Canine parvovirus (CPV) enteritis is characterized by intestinal hemorrhage with severe bloody diarrhea . The causative agent, CPV 2, was first identified in the late 1970s . CPV is a non-enveloped, linear, single-stranded DNA virus with a genome of approximately 5 kb, and it belongs to the genus Parvovirus, together with feline panleukopenia virus (FPV), mink enteritis virus, raccoon parvovirus, and porcine parvovirus . Indeed, CPV 2 is believed to have originated from FPV [4, 5], and various hypotheses for how this may have occurred have been suggested, including direct mutation from FPV and contact between cats and dogs kept as companion animals within the same home .
An antigenic variant, CPV 2a, developed within a few years after the emergence of CPV 2 [6, 7], and another CPV 2 variant, CPV 2b, began appearing in the canine population in the mid-1980s . In 2000, a new antigenic variant, CPV 2c, was first detected in Italy . New antigenic types of CPV 2 have been found in epidemics worldwide and are replacing the original CPV 2. The antigenic variant CPV 2a shows the following substitutions within the VP2 protein: Met87Leu, Ile101Thr, Ala300Gly, and Asp305Tyr. Furthermore, CPV 2b has been confirmed to contain an additional substitution, Asn426Asp [10, 11]. These two variants further evolved into new 2a and 2b types, with substitutions of Ser297Ala, during the 1990s . Antigenic variant CPV 2c was identified with a substitution Asp426Glu . Different antigenic variants of CPV 2 predominate in different countries [12–42].
A retrospective analysis has revealed that the oldest CPV 2c strain was identified in 1996 in Germany , and the results from European epidemiological surveys show that CPV 2c is now predominant in Italy, Germany, and Spain and is also widely co-distributed with CPV 2a or CPV 2b in Portugal, France, and Belgium [18, 43–47]. Outside of Europe, CPV 2a and 2b isolates are common in the United States [19, 41], whereas CPV 2c is more widespread in Uruguay [20, 32], Brazil , and Argentina [30, 48]. Surprisingly, either CPV 2a or CPV 2b is the predominant variant in Asian countries [12, 13, 15, 21, 22, 24–26, 28, 29],[35, 37, 38] and Australia , though a few CPV 2c strains have been isolated in India . Interestingly, a new amino acid substitution, Tyr324Ile, was identified in Korea [21, 24], China , Thailand , Uruguay , Japan , Taiwan , and India [37, 49].
In Taiwan, as in other Asian countries, variants CPV 2a and 2b have predominated since the first outbreak [13, 15, 35]. However, few recent studies have included a genetic analysis of Taiwanese CPV 2 strains. Therefore, the aim of this study was to clarify the evolution of CPV 2 isolated from northern, central, and southern Taiwan during the 2008–2012 period.