Astroviruses belong to the Astroviridae family and were initially associated with gastroenteritis in 1975. Recently, a subset of astroviruses have been identified as a cause of neurologic disease in human, bovine, mink, ovine and porcine.

Porcine astroviruses (PoAstVs) are distributed worldwide. PoAstVs are divided into 5 distinct genotypes (PoAstV1-5), reflecting different origins, interspecies transmission, and recombination events. The pathogenic significance of PoAstVs is questionable with the exception of PoAstV3 which is a putative cause of polioencephalomyelitis in swine. The goal of this thesis was to address some of the epidemiologic characteristics and pathophysiology of PoAstV3 through field research and pathologic evaluation.

Different types of field research including cross-sectional and a prospective longitudinal investigation were carried out on sow farms with and without reported PoAstV3-associated neurologic disease and in a nursery with an extensive history of neurologic disease due to PoAstV3, respectively.

The results of the first study demonstrated a high rate of detection of PoAstV3 in feces by qRT-PCR on the three sow farms sampled regardless of reported neurologic status in the downstream nursery, the endemic potential of PoAstV3 and a possible route of dissemination of PoAstV3 from the gastrointestinal system to the central nervous system through the myenteric plexus neurons of the peripheral nervous system. Results of the second study demonstrated the detection of PoAstV3 using different pig and environmental samples types including feces, oro-pharyngeal swabs, serum, oral fluids, pens, feeders, hallways, load out chutes, and pits. Detection of PoAstV3 over 22 weeks in individually identified animals in feces was intermittent, infrequent in oro-pharyngeal swabs and viremia was rare. This thesis illustrates the frequency of detection, endemic potential, cellular tropism, association of clinical signs with disease, efficiency of cleaning and disinfection, infection dynamics, and shedding patterns in different sample types over a 22 week period using observational studies, pathology, and RNAscope® in situ hybridization to help better understand the overall epidemiologic characteristics of PoAstV3.