A paper recently published by Science online documents the spread of Ebola from Guinea to Sierra Leone. The spread of the virus can be followed by genetic sequencing of virus, as mutations accumulate as the virus is passed from host to host. The scientists document over 300 mutations among 99 viral genomes sequenced.
The data is consistent with a single transmission from an unknown animal to a human (believed to be a two year old child in Guinea) with human to human transmission thereafter.
The genome of Ebola is rather simple, consisting of genes for only six proteins. Mutations have occurred in all six genes, although there is a concentration of mutations in the viral NP gene. The current study does not address the functional significance of the mutations, although a number of the mutations would result in altered proteins.
Sadly, five of the researchers who contributed to the Science study have died in the Ebola outbreak.
A rapid mutation rate would be expected in an RNA virus like Ebola. In general, most mutations are not adaptive, but a worry is that natural selection during exponential spread of the virus might lead to a virus that is even more contagious, particularly since humans (up until now, anyway) have not been the natural host of Ebola.
One might also hope that spread into the human species would attenuate the virus, since a good virus does not rapidly kill its host. However, as long as the spread is exponential (doubling time of epidemic is about 30 days, but probably accelerating), there is no selection pressure to become less lethal, while its victims are still plentiful.
A separate Ebola epidemic now seems to have started in the Democratic Republic of the Congo, with 13 cases now confirmed. Senegal has also now recorded its first case, a student who crossed into the country of Guinea, despite the border being officially closed. Senegal is a major hub for business and aid agencies in West Africa. There is also a suspected case of Ebola now inBrussels, a Doctors without Borders volunteer who recently returned from West Africa.
The World Health Organization now has an action plan to contain the virus, which they think will take 6 to 9 months. However, with the epidemic doubling every month, it is clear that tens of thousands will likely die before this is over, making this epidemic more lethal than all of the previous infections combined.
Hopefully, vaccines and drugs, now in accelerated development will prevent this virus from following HIV out of Africa and becoming endemic worldwide.
