Bergmann M, Schwertler S, Speck S, Truyen U, Reese S, Hartmann K. Faecal shedding of parvovirus deoxyribonucleic acid following modified live feline panleukopenia virus vaccination in healthy cats. Vet Rec. 2019 Apr 30;. doi: 10.1136/vr.104661.
Feline Panleukopenia Virus (FPV; also Feline Distemper, Feline Parvovirus, Feline Infectious Enteritis) is a life-threatening disease of cats with a global distribution. Vaccination against FPV is very effective and is a part of the core vaccine series for cats. Vaccines for FPV may be killed or modified live (MLV). After vaccination with MLV parvovirus vaccines in dogs, there have been reports of fecal shedding due to replication in the intestines in ~23% of dogs for up to 28 days post-vaccination. This may create issues when testing animals for viral infection, as fecal antigen tests will be positive leading to misdiagnosis.
The purpose of this study was to determine if FPV is shed in the stool after vaccination with MLV vaccines. It was designed as a prospective study of 40 cats presenting to a veterinary hospital or animal shelter. Cats were clinically healthy and were at least 1 year of age, and had not received an FPV vaccine in at least 1 year. Cats were excluded if there were immunosuppressive drugs used in the last 4 weeks.
Each cat received a dose of MLV FPV vaccine in combination with feline herpesvirus and calicivirus (Merial PureVax). Fecal samples were collected on days 7, 14, 21, and 28 after vaccination. Serum samples were taken for FPV titres on days 0, 7, and 28. Viral DNA was extracted from the stool and analyzed by quantitative PCR for the VP2 gene. All VP2 amplified was then sequenced and compared to sequenced VP2 for the vaccine. All PCR-positive samples were also cultured on Crandell-Rees cells.
Of the 40 cats enrolled, 52.5% were female, median age was 4 years, and median body weight 4.3kg. 30% of the cats shed parvovirus DNA on at least one of the 4 dates. After sequencing, the FPV vaccine sequence was seen in three cats, field-type FPV in four cats, and field-type canine parvovirus in one cat. The risk of shedding was significantly correlated with pre-vaccination titres and with the degree of titre increase after vaccination. As full culture, PCR, and sequencing could not be performed on all samples, this study may have underestimated the actual prevalence.
The authors conclude that 7.5% of cats vaccinated with FPV will shed vaccinal virus in their stool within 28 days. Cats who have not previously been vaccinated or who have low titres are more likely to shed vaccine in their stool. This may imply that young cats in their first vaccine series are more likely to shed vaccinal DNA, which is unfortunate as these are also the cats most likely to be clinically infected with FPV. 12.5% of healthy cats shed non-vaccine parvoviral DNA in this time period, implying that a significant proportion of healthy cats may be subclinically infected or shedding parvovirus. Further work is needed to determine more effective tests to differentiate infected and vaccinated animals, and it is crucially important to evaluate clinical signs (such as leukopenia) in the context of cats presenting with positive tests.
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