Virological investigation of norovirus infection in calves

Objective: Bovine norovirus (BNoV) and bovine nebovirus (BNeV) collectively constitute the Bovine Enteric Calicivirus (BEC). Bovine norovirus affects the villous epithelial cells of the duodenum and jejunum in calves, giving rise to symptoms such as non-hemorrhagic enteritis, diarrhea, anorexia, reduced appetite, and malabsorption. These viral agents, primarily transmitted via the fecal-oral route, tend to manifest as mixed infections. The development of calf diarrhea leads to growth retardation, necessitating supplementary feeding to address nutritional deficits, and culminating in outcomes such as mortality and subsequent diminished milk yield, thereby engendering substantial economic losses. The aim of the present study was molecular virological investigation BNoV and additionally BNeV infections in cattle with diarrheal symptoms, in Aksaray and Aydın provinces. In addition, the influence of age, gender, and breed on the incidence of the disease was also examined. Materials and Methods: A total of 103 fecal samples were collected from cattle exhibiting diarrhea symptoms in small family farms and intensive farming operations in Aksaray and Aydın provinces. In Aksaray, 71 samples were collected from calves, while in Aydın, 32 samples were obtained from cattle under one year of age and those over one year of age in an organized dairy farming facility with observed cases of diarrhea. The collected samples were subjected to nested RT-PCR targeting the RdRp regions of the viruses. Among the samples that tested positive, 8 were selected, and partial RdRp region sequence analyses were performed using the Sanger sequencing method. Results: A total of 103 samples were subjected to analysis via the nested RT-PCR method, revealing that 26 of them (26.2%) tested positive for BNoV, while 2 samples (1.9%) were found to be positive for BNeV (1.9%). Specifically, among the 71 samples collected from Aksaray province, 3 of them (4.3%) tested positive for BNoV, and 2 samples (2.9%) were positive for BNeV. In contrast, of the 32 samples obtained from Aydın province, a significant majority, constituting 23 samples (71.8%), were identified as positive for BNoV. Subsequent sequence analysis of the BNoV and BNeV positive samples from Aksaray province revealed their affiliation with BNoV GIII-genotype I and the BNeV Nebraska group, respectively. Conversely, the BNoV positive samples from Aydın province were classified under the GIII.2 group. Upon conducting statistical analyses concerning age, gender, and breed, it was observed that the incidence of BNoV infection increased notably in animals older than 6 months and among female cattle. Additionally, a significant disparity among breeds in terms of infection rates was detected. Conclusion: In the present study, the genotypes GIII-1 and GIII-2 of BNoV were detected in provinces of Aksaray and Aydın, respectively. Moreover, the study suggested that BNoV infection, considered as a calf-associated infection, might exhibit sensitivity variations across different breeds, potentially presenting a higher prevalence among female individuals. The virus was found to be capable of affecting animals of all ages, contingent upon host, virus, and environmental factors. In light of both the study's findings and existing literature, the escalating frequency of BNoV infections has underscored the potential threat it poses to cattle husbandry, emphasizing the necessity for comprehensive measures. The study emphasizes the need to acknowledge (BEC) infections in cases of diarrhea and underscores the importance of instituting preventative measures and developing strategies for combating these infections, particularly considering their propensity to coexist with other infectious agents, thereby potentially leading to heightened transmission and more severe outcomes. Consequently, strict adherence to farm hygiene and care practices is advisable. Key words: Bovine Norovirus, Calf, Diarrhea, Nebovirus, RT-PCR.