Serologic methods, such as the enzyme-linked immunosorbent assay (ELISA), can yield both false-positive and false-negative results when testing for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). The detection of FeLV and FIV proviral DNA in peripheral monocytes, however, allows these viruses to be detected independently of the presence of antibodies or viremia. In this study, a nested polymerase chain reaction (PCR) technique was developed for the diagnosis of FeLV and FIV. Unlike some other PCR methods, this method enables both viruses to be detected simultaneously. Blood samples from 179 cats were tested for FeLV and FIV by using this nested PCR method as well as a commercial ELISA kit. Of these samples, 64 (35.7%) were found to contain the FeLV proviral genome. Sixteen (25%) of these were ELISA negative, possibly representing latent FeLV cases in which viremia was not present. An additional 6 samples tested positive for FeLV by ELISA but were PCR negative. Regarding FIV, 20 (11.2%) samples contained the FIV proviral genome, and all of these were ELISA positive. All of the negative ELISA samples were PCR negative; however, 5 samples tested positive for FIV by ELISA yet were PCR negative. The authors conclude that this nested PCR technique is diagnostically effective and that its routine use should be considered for detecting FeLV and FIV.

COMMENTARY: Development of commercial ELISA kits for in-clinic use has been enormously beneficial in helping to control FIV and FeLV. However, cats with latent FeLV infections and in certain stages of FIV can test negative by an ELISA. False-positive results are another problem, occurring in as many as 20% of cats tested for FIV by ELISA. Using PCR for testing may help to lessen or eliminate these confounding factors. For example, testing in kittens by this method would be more reliable because maternal antibodies to FIV may persist for 6 months or more. While the authors state that the method described is simple, reliable, and fast, it will be interesting to see how the study results translate in terms of clinical usefulness (eg, cost and availability).

Evaluation of a novel nested PCR for the routine diagnosis of feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV). Arjona A, Barquero N, Domenech A, et al. J FELINE MED SURG 9:14-22, 2007.