Characterization of rumen and fecal microbiota in dairy cows infected with bovine leukemia virus
Bovine leukemia virus (BLV) is a virus infecting cows, belonging to Retroviridae family Deltaretrovirus genus. BLV is prevalent globally except for some countries that have achieved viral eradication. Because most BLV-infected cattle (approximately 70%) are asymptomatic, the shedding rate of BLV in the cattle population is extremely high and its control is extremely difficult. Approximately 30% of BLV-infected cattle develop persistent lymphopenia (PL), and approximately 1-5% may form malignant B-cell lymphosarcoma after prolonged latency (1-8 years), which is also known as enzootic bovine leucosis (EBL). Subclinical infection causes secondary negative effects such as increased susceptibility to other infections, and decreased lifetime milk production and reproductive efficiency. Cows diagnosed with EBL are generally slaughtered. Thus, because BLV infection greatly causes the significant economic loss worldwide, the pathogenesis by BLV infection should be understood precisely for infection control and management.    The microbiota of digestive tracts, particularly rumen and gut microbiota, play an essential role in maintaining the health in the cows. The rumen microbiota is majorly responsible for digesting and fermenting plant organic matter and converting it into energy for the host. The gut microbiota also contributes to the host health mediated by immunity. Many factors, including food intake, host genetics, age, environment, health state (e.g., infections and chronic disease), and stress can influence the microbiota. According to the adverse health effects by BLV infection, we hypothesized that BLV infection can cause the rumen and gut microbiota imbalance. To support this hypothesis, we have previously shown that the gut microbiota of cows can be modulated with minute changes in microbes with low abundance in the cows with subclinical infection. However, to our best knowledge, both rumen and gut microbiota related with BLV subclinical infection has not been examined by co-occurrence abundance network analysis. In many microbiota studies, the microbes with the high abundance were analyzed with the analytical factors. Because the microbes interact each other and function together, the microbes with lower abundance are considered to be important. Because of the complexity of the structure and function of the bacterial flora, it is necessary to elucidate microbial interactions in order to clarify the ecological role of microbes. To elucidate microbial interactions, co-occurrence network analysis, a method to analyze microbial relationships by modeling the co-occurrence of microorganisms using network analysis, can be used. In this study, we have investigated the rumen and gut microbiota of BLV-infected cows and healthy cows by co-occurrence network analysis, and statistically compare these networks. to illustrate important factors and functional microbes.