Feline Immunodeficiency Virus

Feline immunodeficiency virus (FIV) was first identified in an
immunosuppressed cat in 1986. FIV is a lentivirus (slow virus),
so named because of the slow development of disease. FIV is of
the same family of viruses as human immunodeficiency virus
(HIV), which causes acquired immunodeficiency syndrome (AIDS) in
people. It is important to remember that FIV is infectious only
to cats.

Immunodeficiency related to FIV infection occurs most often in
free-roaming, male cats older than 6 years. Transmission of FIV
is usually through cat bites incurred when fighting. Defense of
territory explains the higher incidence of disease in male cats.
FIV is occasionally transmitted to kittens by their mothers.

Random testing of cats seen by veterinarians shows a healthy cat
prevalence of 1 to 2 per cent in the United States and up to 12
per cent in Japan, where most cats a re kept outside and are not
neutered. Twelve to 40 per cent of sick cats are infected with
FIV. Once cats develop FIV infection, they are infected for
life. Studies of frozen serum samples from 20 years ago show
that the prevalence of FIV infection has not changed.

Cats with FIV, like people with HIV, have an acute phase of
illness that begins 4 to 6 weeks after a bite from an infected
cat. Most cats develop fever, depression, and enlarged lymph
nodes that last from weeks to months. These symptoms are usually
mild enough that owners rarely notice. Kittens infected as
newborns may die in the acute phase. After recovery from the
acute phase, these cats may appear completely normal for 3 years
or more. During this asymptomatic period, the FIV virus is
gradually destroying the immune system, limiting the ability to
fight infection.

When the immune dysfunction is relatively mild, cats have
bacterial and viral infections commonly seen in cats, such as
mouth infections, abscesses, chronic nasal and eye discharges,
skin infections, ear infections, and diarrhea. FIV-infected cats
have ringworm at three times the expected rate. These infections
respond to the usual treatment, but not as well as expected, and
often recur after treatment is completed.

FIV can also affect the bone marrow, causing anemia. Parasitic
diseases such as toxoplasmosis tat normally cause only mild
signs become life threatening. The FIV has an affinity for brain
tissue and can produce personality changes. Shy cats may become
aggressive and outgoing cats may hide. Malignancy of lymph node
cells (lymphosarcoma) may develop. Cats infected with FIV are
also more likely to develop kidney failure.

When immune depression is severe, cats may develop opportunistic
infections (infections that do not usually occur in that
species) such as demodectic mange seen in dogs. During the later
stages, standard treatments are not effective because they
require the help of the immune system to resolve infections.
Nevertheless, immunosuppressed cats may live a year or longer if
treated.

When FIV is suspected, a blood test can be done. A negative test
usually excludes a diagnosis of FIV, but an early infection
(first 2 months) could be missed. A positive test with
appropriate signs is quite reliable, but an occasional
false-positive test can occur. A Western blot test (a more
specific and definitive test) of blood confirms the diagnosis.

A positive test for FIV is not a reason for euthanasia. A study
of newly diagnosed FIV-infected cats showed that 7 of 11 cats
were still alive 2 years later. We rarely know when cats become
infected. A cat with early infection may have 3 or 4 more years
of disease-free life. FIV-positive cats should be kept indoors
for the safety of other cats and to limit their exposure to the
disease.

The response to treatment of FIV-infected cats depends on the
degree of immune suppression. There are no god antiviral drugs
for the cat. Azidothymidine (AZT), a drug used in people to
inhibit virus reproduction, works against the FIV virus but has
a significant toxicity in the cat. There are other promising
drugs but they are not yet available.

Most of the illnesses in FIV-infected cats results from
secondary bacterial infections that can be controlled with
antibiotics. Antibiotics can prolong the cat’s life in spite of
a poorly functioning immune system. Prevention with vaccination
would be helpful but, as in people, an effective vaccine has not
been developed.

The above is general veterinary information. Do not begin
any course of treatment without consulting your regular
veterinarian. All animals should be examined at least once every
12 months.