Prevalence of porcine RVC in suckling piglets and the influence of maternal immunity on RVC disease

Annika Diaz
Category: 
Undergraduate (Animal Sciences – Health)
Advisor: 
Maurice Eastridge/Anastasia Vlasova
Department: 
Animal Sciences
Abstract: 

Rotavirus C (RVC) causes severe diarrhea in young piglets, often resulting in death. We hypothesized insufficient lactogenic RVC antibody (Ab) levels in sows will lead to the development of acute RVC diarrhea in piglets, whereas adequate lactogenic immunity will protect piglets from clinical disease. Our additional hypothesis was RVC disease severity may vary with RVC genotype. We aimed to 1) identify the prevalence and quantity of RVC in samples from nursing piglets, 2) analyze the role of maternal Abs in suckling piglet immunity, and 3) comparatively analyze the pathogenesis of the current (G3 and G6) and historic (Cowden, G1) RVC in gnotobiotic piglets. Rectal swabs from nursing piglets with and without scours were collected. Using RT-qPCR, we demonstrated 86 out of 113 samples (76.1%) were RVC positive. There was a significant positive relationship (p=0.018) between the quantity of RVC RNA detected in piglets with scours compared to healthy piglets. We noted a significantly higher number (p=0.0002) of litters with scours born to gilts (1st parity sows) than to higher parity sows. Because RVC strains (other than Cowden) cannot be propagated in cell culture, RVC virus-like particles (VLPs) were generated using VP2, VP4, VP6, and VP7 structural genes from three strains of RVC (Cowden=G1, RV104=G3, and RV143=G6), and BaculoDirect expression system. Using semi-purified VLPs as antigens in ELISA, RVC Abs were detected in serum and milk from sows. Results from the RVC-VLP ELISA showed gilts with scouring piglets have significantly lower RVC Ab titers in milk, but not in serum, as compared to sows with healthy litters. This suggests insufficient lactogenic protection from gilts plays a critical role in increased prevalence of RVC diarrhea. We also tested the hypothesis that the G3 and G6 strains have enhanced pathogenicity compared to G1. Gnotobiotic piglets (n=4-7/group) were inoculated with G1, G3, and G6 strains of RVC, using two control piglets. Rectal swabs were collected to determine fecal consistency reflective of diarrhea severity. All infected piglets presented clinical signs of RVC infection. There was no significant difference in fecal shedding between strains, however, G6 caused increased destruction of intestinal villi.