Molecular detection of emerging porcine circovirus in Taiwan

Porcine Circovirus type (PCV) 2 is an important pathogen that has been circulating worldwide and has cuased serious economic loss in pig industry. However, both PCV3 and PCV4 are newly emerging viruses. In Taiwan, PCV2 has been one of the critical pathogens in pig frams and PCV3 has been detected since 2016; however, the epidemiolog of PCV3 in Taiwan remains unclear and PCV4 has yet to be identified. Therefore, in order to detect the positive rate of PCV2, to investigate the epidemiolog of PCV3 in the pig farms, and to examine whether pigs were infected with PCV4 in Taiwan, a total of 128 samples from 46 clinical cases of pigs were collected from September 2020 to December 2021. The case detection rates were 54.3 % for PCV2, 43.5 % for PCV3, and 2.2 % for PCV4. The results suggested that the positivity rates for both PCV2 and PCV3 were still high in Taiwan. In addition, PCV3 was detected among cases from all 7 sampled counties and in 11 of the 16 sampling months, suggesting that PCV3 may lead to endemic pig disease in Taiwan. Surprisingly, the PCV4 was also detected, suggesting the first PCV4 case in Taiwan. The complete genomes derived from the identified PCV3 and PCV4 strains were subsequently sequenced followed by phylogenetic analysis. The results suggested that the 17 identified PCV3 strains could be divided into Taiwanese-like and Japanese-like strains. In addition, the amino acid residues at positions 27, 80, and 212 in the identified PCV4 cap protein were asparagine, isoleucine, and methionine, respectively, and thus the identified PCV4 was catalorized into clade PCV4b. Consequently, it is concluded that (i) the prevalence of PCV2 and PCV3 is still high in Taiwanese pigs, (ii) PCV3 has may be an endemic infection in Taiwan and can be classified into Japanese-like and Taiwanese-like strains, (iii) PCV4 was detected for the first time in Taiwanese pigs and can be classified into PCV4b. It remains unclear how PCV2, PCV3, and PCV4 were introduced to Taiwan, and thus continuous investigation of emerging pathogens in pigs is needed.