Abstract
“I can't do anything to help retrovirus-infected cats, so why should I test?” The unfortunate consequence of this commonly expressed sentiment is that, according to industry figures, only about 4% of cats visiting veterinarians in the United States during any given year are tested for FIV (figures for FeLV test frequency are not readily available). It's safe to conclude that many infected cats escape detection. But according to the 2001 Report of the American Association of Feline Practitioners/Academy of Feline Medicine Advisory Panel on Feline Retro-virus Testing and Management (appearing in this issue of the Journal of Feline Medicine and Surgery),
Several issues raised by the panel's report deserve highlighting. First is the necessity of confirming a positive “point-of-care” or “in-house” test result (such tests are most often used as the initial screen) obtained from a cat with a low likelihood of infection—for example, a healthy cat housed exclusively indoors with no known exposure to infected cats. In such a cat, a positive result should be viewed with a healthy dose of skepticism until confirmed with a different type of test. The choice of confirmatory tests varies somewhat between the United States and Europe. In the US, IFA testing is the most commonly performed confirmatory test for FeLV infection; virus isolation is more often performed in Europe. Western blot is the preferred confirmatory test for FIV in the US, but because such testing is not widely available in Europe—and because of the wider availability of different point-of-care tests in the European market— simply performing a point-of-care test from a different manufacturer often suffices. Second is the recommendation to regularly test cats with ongoing viral exposure (as in cats allowed outdoors). Is it reasonable to expect that a negative result obtained in years past still reflects the cat's infection status? Post-cat-bite testing as outlined in the report is a rational course of action, as well. Third is the advisability of testing kittens younger than 6 months-of-age for FIV infection. Understandably, clinicians may be reluctant to test cats of these ages, wishing to avoid confusion that may result from the presence of passively acquired antibody in kittens born to FIV-infected queens. But the test results—whether positive or negative— inform both husbandry and future testing recommendations.
As with FeLV vaccines, FIV vaccines promise to be valuable tools in the quest to prevent infection. But just as widespread FeLV vaccination has not diminished the importance of testing, neither will FIV vaccination: infection and vaccination are not mutually exclusive. Why? First, it's unrealistic to expect all vaccinates to be protected from infection. And second, unless cats are routinely tested and found free of infection prior to vaccination, some infected individuals will receive a vaccination.
Though potentially helpful in preventing infection in some vaccinates, FIV vaccines that induce antibodies indistinguishable from those in infected cats will create a testing conundrum. Negative FIV-antibody test results would remain meaningful, but as the use of these vaccines grows, positive results will become increasingly difficult to interpret. One such vaccine was released in the United States this past year, and— understandably—its use is controversial. FIV vaccines that don't interfere with antibody-based test methodologies would circumvent this problem, but none are available as of this writing. In the interim, we can hope for the development of alternate tests that will detect infection in antibody-positive cats, and that will be convincingly validated, convenient to use, reasonably affordable, and widely available.