Foamy viruses (FVs) are animal retroviruses which present several characteristics linking them to pararetroviruses such as hepadnaviruses, such as the production of a spliced mRNA for the synthesis of Pol and a late occurring reverse transcription leading to the incorporation of infectious full length viral DNA in virions.  In vitro, FV infection induces the formation of syncitia which harbor multiple vacuoles, given the cell culture a foam aspect.  In contrast, in their natural hosts, FVs are thought to be non pathogenic.  These viruses are present in several mammalian species but are not naturally present in humans, although accidental zoonotic infections have been reported.