Cryptosporidium infection in dairy cattle

For almost 25 years, it has been known that Cryptosporidium parasites infect Swedish calves. This thesis explores how common these parasites are at herd level and at individual level in preweaned calves, young stock and periparturient cows. Species distribution and association with diarrhoeal problems are also highlighted. Two field studies were performed and in addition, existing clinical or cohort studies on the cryptosporidiostatic substance halofuginone were examined. Cryptosporidium oocyst shedders were detected in 68 of 69 investigated herds. Calves had the highest prevalences followed by young stock and cows. The four common species in cattle, C. parvum, C. bovis, C. ryanae and C. andersoni, were all detected. Cryptosporidium bovis was most common in all age groups with an overall 77% prevalence, and the prepatent period was shown to be at least three days shorter than previously described. Overall, Cryptosporidium infection was not associated with disease in calves, but a higher percentage of calves infected with C. parvum had diarrhoea compared to calves infected with C. bovis. Nine different C. parvum subtypes were identified, of which three were novel. All subtypes belonged to the zoonotic subtype families iia and iid. Several management factors were associated with shedding of oocysts. One management factor, 'disinfection of single pens', was associated with diarrhoeal problems at herd level, but several more management differences were indicated although they could not be shown statistically. Halofuginone had some beneficial effects on infection and diarrhoeal prevalences when used for prophylaxis, but mortality was not affected. Cryptosporidium parasites were widely spread in the Swedish dairy cattle population, but because most animals were not infected with the zoonotic C. parvum, the potential for zoonotic transfer is fairly low. Management routines are important to decrease infection pressure and prevent infected calves from clinical disease. Halofuginone should be used with great care in a transition period when management routines are changed to improve calf health