#17-073

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Date Abstract Report Received

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In the past few years, diarrhea in neonatal piglets has emerged as a major contributor to decreased pork production efficacy and increased pre-weaning mortality. Rotavirus C (RVC) circulation in swine in the US was reported for many decades; however, only recently was the strong association between RVC and diarrhea in neonatal suckling piglets recognized as having a significant impact on the pork industry. The additional challenge is that most RVC strains do not replicate in cell culture hindering the development of much needed diagnostic tools and vaccines. Therefore, comprehensive studies to evaluate the current prevalence of porcine RVC, its pathogenesis in neonatal piglets and the effect of maternal immune status, as well as development of appropriate diagnostic tools for such studies, are of utmost importance and urgency to develop adequate control and prevention measures. Our study targeted the 3 focus areas for porcine RV research defined in the original NPB RFP: a) development of group specific assays to measure antibody levels following vaccination/exposure; b) identification of factors affecting RVC pathogenesis in young pigs, and c) development of the assays to monitor and understand the mechanisms of RVC spread in the US.
Objective 1. To develop and use an antibody (Ab) ELISA to evaluate porcine RVC Ab prevalence in sows in Ohio in conjunction with qRT-PCR evaluation of the RVC prevalence in their nursing piglets.
Fecal samples were collected form healthy (n=56) and diarrheic (n=56) piglets and blood and milk samples were collected from their sows (n=15, sows with diarrheic piglets; n=15, sows with healthy piglets) from a commercial swine farm in Ohio. Using quantitative RT-PCR, we have confirmed an overall high RVC prevalence (76.1%) and very low prevalence of RVA (6.2%) and RVB (0%) in the fecal samples from both diarrheic and healthy piglets. Further, the amounts of RVC shed by diarrheic piglets were significantly higher than those shed by healthy piglets. Frequency of RVC shedding was also increased in diarrheic piglets. Thus, our data indicated that RVC is indeed the single major pathogen associated with diarrhea in neonatal piglets. Further, we observed that the majority of diarrheic litters (73%) were born to gilts (1st parity) and only 27% to sows (parity ≥2).
Using historic and current RVC strains of different dominant genotypes (collected in our previous studies), we have generated RVC virus-like particles, VLPs, (viral particles that have no genomes and can’t replicate) that were used to develop ELISA assays for RVC antibody detection in swine serum and milk samples. This approach represents the only alternative to classical methods that rely on availability of cell culture adapted viral strains.
Using this ELISA, we demonstrated for the first time that RVC diarrhea occurrence and increased RVC replication in suckling piglets are strongly associated with insufficient RVC antibody titers in the milk of gilts, while most second and higher parity sows were able to protect their piglets (even those infected with RVC) from clinical RVC disease. Thus, we have established a platform to monitor immune responses to RVC, to study RVC pathogenesis and the interplay between the virus pathogenicity and maternal immunity. Additionally, the generated RVC VLPs can be evaluated as a vaccine candidate to boost RVC immunity in pregnant swine. Our findings indicate that gilts may require additional treatments to decrease neonatal piglet morbidity and mortality. These treatments may include the following: booster vaccinations with autogenous or non-replicating vaccines; separate housing to minimize pathogen exposure; cross-fostering of their piglets by sows (with healthy litters) to improve lactogenic (through sow milk) protection.
Objective 2. To comparatively assess the pathogenesis of porcine RVCs of genotypes G3 and G6 in 1-7 and 21 day old germfree piglets.
We originally hypothesized that the currently increasing RVC prevalence may be associated with vaccination against RVAs that led to a relative decrease in their prevalence. However, our results demonstrated very high overall frequency of RVC (76.1%) and very low prevalence of RVA (6.2%) and RVB (0%) infections in suckling neonatal piglets. This likely suggests that in the past decades RVC has emerged as the major viral enteropathogen of concern for this age group. Further, we theorized that the more frequent RVC detection in the in fecal samples of diarrheic nursing piglets may be due to increased pathogenicity of the current RVC. To test this, we compared the pathogenicity of historic (Cowden) and current (G3 and G6 genotype) porcine RVC strains in germfree (microbiota-free) piglets. We observed that some of currently circulating RVC strains produced more intestinal lesions, higher and/or prolonged virus shedding compared to historic or other current RVC strains. Additionally, in contrast to Cowden, the current strains were capable of causing diarrhea in 3-week-old piglets. Thus, our data indicate that some of the current RVC strains can possess increased pathogenicity and abilities to spread (even in older animals) which may contribute to the recent increase in the prevalence of clinical RVC disease in neonatal suckling piglets.

PI contact information: Anastasia N. Vlasova, DVM, PhD; The Ohio State University; Food Animal Health Research Program; 1680 Madison Ave, Wooster, Ohio, 44691; Phone: (330) 263-3740, Fax: (330) 263-3677. Email: vlasova.1@osu.edu