Ecology of Porcine Rotaviruses

Abstract

Rotaviruses (RVs) cause severe diarrhea in young animals including pigs and humans. Porcine RV infections cause severe economic losses for swine farmers. Since RV infections can be symptomatic or asymptomatic in pigs, economic losses are difficult to estimate. Recent studies are lacking to estimate the economic loss to farmers partly due to the historical lack of proper RV diagnostic assay, making any previous estimates inaccurate. While the severity of disease can greatly differ due to many variables, RV morbidity and mortality are highest in piglets (<21 days of age) (Estes and Greenberg, 2013). The high mortality in piglets is due to many factors such as the greater size of the small intestine in proportion to overall body size, the destruction of the enterocytes during RV infection, and the inability to quickly restore intestinal function and structure. In addition, the piglet has an immature immune system and must rely on passive immunity from the sow to protect against a RV infection. As pigs reach 21 days and older, their ability to recover from a RV infection, and the immune response to a RV increases and mortality decreases. Five RV species have been identified in swine: rotavirus A, B, C, E, and H (RVA, RVB, RVC, RVE, and RVH, respectively) (Estes and Greenberg, 2013). Rotavirus A (RVA) has commonly been identified as an important cause of diarrhea in pigs and numerous porcine RVA studies have been conducted, illustrating the importance of RVA in swineherds (Miyazaki et al. 2011; Amimo et al. 2013a; Miyazaki et al. 2013; Hong Anh et al. 2014; Li et al. 2014; Monini et al. 2014). However, research on RVB, RVC, RVE and RVH is only in its infancy. RV epidemiology and molecular diversity depends on viral, host and environmental factors. Understanding the occurrence of RVA, RVB, RVC, and RVH within the pig population will allow us to ascertain predominant RV species in specific swine age groups. While several studies have investigated the occurrence and molecular diversity of RVA in swine, there is limited data available on the occurrence and molecular diversity of RVB, RVC, and RVH. To prevent and control of RV infections in swineherds and estimate the economic losses associated with RV infections, more research is needed on RVB, RVC, RVE, and RVH, including the development and validation of new diagnostic tools to identify RV in an efficient and timely matter. In conclusion, swine RVA has been known as the most important cause of diarrhea in swine, but the information on swine RVB, RVC, and RVH is severely lacking. Understanding the ecology of swine RV species is important to help prevent and control RV infections in swineherds. This thesis will 1) establish swine RVB as an important cause of diarrhea and assess the genetic diversity of the VP7 and VP6 gene segments, 2) develop real time RT-PCR assay to estimate the occurrence of RVA, RVB, and RVC in porcine samples, 3) assess the VP7 genetic diversity of porcine RVC strains, and 4) identify and estimate the emergence of RVH in the US swine population.