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Title: Comparative pathogenesis and characterization of contemporary 1-7-4 PRRSV isolates in weanling age piglets

item VAN GEELEN, ALBERT - Orise Fellow
item Faaberg, Kay
item DAS, PHANI - Orise Fellow
item MONTIEL, NESTOR - Orise Fellow
item Miller, Laura
item KULSHRESHTHA, VIKAS - Orise Fellow
item BUCKLEY, ALEXA - Orise Fellow
item Lager, Kelly

Submitted to: Proceedings of Allen D Leman Swine Conference
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Porcine respiratory and reproductive syndrome (PRRS) continues to be an economically important disease affecting commercial pig production in the United States and worldwide. Its considerable sequence and antigenic variation, coupled with the limited protection offered by current vaccine options impedes our abilities to control PRRS virus (PRRSV). Recently, PRRSV isolates of 1-7-4 lineage have been associated with clinical cases of severe maternal reproductive failure. Next-generation sequencing was used to analyze 22 contemporary PRRSV isolates that were all previously determined to have a restriction fragment length polymorphism (RFLP) 1-7-4 pattern. Four isolates were selected for a comparative pathogenesis study in weanling pigs that included a PRRSV isolate of known moderate pathogenicity in weanling age piglets. Eighty-five 4-week-old piglets were inoculated with 5 x 10E4 TCID50 intranasally. Although the isolates were 87.4% to 95.1% identical in genomic sequence for ORFs2-7, but there was considerable difference in pathogenicity among the isolates. Pathogenicity was determined by analyzing average daily gain (ADG), pyrexia measured by intramuscular temperature, viral titers in serum and bronchiolar-alveolar lavage and gross lung lesions. We identified two isolates, not previously described that caused more severe disease than our reference pathogenic isolate. Both of these 1-7-4 isolates caused 14% mortality within 2 weeks. The group of pigs infected with NADC-34 isolate had the highest average body temperatures of 41C on 5, 8 and 9 days post infection (dpi)., a decrease in ADG of 98.4%, and peak serum titers of 10E2.9 at 4 dpi. Isolate ISU/2014/3 with peak viral titers at 7 dpi of 10E3.7 caused a 63.2% decrease of ADG, reached peak temperatures of 40.5 to 40.7 between 5-8dpi. On the other hand, isolate ISU/2014/2 caused no pyrexia, had a 4.6% decrease in ADG but still had peak viral titers of 10E2.6 at 7dpi. This study shows that there is considerable difference in disease outcome caused by PRRSV isolates grouped under the 1-7-4 lineage and that other parameters of pathogenicity remain to be identified for future evaluation of disease.