Retrovirus infection (FeLV and FIV) is a common occurrence in domestic cats. In a large number of cases the disease is subclinical until it is very progressed. In the case of FIV< clinical signs may never occur. There is a concern that vaccination with Modified Live Vaccines (MLV) may lead to a reversion to virulence in cats with retrovirus infection, or that increased immune stimulation may lead to progression of retroviral infection, though neither of these has been conclusively proven. Another concern is whether retrovirus infected cats are able to mount a sufficient immune response to generate protective titres.
The purpose of this study was to determine the efficacy and safety of vaccination of retrovirus infected cats with a feline panleukopenia virus vaccine. Panleukopenia virus is a parvovirus that infects cats worldwide and leads to immunosuppression and enteritis, which may be fatal. The study was designed as a prospective case-control trial. Cats presenting to a teaching hospital or animals shelters in Germany over a two year period were recruited.
Cats that were recruited were between 2 and 6 years of age and were clinically healthy on physical exam. Cats were on no concurrent medications other than antiparasitics. If vaccinated for FPV is must have been no less than 12 months previously. Cats were tested with an in-house ELISA for FeLV antigen and FIV antibody. Data on signalment, origin, housing, lifestyle, and vaccine history were recorded.
4 FIV and 4 FeLV positive cats were recruited to the study. These were compared with 67 age matched controls. None of the retrovirus infected cats had received a full FPV vaccination series. 28% of control cats had received a full series.
Each cat received a modified live FPV vaccination on study day zero. Vaccines also contained FHV-1 and calicivirus, but these were not examined in the study. Cats received physical examinations on days 7 and 28, and owners were instructed to record any adverse health effects. Serum samples were collected on days 0, 7, and 28. Antibody titres were determined by hemagglutination inhibition, and titres >1:40 were considered protective, and cats with greater than 4 fold change in titre were considered to respond to vaccination.
100% of retrovirus infected cats had titres >1:40 on day zero. 1/8 cats (12.5%) had an adequate response to vaccination. 32.8% of control cats had an adequate response. When evaluating only cats with a pre-vaccination titre >1:160, .5 % of control cats vs 12.5% of retrovirus infected cats had a response to vaccination.
There was no statistically significant difference in antibody response between any subset of retrovirus infected and control cats.
While the high titres in retrovirus positive cats suggests that they had at some point responded to vaccination or natural challenge, it is not known if this event occurred before or after retrovirus infection. However, the continued production of antibodies suggests there was not marked immune compromise.
No vaccine associated adverse events were seen in any retrovirus cat, however 13.4% of control cats had mild adverse events (ie lethargy). This difference was not statistically significant.
There were several drawbacks to this study. Perhaps the most significant was the very small sample size for retrovirus infected cats. A larger population of FeLV and FIV positive animals may have allowed for more significant results. Another drawback was that all retrovirus positive cats had pre-existing protective tires; investigating naïve cats may have had different results.
Despite some drawbacks, this study suggests that vaccination with MLV FPV is safe in retrovirus positive cats, and is associated with a similar antibody response as seen in retrovirus negative animals.
See Also
Parvovirus
Retrovirus
Vaccinology
Immunology
