Serum antibody responses in Creole kids experimentally infected with Haemonchus contortus

The objective of this study was to evaluate the relationship of parasite-specific serum antibodies with the resistance status of Creole kids. The average breeding values on egg output predicted in a context of natural infection at 11 months of age were distant of 1.07 genetic standard deviation between resistant and susceptible animals. After drenching the animals were maintained worm-free during 1 month until experimental infection with 10,000 Haemonchus contortus infective larvae (L3). Enzyme-linked immunosorbent assay was carried out in serum samples to determine the level of IgG, IgA and IgE anti-H. contortus L3 crude extracts and adult excretion/secretion products (ESP). Parasitological and blood immunological parameters were measured on the 2 extreme groups. Despite the absence of any typical signs of haemonchosis, susceptible kids had more than 11 times higher faecal egg counts (FEC) at 35 days post-infection (d.p.i.) than resistant kids had. Levels of immunoglobulin against H. contortus L3 and ESP increased significantly after infection in both groups. However, no difference in the host immune response mediated by immunoglobulin against H. contortus was evidenced between groups. This finding suggests that, in goats previously infected by H. contortus, a degree of protection occurred and the phenotypic and genetic segregation in resistant and susceptible animals were not related to the humoral immune response. The correlation coefficients between FEC and IgE anti-ESP (r=0.593; P<0.05 was significant in both resistant and susceptible animals. Such correlation suggesting a hypersensitivity reaction dependent on worm prolificacy has never been described. This result needs further studies to understand the mechanisms underlying this observation.