Feline immunodeficiency is not a zoonotic disease. Studies of veterinarians and their staff have shown no evidence of human FIV infection (Butera, 2000). Pathophysiology of FIV The initial stages of acute FIV infection may be associated with transient fever and lymphadenopathy. In many cats, however, this acute stage of FIV infection goes undetected by pet owners. During this phase, large amounts of virus begin to circulate in the bloodstream. The immune system then develops antibodies against the virus. Although the infection is not typically eliminated, the immune system effects may be sufficient to cause a decrease in viral load during the later stages of the acute phase (Litster, 2015b). After this initial acute phase, infected cats enter a long asymptomatic phase. During this asymptomatic phase, CD4+ T-lymphocytes begin to decline in number. This leads to both a decrease in the number and the relative proportion of CD4+ T-lymphocytes in the blood and lymphoid tissue (Hartmann et al., 2022). In some cases, a reduction in the CD4:CD8 lymphocyte ratio occurs; this may Clinical signs of FIV Clinical signs during the acute stage of infection are missed by many owners. They include fever, lymphadenopathy, lethargy, anorexia, and weight loss (Fenimore, 2014). These stages are caused by viral replication and the resulting immune response to the virus. Following this acute phase, infected cats enter a prolonged period (years) in which they are mostly or entirely asymptomatic. Clinical signs in the later stages of FIV are typically related to secondary infections that develop as a result of immunodeficiency. These secondary infections may be bacterial, viral, fungal, or protozoal and can affect a variety of organs and organ systems. Affected cats may develop chronic respiratory issues, gastrointestinal disease caused by bacterial overgrowth, or other infections. Cats with FIV are at a higher risk of developing a number of different malignancies. These include lymphoma and Diagnosis of FIV All sick cats should be tested for FIV. Additionally, newly adopted cats or kittens and all cats that are to be group housed should be tested. It can take up to two months for a cat to test FIV-positive after exposure. Therefore, testing should be repeated two months after the last potential exposure, and any cat with exposure to an FIV-infected cat or a bite wound from a cat of unknown status should be tested two months after exposure. High-risk cats, including cats living outdoors and cats living with an FIV-positive cat, should be tested annually. All cats should be tested before vaccination. Finally, all blood donor cats should be tested to ensure that they are FIV negative (Litster, 2015b). The most common test for FIV involves screening for FIV antibodies using an in-house ELISA test. These tests detect antibodies, not viral antigen, because circulating levels of the virus are typically very low following infection (Little, 2013). Because FIV results in a persistent, life-long infection, detection of antibodies in an unvaccinated cat is sufficient to meet the criteria for diagnosis of FIV. Cats that have received the FIV vaccine will test positive on a FIV ELISA test, presenting a diagnostic challenge. Although there has not been a commercially available FIV vaccine in the United States since 2016, this vaccine may be available in other parts of the world. Consider vaccination in positive cats with a history of international travel, keeping in
be observed with specialized testing. During this phase of infection, complete blood cell count (CBC) changes— including anemia, lymphopenia, and neutropenia—may also be observed on laboratory testing (Little, 2013; Litster, 2015b). Hyperglobulinemia may also be observed. This elevation occurs as cell-mediated immunity is reduced, stimulating antibody-mediated immunity (Litster, 2015b). With progression, cats may develop an AIDS-related complex or terminal stage of FIV infection. This phase typically takes years to develop and is often observed in older cats. In this stage, cats become more susceptible to secondary infection and begin showing clinical signs that can suggest an underlying immunodeficiency (Litster, 2015b). In many cats, this is the stage at which FIV becomes apparent and is diagnosed. other lymphoid neoplasias, myeloproliferative diseases, and several types of sarcomas and carcinomas (Fenimore, 2014). In some cats, the first sign of FIV may be clinical signs associated with secondary neoplasia. Other viral effects can include slow, progressive weight loss, with or without chronic small-intestinal diarrhea. Infected cats may develop ocular inflammation, including anterior uveitis or pars planitis (inflammation in the anterior vitreous humor). Chronic oral inflammation is frequently observed, and these cats may initially present to the veterinarian for evaluation of gingivostomatitis. Neurologic disease—including seizures, ataxia, nystagmus, and other abnormalities—is another common manifestation of FIV. Renal disease may also be observed, including glomerulonephritis. (American Association of Feline Practitioners, 2013b; Litster, 2015b; Fenimore, 2014). mind that vaccinated cats may test positive for up to seven years after their last vaccine (Stone et al., 2020). The most common cause of a false-negative FIV test is testing too early in infection. Because the FIV test is an antibody test, testing before seroconversion will result in a false-negative test. In general, it takes approximately 60 days after exposure before an infected cat will begin to test positive (Little et al., 2020). False negatives can also be seen in cats in the late terminal stages of the disease, because FIV-induced immunodeficiency may result in decreased antibody production that is not detectable by the test (Little S. , 2013). Less commonly, false-negative tests may be attributed to exceptionally high viral loads. In these patients, all of the FIV antibodies may be bound to circulating virus and therefore not available for detection by the test (Little, 2013). Commercially available ELISA SNAP tests have high sensitivity and specificity in unvaccinated cats. False-positive tests can occur, however, especially in low-risk populations. Therefore, all positive results on FIV ELISA tests should be confirmed using an alternative test. The most common test used to confirm the diagnosis is polymerase chain reaction (PCR) testing that looks for FIV proviral DNA or viral RNA (Little et al., 2020).
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