Abstract
NADC34-like PRRSV strains were first detected in China in 2017, with
epidemic potential. In this study, the phylogenetic, epidemic, and
recombinant properties of NADC34-like PRRSV in China were evaluated
comprehensively. From 2020 to October 2021, 82 NADC34-like PRRSV
isolates were obtained from 433 PRRSV-positive clinical samples. These
strains accounted for 11.5% and 28.6% of positives in 2020 and 2021,
respectively, and have spread to eight provinces. We selected 15 samples
for whole-genome sequencing, revealing genome lengths of 15,009 to
15,113 nt. Phylogenetic analysis revealed that Chinese NADC34-like
strains cluster with American sublineage 1.5 strains and do not form an
independent branch. Recombination analysis revealed that six of fifteen
complete genome sequences derived from recombination between NADC34-like
and NADC30-like or HP-PRRSV; they all recombined with local strains in
China, exhibiting a complex recombination pattern. Partial Nsp2 sequence
alignment showed that nine of fifteen isolates have a continuous 100-aa
deletion (similar to IA/2014/NADC34); other isolates have a 131-aa
discontinuity deletion (similar to NADC30). Five of them also have
additional amino acid deletions, all of which are reported for the first
time here. In the last two years, NADC34-like PRRSV has become one of
the main epidemic strains in some areas of China; it has changed
significantly, its homology has decreased significantly, and it has
undergone complex recombination with local Chinese strains. These
results are of great significance for understanding the current epidemic
situation of PRRSV in China.