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4:02 PM   April 23, 2014
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Vaccination and Parvovirus Testing in Kittens

By Anthony Carr, DVM, Dipl. ACVIM

It is a common practice to vaccinate cats immediately upon being brought to a shelter. This is based upon a resurgence of feline panleukopenia (FPV) cases. The vaccine is highly efficacious, with antibody titers appearing within a week, so that it makes sense to vaccinate early.

There is, however, concern that the vaccine may cloud the diagnosis of  panleukopenia in a cat. Test kits are relied upon to diagnose panleukopenia in cats with clinical signs such as vomiting and diarrhea.

The vaccine is a modified live virus (MLV) and potentially 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 some time ago that vaccination with 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 an 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 of the vaccines were given subcutaneously, one was given 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 vaccine groups except the intranasal group.

A very 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 these protective titers.

This study shows that the 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
The population of feral cats is of great concern. Trap, neuter and return (TNR) programs are popular to help reduce the population of cats and at the same time improve the health of the feral cat population. It is not uncommon to vaccinate the trapped 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 TNR program.3 Sixty-one cats were included in the study. The cats were trapped and then 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 (FCV), 21  percent for feline herpesvirus (FHV) 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 fact that vaccination was effective is not surprising. Other work in dogs has shown that immune suppressive therapy does not significantly affect vaccine responses.

In one study, dogs being treated with chemotherapy for lymphoma or osteosarcoma were vaccinated with an antigen. There was no statistical difference in antibody response between normal control dogs and dogs getting chemotherapy.4

Similar results were found with vaccines given to dogs put on immune suppressive dosages of prednisolone.5

Maternal Antibodies
The research group from Florida looked at the efficacy of MLV and inactivated vaccines in kittens.6 The kittens 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 8, 11 and 14 weeks.

The kittens were sterilized either at week 7, 8, 9 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 feline calicivirus (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, though obviously it would ideal to have more data to confirm these findings.

Based on abstracts presented at the 24rd  annual ACVIM Forum in Louisville, Ky. (2006)

1. Bass EP, Gill MA, Beckenhauer WH. Development of a modified live, canine origin parvovirus vaccine. JAVMA 181;909-913: 1982.
2. Levy JK, Patterson EV at al.  Impact of vaccination on parvovirus testing in kittens. J Vet Intern Med 20; 711:2006.
3. Levy JK, Fisher SM, et al. Serological responses of feral cats to vaccination in trap-neuter-return programs. J Vet Intern Med 20; 711:2006.
4. Walter CU, Biller BJ et al. Effects of chemotherapy on immune responses in dogs with cancer. J Vet Intern Med 20; 342-347: 2006.
5. Nara PL. Krakowka S. Powers TE. Effects of prednisolone on the development of immune responses to canine distemper virus in beagle pups. AJVR 40;1742-7: 1979.
6. Levy JK, Reese MJ et al. The effect of anesthesia and surgery on serological responses to vaccination in kittens. J Vet Intern Med 20; 759:2006

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