Feline foamy virus
FeFV belongs to the family of retroviral Spumaviruses to which FIV also belongs.
Feline foamy virus (FeFV) is a rare group of feline viral diseases and has been isolated from both healthy and diseased cats but are considered non-pathogenic. Two serotypes have been reported for FFV designated FUV7-like and F17/951-like. Serotype-specific neutralization has been shown to correlate with sequence divergence in the surface (SU) domain of the envelope protein (Env).
The primary mode of transmission of those common viruses remains undefined. In a large survey recently conducted, both FeFV and FIV infection rates were found to gradually increase with age, and over 70% of cats older than 9 years were seropositive for FeFV. In domestic cats, the prevalence of FeFV infection was similar in both sexes. In feral cats, FeFV infection was more prevalent in female cats than in male cats.
Although both FeFV and FIV have been reported to be transmitted by biting, the patterns of infection observed are more consistent with an interpretation that transmission of these two retroviruses is not the same. The gradual increase in the proportion of FeFV-infected animals is consistent with transmission of foamy viruses by intimate social contact between animals and less commonly by aggressive behavior. Although vertical transmission of FeFV from queen to kitten has been reported, this mechanism did not appear to be the predominant mode of transmission in the two populations of cats studied. The strong association of FeFV infection with age of the cat found in this study is consistent with the results of a previous study with 286 healthy male domestic cats by Pedersen et al. and may explain the diversity of earlier reports on the prevalence of FeFV infection in cat populations of unspecified age (range 7 to 100%).
Infectious FIV and FeFV are present in the saliva of many infected cats, and transmission of both FIV and FeFV through experimental bites has been reported. In previous reports on the prevalence of FIV infection in domestic cats, a greater proportion of male cats than female cats was infected with FIV. The results of this study are consistent with those reports and consistent with the hypothesis that the major mode of transmission of FIV is by aggressive behaviour such as biting between male cats. In contrast to the results for FIV, the prevalence of naturally occurring FeFV infection was found to be similar in both female and male domestic cats, suggesting that the predominant mode of transmission of FeFV is not by biting, as for FIV, but that transmission occurs slowly with intimate, social contact between individuals. This hypothesis also applies to the population of feral cats, in which a significantly greater proportion of female feral cats (52%) than male feral cats (23%) was infected with FeFV. The major mode of FeFV transmission proposed in this study is similar to that proposed previously for bovine foamy virus, for which infection is believed to be spread through saliva, mainly by social licking between infected and non-infected individuals.
Social interactions between individual animals in domestic cat populations are different from the interactions observed in feral cat populations and are greatly influenced by the desexing of domestic cats. Over half of the domestic cats in this survey were recorded by their veterinarian as having been desexed. The prevalence of FeFV infection was significantly higher in young domestic cats which were recorded as having been desexed (44%) than in domestic cats of the same age group which were not recorded as having been desexed (15%). This observation suggests that either the visit to the veterinary surgery for desexing (and association with other cats) or behavioural modifications following desexing are associated with an increased risk of FeFV infection in cats.
It is interesting that although saliva appears to be a medium for transmission of both FeFV and FIV, the major mode of transmission in cats appears to be different for these two retroviral groups. One possible explanation for this difference is that FIV requires contact with peripheral blood mononuclear cells for initial infection, while FeFV can directly infect and replicate in the cells of the oropharyngeal mucosa. This hypothesis is supported by two previous studies that have reported that transmission of simian (monkey) foamy virus type 1 into rabbits and bovine foamy virus into cows is more effective when virus is administered by the oropharyngeal route than by systemic inoculation.
- Mühle, M et al (2011) Immunological properties of the transmembrane envelope protein of the feline foamy virus and its use for serological screening. Virology 412(2):333-340