Molecular typing of canine parvovirus strains circulating from 2008 to 2012 in an organized kennel in India reveals the possibility of vaccination failure

Canine parvovirus-2 (CPV-2), which emerged in 1978, is considered as the major viral enteric pathogen of the canine population. With the emergence of new antigenic variants and incidences of vaccine failure, CPV has become one of the dreaded diseases of the canines worldwide. The present study was undertaken in an organized kennel from North India to ascertain the molecular basis of the CPV outbreaks in the vaccinated dogs. 415 samples were collected over a 5 year period (2008-2012). The outbreak of the disease was more severe in 2012 with high incidence of mortality in pups with pronounced clinical symptoms. Molecular typing based on the VP2 gene was carried out with the 11 isolates from different years and compared with the CPV prototype and the vaccine strains. All the isolates in the study were either new CPV-2a (2012 isolates) or new CPV-2b (2008 and 2011 isolates). There were amino acid mutations at the Tyr324Ile and at the Thr440Ala position in five isolates from 2012 indicating new CPV mutants spreading in India. The CPV vaccines used in the present study failed to generate protective antibody titer against heterogeneous CPV antigenic types. The findings were confirmed when the affected pups were treated with hyper-immune heterogeneous purified immunoglobulin's against CPV in dogs of different antigenic types.