Genetic Diversity of Bovine Group A Rotavirus Strains Circulating in Korean Calves during 2014 and 2018

Simple Summary Morbidity and mortality rates due to bovine group A rotavirus (BoRVA) infections are high, resulting in direct and indirect economic losses to the beef and dairy industries. RVA strains, which are antigenically heterogeneous, are classified into multiple G and P types; these two types are defined by the two outer capsid proteins VP7 and VP4, respectively. A clear understanding of the various VP7 and VP4 type-specificities is required to ascertain whether it is necessary to construct polyvalent RVA vaccines for calves. In the past, BoRVA G8P[7] was the predominant type in Korean calves; however, we consistently identified G6P[5] as the main cause of diarrhea in young calves from 2014 to the present day. The purpose of this study was to investigate annual changes in BoRVA strains by examining the VP4 and VP7 genes of rotaviruses in Korean calves. Between 2014 and 2018, 35 out of 138 samples of calf diarrhea feces collected nationwide were positive for BoRVA. Further genetic characterization of the VP7 and VP4 genes of 35 BoRVA isolates identified three different G-genotypes (G6, G8, and G10) and two different P genotypes (P[5] and P[11]). The G6 genotype was most common (94.3%) in BoRVA-positive calves, followed by the P[5] genotype (82.9%). Four genotypes comprised combinations of VP4 and VP7: 80% were G6P[5], 14.2% were G6P[11], 2.9% were G8P[5], and 2.9% were G10P[11]. Susceptibility to infection was highest in calves aged < 10 days (35%) and lowest in calves aged 30-50 days (15.4%). The data presented herein suggest that the G6P[5] genotype is the main causative agent of diarrhea in Korean calves. In addition, it is predicted that G6P[5] will continue to act as a major cause of diarrhea in Korean calves.