Occurrence of respiratory and enteric bacteria and viruses in calves in Iceland

Respiratory and gastrointestinal diseases in calves pose a significant challenge to the cattle industry due to their impact on mortality rates, economic losses, animal welfare, and antimicrobial usage. Understanding which pathogens are involved is crucial for optimizing both treatment and preventive measures. In Iceland, bovine respiratory disease in calves is relatively rare, whereas neonatal calf diarrhea is more frequent. However, limited diagnostic resources in the country have resulted in a lack of knowledge about the specific pathogens involved. This study aimed to investigate the occurrence of respiratory and enteric bacteria and viruses in Icelandic calves from birth to three months of age. Twenty (20) herds participated in this cross-sectional study, twelve located in Northeastern (NE) part of Iceland and eight in the Western (W) part, and a total of 197 calves were enrolled in the study. The calves underwent clinical examination, and nasal swab and fecal samples were collected. Herd owners completed a questionnaire regarding calf health, biosecurity, and management practices. The samples were pooled according to regions, seasons, and age groups and analyzed for the presence of selected viruses and bacteria using quantitative real-time PCR.

Among the nasal swab pools, the most identified pathogens were Trueperella pyogenes (75%), Mycoplasma spp. (45%), Histophilus somni (36%), bovine coronavirus (BCoV) (28%), Pasteurella multocida (17%), and Mannheimia haemolytica (6%). Among the feces pools, BCoV (24%) and rotavirus A (RVA) (23%) were the sole detected pathogens. A greater diversity of pathogens was detected in the NE region than in the W region, since BCoV, P. multocida and M. haemolytica were not identified in the latter. Diarrhea was the most common clinical sign, and half of the diarrheic calves tested positive for RVA.

This study provides novel insight into the bacterial and viral pathogens circulating in Icelandic calves. Although pathogen diversity was higher in the NE region than in the W region, few clinical signs were observed. Most pathogens were detected across age groups, while seasonal variation in pathogen occurrence was limited in the NE region. These findings improve our understanding of pathogen distribution in Iceland and may support future disease surveillance and preventive strategies.