Importance and Characterisation of Concurrent Pathogens in Diarrhoeic Calves from North-Western Spain

Neonatal calf diarrhoea (NCD) is the leading cause of mortality in calves under 30 days old. Although several pathogens are usually involved in outbreaks, most previous research has focused on specific enteropathogens or on the four agents traditionally associated with this syndrome. This study aimed to determine the prevalence of thirteen enteropathogens in 420 diarrhoeic calves under a month of age from north-western Spain and to identify the most frequent co-occurrences. Four diarrhoeagenic pathotypes of <i>Escherichia coli</i>, bovine rotavirus A, coronavirus, norovirus, nebovirus and torovirus were identified using qPCR. Presence of <i>Salmonella</i> spp. was studied using a serum agglutination test. A direct immunofluorescence assay was employed to identify <i>Cryptosporidium</i> and <i>Giardia duodenalis</i> oo/cysts. <i>Eimeria</i> oocysts were found by the floatation technique. Our results confirm the co-occurrence of agents in most cases of NCD. A total of 172 pathogen combinations, involving up to seven agents, were identified. Cases involving one or more viral agents and <i>Cryptosporidium parvum</i> were predominant, maybe because viral immunosuppression facilitates the protozoan life-cycle. The frequent detection of agents typically overlooked in the aetiological diagnosis of NCD suggests that they may play a role in this syndrome and thus should be included in routine diagnostic panels, allowing implementing the most effective control measures.