The primary mode of transmission for FIV is deep bite wounds whereas FeLV is
easily spread by casual contact such as grooming and shared water bowls; experts
disagree as to whether FIV can be spread by casual contact. FIV attacks the
immune system of cats, much like the human immunodeficiency virus (HIV) attacks the immune system of human
beings. FIV and HIV are both lentiviruses, however, neither can infect the
other's usual host: humans cannot be infected by FIV nor can cats be infected by
HIV. Because biting is the most efficient means of viral transmission,
free-roaming, aggressive male cats are the most frequently infected, while cats
housed exclusively indoors are much less likely to be infected.
FIV infected cats are often unnecessarily euthanised. A vigilant pet owner
that treats any secondary infections can make the difference. An infected cat
can often live a nearly normal life span. The chance that an FIV infected cat
will pass the disease onto other cats within a household is less than 2% as long
as there is no fighting or biting. Keeping infected cats separated from disease
free cats is the only sure way of preventing the spread of the disease.
FIV can infect other feline species, and in fact in some large wild cat
species, such as African lions, the virus is commonly present. However, unlike
in domestic cats, the virus does not necessarily cause disease in these species,
perhaps because these species have acquired, during evolution, mutations that
confer resistance to it.