Search

Highlights • Vaccination of sows with an inactivated MRV3 vaccine induced only a low level humoral response. • Maternal immunity acquired from vaccinated sows reduces MRV3 replication. • The U.S. MRV3 infects but only causes very mild diarrhea in pigs. Abstract A novel U.S. strain of mammalian orthoreovirus type 3 (MRV3) isolated from diarrheic pigs in 2015 was reportedly highly pathogenic in pigs. In this study, we first developed an inactivated MRV3 vaccine and determined its protective efficacy against MRV3 infection in conventional neonatal piglets. A pathogenicity study was also conducted in gnotobiotic pigs to further assess the pathogenicity of MRV3. To evaluate if piglets could be protected against MRV3 infection after immunization of pregnant sows with an inactivated MRV3 vaccine, pregnant sows were vaccinated with 2 or 3 doses of the vaccine or with PBS buffer. Four-day-old piglets born to vaccinated and unvaccinated sows were subsequently challenged with MRV3. The results showed that piglets born from vaccinated sows had lower levels of fecal viral RNA shedding at 1, 3, and 4 days post-challenge, suggesting that the inactivated MRV3 vaccine can reduce MRV3 replication. Surprisingly, although the conventional piglets were infected, they did not develop severe enteric disease as reported previously. Therefore, in an effort to further definitively assess the pathogenicity of MRV3, we experimentally infected gnotobiotic pigs, a more sensitive model for pathogenicity study, with the wild-type MRV3 virus. The infected gnotobiotic piglets all survived and exhibited only very mild diarrhea in some pigs. Taken together, the results indicate that the novel strain of MRV3 recently isolated in the United States infected but caused only very mild diarrhea in pigs, and that maternal immunity acquired from sows vaccinated with an inactivated vaccine can reduce MRV3 replication in neonatal pigs. [ABSTRACT FROM AUTHOR]

More than two decades after its emergence, porcine circovirus type 2 (PCV2) remains an economically important swine pathogen. Commercial vaccines which were first introduced to the U.S in 2006, have been highly effective in reducing clinical signs and improving production. Recent studies have indicated a declining level of PCV2 prevalence and viremia in the field. However, reports on the emergence of new viral variants have also continued to increase. This article reviews topics of current interest in the field of PCV2 vaccines; including the comparative efficacy of the available commercial products, efficacy of current vaccines against new and emerging strains, findings on the differences between immunity in natural infection versus vaccination, limitations of current experimental models for PCV2 vaccine studies, and new developments in novel experimental vaccines. The discussion is framed in the context of attempts for the possible eradication of PCV2 in the future. [ABSTRACT FROM AUTHOR]