Foamy viruses--a world apart.

Foamy viruses (FVs) or spumaviruses were described for the first time in the early 1950s in cell cultures derived from monkey kidneys. Later, FVs were isolated in several mammal species such as cats, cattle and horses. Highly prevalent in non-human primates they are not naturally present in humans, although several cases of simian-to-human transmissions have been described. Interestingly, the replication strategy of FVs differs in many aspects from that of other retroviruses, presenting features that are closely related to pararetroviruses, exemplified by the hepatitis B virus (HBV), but also characteristics that are closely related to yeast retrotransposons. These characteristics led to the creation of a distinct viral subfamily by the International Committee on Virus Taxonomy in 2002; the Spumaretrovirinae.