Prevalence of <i>Cryptosporidium parvum</i> , <i>Giardia duodenalis</i> and <i>Eimeria</i> spp. in diarrhoeic suckling calves from north-western Spain and analysis of their interactions

Although <i>Cryptosporidium parvum</i>, <i>Giardia duodenalis</i> and some <i>Eimeria</i> species are frequently involved in neonatal calf diarrhoea (NCD), detailed studies on their interactions are scarce. Therefore, a cross-sectional study including faecal samples from 404 diarrhoeic calves aged 0-30 days was performed. <i>Cryptosporidium</i> oocysts and <i>G. duodenalis</i> cysts were detected by immunofluorescence antibody test and positive samples were molecularly characterized. <i>Eimeria</i> oocysts were microscopically detected using the modified McMaster technique and morphometric species identification was performed. <i>Cryptosporidium</i> infections (53.7%) predominated over those by <i>G. duodenalis</i> (12.4%) and <i>Eimeria</i> spp. (6.9%). Three <i>Cryptosporidium</i> species were identified: <i>C. parvum</i> (98.0%), <i>C. bovis</i> (1.0%) and <i>C. ryanae</i> (1.0%). Eleven <i>C. parvum</i> zoonotic subtypes were detected, with IIaA15G2R1 as the most common; only <i>G</i>. <i>duodenalis</i> assemblage E was identified. Moreover, 10 <i>Eimeria</i> species were found, being <i>Eimeria ellipsoidalis</i> (96.4%), <i>Eimeria bovis</i> (85.7%), and <i>Eimeria zuernii</i> (71.4%) predominant. A significant positive association between <i>G. duodenalis</i> and <i>Eimeria</i> spp. was detected as well as a negative association between <i>C. parvum</i> and <i>Eimeria</i> spp. Our results showed that <i>C. parvum</i> wasprevalent in diarrhoeic calves under 21 days of life; <i>Eimeria</i> spp. and <i>G. duodenalis</i> were especially common in animals in their fourth week of life. Concurrent infections increased with age. Moreover, the study also revealed potential public health risks since a noticeable percentage of animals were infected with <i>C. parvum</i> zoonotic subtypes. Further studies are needed for determining the role of these parasites in co-infections with other enteropathogens and their implications in the pathogenicity of NCD.