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We intended to relate the geographic distribution of ruminant gastrointestinal nematodes in relation to steppe climate (and vegetation). Data are either from literature or from newly acquired/ available results. Simple or more sophisticated meteorological indices were used to characterize the climate. Regression analyses were used to correlate climatic factors and presence of endoparasites from steppe areas. The distribution of one (Marshallagia) out of five endoparasite genera was concentrated mostly in steppic areas whereas other species were found also in other areas. In wild hosts the distribution of Marshallagia was much larger from Sptizberg to New World (northern territories in Canada or extreme south of America). In domestic small ruminants the presence of Marshallagia was identified more frequently and constantly in the area of original domestication and its early diffusion (from Northern Africa to Kashmir, Caucasia). The distribution of this parasite was correlated to low rainfalls which were not the case for all other endoparasites. After host switch (reindeer or south America camelids), it has expanded in other climatic areas, either colder or dryer.

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Population genetic data on helminths are scarce and it is important to fine tune analyses of these data, the interpretation of which is based on between-(Fst) and within-(Fis) population variability. Several computer programs are available and confidence intervals of each index are based on different procedures. These programs (Genetix, Diploid, Genepop) were compared with a classical program (Biosys-1) using a large set of Haemonchus contortus isozyme data. The results were identical for all softwares for large differences when natural populations were studied (Fst > 0.25 and Fis > 0.15 or <-0.15). When small Fst were investigated in laboratory-reared populations, the significance of differences was often related to the software used. As a rule of thumb, it is suggested that at least two out of three software packages (based on different calculation procedures) should give similar results before differences are validated.