Simian foamy virus

The simian foamy virus (SFV) is a spumavirus closely related to HIV, the virus that causes AIDS. 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 and monkeys through hunting bushmeat.

Description
The simian foamy virus is endemic in African apes and monkeys. They all seem to be passive carriers in a "Typhoid Mary" scenario. There is no evidence so far that it does them any harm. 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 non-human primate.

While this only accounts for 1% of the population, this detail is alarming to some groups that fear the outbreak of another AIDS-like epidemic.

SFV causes cells to fuse with each other to form so called syncythia, or more figurative, "giant cells" and look, on a slide, like foamy bubbles, hence its name. It has been tentatively linked to several diseases but without any real evidence.