Feline leukemia virus (FeLV) and Feline immunodeficiency virus (FIV) are among the most common infectious diseases of cats, although prevalence in the general cat population varies by geographic location and risk factors. Comprehensive data on the seroprevalence of retrovirus infections and risk factors for cats in Canada were published in 2009. The national seroprevalence is 3.4% for FeLV and 4.3% for FIV, with some geographic variation. While these viruses are present in all parts of Canada, the highest prevalence for FeLV is in Nova Scotia, Quebec, and Manitoba. The highest prevalence for FIV is in Newfoundland, Quebec, and Saskatchewan.
In general, the retrovirus status of all cats should be known. Guidelines for retrovirus testing of cats in Canada have been published. Point-of-care testing kits available to veterinarians have good sensitivity and specificity for both viruses. These kits comprise enzyme linked immunoassay (ELISA) tests that detect the presence of FIV antibodies and FeLV antigen.
Who should be tested for FeLV and FIV?
Vaccination against FeLV does not interfere with testing.
Cats that should be tested for FeLV and FIV include:
- At-risk cats: All sick cats, cats with bite wounds or oral disease, cats with known exposure to a retrovirus-infected cat, cats living in multi-cat environments where the status of every cat is not known. Sick cats should be tested regardless of a previous negative FeLV or FIV test result.
- Newly acquired cats and kittens.
- Cats about to be vaccinated against FeLV or FIV.
- Cats at ongoing risk of infection (e.g., cats with access to outdoors) should be tested annually for FeLV and FIV with patient-side or referral laboratory tests. Cats vaccinated against FIV will require special consideration (see below).
- Cats in shelters are often not tested before adoption although this may be routine in some shelter and rescue groups. If the cat has been tested, the results should be provided to the client. If cats are not tested prior to adoption, the client should be made aware that testing is required as soon as possible.
Recommendations for Follow-up Testing
A single negative FIV and/or FeLV test does not rule out infection for life. There are multiple situations in which the testing status may change. These include:
- Recent exposure. It can take months for a patient to develop detectable FIV antibodies following exposure. Retesting should be conducted at least 60 days following the first negative test and/or most recent potential exposure. Feline leukemia virus testing should be repeated at least 30 days after the first negative test.
- False negative or false positive test results. Improperly handled samples or improperly run tests can lead to false results in point-of-care testing. Because of low levels of proviral DNA and antigen in regressive FeLV infections, complicate interpretation of test results.
- New exposure. Cats that are at continued risk of exposure cannot be presumed negative for life based on one ELISA test. Regular testing is recommended.
Concerns with FIV Vaccinations and Testing Results
As of 2015, the FIV vaccination is no longer available in Canada or the United States. The vaccine continues to be available in Australia and New Zealand. Cats vaccinated against FIV may be antibody-positive on serology testing due to immunity raised by vaccination for some years following the last vaccination. Knowledge of the cat’s vaccination history is beneficial, but where the vaccination status is unknown, certain point-of-care tests and referral laboratory PCR tests may assist in determining whether a cat is truly infected or previously vaccinated.
FELINE SPECIALIST AUTHORS
- Susan Little, DVM, DABVP (Feline Practice) Bytown Cat Hospital, Ottawa, Ontario
- Diane McKelvey, DVM, DABVP (Feline Practice) Aberdeen Veterinary Hospital, Kamloops, British Columbia
- Elizabeth O’Brien, DVM, DABVP (Feline Practice) The Cat Clinic, Hamilton, Ontario
- Elizabeth Ruelle, DVM, DABVP (Feline Practice) Wild Rose Cat Clinic of Calgary, Calgary, Alberta
- Kelly St. Denis, MSC, DVM, DABVP (Feline Practice)
- Margie Scherk, DVM, DABVP (Feline Practice) catsINK, Vancouver, British Columbia
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