Adaptation to arid environment: Haemonchus longistipes in dromedaries of Saharo-Sahelian areas of Mauritania

The adaptations of the trichostrongylid nematode Haemonchus longistipes of dromedaries ( Camelus dromedarius) to the harsh environment of Saharo-Sahelian climate were assessed by means of (i) an epidemiological survey of dromedary infection in the south-west of Mauritania, (ii) an estimate over a 3 year period of parasite distribution within the host population and of prolificacy of H. longistipes females recovered from natural populations of infected dromedaries sampled at Nouakchott's slaughterhouse, and (iii) experimental infections of young dromedaries during three different periods of the year (end of the rainy season, middle and end of the dry season). Egg excretions (estimated by faecal egg counts), infective larvae derived from eggs as well as female prolificacy showed a marked seasonal pattern: high values in the rainy season and very low values in the dry season (especially March and April). Female prolificacy differed slightly betweent morphotypes: the knobbed type excreting over a longer period than the linguiform and smooth types. Following experimental infections in young dromedaries, arrest of larval development took place irrespective of the period. The survival strategy of H. longistipes in the dry season was based only on arrested larval development. Patent infections occurred from July to October, i.e. during the rainy season and was facilitated by the conjunction of high prevalence and intensity of adult worm burdens associated with high female prolificacy.