Comparative pathogenesis of a Chinese highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) to a contemporary L1C variant from the United States

Authors: Devries, Alexandra; Arruda, Bailey; ZANELLA, ERALDO - Oak Ridge Institute For Science And Education (ORISE); HANSEN, LAUREN - Oak Ridge Institute For Science And Education (ORISE); Wiarda, Jayne

Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/15/2024
Publication Date: 3/1/2025
Citation: Devries, A.C., Arruda, B.L., Zanella, E., Hansen, L., Wiarda, J.E. 2025. Comparative pathogenesis of a Chinese highly pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) to a contemporary L1C variant from the United States. American Association of Swine Veterinarians Annual Meeting. https://doi.org/10.54846/am2025/102.
DOI: https://doi.org/10.54846/am2025/102

Interpretive Summary:

Technical Abstract: Introduction Highly pathogenic PRRSV (HP-PRRSV) strains were documented circulating in China around 2006 and were characterized by high fevers and morbidity/mortality. In 2020 reports of high mortality PRRSV isolates came from farms in the Midwest of the United States. These isolates clustered in the sublineage L1C and many had 1-4-4 RFLP patterns. Subsequently, L1C isolates have spread through the United States swine industry resulting in significant pig mortality and economic losses. The objective of this study was to compare the pathogenesis of a Chinese HP-PRRSV strain to a recent L1C strain in a weaned pig model. Materials and Methods Three PRRSV isolates were utilized for challenge. A Chinese isolate, rJXwn06, that was rescued from a full-length cDNA of the JXwn06 virus, an L1C.5 isolate USA/MN/01775GA/2021, and a commonly utilized challenge strain MN184. Three groups of weaned pigs (n=20/group) were challenged with 2 mL of 1x10^5 TCID50/mL intranasally: rJXwn06, L1C.5, MN184 with a fourth group receiving 2 mL of sham cell culture media. Severity of clinical disease was evaluated by scoring lethargy and respiratory distress, measuring febrile response, weighing pigs, and comparing mortality rates. Viral pathogenesis was compared by analyzing acute viremia and virus in bronchoalveolar lavage fluid via PCR, gross and histologic lung scores, and viral load in selected tissues. Five pigs were necropsied on 2 days post inoculation (dpi), 6 dpi, and 10 dpi for tissue collection and evaluation. Results The L1C.5 group developed a febrile response on 3 dpi and peaked at 8 dpi (41.0°C). The rJXwn06 group had a similar febrile response starting around 4 dpi and peaking at 9 dpi (41.7°C). The MN184 group had a lower febrile response that peaked at 7 dpi (40.4°C). Both the L1C.5 and rJXwn06 groups had multiple lethargic pigs and some with respiratory distress, while the MN184 and sham groups did not have pigs with clinical scores above zero. Similarly for body weight, the L1C.5 and rJXwn06 groups had the lowest average weight gains during this study, while the MN184 group had average weight gains slightly less than the sham challenged group. Both the L1C.5 and rJXwn06 groups had comparable levels of viremia. Starting at 7 dpi, animals in the rJXwv06 group had to be euthanized with the remainder of the animals euthanized on 10 dpi. Mortality in the L1C.5 group was delayed compared to the rJXwn06 group with animals euthanized starting on 9 dpi and all remaining animals euthanized by 12 dpi. Gross and histologic scores of the lungs as well as tissue viral load results are pending. Conclusion This study has demonstrated that this L1C.5 PRRSV isolate from the United States in 2021 has a similar level of pathogenicity to a highly pathogenic Chinese PRRSV strain from 2006. A better understanding of these isolates can help guide intervention strategies and control measures to reduce the spread of PRRSV in the swine industry.