ADAPTATION TO ARID ENVIRONMENT - HAEMONCHUS LONGISTIPES IN DROMEDARIES OF SAHARO-SAHELIAN AREAS OF MAURITANIA

The adaptations of the trichostrongylid nematode Haemonchus longistipe s of dromedaries (Camelus dromedarius) to the harsh environment of Sah aro-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 hos t population and of prolificacy of H. longistipes females recovered fr om natural populations of infected dromedaries sampled at Nouakchott's slaughterhouse, and (iii) experimental infections of young dromedarie s during three different periods of the year (end of the rainy season, middle and end of the dry season). Egg excretions (estimated by faeca l egg counts), infective larvae derived from eggs as well as female pr olificacy showed a marked seasonal pattern: high values in the rainy s eason and very low values in the dry season (especially March and Apri l). Female prolificacy differed slightly between morphotypes: the knob bed 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 surv ival strategy of H. longistipes in the dry season was based only on ar rested larval development. Patent infections occurred from July to Oct ober, i.e. during the rainy season and was facilitated by the conjunct ion of high prevalence and intensity of adult worm burdens associated with high female prolificacy.