AGE-RELATED RESISTANCE IN OVINE CRYPTOSPORIDIOSIS - PATTERNS OF INFECTION AND HUMORAL IMMUNE-RESPONSE

The phenomenon of age-related resistance to infection with Cryptospori dium parvum has been well characterized in rodent models, and its exis tence has been demonstrated in calves. To determine whether this is a genuine age effect in a fully susceptible animal model or the result o f infection with related pathogens inducing a nonspecific immunity, an d to examine several parameters associated with severity of clinical d iseases, lambs maintained in a parasite-free environment were infected with C. parvum oocysts at increasing ages. A marked decrease in the s everity of clinical symptoms was observed as the age at infection incr eased, though the kinetics of both fecal and serum antibody responses were similar in all age groups, suggesting that mechanisms other than humoral response may play an important role in the development of age- related resistance. This study demonstrates the first experimental evi dence for age-related resistance to ovine cryptosporidiosis and examin es parameters which may influence the acquisition of resistance to inf ection.