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What is Feline
Immunodeficiency Virus? |
Virologists classify feline
immunodeficiency virus (FIV) in the same Retroviridae family
as the
Feline Leukemia Virus
(FeLV), but with one major
difference: FIV is not considered to be in the oncornavirus
subfamily of retroviruses, as is FeLV. Instead, FIV is
classified as a lentivirus (or "slow virus"), along with the
viruses that cause progressive pneumonia in sheep, infectious
anemia in horses, arthritis–encephalitis in goats, and
acquired immunodeficiency syndrome (AIDS) in human beings.
FIV and FeLV often cause similar types of disease, but the
viruses themselves differ in many ways, including the shape
of the viral particle. The FIV particle is elongated, while
FeLV is more circular. In addition, the two viruses are quite
different genetically, and their structural proteins are
dissimilar in size and composition. This means that the two
viruses are antigenically unrelated; antibodies to FIV do not
bind to FeLV, nor do antibodies to FeLV bind to FIV.
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How prevalent is
the infection? |
FIV–infected cats are found worldwide, but
the prevalence of infection depends on geographic locale and
the population of cats tested. In the United States,
approximately 1.5 to 3% of healthy cats are infected with FIV.
Infection rates rise significantly in cats that are sick; up
to 15% of cats with clinical signs of other disease also are
infected with FIV. Free–roaming male cats –– especially
aggressive ones –– are the most frequently infected, while
cats housed exclusively indoors are much less likely to be
infected. |
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How is FIV
spread? |
The primary mode of transmission is
through bite wounds. Casual, nonaggressive contact among cats
does not appear to be an efficient route of spreading FIV. On
rare occasions, the disease is transmitted from an infected
mother cat to her kittens during gestation, during passage
through the birth canal, or when the newborn kittens ingest
infected milk. Sexual contact probably is not a primary means
of spreading FIV. |
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How does the
virus affect the cat? |
Following initial infection, the virus is
carried to regional lymph nodes, where it may replicate in
white blood cells known as T–lymphocytes. The virus then
spreads to lymph nodes throughout the body, resulting in a
generalized enlargement of the nodes. This stage of the
disease usually passes unnoticed by an owner unless the nodes
are greatly enlarged. Some time later––perhaps days but
usually weeks to months––the cat may develop a fever and a
drop in the white blood cell count. This decrease in white
cells is due primarily to a lack of neutrophils, the white
blood cells that help protect cats against bacterial
infections, and to a loss of certain types of lymphocytes
called T–helper cells, which play an important role in almost
every aspect of immune protection. Anemia (or low red blood
cell count ) also may develop, especially later in the
disease.
Persistently infected cats may appear
normal for years. Eventually, signs of immunodeficiency begin
to develop, and the cat's ability to protect itself against
infection is compromised. The same bacteria, viruses,
protozoa, and fungi that are found in cats' everyday
environment––where they usually do not affect healthy
animals––can cause severe illness in cats with weakened
immune systems. These secondary infections are responsible
for most of the clinical signs associated with FIV infection,
and are the major cause of death in FIV–positive cats.
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What are the
signs of the disease? |
Clinical signs of the immunodeficiency
syndrome appear throughout the body. Poor coat condition and
persistent fever with a loss of appetite are commonly seen.
Infection and inflammation of the gums (gingivitis) and mouth
(stomatitis) are present in about half of the cats infected
with FIV. Chronic or recurrent infections of the skin,
urinary bladder, and upper respiratory tract are often
present.
Persistent diarrhea can be a problem.
Inflammation of the tissues of the eye occurs frequently, but
in most cats the damage is not clinically apparent. Slow but
progressive weight loss also is common, followed by severe
wasting late in the disease process. FIV–infected cats have
an increased risk of developing certain types of cancer, such
as lymphomas, although the cancer risk is greater with FeLV
infection. Abortion of kittens or other reproductive failures
have been noted in infected queens. Some infected cats
experience seizures, mental deterioration, and other
neurologic disorders. Some FIV–infected cats have recurrent
illness interspersed with periods of relative health between
episodes. In those cases, low white blood cell counts and
anemia also appear to cycle, with episodes of low cell counts
followed by recovery to nearly normal levels. However, the
overall trend seems to be progressive, with cell counts
dropping lower with each subsequent episode. |
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How is a
diagnosis of the disease made? |
Diagnosis is based on the history,
clinical signs, and results of an FIV antibody test. This
test is performed by most commercial and university
veterinary diagnostic laboratories, and also is available in
kit form for use in private veterinary clinics. The presence
of FIV antibody in "positive " test results indicates that a
cat is infected with FIV––probably for its lifetime––and thus
is capable of transmitting the virus to other cats. Since
false–positive test results can occur, positive results
should be confirmed using a test with a different format.
Occasionally, an FIV test is reported as equivocal or
indeterminate. Retesting in 8 to 12 weeks usually results in
either a positive or a negative result. However, a few cats
will continue to have equivocal results, often because of
some factor in the blood that interferes with the test.
Young kittens may have positive test
results for 12 to 16 weeks after birth, without actually
being infected with FIV, because of passive transfer of FIV
antibodies from the mother. Only a small percentage of these
kittens actually are or will become infected. For this
reason, kittens with positive antibody tests must be retested
when they are 6 to 8 months of age to determine their true
infection status.
A negative test result indicates that
antibodies directed against FIV have not been detected. In
most cases, a negative test result means that the cat is not
infected. However, it takes 8 to 12 weeks after infection
(and sometimes even longer) before detectable levels of
antibody appear. If the test is performed during this
interval, inaccurate results might be obtained. Therefore,
antibody–negative cats with either an unknown or a known
exposure to FIV–infected cats should be retested about 8 to
12 weeks after their most recent exposure in order to allow
adequate time for development of antibodies. (On very rare
occasions, cats in the later stages of FIV infection may test
negative because their immune systems are so compromised that
they no longer produce antibodies.) |
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What can be done
if my cat is infected with FIV? |
One of the most important things you can
do is to protect your cat from exposure to the infectious
agents that cause severe disease and death in
immunosuppressed animals. Keep your cat strictly indoors and
away from other cats, not only to protect your cat, but also
to prevent transmission of FIV to other cats as well. The use
of antimicrobial drugs to control bacterial and fungal
infections may be moderately successful but must be continued
for long periods, or reinstituted as new infections occur.
Supportive care, including intravenous fluids, blood
transfusions, and feeding of high–caloric dietary
supplements, is frequently required. The use of
corticosteroids or other anti–inflammatory drugs may be
indicated in some cases to control gingivitis and stomatitis.
Anabolic steroids may help to combat weight loss and wasting.
Keep in mind that these measures are not directed at
combating the virus itself. Some of the drugs useful in
therapy for AIDS patients may also have the potential against
FIV, but they are expensive and difficult to obtain, and
side–effects appear to be greater in cats than in humans.
Drugs designed to enhance or modify the immune system might
be of benefit in treating FIV infections. However, most
potentially effective treatments are still in the
experimental stages of development and testing. Even these
drugs only suppress the effects of the virus and do not
destroy it. |
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I just discovered
that one of my cats has FIV, yet I have other cats as well.
What do I do now? |
Cat–to–cat transmission of FIV in
multiple–cat households where there is no fighting among cats
appears to be quite uncommon. Many FIV–positive cats are not
diagnosed until after they have lived in the multicat
environment for years. Ideally, any infected cats in such
households should be separated from the non–infected ones,
but in reality, if fighting or rough play is not taking
place, the risk to the non–infected cats appears to be low.
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How long can I
expect my FIV–positive cat to live? |
It is impossible to accurately predict the
life expectancy of a cat infected with FIV. Under ideal
conditions, such as isolation of the FIV–infected cat from
other cats, many cats will remain in apparent good health for
many months to a number of years after the initial infection.
If your cat has already had one or more severe illnesses as a
result of FIV infection, or if persistent fever and weight
loss are present, a much shorter survival time can be
expected. The immune status of an FIV–infected cat can be
determined by testing the ratio of CD4+ to CD8+ lymphocytes.
This test, available through several veterinary laboratories
including the Veterinary Diagnostic Laboratory at Cornell, is
a measurement of the degree of immunosuppression. The
CD4+:CD8+ ratio is often a useful prognostic indicator: the
lower the ratio, the more dire the prognosis.
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My FIV–positive
cat died recently after a long illness. Is it safe to bring a
new cat into my home? |
Feline immunodeficiency virus is fairly
unstable outside the cat and will not survive for more than a
few hours in most environments . In addition, transmission of
FIV occurs primarily through bites, so a waiting period
between cats is not required to prevent FIV infection.
However, FIV–positive cats are frequently infected with other
infectious agents which may pose some threat to a newcomer,
so precautions should be taken. Thoroughly clean and
disinfect or replace food and water dishes, bedding, litter
pans and toys. A dilute solution of household bleach (4 oz.
bleach in 1 gal. water) makes an excellent disinfectant.
Vacuum carpets and mop floors with an appropriate cleanser.
Any new cats or kittens should be properly vaccinated against
other infectious agents before entering the household.
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How can I prevent
my new cat from contracting FIV? |
No vaccine against FIV is available.
Owners can protect their cats only by preventing them from
contacting infected cats. Pets kept indoors and away from
free–roaming cats are highly unlikely to contract FIV
infection. Ideally, catteries and multiple–cat households
should test all their cats and remove any that are infected.
Once FIV–negative status of resident cats has been
established, all prospective feline newcomers should be
tested for FIV antibodies, and only FIV–negative animals
should be brought into the household or cattery. A quarantine
period of about 8 weeks to 12 weeks, followed by a repeat
test, is recommended for a cat with an uncertain history of
exposure to the virus, such as a stray cat. |
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Can I become
infected with FIV from an infected cat? |
No, almost certainly not. Although FIV is
structurally similar to HIV (the human immunodeficiency
virus) and causes a disease in cats similar to AIDS in
humans, it is a highly species–specific agent and affects
only felines. In several studies, veterinarians, owners, and
researchers who have had close contact with FIV–infected cats
have shown absolutely no evidence of infection. Based on
current evidence, it appears that FIV infections are
restricted solely to cats.
Prepared by the Cornell Feline Health
Center, Cornell University, College of Veterinary Medicine,
Ithaca, New York 14853-6401. The ultimate purpose of the Feline
Health Center is to improve the health of cats by developing
methods to prevent or cure feline diseases and by providing
continuing education to veterinarians and cat owners. Much of
that work is made possible by the financial support of friends.
©1997 by Cornell University. All rights reserved. Cornell
University is an equal opportunity, affirmative action educator
and employer. |
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