The steppe species of gastrointestinal nematodes of small ruminants, with a focus onMarshallagia: climate as a key determinant

S Meradi,J Cabaret,B Bentounsi,I Zouyed

doi:10.1051/parasite/2011183261

Abstract

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.

Highlights

It may look surprising that parasites would display macroecological and biogeographical patterns similar to those described for free-living organisms (Gueguan, 2006)
The B stands for dry climates, and the S for steppe climate
Either defined by climate or vegetation is not a very clear concept and we will substitute simple measures such as annual mean temperature or yearly rainfall in areas where Marshallagia is highly represented, since it was associated with steppe vegetation in a previous analysis (Suarez & Cabaret, 1991)

Summary

Introduction

It may look surprising that parasites would display macroecological and biogeographical patterns similar to those described for free-living organisms (Gueguan, 2006). Nematodirus species are highly prevalent in steppe regions but they are found in many different climatic areas (Morgan et al, 2006) Genus such as Haemonchus (from temperate down to tropical areas where it predominates) or Teladorsagia (not found under the tropics but well adapted to temperate or cold climates) are found under a large range of climates; Trichostrongylus genera is nearly present under any type of climate. North Africa has a large part of the inland under typical steppe climate and vegetation (Slimani et al, 2010), and as expected, Marshallagia has been very frequently recorded (Morocco: Cabaret, 1984; Algeria: Bentounsi et al, 2007 and Boulkaboul & Moulaye, 2006); but other trichostrongylid nematodes such as Teladorsagia circumcincta, Haemonchus contortus, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Trichostrongylus probolurus and Nematodirus filicollis are frequently recorded (Graber, 1979). We intend to answer to the following questions: 1) is Marshallagia associated to particular climatic characteristics such as average temperature and annual rainfalls or rather to a set geographical locations in domestic sheep and goats? 2) is Marshallagia associated with other nematode species in sheep and goats? 3) could the wild hosts infection with Marshallagia help to decipher the distribution of this species?

Methods

Results

Discussion

Conclusion