The foamy viruses differ from other groups of retroviruses in that they do not appear to cause disease in their natural hosts or in other species. We are using mouse strains in order to understand why foamy viruses are not pathogenic. We hope that by learning which cells are infected and which cells express virus in vivo , as well as the details of the host immune response, we can understand better host mechanisms for limiting viral growth and pathogenic effects. This work should be useful for designing strategies for prevention and treatment of other retroviral diseases. The foamy virus genome is very similar to those of other complex retroviruses such as HIV, leading to classification in the Retroviridae family.
Foamy viruses appear to occupy a unique niche quite distinct from all other groups of retroviruses.
For example, the mechanism of expression of their reverse transcriptase from a specific, spliced mRNA has not been seen in any other reverse transcriptase encoding virus. In addition, unlike either HIV or HBV, HFV requires the Env proteins, but not the Pol proteins, to bud from cells. We have also found that the genome of HFV is more likely to be DNA than RNA clearly setting it apart from other retroviruses.