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Compendium June 2009 (Vol 31, No 6)

Feline Focus — 2008 Feline Retrovirus Management Guidelines

    FeLV and FIV are among the most common infectious diseases of cats. Risk factors for infection include male gender, adulthood, and outdoor access, whereas indoor lifestyle and sterilization are associated with reduced infection rates.1-5

    The retroviral status of all cats should be known. Cats may require retrovirus testing at different times in their lives. Here are some general principles for retrovirus testing:

    • A cat with a confirmed-positive test result should be diagnosed as having a retroviral infection—not clinical disease. Diseases in cats infected with FeLV or FIV may not necessarily be the result of the retrovirus infection.
    • Cats infected with FeLV or FIV may live for many years. A decision for euthanasia should never be made solely on the basis of whether the cat is infected.
    • No test is 100% accurate at all times under all conditions. All test results should be interpreted along with the patient's health and prior likelihood of infection. All positive results should be confirmed by another test method.

    While FeLV and FIV can be life-threatening viruses, proper management can give infected cats longer, healthier lives. The following article reflects the recommendations of the AAFP on managing these infections.


    The prevalence of FeLV infection has reportedly decreased during the past 20 years, presumably as a result of implementation of widespread testing programs and development of effective vaccines.1,2,6 In contrast, the prevalence of FIV has not changed since the virus was discovered in 1986.

    In a study of more than 18,000 cats tested in 2004, 2.3% were positive for FeLV and 2.5% were positive for FIV.1 Infection rates for FeLV and FIV (TABLE 1) varied among subpopulations and sources of cats.

    Preventing FELV and FIV Infection

    Vaccines are available for both retroviruses. Both FeLV and FIV vaccines are non-core. Risk assessment of the individual animal should dictate their use. No vaccine is 100% effective, and repeat testing should be performed as warranted.

    FeLV Vaccination

    The decision to vaccinate an individual cat against FeLV should be based on the cat's risk of exposure. Cats that live in an FeLV-negative, indoor environment are at minimal risk.

    FeLV vaccination is recommended for:

    • All kittens because the lifestyles of kittens frequently change after acquisition, and kittens may subsequently be at risk for FeLV exposure
    • Cats that go outdoors
    • Cats that have direct contact with cats of unknown status or in high-turnover situations such as foster homes or other group housing
    • Cats that live with FeLV-positive cats

    Because sufficient protection is not induced in all vaccinates, vaccination against FeLV does not diminish the importance of testing cats to identify and isolate those that are viremic. In addition, cats should be tested for FeLV infection before initial vaccination and whenever the possibility exists that they have been exposed to FeLV since they were last tested. Administering FeLV vaccines to cats confirmed to be FeLV infected is of no value.

    FIV Vaccination

    The decision to vaccinate a cat for FIV is complicated. FIV vaccines may be considered for cats with lifestyles that put them at high risk for infection, such as outdoor cats that fight or cats living with FIV-infected cats. Because FIV infection is more often spread by unfriendly exchanges (usually biting), cats in households with a stable social structure are at lower risk for acquiring FIV infection.

    Current FIV antibody tests cannot distinguish vaccinated cats from infected cats. Clients should be informed that vaccinated cats will have positive FIV test results, and the decision to vaccinate should be reached only after careful consideration of this implication. If the decision falls in favor of vaccination, cats should test negative immediately before vaccination.

    A permanently placed identification microchip and collar are recommended for all cats to increase the chance of returning lost cats to their owners. Microchip databases can also record FIV vaccination histories. This information can be used by animal shelters to help assess the significance of positive FIV test results when screening cats before adoption.

    Limiting Transmission in the Veterinary Practice

    Retroviruses are unstable outside their host animals and can be quickly inactivated by detergents and routine disinfectants.7-11 Simple precautions and routine cleaning procedures prevent transmission of these agents in veterinary hospitals.

    As a guide:

    • All infected patients should be housed in individual cages when hospitalized and not in isolation/contagious wards where they may be exposed to infectious agents.
    • Hospital staff should wash their hands between patients and after cleaning cages.
    • Because FeLV and FIV can be transmitted in blood transfusions, donors should be tested before donating. A real-time polymerase chain reaction (PCR) test for FeLV is recommended for blood donors because proviral elements in seronegative cats with regressive FeLV infection may cause infection in transfusion recipients.
    • Dental and surgical instruments, endotracheal tubes, and other items potentially contaminated with body fluids should be thoroughly cleaned and sterilized between uses.
    • Fluid lines, multidose medication containers, and food can become contaminated with body fluids (especially blood or saliva) and should not be shared among patients.

    Recommendations on testing for and controlling transmission of FeLV and FIV in shelters and catteries are listed in BOX 1 .

    Diagnosing FELV and FIV

    The retroviral status of all cats should be known because the serious health consequences of infection influence patient management both in illness and wellness care. Failure to identify infected cats may lead to inadvertent exposure and transmission to uninfected cats. Misdiagnosis of infection in uninfected cats may lead to inappropriate changes in lifestyle or even euthanasia.

    Cats should be tested when they are:

    • Sick, regardless of age, despite previous negative test results or previous vaccination. FeLV and FIV are associated with a wide variety of health disorders4,5 (BOX 2). Identification of retroviral infection as a complicating factor can assist in the development of optimal management plans.
    • About to be adopted or brought into a new household, regardless of age. Even if no other cats are present in the household, testing will protect future cats that may join the family as well as neighborhood cats, should the pet escape or be allowed outside.
    • At risk of exposure, even if their most recent test was negative. As an example, a 2008 study12 showed that more than 19% of cats with cutaneous abscesses were FIV or FeLV positive at the time of presentation. Because of delay in seroconversion after initial infection, these cats should also be retested (a minimum of 30 days after the last potential FeLV exposure and 60 days after potential FIV exposure).
    • Of "unknown" viral status. Infected cats can remain asymptomatic for years, during which time they may serve as hidden sources of infection to other cats in the household.
    • About to be vaccinated against FeLV or FIV. These vaccines should not be administered to cats that are already infected. Vaccination does not affect the carrier state, the capacity to infect other cats, or the development of disease in cats with preexisting infection.

    Diagnosis of FeLV

    Soluble-antigen tests are preferred for initial screening (FIGURE 1). These include ELISA and other immunochromatographic tests.

    While screening tests detect the presence of free antigen in the circulating blood, the immunofluorescence assay (IFA) tests for the presence of antigen within infected white blood cells and platelets. Positive results from tests that detect free antigen may be reflective of the transient period of antigenemia associated with regressive infections. Positive results from tests that detect cell-associated antigen, such as the IFA, are likely to be reflective of progressive infections. Tests that use saliva and tears yield an unacceptably high percentage of inaccurate results, and their use is not recommended.13

    Although there are no published assessments of diagnostic accuracy of PCR testing for FeLV, the test is offered by a number of commercial laboratories. Recent studies14,15 using real-time PCR have shown that 5% to 10% of cats with negative results on soluble antigen tests were positive for FeLV provirus by PCR (regressive infection).

    Diagnosis of FIV

    FIV produces a persistent, lifelong infection, so detection of antibodies in peripheral blood has been judged sufficient for routine diagnostic screening if the cat has not been previously vaccinated against FIV and has not acquired FIV antibodies in colostrum16,17 (FIGURE 2).

    ELISA and other immunochromatographic tests are the preferred screening tests. Confirmation of positive screening tests should include a different method or at least an antibody test from a different manufacturer.18,19 Western blot tests have been the recommended confirmation tests in the past, but they were found to be less sensitive and specific than in-clinic screening tests in one study.17

    Vaccination of cats against FIV induces anti-FIV antibodies that cannot be distinguished from natural infection. These antibodies persist for at least 1 year and can be transferred in colostrum to kittens.

    While PCR assays may help distinguish cats infected with FIV from cats vaccinated against FIV, one study found marked variability in diagnostic accuracy among commercial laboratories.20


    Negative results for either FeLV or FIV are much more reliable than positive results because of the low prevalence of infection in most cat populations. Positive test results should be confirmed, especially in asymptomatic and low-risk cats. No test is 100% accurate all the time, under all conditions. In cat populations with a low prevalence (e.g., <1%), more than half of the cats that test positive are likely to be uninfected.21

    Kittens may be tested for FeLV and FIV at any age. Most kittens test negative, indicating no infection. Antibody tests for FIV can detect antibodies passed in colostrum from an infected or vaccinated mother, which can be mistaken for infection in the kitten. Kittens that test positive for FIV antibodies should be retested every 60 days up to 6 months of age. If the kitten becomes seronegative, it most likely is not infected. If results of tests performed after 6 months of age are still confirmed positive, these kittens should be considered infected.

    FeLV vaccinations will not induce positive test results.

    FIV vaccinations will induce positive test results.

    Managing Positive Cats

    Both FeLV-infected and FIV-infected cats can live for many years and may succumb at older ages to causes unrelated to their retrovirus infections. In recent studies,22 the median survival after diagnosis of FeLV-infected cats was 2.4 years; for FIV-infected cats, it was 4.9 years. Thus, a decision for treatment or for euthanasia should never be based solely on the presence of a retrovirus infection.

    Managing Healthy Positive Cats

    Examinations should be performed at least twice a year. At each visit:

    • Update medical history. Monitor for any signs of weight loss.
    • Perform a thorough physical examination; pay close attention to the lymph nodes, eyes, and oral cavity.
    • Conduct a complete blood count, biochemical analysis, urinalysis, and fecal examination at least once a year. FeLV-positive cats may need a complete blood count twice a year.
    • Spay or neuter intact cats.
    • Control internal and external parasites.
    • Vaccinate as lifestyle indicates. Most retrovirus-infected cats mount adequate immune responses when vaccinated, and there is no need to modify standard vaccination intervals.23 There is controversy about the use of inactivated versus modified-live vaccines. Current recommendations are to use inactivated vaccine products due to the theoretical risk of a modified-live product regaining its pathogenicity in cats with compromised immune systems.

    Infected queens should not be bred and should be spayed if their condition is sufficiently stable to permit them to undergo surgery.

    Managing Clinically Ill Positive Cats

    Prompt and accurate diagnosis is essential to allow early therapeutic intervention and a successful treatment outcome. Therefore, intensive diagnostic testing should proceed early in the course of illness for infected cats. Many cats infected with FeLV or FIV respond as well as their uninfected counterparts to appropriate medications and treatment strategies, although a longer or more aggressive course of treatment may be needed.

    Few attempts have been made to evaluate antiviral drugs, immunomodulators, or alternative therapies in large controlled studies of naturally infected cats. To date, no treatment has been shown to reverse well-established retrovirus infection in cats.

    Clients with a healthy or ill retrovirus-positive cat may be frightened by the initial diagnosis. It is important to alleviate these fears when appropriate and offer encouraging advice on the proper care and management of the cat (BOX 3).

    This is an abridged version of the full guidelines (Levy JC, Crawford C, Hartmann K, et al. 2008 American Association of Feline Practitioners' feline retrovirus management guidelines. J Feline Med Surg 2008;10[3]:300-316) available at catvets.com from the American Association of Feline Practitioners (AAFP). Adapted with permission from AAFP.

    Downloadable PDF

    1. Levy JK, Scott HM, Lachtara JL, Crawford PC. Seroprevalence of feline leukemia virus and feline immunodeficiency virus infection among cats in North America and risk factors for seropositivity. JAVMA 2006;228:371-376.

    2. O'Connor TP Jr, Tonelli QJ, Scarlett JM. Report of the National FeLV/FIV Awareness Project. JAVMA 1991;199:1348-1353.

    3. Levy JK, Crawford PC. Feline leukemia virus. In: Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine. 6th ed. Philadelphia: WB Saunders; 2005:653-659.

    4. Hoover EA, Mullins JI. Feline leukemia virus infection and diseases. JAVMA 1991;199:1287-1297.

    5. Levy JK. Feline immunodeficiency virus update. In: Bonagura J, ed. Current Veterinary Therapy XIII. Philadelphia: WB Saunders; 2000:284-288.

    6. Moore GE, Ward MP, Dhariwal J, Al E. Use of a primary care veterinary medical database for surveillance of syndromes and diseases in dogs and cats. J Vet Intern Med 2004;18:386.

    7. Francis DP, Essex M, Gayzagian D. Feline leukemia virus: survival under home and laboratory conditions. J Clin Microbiol 1979;9:154-156.

    8. van Engelenburg FA, Terpstra FG, Schuitemaker H, Moorer WR. The virucidal spectrum of a high concentration alcohol mixture. J Hosp Infect 2002;51:121-125.

    9. Moorer WR. Antiviral activity of alcohol for surface disinfection. Int J Dent Hyg 2003;1:138-142.

    10. Kramer A, Schwebke I, Kampf G. How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect Dis 2006;6:130.

    11. Terpstra FG, Van Den Blink AE, Bos LM, et al. Resistance of surface-dried virus to common disinfection procedures. J Hosp Infect 2007;66:332-338.

    12. Goldkamp CE, Levy JK, Edinboro CH, Lachtara JL. Seroprevalences of feline leukemia virus and feline immunodeficiency virus in cats with abscesses or bite wounds and rate of veterinarian compliance with current guidelines for retrovirus testing. JAVMA 2008;232:1152-1158.

    13. Panel report on the colloquium on feline leukemia virus/feline immunodeficiency virus: tests and vaccination. JAVMA 1991;199:1273-1277.

    14. Hofmann-Lehmann R, Huder JB, Gruber S, et al. Feline leukemia provirus load during the course of experimental infection and in naturally infected cats. J Gen Virol 2001;82:1589-1596.

    15. Gomes-Keller MA, Go¨nczi E, Tandon R, et al. Detection of feline leukemia virus RNA in saliva from naturally infected cats and correlation of PCR results with those of current diagnostic methods. J Clin Microbiol 2006;44:916-922.

    16. Hartmann K. Feline immunodeficiency virus infection: an overview. Vet J 1998;155:123-137.

    17. Levy JK, Crawford PC, Slater MR. Effect of vaccination against feline immunodeficiency virus on results of serologic testing in cats. JAVMA 2004;225:1558-1561.

    18. Barr MC. FIV, FeLV, and FIPV: interpretation and misinterpretation of serological test results. Semin Vet Med Surg Small Anim 1996;11:144-153.

    19. Hartmann K, Werner RM, Egberink H, Jarrett O. Comparison of six in-house tests for the rapid diagnosis of feline immunodeficiency and feline leukemia virus infections. Vet Rec 2001;149:317-320.

    20. Bienzle D, Reggeti F, Wen X, et al. The variability of serological and molecular diagnosis of feline immunodeficiency virus infection. Can Vet J 2004;45:753-757.

    21. Jacobson RH. How well do serodiagnostic tests predict the infection or disease status of cats? JAVMA 1991;199:1343-1347.

    22. Levy JK, Lorentzen L, Shields J, Lewis H. Long-term outcome of cats with natural FeLV and FIV infection. In: 8th Int Feline Retrovirus Res Symp 2006.

    23. Richards JR, Elston TH, Ford RB, et al. The 2006 American Association of Feline Practitioners Feline Vaccine Advisory Panel Report. JAVMA 2006;229:1405-1441.

    References »

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