The genetic stability of Ebola virus

PSE evans at ahabs.wisc.edu
Fri Jul 28 16:08:00 EST 1995


     Has anybody read the current issue of the "Emerging Infectious
Diseases" issue (published by the CDC, available on-line at
http://www.cdc.gov/ncidod/EID/eid.htm)?  

I quote from the article "Reemergence of Ebola Virus in Africa" by Sanchez
et al:

"... analysis of the genetic profile of the virus was especially important
to understanding the epidemiology of the Kikwit outbreak.  Within 48 hours
of receiving the specimens, sequence analysis on the PCR DNA (528 bp)
amplified from the glycoprotein gene derived from four different patients
showed that the Ebola virus was a Zaire subtype that differed from the
original 1976 strain in four bases (<1%). No differences were seen when
the polymerase gene PCR products (~350 bp) from those four patients were
sequenced, which indicated that they had been infected with the same
virus. Three days later, sequence data from expanded analysis of the
entire glycoprotein gene were compared with those of the original 1976
Yambuku isolate (9) and showed that the overall difference between these
Ebola viruses was less than 1.6%. Such little change in viruses that
caused outbreaks of disease at extreme ends of Zaire separated by a span
of nearly 19 years, may indicate that the genomes of Ebola viruses (and
filoviruses in general) are unusually stable and have evolved to occupy
special niches in the wild." 
  

Does it surprise anybody that an RNA virus that has been replicating in
the wild for almost 20 years has accumulated very few variations at the
nucleic acid level?  Sanchez et al do not comment about the resulting
proteins, so many or all of these mutations may have been silent.  

Is this the kind of variation that would be expected from an RNA virus
over such a time period due to genetic drift (ie: neutral evolution")?  
Is there any data about genetic drift in filoviruses, or other RNA
viruses?

Does the lack of genetic changes imply anything about Ebola's natural
reservior?   

Peter



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