to its first imported case, just does not bear living through again.

Whether human cases were just kicking off, or after they began accruing at an exponential rate of hundreds per day, the hotspot countries have been the source of export of a case to another country. 

That said, in my opinion we are in a much better global position today than we were six to twelve months ago. We can much more effectively engage and thwart the spread of infection from an EVD case that appears on our doorstep because we now know Ebola virus is out there and can hop on a plane, and many countries and regions within countries have done something to prepare for that rare arrival. Some countries were already in a better position than others, simply because they have (relatively) huge healthcare 
processes in place and are now aware of how to help, and how quickly to respond, should a foreign neighbour acquire a case. 

None of that is to say zero spread in other countries is a given in the near future; humans being humans, accidents and mistakes will always happen. But we are just very unlikely to see EVD spread in a new country to the extent that we saw last year. Hopefully I'm not being too naive on that call.

If we look at the images below, it's plain to see that EVD cases were exported from these countries both early on and late in the outbreaks and later epidemic. Guinea being slightly more of a culprit than the other two countries of intense and widespread transmission (Liberia and Sierra Leone).

Guinea's Ebola virus disease experience. The approximate time at which 
another country receives a person infected by Ebola virus, most likely acquired
from within Liberia, are indicated by an arrow.
Click on graph to enlarge.
Sierra Leone's Ebola virus disease experience. The approximate time at which 
another country receives a person infected by Ebola virus, most likely acquired
from within Liberia, are indicated by an arrow.
Click on graph to enlarge.


Liberia's Ebola virus disease experience. The approximate time at which
another country receives a person infected by Ebola virus, most likely acquired
from within Liberia, are indicated by an arrow.
Click on graph to enlarge.