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Feline Immunodeficiency Virus (FIV)

Understanding Your Pet's Medical Diagnosis

What is feline immunodeficiency virus?

Feline immunodeficiency virus (FIV) is a virus that damages the immune system of cats, making them more susceptible to other infections and disease. Usually cats become infected with FIV when they are bitten by another FIV infected cat. Thus cats that are allowed to roam freely with other cats have the greatest risk of infection. Male cats are more likely than female cats to be infected because they tend to fight more.

What are the signs of FIV infection?

The signs of early FIV infection may include low fever, diarrhea, and swollen glands (lymph nodes). These signs usually disappear after several weeks, and the cat will appear healthy for many months. Gradually, as immune system damage occurs, your cat may begin to have signs of high fever, enlarged lymph nodes, diarrhea, gum and mouth sores (gingivitis and stomatitis), skin and respiratory infections, and weight loss. Because damage due to the virus takes time to develop, signs are usually seen only in adult cats. When FIV infects a cat, the virus grows within two main types of white blood cells: a subset of T lymphocytes called CD4+ T cells, and macrophages. These cells are vital for normal immune system function of the cat; providing the cat's defense against other infections. FIV infection leads to damage or death of many of these key cells. This damage usually occurs very slowly over several months (or even years) following infection.

How is FIV infection diagnosed?

Your veterinarian may recommend testing for FIV when you first get your cat, or in some cases, on a routine basis -- if your cat has been in contact with other cats or has some of the clinical signs described above. FIV infection is diagnosed with a blood test (serology) that detects antibodies to FIV. These antibodies are produced by the cat's immune cells and appear in the blood about six - eight weeks after infection. The two most common tests are called an ELISA, performed in your veterinarian's clinic, and a Western Blot, performed at a diagnostic laboratory. The ELISA is used for preliminary testing, and the Western Blot is used to confirm positive ELISA results.

How is FIV infection treated?

FIV infection may be "treated" (managed, but not cured) with drugs that stimulate immune function, thereby reducing the amount of virus in the cat. These drugs do not eliminate the virus. Cats infected with FIV usually become sick because of secondary or opportunistic infections with bacteria, parasites, or viruses. Antibiotics are effective against some of these secondary infections. Keeping your cat indoors away from other cats not only prevents the spread of FIV to other cats, but also protects your cat against contracting secondary infections. Good nutrition and preventive health care are essential. Vaccines for FIV are not yet available

What is the prognosis for cats with FIV infection?

Cats infected with FIV may remain healthy for five years or more. Once severe immune suppression develops, frequent infections become more difficult to treat, and death usually occurs within a year.

Although FIV belongs to the same family of viruses (retroviruses) as human immunodeficiency virus (HIV, AIDS), FIV only causes disease in members of the cat family. It is not a threat to humans.


Feline immunodeficiency virus (FIV) is a retrovirus that causes an immunodeficiency disease in domestic cats. It is in the same subfamily (lentiviruses) as human immunodeficiency virus, the causitive agent of human AIDS.


Immune system function is disrupted by FIV infection, with feline lymphocytes and macrophages serving as the main targets for virus replication. Both CD4+ and CD8+ subsets of T cells can be infected lytically in culture; however, FIV selectively and progressively decreases feline CD4+ cells in the infected cat. Inversion of the CD4+:CD8+ ratio develops slowly, with an absolute decrease of CD4+ T cells after several months of infection. The loss of T helper cells results in dysfunction of both humoral and cell-mediated immunity.

Macrophages are the main "reservoir" of virus in FIV-infected cats; infected macrophages have several defects in function including an increased production of tumor necrosis factor. Astrocytes and microglial cells in the brain and megakaryocytes and mononuclear bone marrow cells may be infected in some cats. Coinfection with FeLV extends the host cell range of FIV to include kidney, brain, and liver cells.

Systems Affected

Hemic/lymphatic/immune--immune system initially a result of loss of CD4+ T cells

All other body systems a result of immunosuppression and secondary infections


No genetic predisposition for infection. Genetics may play some role in the progression and severity of disease.


In the United States and Canada, the prevalence of FIV infection is estimated to be 1.5-3% in the healthy cat population and 9-15% in cats exhibiting signs of clinical illness.

Geographic Distribution

The distribution of FIV is worldwide, but seroprevalence rates vary greatly.


Because of the immunosuppressive nature of FIV infection, clinical signs in domestic cats are diverse. Diseases associated with FIV infection cannot be distinguished clinically from FeLV-associated immunodeficiencies.

Historical Findings

Physical Examination Findings


risk factors




Hemogram may be normal. Anemia, lymphopenia, or neutropenia may be present; however, neutrophils can be elevated in response to secondary infections. Urinalysis and serum chemistry profile are usually normal except for increased serum protein resulting from hypergammaglobulinemia.

Other laboratory tests

Serologic testing to detect antibodies to FIV. Enzyme-linked immunosorbent assay (ELISA) is used for routine screening and the Western blot for confirmatory testing of ELISA-positive samples. The format of the ELISA varies from kits designed for "in-house" use to a microtiter plate format designed for diagnostic laboratory use. Positive results on ELISA should be confirmed by additional testing, especially in healthy, low-risk cats or when diagnosis of FIV may result in euthanasia of the cat. Kittens less than 6 months of age may test positive as a result of passive transfer of antibodies from the FIV-positive queen; thus a positive test in a kitten does not indicate virus infection. Retest kittens at 8-12 months of age to determine if they are FIV-infected.

Virus isolation or detection by other methods occasionally is available on an experimental basis. Virus antigen detection procedures usually are not sensitive enough to be useful for diagnostic purposes. CD4+:CD8+ evaluation is sometimes available.
Gross and histopathologic findings

Lymphadenopathy is associated with follicular hyperplasia and massive paracortical infiltration of plasmacytes. Later, a mixture of follicular hyperplasia and follicular depletion or involution may be observed. In the terminal stage of disease, lymphoid depletion is the predominant finding.

Lymphocytic and plasmacytic infiltrates of the gingiva, lymph nodes and other lymphoid tissues, spleen, kidney, and liver of affected cats

Intestinal lesions similar to those seen with feline parvovirus infection (feline panleukopenia-like syndrome)


FIV infection is slowly progressive. Healthy antibody-positive cats may remain healthy for years. Clients should expect cats with clinical signs of immunodeficiency disease to have recurrent or chronic health problems that will require medical attention.

Discuss the importance of keeping cats indoors to protect them from exposure to secondary pathogens and to prevent spread of FIV to other cats.

Drugs and fluids

Immunomodulatory drugs may allieviate some clinical signs.

Management of secondary and opportunistic infections is a primary consideration. Additional supportive therapy, such as parenteral fluids and nutritional supplements, may be required. Yearly vaccination for respiratory and enteric viruses with inactivated vaccines is recommended.

Gingivitis and stomatitis may be refractory to treatment. Antibacterial or antimycotic drugs are useful for overgrowth of bacteria or fungi, but prolonged therapy or increased dosages may be required.

Anorexic cats may benefit from IV diazepam. Anabolic steroids or megestrol acetate may achieve more prolonged stimulation of appetite and reversal of cachexia; however, the efficacy of these drugs in FIV-infected cats is not known.

Anterior uveitis is treated with application of topical corticosteroids, but long-term response to therapy may be incomplete or poor. Pars planitis often will regress spontaneously and may recur. Management of FIV-related glaucoma is the same as for glaucoma resulting from other causes.

Severe neutropenias have been induced in several FIV-infected cats treated with griseofulvin. Although the neutropenia is reversible if the griseofulvin is withdrawn early enough, secondary infections associated with the condition can be life-threatening; therefore, this drug should be avoided or used with extreme caution in FIV-positive cats.

Modified live vaccines may cause disease in immunosuppressed cats. Systemic corticosteroids should be used with caution because of the potential for further immunosuppression.

Patient monitoring

Varies according to the secondary infections and other manifestations of disease

Prevent contact of cats with FIV-positive cats. Quarantine and test incoming cats for FIV before introduction into multiple cat households.

Course and prognosis

Variable disease progression--death occurs in about 20% of cats within the first 2 years after diagnosis (4.5-6 years after the estimated time of infection); however, more than 50% of the infected cats remain asymptomatic during the same time period. Once a cat is in the late stages of disease (wasting and frequent or severe opportunistic infections), life expectancy is 1 year or less.

zoonotic potential

None known (evidence against FIV transmission to humans is compelling but cannot be considered conclusive owing to the relatively short period of time the virus has been studied)

A more important consideration is the potential zoonotic transmission of secondary pathogens such as Toxoplasma gondii from FIV-positive cats to immunocompromised humans.


Abortions and stillbirths have been reported in FIV-positive queens. Transmission of FIV from queen to kittens is infrequent if the queen is antibody-positive before conception.


Barr MC, Olsen CW, and Scott FW. Feline viral diseases. In: Ettinger SJ, Feldman EC, eds. Textbook of veterinary internal medicine. 4th ed. Philadelphia: WB Saunders, 1994.
English RV, Nelson P, Johnson CM, Nasisse M, Tompkins WA, Tompkins MB. Development of clinical disease in cats experimentally infected with feline immunodeficiency virus. J Inf Dis 1994;170:543-552.
Ishida T, Taniguchi A, Matsumura S, Washizu T, Tomoda I. Long-term clinical observations on feline immunodeficiency virus infected asymptomatic carriers. Vet Immunol Immunopathol 1992;35:15-22.

Sparger EE. Current thoughts on feline immunodeficiency virus infection. Vet Clin
N Am (Small Anim Pract) 1993;23:173-191.

Author Margaret C. Barr

Consulting Editor Fred W. Scott

More Information take from Cornell University's Site

Feline Immunodeficiency Virus (FIV)

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.

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 FIV.

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 household.

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.