THE feline leukemia virus (FeLV) is one of the
most deadly diseases affecting domestic cats, resulting in
more deaths than any other infectious feline disease. The condition
was originally identified in Scotland in the 1960s. Cats throughout
the world are now infected with FeLV, and it is estimated that
about 2 percent to 3 percent of all cats in the U.S. carry
The riskiest situation for FeLV transmission is a crowded,
multicat household. Outdoor and indoor/outdoor cats are also
at an increased risk of contracting the disease. In addition,
sick cats, male cats and cats ages 1 to 6 have a higher risk
of being infected. Less than 1 percent of strictly indoor cats
are infected with the FeLV virus.
The virus itself is not particularly hardy and can only live
a few days in the environment. It is easily killed by common
detergents and disinfectants. Thus the risk of transmission
is mostly because of direct contact between cats.
This contact usually includes transmittal through virus-infected
saliva via cat-fight wounds (most commonly outdoor or indoor/outdoor
cats); mutual grooming; shared food and water dishes; nose-to-nose
contact with infected saliva, urine or feces; shared litter
boxes; tears and sneezing; and blood transfusions. The virus
also can be transmitted by a FeLV-positive mother to her nursing
Most cats with feline leukemia die within two or three years
after being infected. The most common problem affecting these
cats is depression of the immune system. Secondary infections
stemming from this condition include persistent and recurring
abscesses, chronic mouth infections, chronic respiratory diseases,
diarrhea and poor appetite. The virus can also suppress the
cells of the bone marrow that produce red and white blood cells.
Red blood cell suppression results in severe anemia, and white
blood cell suppression allows for the development of unrestrained
After the initial infection, many cats develop malignancies
of the lymph nodes and bone marrow. Once these malignant cells
are found in the blood, the malignancy is called leukemia.
These malignancies can also be found in many organs, including
the chest, kidneys, liver and intestinal tract.
Your veterinarian can perform a number of blood tests to identify
a FeLV-infected cat. Cats in multiple-cat households should
be checked to make sure they do not carry the virus. Any new
cat introduced into a household should be quarantined for three
months and checked twice in that time for FeLV infection.
There is no treatment to cure FeLV. Only care and treatment
of the secondary bacterial infections with antibiotics, or
chemotherapeutic drugs for some malignancies, are possible.
There is a vaccine for FeLV but its efficacy is not yet known.
Unfortunately, the vaccine produces a status in vaccinated
cats that makes it impossible to differentiate these cats from
FeLV positive cats. A lost, vaccinated cat could be diagnosed
as suffering from FeLV and euthanized. Because of this, strictly
indoor cats with absolutely no contact with outdoor cats are
usually not vaccinated. You should speak to your veterinarian
about the question of vaccinating your cat against feline leukemia.