Canine parvovirus-2 (CPV-2) emerged in the late 1970s as a highly contagious and potentially lethal viral pathogen in dogs. CPV-2a and CPV-2b appeared subsequently as antigenic variants. A third variant (CPV-2c) recently emerged in Italy and has become widely distributed in Europe, Australia, North America, and South America. Most modified-live vaccines contain the CPV-2 and CPV-2b strains and therefore may be less protective against new variants. This study evaluated the genetic variability of CPV virus collected from the fecal samples of 37 vaccinated puppies in Brazil that presented with enteric illness from 1995 through 2009. Puppies had previously received either multivalent CPV-2 vaccine (n = 20), CPV-2b vaccine (n = 3), or unknown CPV vaccine (n = 14). Polymerase chain reaction (PCR) and hemagglutination/hemagglutination inhibition (HA/HI) tests were used to confirm infection and differentiate among parvoviral types. Viral DNA was extracted from samples, and 2 regions of the VP2 gene were amplified by PCR. PCR amplicons were directly sequenced and aligned for phylogenetic analysis. From 1995 to 2006, only CPV-2a strains were detected. From 2007 to 2009, both CPV-2a and CPV-2b strains were identified, with the majority (14/19) classified as CPV-2b strains. All CPV-2a strains evaluated in this study demonstrated a nonsynonymous mutation at amino acid residue 297 (Ser → Ala). A synonymous substitution at amino acid residue 574 (A → G substitution in nucleotide 5408) was identified in 15 of 37 samples, 14 of which were in CPV-2a strains and 1 of which was in a CPV-2b strain. No CPV-2c strains were identified.

Commentary: The nonsynonymous mutations detected in CPV-2a strains in this study were not clearly supportive of documented changes in CPV antigenicity; however, such changes may indicate altered viral antigenic properties secondary to vaccine-induced and other adaptive pressures. This study did reveal significant temporal diversity and apparent evolution of circulating viruses in this parvoviral population over time. Vaccines may need to undergo periodic reformulation to accommodate dynamic viral strains.—Indu Mani, DVM, DSc

Monitoring of canine parvovirus (CPV) strains detected in vaccinated puppies in Brazil. Castro TX, Costa EM, Leite JP, et al. RES VET SCI 90:336-340, 2011.