OBJECTIVES

A new modified live vaccine containing a Canine Parvovirus variant CPV-2b was developed in order to better match the current field strains which have replaced the original CPV-2 type and to allow an earlier and efficient immunization in young pups, despite the obstacle of maternally derived antibodies (MDA). The objective of the study was to compare the immunogenicity of four monovalent modified live vaccines, one vaccine containing the CPV-2b variant (vaccine A) and the three other being conventional CPV-2 vaccines, currently marketed in Europe (vaccines B, C and D).

MATERIALS

181 puppies aged 5 weeks completed the study in the area of Barcelona. All pups of a same litter were randomly assigned to a vaccine group. Dogs were vaccinated at 5 and 7 weeks (days 0 and 14). Antibody titers to CPV-2, CPV-2a and CPV-2b were determined on D0, D14 and D28 by the hemagglutination inhibition test. At D0, pups were seropositive (SP) when MDA titer were > or = 1:20 and seronegative (SN) when <1:20. Seroconversion (SC) at D14 and D28 was defined as a four-fold increase or greater in titers when SP at D0, or when titer increased from a SN to a SP value. Geometric means CPV-2, 2a and 2b titers were determined and ANOVA was used to compare the mean titers, with the group, time and MDA status as factors. The SC rates were compared using the Chi-square test. Fischer's exact test was used for 2X2 comparisons. Difference was significant at P<0.05.

RESULTS

96% of pups in group A seroconverted regarding CPV-2, 2a and 2b by 7 weeks (D14), when the SC rates with vaccines B, C and D ranged from 49 to 68%. In every case, the SC rate in group A was significantly higher than the one in the other groups. At D28, SC rates in group A regarding CPV-2, 2a and 2b were 92, 96 and 98% when the SC rates in groups B, C and D increased but remained lower than the rates in group A (from 60 to 73%). CPV-2 titers (D14 - D28) were: A (1:4817 - 1:1856), B (1:774 - 1:532), C (1:266 - 1:411), D (1:291 - 1:664). CPV-2a titers were: A (1:6211 - 1:2477), B (1:201 - 1:72), C (1:65 - 1:78), D (1:74 - 1:147). CPV-2b titers were: A (1:6301 - 1:2662), B (1:197 - 1:71), C (1:87 - 1:101), D (1:75 - 1:172). CPV-2a and 2b titers with vaccine A were significantly different when compared to the 3 other vaccines at D14. CPV-2 titers with vaccine A were significantly different when compared to the 3 other vaccines at D14 in pups presenting with MDA.

CONCLUSION

The presence of MDA at D0 didn't prevent the development of a strong immune response as early as D14 in pups that received the CPV-2b variant vaccine (A), contrary to vaccines B, C and D. The results indicate that an early and high humoral response was achieved with the new CPV-2b vaccine and suggest that a high level of immunization can be expected in pups as early as 5 weeks of age against the current field CPV strains.