Simian foamy virus
|Simian foamy virus|
|Group:||Group VI (ssRNA-RT)|
|Species:||Simian foamy virus|
The simian foamy virus (SFV) is a spumavirus. Its discovery in primates has led to some speculation that HIV may have been spread to the human species in Africa through contact with blood from apes, monkeys, and through handling or consuming bushmeat.
About 70–90% of primates born in captivity have SFV. Animals with SFV do not display symptoms or become ill. However, recent research suggests some primates that contract SFV would become predisposed to other viruses. People who have had contact with nonhuman primates can become infected with SFV.
Although the simian foamy virus is endemic in African apes and monkeys, no evidence indicates it causes any harm to primate hosts. Its ability to cross over to humans was proven in 2004 by a joint United States and Cameroonian team which found the retrovirus in gorillas, mandrills, and guenons; unexpectedly, they also found it in 10 of 1,100 local Cameroon residents. Of those found infected, the majority are males who had been bitten by a primate. While this only accounts for 1% of the population, this detail alarms some who fear the outbreak of another zoonotic epidemic.
SFV causes cells to fuse with each other to form so-called syncytia, or more figurative, "giant cells", which look, on a slide, like foamy bubbles, hence its name. It has been tentatively linked to several diseases, but without any real evidence.
Cospeciation of SFV and primates
The phylogenetic tree analysis of SFV polymerase and mitochondrial cytochrome oxidase subunit II (COII has been shown as a powerful marker used for primate phylogeny) from African and Asian monkeys and apes provides very similar branching order and divergence times among the two trees, supporting the cospeciation. Also, the substitution rate in the SFV gene was found to be extremely slow, i.e. the SFV has evolved at a very low rate (1.7×10−8 substitutions per site per year). These results suggest SFV has been cospeciated with Old World primates for about 30 million years, making them the oldest known vertebrate RNA viruses.
The SFV sequence examination of species and subspecies within each clade of the phylogenetic tree of the primates indicated cospeciation of SFV and the primate hosts, as well. A strong linear relationship was found between the branch lengths for the host and SFV gene trees, which indicated synchronous genetic divergence in both data sets.
By using the molecular clock, it was observed that the substitution rates for the host and SFV genes were very similar. The substitution rates for host COII gene and the SFV gene were found out to be (1.16±0.35)×10−8 and (1.7±0.45)×10−8 respectively. This is the slowest rate of substitution observed for RNA viruses and is closer to that of DNA viruses and endogenous retroviruses. This rate is quite different from that of exogenous RNA viruses such as HIV and influenza A virus (10−3 to 10−4 substitutions per site per year).
Researchers in Cameroon, the Democratic Republic of Congo, France, Gabon, Germany, Japan, Rwanda, the United Kingdom, and the United States have found that simian foamy virus is widespread among wild chimpanzees throughout equatorial Africa.
Humans exposed to wild primates, including chimpanzees, can acquire SFV infections. Since the long-term consequences of these cross-species infections are not known, it is important to determine to what extent wild primates are infected with simian foamy viruses. In this study, researchers tested this question for wild chimpanzees by using novel noninvasive methods. Analyzing over 700 fecal samples from 25 chimpanzee communities across sub-Saharan Africa, the researchers obtained viral sequences from a large proportion of these communities, showing a range of infection rates from 44% to 100%.
Major disease outbreaks have originated from cross-species transmission of infectious agents between primates and humans, making it important to learn more about how these cross-species transfers occur. The high SFV infection rates of chimpanzees provide an opportunity to monitor where humans are exposed to these viruses. Identifying the locations may help determine where the highest rates of human–chimpanzee interactions occur. This may predict what other pathogens may jump the species barrier next.
- Wolfe ND, Switzer WM, Carr JK, et al (March 2004). "Naturally acquired simian retrovirus infections in central African hunters". Lancet 363 (9413): 932–7. doi:10.1016/S0140-6736(04)15787-5. PMID 15043960.
- Switzer WM, Salemi M, Shanmugam V, et al. (March 2005). "Ancient co-speciation of simian foamy viruses and primates". Nature 434 (7031): 376–80. doi:10.1038/nature03341. PMID 15772660.
- Details are published July 4 in the open-access journal PLoS Pathogens.
- Switzer WM, Bhullar V, Shanmugam V, et al (March 2004). "Frequent simian foamy virus infection in persons occupationally exposed to nonhuman primates". J. Virol. 78 (6): 2780–9. doi:10.1128/JVI.78.6.2780-2789.2004. PMC 353775. PMID 14990698.
- Public Health Agency of Canada
- U.S. FDA Blood Products Advisory Committee Meeting, December 13-December 14, 2001
- Simian foamy virus at the US National Library of Medicine Medical Subject Headings (MeSH)