Molecular epidemiology and phylogenetic analysis of diverse bovine astroviruses associated with diarrhea in cattle and water buffalo calves in China

ALFRED, Niyokwishimira; LIU, Huan; LI, Mu Lan; HONG, Shao Feng; TANG, Hai Bo; WEI, Zu Zhang; CHEN, Ying; LI, Fa Kai; ZHONG, Yi Zhi; HUANG, Wei Jian

Our phylogenetic analysis showed that all isolates in this study were closely related to BAstV-B76-2/HK, BAstV-B18/ HK, CcAstV-1/DNK/2010 and CcAstV-2/DNK/2010, but highly divergent from a BAstV NeuroS1 isolate previously associated with neurologic disease in cattle in the U.S.A. [10] . Nonetheless, our results support that proposal [21] that BAstV and CcAstV may be different strains of the same virus, and water buffalo may be a new host of the BAstV variant of this virus. Moreover, most sequences derived from one farm belonged to one subgroup, although sequence analysis clearly demonstrated origins from different strains. In addition, no significant genetic differences were observed between the bovine and water buffalo astrovirus strains investigated in this study (Table 4 ). These results further support previous evidence that one farm could serve as a reservoir of different bovine astrovirus strains, suggesting possible outbreaks of novel astroviruses due to mutation or recombination events. Notably, considering the history of astroviruses, recombination events have been described in cattle, swine, humans and poultry [19, 21, 22] , and coinfection of two different astroviruses in one head of cattle has been previously reported as well [21] . Consequently, it is important to screen for and control astrovirus infection in order to prevent eventual outbreaks of highly pathogenic astroviruses resulting in mutation or recombination events on farms. Furthermore, the astrovirus isolates from cattle and water buffalo isolated in this study displayed relatively close relationships, indicating that these animals were infected with diverse astroviruses, which probably evolved from the same viral ancestor. Consequently, given these close relationships, evidence exists of possible cross-infection between the two hosts; therefore, control measures against bovine astrovirus should also be taken into consideration when screening of viruses in water buffalo populations.