This column is based on abstracts presented at the 24th annual ACVIM Forum in Louisville (2006).
It is a common practice to vaccinate a cat immediately upon its arrival to a shelter. This protocol is based on a resurgence of feline panleukopenia (FPV) cases. The vaccine is highly efficacious, with antibody titers appearing within a week.
There is concern that the vaccine may cloud the diagnosis of panleukopenia. Practictioners rely on test kits to diagnose panleukopenia in cats with clinical signs.
The vaccine is a modified-live virus and could result in the fecal shedding of virus, which would cross-react with the commonly used canine parvovirus test kits. In dogs it was shown that using an MLV vaccine resulted in positive fecal parvovirus testing for four to five days after vaccination.1
Researchers from the University of Florida looked at the effects of MLV vaccine on parvovirus shedding in kittens.2 A total of 64 SPF kittens (8 to 10 weeks old) were included in the study. The kittens were divided into groups and eight different vaccines were given.
These vaccines included six MLV and two inactivated vaccines. Seven vaccines were given subcutaneously, one intranasally. Antibody titers for FPV were determined before and two weeks after vaccination. Feces were tested for parvovirus antigen daily for 15 days using three different commercially available tests (Synbiotics, Idexx, Agen).
In the kittens, positive fecal tests were found for one to eight days. The Synbiotics test had the highest number of positive results. Only one kitten had a strong positive reaction. Positive reactions were seen in all groups except the intranasal group.
An important finding was that after two weeks, 75 percent to 100 percent of kittens vaccinated with MLV vaccine had protective antibodies, whereas only 25 percent to 38 percent that got an inactivated vaccine had protective titers.
This study shows that vaccines can interfere with accurate diagnosis of FPV if given recently and that MLV vaccines are better able to produce protective antibody titers than inactivated vaccines.
Vaccinating Feral Cats
It is not uncommon to vaccinate the trapped feral cats when they are under anesthesia for a neutering surgery. This is quite stressful, and raises concern that the stress might blunt the response to the vaccine.
Researchers from Florida State University looked at the ability of vaccines to protect cats from a trap-neuter-return program.3 Sixty-one cats were included. They were trapped and anesthetized for castration or spaying. MLV vaccine was given to 29 cats and inactivated vaccine to 32 cats. Blood was collected initially as well.
After eight to 12 weeks, the cats were trapped again and blood work was repeated. The cats had varying levels of antibody protection before vaccination (33 percent had a titer for FPV, 64 percent for feline calicivirus, 21 percent for feline herpesvirus and 10 percent for rabies).
Vaccination increased these percentages to 90 percent for FPV, 93 percent for FCV, 56 percent for FHV and 98 percent for rabies. The cats were anesthetized on average for 44 ± 25 minutes and body temperature at the time of reversal was 97.6 ± 2.0 degrees. There was no difference in the proportion of cats protected by vaccines based on vaccine type, though MLV vaccines produced higher titers for FPV and inactivated vaccines produced higher titers for FHV.
This study shows that a single vaccine at the time of spaying or neutering in trap-neuter programs is highly effective in providing protective titers even with the stress of capture, anesthesia and surgery.
In this case, 92 percent of the cats were adults, so maternal antibodies did not interfere with the vaccine.
The research group from Florida looked at the efficacy of MLV and inactivated vaccines in kittens.4 The study consisted of cats that were SPF seronegative and kittens that had maternal antibodies.
In the seronegative cats, both MLV and inactivated vaccines were used, in the seropositive kittens only MLV were used. The kittens were vaccinated at eight, 11 and 14 weeks.
The kittens were sterilized either at week seven, eight, nine or not at all to determine whether anesthesia and surgery changed antibody response.
In the kittens without maternal antibodies, the MLV vaccine resulted in 75 percent protection against FPV, 50 percent FCV, 0 percent FHV within one week. The inactivated vaccines were less efficacious, with 0 percent FPV, 25 percent FCV and 0 percent FHV.
Maternal antibodies delayed the response to vaccines so that finally at 17 weeks, 75 percent had protective titers to FPV and 50 percent for FHV. Anesthesia and surgery did not affect titer response.
This study demonstrated that it is possible to vaccinate during anesthesia and surgery if needed. What was surprising was the relatively low level of protection at 17 weeks in the seropositive cats. Certainly if a rapid response to vaccination is required, an MLV is preferable. Vaccinating past the currently recommended 12 weeks may be a consideration given this data.
Anthony Carr, DVM, Dipl. ACVIM, is an associate professor at the Western College of Veterinary Medicine in Saskatoon, Saskatchewan, Canada.