Chinese and Vietnamese strains of HP-PRRSV cause different pathogenic outcomes in United States high health swine

•Two strains of highly-pathogenic porcine reproductive and respiratory syndrome virus were compared.•Thirty-one amino acids varied between the two HP-PRRSV strains.•Swine were inoculated with a low and high dose.•Animal studies showed that the HP-PRRSV strains resulted in different pathogenicities.

An infectious clone of a highly pathogenic PRRSV strain from Vietnam (rSRV07) was prepared and was demonstrated to contain multiple amino acid differences throughout the genome when compared to Chinese highly pathogenic PRRSV strain rJXwn06. Virus rescued from the rSRV07 infectious clone was compared to rJXwn06 and US Type 2 prototype strain VR-2332 to examine the effects of virus genotype and phenotype on in vitro growth, and virus challenge dose on in vivo pathogenicity and host response. After swine inoculation at high- and low-doses of virus, rSRV07 was shown to replicate to an approximately 10-fold lower level in serum than rJXwn06, produced lower body temperatures than rJXwn06 and resulted in decreased mortality. Furthermore, a 9-plex cytokine panel revealed that the cytokine responses varied between different strains of PRRSV, as well as between tissues examined and by inoculum dose.