Pathobiology of rotaviral diarrhea in calves and its diagnosis and control: A review
Among all the etiological agents causing diarrhea in calves, rotaviruses have a significant role and are considered as pathogens with the potential to cause huge economic losses to the livestock industry, besides causing death of millions of children in developing countries. Bovine rotavirus (BRV), a segmented ds RNA virus belonging to the family Reoviridae, is capable of cross-species transmission also. Rotavirus infection, a nonviremic disease, and causing enteritis and diarrhea in young calves, mainly gets transmitted through ingestion of feces-contaminated material. Incubation period of the disease is very short and the virus multiplies in the cytoplasm of intestinal epithelial cells (enterocytes) and gets released by cell lysis. Affected calves are presented with watery diarrhea following which fatal results are observed due to severe dehydration. The sialic acid receptors and integrins are known to act as receptors for the virus to initiate the pathogenesis, contrary to the earlier belief of direct virus entry by pinocytosis. Pathological lesions reveal mucosal congestion and the presence of catarrhal exudate in lumen of small intestine. Concurrent infection with other pathogens like Escherichia coli or bovine viral diarrhea virus (BVDV) can potentiate the disease severity. Rotavirus induces diarrhea primarily due to malabsorption based on the destruction of mature enterocytes, activation of enteric nervous system and also due to secretion of a viral enterotoxin known as non-structural protein 4 (NSP4). For diagnosis of rotaviruses, various techniques viz., electron microscopy, viral RNA-PAGE, antigen capture ELISA, dot-immunobinding, immunofluorescence test, immunoperoxidase test, passive Heme Agglutination and latex agglutination test are employed. Virus characterization is performed using Reverse Transcription-PCR (RT-PCR), Restriction Fragment Length Polymorphism (RFLP), dot blot hybridization, sequencing and microarray hybridization. For prevention and control of BRV in young calves, good management practices along with vaccinating dam with inactivated BRV vaccine a few weeks before parturition, is commonly followed. Feeding of colostrum and mucosal immunity play crucial role in providing resistance to infection in young calves. New generation vaccines like DNA vaccine, subunit vaccines, virus-like particles (VLPs) and plantbased edible vaccines are also being explored to counter this economically important disease of livestock.
Bovine rotavirus, calf diarrhea, neonatal diarrhea, enteritis, immunity, diagnosis, vaccination.