Serum antibody response in lambs naturally and experimentally infected with Cryptosporidium parvum

The immunoglobulin (IgG), IgM and IgA responses in Castellana-Manchega cross-bred colostrum-deprived and colostrum-fed lambs infected neonatally with Cryptosporidium parvum were measured using an enzyme-linked immunosorbent assay. A comparison of oocyst shedding and anti-C. parvum serum IgG levels in lambs suffering either natural or experimental infection was undertaken. Effects on the oocyst shedding and IgG levels of C. parvum rechallenge at 30 and 120 days of age in neonatally infected lambs were also evaluated. Anti-C. parvum immunoglobulin levels in colostrum-deprived animals peaked on Day 30 of life for IgG and on Day 15 for IgM and IgA. Lambs that received maternal colostrum showed elevated anti-C. parvum IgG, IgM and IgA levels at 3 days old indicating a transfer of colostral immunoglobulins. Experimentally infected lambs showed a IgG response similar to naturally infected lambs, suggesting that the serum IgG response is independent of the infective dose. Finally, lambs rechallenged at 30 and 120 days old did not show either appreciable oocyst shedding or any increase in their anti-C. parvum IgG levels when compared with prechallenged animals.