IMMUNOGENICITY OF A LOW PASSAGE, HIGH-TITER MODIFIED-LIVE CANINE PARVOVIRUS VACCINE IN POPS WITH MATERNALLY DERIVED ANTIBODIES

The study evaluated the ability of a low-passage, high-titer modified live canine parvovirus (CPV) vaccine to produce seroconversion in pups with maternally derived hemagglutination inhibition (HI) titers rangi ng from <8 to less than or equal to 256. The vaccine's low-passage CPV strain was less attenuated and therefore more infective than conventi onal modified live CPV strains in order to overcome relatively greater levels of maternally derived antibodies, the principal cause of CPV v accine failures in pups. To assess vaccine performance under field con ditions, healthy pups presented at five private veterinary clinics wer e used as test animals. A single dose of vaccine was given to 59 pups at 12 weeks of age (Group A). To accommodate the protocol of clinics w here earlier CPV vaccination was practiced, 87 other pups were vaccina ted with two noses, the first at 8-10 weeks of age, and the second at 12 weeks of age (Group B). Geometric mean HI titers were measured for blood samples obtained at the time of vaccination and at 14 weeks of a ge. Seroconversion was considered to have occurred if pups developed a fourfold or greater increase in HI liter to a level greater than or e qual to 64. Of the 59 pups in Group A, 100% seroconverted following th e single vaccine dose at 12 weeks of age. Of the 87 Group B pups, 82 ( 94.3%) seroconverted following either of the two vaccine doses. A geom etric mean HI titer of 4828 was measured for Group A, and a geometric mean HI liter of 2028 was measured for Group B. An overall seroconvers ion rate of 96.5% was achieved in pups with maternally derived HI tite rs less than or equal to 256. (C) 1997 Elsevier Science Ltd.