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were not confirmed by subsequent IFA tests. 5 In other words, almost one of three positiveELISA results turned out to be potentially mistaken. The frequency of false positiveswith FeLV ELISA tests is why The Merck Veterinary Manual states, “Confirmation ofpositive results, especially in asymptomatic cats, should be pursued by testing for cellassociatedantigen, e.g., with an immunofluorescent antibody assay [IFA test].” 6To summarize, the common practice when feral cats are tested is to use the ELISAsnap tests and then euthanize when results are positive for FIV or FeLV. This protocol ishighly flawed because the ELISA tests are prone to false positives and, in accordancewith best practices, require more precise follow-up laboratory tests to confirm a positiveresult, especially with asymptomatic cats. A TNR program that tests all cats andeuthanizes based only on ELISA test results is not only incurring added expense, but mayeuthanize cats who are not infected.4. FIV positive cats can lead relatively long livesCats infected with FIV have commonly been known to live for many years and somenever get sick. While their immune systems are compromised, proper care and nutritioncan compensate to at least some degree. Even in outdoor colony settings, FIV cats canlive long lives. The caretaker does need to be alert for any symptoms of illness, whichmay require re-trapping and a visit to the veterinarian. By contrast, research shows thatFeLV positive cats have a much higher mortality rate, 83% within 3.5 years of full-blowninfection. 7 Still, while they are alive, they can often live symptom-free until near the endif properly fed and sheltered.5. Euthanizing positive cats is ineffective colony managementAdvocates of testing all cats argue that positive ferals need to be identified so theycan be removed from the colony and the remaining cats can be protected from thedisease. In truth, removing the positive cat makes little difference. By the time you catchand identify the positive cat, it’s most likely the other cats in the colony have alreadybeen exposed to the virus and will have become infected or not. Furthermore, no matterhow many ferals are removed because of positive test results, FIV and FeLV will remainin the environment and be an ongoing threat. New cats passing through or entering thecolony could carry the diseases and even colony members who test negative might beharboring one of the viruses. While false negatives occur less frequently than falsepositives with the ELISA tests, they are known to happen. Exposure may have occurredtoo soon before the test for antigen (FeLV) or antibodies (FIV) to appear in the blood.Or, in the case of FeLV, the virus might be absent from the blood but hiding in the bonemarrow.5 National Veterinary Laboratory Newsletter, Current Feline Leukemia Virus Research Supports:Confirm All In-Hospital FeLV ELISA Positive Tests by IFA (2006), Vol. 5, No. 4.6 The Merck Veterinary Manual, Feline Leukemia Virus (2012),http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/150225.htm (click on Feline LeukemiaVirus.”)7 Beatty, J., Markers of Feline Leukaemia Virus Infection or Exposure in Cats from a Region of LowSeroprevalence (2011) Journal of Feline Medicine and Surgery 13: 927.123