Objective

A major problem with the immunization of dogs against CPV is the persistence in pups of varied levels of maternally derived antibodies (MDA), which may strongly interfere with the development of vaccine-induced immunity. Hemagglutination inhibition (HAI) titres of >1:20 may interfere with an active immune response after administration of some vaccines. This results in an "immunity gap" as such titres do not prevent infection with a virulent virus. Therefore, in this study the efficacy of the canine parvovirus (CPV) component of Vanguard^TM 7 was evaluated in the presence of moderate to high MDAs.

Method

Five puppies at 6 weeks of age with CPV MDA levels of 1:40-1:80 as measured by HAI and CPV negative were vaccinated at 6 weeks and 9 weeks. Two unvaccinated controls with no MDA and CPV negative were enrolled in the study. All seven puppies were challenged at 12 weeks of age with a virulent canine parvovirus strain labelled CHSV Bio-1: CPV 12/1/04 (CPV type 2a) and clinically monitored for 14 days after the challenge according to the guidelines of the relevant European Pharmacopoeia monograph. In addition the White Blood Cell counts (WBC) of the individual dogs were also monitored in order to evaluate the possible development of leucopoenia. Animals were also monitored to evaluate the shedding of virus in their faeces post-challenge.

Results

Severe, clinical signs typical of CPV infection and leucopoenia were observed in the two control animals. The vaccinates were 100% protected against leucopoenia and the manifestation of clinical signs of the disease. Faecal viral shedding was very high in the controls (>4096 HA) following challenge while in only one of the vaccinates very low shedding of the virus was detected (16 HA) on only one occasion.

Conclusion

The CPV fraction of Vanguard^TM 7 found to be 100% effective in the presence of MDA and to induce almost sterilising immunity when administered to puppies of 6 weeks of age.