Circulating Lineage 3 Recombination with NADC30-Like and NADC34-Like 2 in Taiwan.

Porcine respiratory and reproductive syndrome (PRRS) caused by leads to severe economic losses. The emergence of highly pathogenic 2 (PRRSV-II), such as NADC30 and NADC34, has been reported in the USA and several Asian countries. NADC30-like PRRSV-II was first reported in 2018 in Taiwan. To investigate the PRRSV variants currently circulating in Taiwan, sequences covering ORF2-5 of Taiwan PRRSV isolates collected between 2020 and 2023 were analyzed. Phylogenetic analysis of the ORF5 nucleotide sequence indicated that most of the Taiwan isolates were clustered in lineage 3 and three isolates were grouped in lineage 1 and were closely related to the NADC34 strain. Interestingly, these three NADC34-like Taiwan PRRSV isolates carried amino acid deletions similar to NADC30 and were more closely related to NADC30 strains than the NADC34 strains in the Nsp2 gene. Next-generation sequencing and recombination detection program showed potential recombination of lineage 3 with NADC30- and NADC34-like PRRSV-II. Our results suggest the presence of circulating mosaic recombinants and lineage 3 PRRSV-II in Taiwan during 2020 and 2023.