GENETIC AND ECOLOGIC VARABILITY OF THE NEMATODE HAEMONCHUS CONTORTUS, A PARASITE OF SMALL RUMINANTS

Abstract

Haemonchus contortus is a widely distributed nematode parasite of sheep and goats. Due to its distribution under very different climatic and diverse breeding management conditions of hosts, it might be expected that isolates from different part of the world should have different capabilities to cope with favourable and unfavourable environments. This could reflect in ecological and possibly genetic differences among isolates. Only few studies are available on these subjects. Ecotypes were described based on the proportions of female morphotypes, but no experimental validation is available on the reality of these ecotypes. Several isolates were also studied recently in the United States, which concluded that H. contortus isolates were very similar in North America. We intended on a larger geographic scale to study the genetic and ecological differences between morphs of the saure isolate in order to verify if the ecotype hypothesis could be retained as valid. We studied isolates from Europe (3 sites in France), Africa (Mauritania, Zaire-Congo, Sao Tomé), America (Martinique and Argentina) and Asia (2 sites in Malaysia). We also used experimentally selected unes (one for each of the 3 morphotypes of females) from a Zaire-Congo strain in order to study their ecological capabilities. Genetic studies were performed using polymorphic allosymes (Malate deshydrogenase -MDH 1 and MDH 2 Mannose phosphate isomerase -MPI, Phosphoglucomutase -PGM). Isofocusing technique was used on polyacrylamide gels. The structuration indices (Fst and Fis) were evaluated using several softwares in order to assess their comparative values in different environmental sets. Among ecological characteristics we were interested in the influence of dryness during the free-living stage as it appears to be the most critical for the dispersion of H. contortus in larger areas of the world. The differences between isolates were important: the Malaysian isolates wee the most different compare