Feline leukemia virus (
FeLV) is a
retrovirus that infects
cats. FeLV can be transmitted between infected cats when the transfer of saliva or nasal secretions is involved. If not defeated by the animal’s
immune system, the virus can be lethal. The disease caused by this virus is a form of cancer of the blood cells called lymphocytes (a
leukemia).
The signs and symptoms of infection with feline leukemia virus are quite varied and include
loss of appetite, poor coat condition, infections of the skin, bladder and respiratory tract,
oral disease,
seizures,
lymphadenopathy (swollen lymph nodes),
skin lesions,
fatigue,
fever,
weight loss,
stomatitis,
gingivitis, litter box avoidance,
pancytopenia, poor grooming, recurring bacterial and viral illnesses,
anemia,
diarrhea, and
jaundice
Cats infected with FeLV can serve as sources of infection. Transmission is related to the subgroup (see below). Cats can possibly pass the virus between themselves through saliva and close contact, by biting another cat, through a litter box or food dish used by an infected cat (rarely happens), and from milk during nursing. Transmission can also take place from an infected mother cat to her kittens, either before they are born or while they are nursing.
Initially thought to survive only about 2 hours in a dry environment, and about 48 hours in a damp environment (such as a litter box)
[citation needed] a new paper published by Cornell vets (
http://www.vet.cornell.edu/FHC/news/) titled "Can FeLV survive in the environment?" likened FeLV to HIV (which can survive for several weeks in the environment
[citation needed] and is structurally related to FeLV). In the absence of any meaningful studies in to the survival of FeLV in the environment, it may be sensible to exercise caution when assuming FeLV survival in the environment is so short (2 hours to 2 days).
FeLV causes
immunosuppression in pet cats, and there is also evidence for existence of the virus in larger wild cat populations also (e.g.
lynx,
cheetahs, and
lion)s. Overwhelming
epidemiologic evidence suggests FeLV is not transmissible to either humans or dogs. This statement is based on the fact that approximately one pet dog in five lives with a cat, and all pet cats live with humans (some 60 million pet cats in the
USA). It is species-specific, and does not infect other animals, such as dogs (in fact, there is apparently no canine version of this disease at all).
Approximately 0.5% of pet cats are persistently infected with FeLV, but many more pet cats (>35%) have specific
IgG antibodies which indicate prior exposure and subsequent development of
immunity instead of
infection. Transmission of FeLV is mainly via
saliva and friendly behaviors, such as sharing feeding bowls and mutual grooming (as distinct from fighting and biting).
There is strong evidence kittens under 4 months of age are susceptible to infection, but by 8 months are resistant to it.
[citation needed]
Kittens can be born with it, having contracted it from their mother while
in utero.
Infection is far higher in city cats, stray or owned, than in rural cats: this is entirely due to the amount of contact the cats have with each other.
Four subgroups of FeLV exist: A; B; C, and T, but only subgroup A is transmissible between cats. The other subgroups arise
de novo and as results of
recombination with an endogenous DNA feline sequence. Hence, there is very good evidence this virus is quite ancient, and may well have evolved more than one time over the last 10,000,000 years.
Subgroups are defined on the basis of viral interference and in vitro host range. The differences are due to polymorphism in the envelope glycoprotein gp70 with the highest level of divergence lying in the region of gp70 which is thought to interact with the cellular receptor. In an infected cell, gp70 is thought to block viral receptors, so preventing further infection by the same subgroup.
