Feline Immunodeficiency Virus
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
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.
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.
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
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.
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.
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.)
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.
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.
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.
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
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.
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.