Feline panleukopenia virus DNA shedding following modified live virus vaccination in a shelter setting

•Administration of panleukopenia vaccine can result in positive PCR test results.•Positive results occurred in 8/37 shelter cats (21.6%) without clinical signs.•DNA copy numbers were lower following vaccination than in clinically affected cats.•Positive results in healthy cats can be due to vaccine virus or subclinical infection.•PCR should be reserved for cats with clinical concern for panleukopenia. This study assessed the frequency and timing of feline panleukopenia virus (FPV) shedding in feces following administration of a modified live FPV vaccine. Feces were collected from 37 shelter cats that did not meet clinical criteria for panleukopenia on the day of vaccination or on days 3, 7, 14, and 21 post-vaccination (NCL group). A commercial quantitative PCR (qPCR) fecal pathogen panel and a canine parvovirus point-of-care antigen test were performed. FPV DNA copy numbers from a concurrent study of 39 cats with panleukopenia (CL group) were compared with the NCL group. Of the 165 samples from the NCL group, one had a weak positive antigen test result on day 7, while nine samples (5.5%) from eight cats (21.6%) produced positive FPV qPCR test results, one on day 3 and eight on day 7. There were no day 21-positive qPCR results in the 11 cats that were revaccinated on day 14. There was no association between the number of additional fecal pathogens identified and a positive FPV qPCR result. Of the cats with positive results, FPV DNA copy numbers differed between NCL group and CL group (median 1.13 × 107 and 5.01 × 10⁸ copies/g feces, respectively; P < 0.001). The FPV qPCR cannot differentiate subclinical infection from vaccine virus shedding. To avoid unnecessary isolation and euthanasia, shelters should therefore limit FPV PCR testing to cats with a high index of suspicion of panleukopenia. The timing of recent vaccination should also be considered when interpreting test results.