Metagenomic insights into the complex viral composition of the enteric RNA virome in healthy and diarrheic calves from Ethiopia.

Background: Viruses and the virome have received increased attention in the context of calf diarrhea and with the advancement of high-throughput sequencing the detection and discovery of viruses has been improved. Calf diarrhea, being the main contributor to calf morbidity and mortality, is a major issue within the livestock sector in Ethiopia. However, studies on viruses and the virome in calves is lacking in the country. Therefore, we utilized viral metagenomics to investigate the diversity of RNA viruses in healthy and diarrheic calves from central Ethiopia.

Methods: Fecal material from 47 calves were collected, pooled, and sequenced using Illumina. Following sequencing, the virome composition and individual viral sequences were investigated using bioinformatic analysis.

Results: The metagenomic analysis revealed the presence of several RNA viruses, including rotavirus and bovine coronavirus, known causative agents in calf diarrhea. In addition, several enteric RNA viruses that have not been detected in cattle in Ethiopia previously, such as norovirus, nebovirus, astrovirus, torovirus, kobuvirus, enterovirus, boosepivirus and hunnivirus were identified. Furthermore, a highly divergent viral sequence, which we gave the working name suluvirus, was found. Suluvirus showed a similar genome structure to viruses within the Picornaviridae family and phylogenetic analysis showed that it clusters with crohiviruses. However, due to its very divergent amino acid sequence, we propose that suluvirus represent either a new genus within the Picornaviridae or a new species within crohiviruses.

Conclusions: To our knowledge, this is the first characterization of the RNA virome in Ethiopian cattle and the study revealed multiple RNA viruses circulating in both diarrheic and healthy calves, as well as a putative novel virus, suluvirus. Our study highlights that viral metagenomics is a powerful tool in understanding the divergence of viruses and their possible association to calf diarrhea, enabling characterization of known viruses as well as discovery of novel viruses.