Epidemiology and molecular characterization of chicken anaemia virus from commercial and native chickens in Taiwan

Chicken infectious anaemia (CIA) is a disease with a highly economic impact in the poultry industry. The infected chickens are characterized by aplastic anaemia and extreme immunosuppression, followed by the increased susceptibility to secondary infectious pathogens and suboptimal immune responses for vaccination. Commercially available CIA vaccines are routinely used in the breeders in Taiwan to protect their progeny with maternal-derived antibodies. However, CIA cases still occur in the field and little is known about the genetic characteristics of Taiwanese chicken anaemia viruses (CAVs). In this study, CAV DNA was detected in 72 of 137 flocks collected during 2010-2015. Among the PCR-positive samples, the coding regions of 51 CAVs were sequenced. Phylogenetic analysis of the VP1 gene revealed that, although most of Taiwanese CAVs belonged to genotypes II and III, some isolates were clustered into a novel genotype (genotype IV). Moreover, a Taiwanese isolate in this novel genotype IV appeared to be derived from a recombination event between genotypes II and III viruses. Five Taiwanese CAV isolates were highly similar to the vaccine strains, 26P4 or Del-Ros. Taken together, these results indicate that the sequences of CAVs in Taiwan are variable, and inter-genotypic recombination had occurred between viruses of different genotypes. Moreover, vaccine-like strains might induce clinical signs of CIA in chickens. Our findings could be useful for understanding the evolution of CAVs and development of a better control strategy for CIA.