Ebola followup NEW!

Joao Vasconcelos Costa jcosta at pen.gulbenkian.pt
Tue Jan 30 03:01:26 EST 1996


Giovanni Maga wrote:
> 
(...)
> This quotation per se,i.e. when extrapolated from a precise context and
> when not read in terms of molecular evolution, surely gives the idea that
> Ebola will very probably mutate into a more dangerous form. But we know
> that the mutations that appear within a population are selected by the
> enviroment. They should confere an advantage to the virus, to be *fixed*
> in a new strain. If they are neutral, then they will be diluted into the
> gene pool, never emerging (except if they are linked to another selected
> mutation). If they confers a negative phenotype, they will be lost. This
> mechanism DOES NOT imply that positive mutations must go in the sense of
> higher mortality. It is entirely possible, on the other way round, that
> adaptative mutations in viruses will REDUCE the mortality of the infected
> host and also the severity of the symptoms. This because a well adapted
> virus could have more advantage not in affecting too severely its host or
> killing it too fastly.
(...)

A typical example: African swine fever virus lives endozootically
in Africa, causing inapparent infections of wild boars. When the
disease appeared in Europe for the first time, in 1957 and later
in 1960, it killed practically all the infected pigs, appearing as
a hyperacute disease.
Although being a DNA virus, it has a high variability, due to the
recombinogenic properties of the virus. In the Iberian peninsula,
where the virus established itself until recently, the disease pro-
gressively changed its character to a much milder disease, so that
lately virus or antiviral antibodies could be frequently found in
apparently healthy animals.

-- 
***  JOAO VASCONCELOS COSTA, MD, PhD
***  Instituto Gulbenkian de Ciencia - Oeiras, Portugal
***  mailto:jcosta at pen.gulbenkian.pt



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