Detection and Cellular Tropism of Porcine Astrovirus Type 3 on Breeding Farms

Abstract

Astroviruses cause disease in a variety of species. Yet, little is known about the epidemiology of a majority of astroviruses including porcine astrovirus type 3 (PoAstV3), which is a putative cause of polioencephalomyelitis in swine. Accordingly, a cross-sectional study was conducted on sow farms with or without reported PoAstV3-associated neurologic disease in growing pigs weaned from those farms. Additionally, a conveniently selected subset of piglets from one farm was selected for gross and histologic evaluation. The distribution of PoAstV3 in the enteric system was evaluated through in situ hybridization. PoAstV3, as detected by RT-qPCR on fecal samples, was frequently detected across sows and piglets (66–90%) on all farms (65–85%). PoAstV3 was detected subsequently at a similar detection frequency (77% vs 85%) on one farm after three months. Viral shedding, as determined by the cycle quantification value, suggests that piglets shed higher quantities of virus than adult swine. No link between gastrointestinal disease and PoAstV3 was found. However, PoAstV3 was detected by in situ in myenteric plexus neurons of piglets elucidating a possible route of spread of the virus from the gastrointestinal tract to the central nervous system. These data suggest PoAstV3 has endemic potential, is shed in the feces at greater quantities by suckling piglets when compared to sows, and infection is widespread on farms in which it is detected.

Ecology of Porcine Astrovirus Type 3 in a Herd with Associated Neurologic Disease

“…Xiao et al [10] reported overall detection of PoAstV3 by RT-qPCR in the US as 1.2% (6 of 509) in fecal samples from routine diagnostic cases submitted between 2011 and 2012 to the Iowa State University Veterinary Diagnostic Laboratory. Yet, a recent report found a high frequency of detection of PoAstV3 (65-85%) on three sow farms [19]. These data and the data presented in this report suggest that, while PoAstV3 is infrequently detected in the US swine herd, it can be highly prevalent on farms where it is detected.…”

“…This could suggest that, at the time of clinical neurologic disease, PoAstV3 is not being shed in feces; however, it may also reflect that there are multiple etiologies that can cause similar clinical signs. Astroviruses, including PoAstV3, are known to infect and be shed by apparently healthy animals [8,19,[24][25][26][27]. In the four cases from the case-control study that were selected for a diagnostic investigation, only two cases had lesions consistent with a viral infection in the CNS.…”

“…The RT-qPCR methods for PoAstV3 RNA detection were done at the Iowa State University Veterinary Diagnostic Laboratory (ISU-VDL), as previously described [19]. The standard curve is presented in Supplementary Materials file 1.…”

“…The advent of next-generation sequencing (NGS) methods has provided additional insight into astroviruses and their role in disease. As technology progresses, the spectrum of astrovirus genotype species has increased significantly with concurrent growing evidence that MAstVs are involved in neurologic disease in several mammals including humans, cattle, mink, sheep, and more recently pigs [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. The pathogenic significance of PoAstVs is not well characterized with the exception of PoAstV3 (MAstV22), which has been recently associated with outbreaks of polioencephalomyelitis in swine in the United States [ 17 , 18 , 19 ] and Hungary [ 20 ].…”

Postweaning mortality in commercial swine production II: review of infectious contributing factors

“…In recent years, an increase in the incidence of neurological syndromes has been observed and, in many cases, associated with diagnosis of viral infectious agents. This is still an area of ongoing research efforts, but multiple viruses recently have been associated with neurological syndromes, including porcine sapelovirus ( Schock et al, 2014 ; Arruda et al, 2017b ), porcine astrovirus type 3 ( Boros et al, 2017 ; Rawal et al, 2019 ; Matias Ferreyra et al, 2020 ), and porcine teschovirus ( Bangari et al, 2010 ; Deng et al, 2012 ; Carnero et al, 2018 ). The recently described atypical porcine pestivirus has been associated with congenital tremors ( de Groof et al, 2016 ; Postel et al, 2016 ; Schwarz et al, 2017 ) but is not believed to be a major contributor to postweaning mortality ( Gatto et al, 2019 ).…”