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Abstract
The increased prevalence of porcine group C rotavirus (PRVC) in suckling piglets and the emergence of new genetically distinct PRVC strains are concerning due to the associated significant economic losses they cause to the swine industry. We sequenced and analyzed two new PRVC strains, RV0104 (G3), and RV0143 (G6) and compared their pathogenesis with that of the historic strain Cowden (G1) in gnotobiotic (Gn) pigs. Near complete genome sequence analysis confirmed that these two strains were distinct from one another and the Cowden strain. VP1, VP2, VP6, NSP1-NSP3, and NSP5 genes were more similar between Cowden and RV0143, whereas VP3, VP7, and NSP4 shared higher nucleotide identity between Cowden and RV0104. Three-day-old and 3-week-old Gn piglets were inoculated with 105 FFU/piglet of Cowden, RV0104 or RV0143, or mock. All 3-day-old piglets developed severe diarrhea, anorexia, and lethargy, with mean PRVC fecal shedding titers peaking and numerically higher in RV0104 and RV0143 piglets on post infection day (PID) 2. Histopathological examination of the small intestine revealed that the 3-day-old Cowden and RV0104 inoculated piglets were mildly affected, while significant destruction of small intestinal villi was observed in the RV0143 inoculated piglets. Consistent with the highest degree of pathological changes in the small intestines, the RV0143 inoculated piglets had numerically higher levels of serum IL-17 and IFN-α cytokines and numerically lower PRVC IgA geometric mean antibody titers. Milder pathological changes and overall higher titers of PRVC IgA antibodies were observed in 3-week-old vs. 3-day-old piglets. Additionally, diarrhea was only observed in RV0104 and RV0143 (but not Cowden) inoculated 3-week-old piglets, while levels of serum IL-10 and PRVC IgA antibodies were higher in Cowden inoculated pigs, consistent with the lack of diarrhea. Thus, we confirmed that these current, genetically heterogeneous PRVC strains possess distinct pathobiological characteristics that may contribute to the increased prevalence of PRVC diarrhea in neonatal suckling piglets.
Highlights
Rotaviruses (RVs) infect small intestinal mature enterocytes on the tips of the villi in the small intestines causing diarrhea and destruction of these enterocytes (Estes et al, 2001)
Nucleotide identity between RV0104 and RV0143 ranged from 73% (NSP1) to 97% (NSP2) with overall higher nucleotide identity between RV0104 and Cowden noted in VP1 an NSP (Table 2)
3-week-old piglets inoculated with the new Porcine rotavirus group C (PRVC) strains developed diarrhea in contrast to those inoculated with Cowden, which supports our other findings suggestive of increased pathogenicity of the current PRVC strains
Summary
Rotaviruses (RVs) infect small intestinal mature enterocytes on the tips of the villi in the small intestines causing diarrhea and destruction of these enterocytes (Estes et al, 2001). Several mechanisms of diarrhea induction by RVs have been described: malabsorption of fluids and electrolytes that occurs due to the extensive damage to small intestinal villous epithelium, activation of the enteric nervous system induced by neurological dysfunction and the resulting disruption of blood flow due to damaged enterocytes, and the action of RV non-structural protein, NSP4, an enterotoxin that increases intracellular Ca2+ levels further disrupting fluid homeostasis in infected and noninfected adjacent cells (Ruiz et al, 2000; Estes et al, 2001; Vlasova et al, 2017). The complete genome analysis of rotavirus group C (RVC) strains has been done recently and it confirmed the existence of at least 18G, 21P, 13I, 4R, 6C, 6M, 9A, 8N, 6T, 5E, and 4H genotypes for the genes VP7, VP4, VP6, VP1, VP2, VP3, NSP1, NSP2, NSP3, NSP4, and NSP5, respectively, in terrestrial mammals (Suzuki and Hesebe, 2017). Understanding the pathogenesis of these strains will allow diagnostic tools and preventive measures to be developed, since RVC is increasingly being detected in both animals and humans and interspecies and zoonotic transmission has been confirmed (Saif et al, 1980; Rahman et al, 2005; Amimo et al, 2013; Marthaler et al, 2014; Kattoor et al, 2017; Vlasova et al, 2017)
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