Desiccation tolerance of gastrointestinal nematode third-stage larvae: exploring the effects on survival and fitness.

The free-living third-stage larvae (L3) of gastrointestinal nematodes are able to tolerate extreme weather conditions such as desiccation, but little is known about the consequent effects this has on their fitness. This study explored how the desiccation of Haemonchus contortus L3 larvae affected their absolute fitness by examining their success at consequent life cycle stages for a complete generation, and comparing them against a control. The stages examined include establishment, fecundity, larval development and pathogenicity. The results show that while desiccation greatly reduced the survival of the L3 prior to infection in sheep, their absolute fitness was not negatively impacted. Instead, it appears desiccation slightly augmented H. contortus fitness by triggering increases in fecundity. The study further explored what influence different gastrointestinal nematode (GIN) species (H. contortus, Trichostrongylus colubriformis, Teladorsagia circumcincta), isolates and age of L3 had on their capacity to revive following various periods of desiccation. The results showed desiccation tolerance varied as a function of each of these variables. The greatest L3 survival was found in Te. circumcincta followed by Tr. colubriformis and finally H. contortus. Significant variation was observed between individual species isolates and as a function of age. The results of this study carry important practical implications for the epidemiological understanding of gastrointestinal nematode species of economic importance.