Age related susceptibility of pigs to Cryptosporidium scrofarum infection.

Piglets from 4 to 8 weeks of age originated from a Cryptosporidium-free research breed were orally inoculated with 1 × 10(6) infectious oocysts of Cryptosporidium scrofarum. The number of shed oocysts per gram of faeces served to describe the infection intensity and prepatent period. In addition, faecal samples collected daily and tissue samples of the small and large intestine collected at 30 days post-inoculation were examined for the C. scrofarum small subunit ribosomal RNA gene using PCR. The piglets inoculated at 4-weeks of age remained uninfected, whereas 5-week-old and older animals were fully susceptible with a prepatent period ranging from 4 to 8 days. Susceptible pigs shed oocysts intermittently, and shedding intensity, reaching a mean maximum of 6000 oocysts per gram, did not differ significantly among infected animals. This study demonstrates that pigs become susceptible to C. scrofarum infection as late as 5-weeks of age. The mechanisms of age related susceptibility remain unknown.