Does host immunity influence helminth egg hatchability in the environment?

Transmission success for helminths with free-living stages depends on the ability of eggs and larvae to develop and survive once in the environment. While environmental conditions are often suggested to influence egg phenology and hatching rate, immunity against parasite eggs might also play a role. We examined this hypothesis using the gastrointestinal helminths Trichostrongylus retortaeformis and Graphidium strigosum, two common infections of the European rabbit. Changes in egg hatching rate and volume were examined in relation to specific antibodies in the serum and bound to eggshells, using eggs shed in host faeces over a 15-week period. Hatching rate was consistently higher for T. retortaeformis than G. strigosum and no changes were observed between weeks. Egg volume increased for G. strigosum but decreased for T. retortaeformis. We did find evidence of egg-specific antibody responses and fewer antibodies were bound to eggs of T. retortaeformis compared to G. strigosum. Little to no association was found between antibodies and hatchability, or volume, for both helminths. We suggest that host antibodies play a relatively minor role in the egg hatching rate of these gastrointestinal helminths.