Dynamics of infection of atypical porcine pestivirus in commercial pigs from birth to market: a longitudinal study

Authors: Buckley, Alexandra; MORA-DIAZ, JUAN-CARLOS - Iowa State University; MAGTOTO, RONALDO - Iowa State University; VAN HULZEN, AMBERLY - Iowa State University; FERREYRA, FRANCO MATIAS - Kansas State University; FALKENBERG, SHOLLIE - Auburn University; GIMENEZ-LIROLA, LUIS - Iowa State University; Arruda, Bailey

Submitted to: Viruses
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2023
Publication Date: 8/18/2023
Citation: Buckley, A.C., Mora-Diaz, J., Magtoto, R., Van Hulzen, A., Ferreyra, F., Falkenberg, S., Gimenez-Lirola, L., Arruda, B.L. 2023. Dynamics of infection of atypical porcine pestivirus in commercial pigs from birth to market: a longitudinal study. Viruses. 15(8):1767. https://doi.org/10.3390/v15081767.
DOI: https://doi.org/10.3390/v15081767

Interpretive Summary: Atypical porcine pestivirus (APPV) is a pestivirus that infects swine first sequenced in 2015 during an investigation into a viral cause for congenital tremors in piglets. Congenital tremors (CT) are characterized by contractions of skeletal muscle and have been observed in swine for nearly a century with clinical pigs also referred to as shaker pigs. CT resolves in most pigs over time; however, it can be severe enough to negatively impact the piglets ability to nurse. Experimental studies inoculating pregnant sows with the virus produced shaker pigs at birth supporting APPV as a causative agent for CT in pigs. Subsequently, APPV has been found in swine samples not only from CT piglets but also apparent healthy animals. Small scale longitudinal studies from the field have followed CT piglets and sampled them over time through the resolution of clinical signs and have found evidence of viral persistence in multiple sample types including serum, feces, and oral fluids. The goal of this research was to gain a better understanding of the pathogenesis of APPV in swine by following a large cohort of pigs over time to characterize viral load in the blood and the correlating antibody response specifically comparing CT positive pigs to littermates without CT as well as those born in CT negative litters. There were 60 pigs in CT positive litters and 37 pigs from CT negative litters for a total of 97 pigs. Once a month for a total of six months, enrolled animals were bled for serum collection and observed for clinical signs of CT. There was a wide range in the percentage of CT affected pigs (8-75%) within CT positive litters and APPV was detected in serum of both affected and unaffected pigs. Both groups had evidence of maternal antibodies in their serum at the first sample timepoint. Pigs from CT positive litters were co-mingled with pigs from CT negative litters at weaning and pigs from CT negative litters quickly developed viremia that was cleared after a couple months, and a majority seroconverted by the end of the study. In contrast, a greater percentage of pigs exhibiting CT remained PCR positive for APPV throughout the growing phase with less than one third of these animals developing a detectable individual antibody response. APPV nucleic acid was present in multiple tissues from pigs in both groups at the time of marketing. In summary, APPV and CT positive pigs tended to have longer lasting viremia and delayed or absent antibody responses; however, there was PCR evidence of viral persistence in tissues of all animals exposed to APPV. This study has improved understanding of the infection dynamics of APPV in swine and the impact that the immune status and timing of infection have on persistence of APPV in serum and tissues.

Technical Abstract: Congenital tremors (CT) have been observed sporadically in pigs for over a century. Recently, atypical porcine pestivirus (APPV) was found to be associated with pigs demonstrating CT and clinical signs in pigs were reproduced after experimental challenge. Subsequently, APPV has been identified in both symptomatic and asymptomatic swine of all ages globally. The objective of this research was to perform a longitudinal study following two cohorts of pigs, those born in litters with pigs exhibiting CT and those born in litters without CT, to analyze the virus and antibody dynamics of APPV infection in serum from birth to market. There was a wide range in the percentage of affected pigs (8-75%) within CT positive litters and APPV nucleic acid was detected in serum of both affected (100%) and unaffected pigs (31%). Pigs from CT positive litters were co-mingled with pigs from CT negative litters at weaning and pigs from CT negative litters quickly developed viremia that was cleared after a couple months, and a majority seroconverted by the end of the study. In contrast, a greater percentage of pigs exhibiting CT remained PCR positive throughout the growing phase with less than one third of these animals developing a detectable individual antibody response. APPV nucleic acid was present in multiple tissues from pigs in both groups at the time of marketing especially the cerebellum, nasal turbinate, and salivary gland. This study has improved understanding of the infection dynamics of APPV in swine and the impact that the immune status and timing of infection have on persistence of APPV in serum and tissues.