Adopt Isolate-Specific Life History Strategies to Optimize Fitness and Overcome Obstacles in Their Environment: Experimental Evidence.

Gastrointestinal nematodes (GIN) use flexible life history strategies to maintain their fitness under environmental challenges. Costs incurred by a challenge to one life trait can be recouped by increasing the expression of subsequent life traits throughout their life cycle. Anticipating how parasites respond to the challenge of control interventions is critical for the long-term sustainability of the practice and to further ensure that the parasites withstand favourable adaptive responses.

Genetic × environment variation in sheep lines bred for divergent resistance to strongyle infection.

Drug-resistant parasites threaten livestock production. Breeding more resistant hosts could be a sustainable control strategy. Environmental variation linked to animal management practices or to parasite species turnover across farms may however alter the expression of genetic potential.

Integrative biology defines novel biomarkers of resistance to strongylid infection in horses.

The widespread failure of anthelmintic drugs against nematodes of veterinary interest requires novel control strategies. Selective treatment of the most susceptible individuals could reduce drug selection pressure but requires appropriate biomarkers of the intrinsic susceptibility potential. To date, this has been missing in livestock species.

Nicotine-sensitive acetylcholine receptors are relevant pharmacological targets for the control of multidrug resistant parasitic nematodes.

The control of parasitic nematodes impacting animal health relies on the use of broad spectrum anthelmintics. However, intensive use of these drugs has led to the selection of resistant parasites in livestock industry. In that respect, there is currently an urgent need for novel compounds able to control resistant parasites.

Strongyle Infection and Gut Microbiota: Profiling of Resistant and Susceptible Horses Over a Grazing Season.

Gastrointestinal strongyles are a major threat to horses' health and welfare. Given that strongyles inhabit the same niche as the gut microbiota, they may interact with each other. These beneficial or detrimental interactions are unknown in horses and could partly explain contrasted susceptibility to infection between individuals.

Ivermectin failure in the control of Oxyuris equi in a herd of ponies in France.

Drug resistance in equine gastro-intestinal parasitic nematodes has been reported throughout the world. While the focus is usually put on cyathostomins, observations of macrocylic lactone failure against Oxyuris equi have accumulated over the last decade. Here we report the failure of ivermectin in the control of O.

Economic assessment of FEC-based targeted selective drenching in horses.

In the face of an increased prevalence of drug-resistant cyathostomin populations, a targeted selective treatment (TST) strategy based on Faecal Egg Counts (FECs) has been proposed as an alternative management strategy. However, associated costs may be a barrier to the uptake of this strategy. Our study aims to provide an economic assessment of FEC-based TST.

Investigation of acetylcholine receptor diversity in a nematode parasite leads to characterization of tribendimidine- and derquantel-sensitive nAChRs.

Nicotinic acetylcholine receptors (nAChRs) of parasitic nematodes are required for body movement and are targets of important "classical" anthelmintics like levamisole and pyrantel, as well as "novel" anthelmintics like tribendimidine and derquantel. Four biophysical subtypes of nAChR have been observed electrophysiologically in body muscle of the nematode parasite Oesophagostomum dentatum, but their molecular basis was not understood. Additionally, loss of one of these subtypes (G 35 pS) was found to be associated with levamisole resistance.

A suite of genes expressed during transition to parasitic lifestyle in the trichostrongylid nematode Haemonchus contortus encode potentially secreted proteins conserved in Teladorsagia circumcincta.

The control of gastro-intestinal nematodes remains largely based on anthelminthic treatments, however spreading of anthelmintic resistance has reduced their efficacy. The genes involved in the transition to parasitic lifestyle could constitute targets of interest to develop alternative control strategies. In the trichostrongylid nematode Haemonchus contortus, we have used a SSH (Suppressive Subtractive Hybridization) based approach to generate two distinct subtracted cDNA libraries specifically enriched in cDNA expressed during the early parasitic fourth stage larvae L4 (5 days post-infection).

Genetic diversity of levamisole receptor subunits in parasitic nematode species and abbreviated transcripts associated with resistance.

Objectives: The molecular mechanisms of levamisole (LEV) activity and expression of resistance remain largely unknown in parasitic nematodes. In contrast, genetic screens for mutants that survive exposure to LEV in the free-living nematode Caenorhabditis elegans have led to the identification of five genes (unc-38, unc-63, unc-29, lev-1 and lev-8) that encode a LEV-sensitive acetylcholine receptor (L-AChR). Loss of these genes leads to LEV resistance.

cDNA-AFLP analysis in levamisole-resistant Haemonchus contortus reveals alternative splicing in a nicotinic acetylcholine receptor subunit.

The cDNA-AFLP (cDNA-amplified fragment length polymorphism) method comparing transcripts from levamisole-resistant and susceptible Haemonchus contortus isolates has led to the successful identification of a number of potentially useful levamisole-resistance markers. In the present study, we report the characterization of the transcript-derived fragment (TDF) named HAX which was confirmed to be specifically expressed in three levamisole-resistant isolates by RT-PCR experiments. Cloning and sequencing of the full-length cDNA sequence of HAX revealed high similarity to the Caenorhabditis elegans acr-8 gene and its putative H.

Benzimidazole resistance in Trichostrongylus axei in sheep: long-term monitoring of affected sheep and genotypic evaluation of the parasite.

This is the first report of benzimidazole (BZ) resistance in the nematode Trichostrongylus axei in sheep. Trichostrongylus axei infects several species of herbivores including sheep, cattle and horses, and the emergence of anthelmintic resistance could lead to significant problems in its control. Benzimidazole resistance in two sheep flocks in central France was detected by post-treatment worm counts.

Nematode parasites and scrapie: experiments in sheep and mice.

To demonstrate the possible role of nematode parasites in the modification of host susceptibility to scrapie, experiments were conducted using sheep naturally exposed to scrapie, chosen by their genotype at the PrP gene, and infected with Teladorsagia circumcincta. Two 4-year duration experiments demonstrated that the nematode infection shortened the development of scrapie with a significant regression between the level of infection and age at first scrapie symptoms (P < 0.006).

Regulation of Teladorsagia circumcincta and Trichostrongylus colubriformis worm populations by grazing sheep with differing resistance status.

In an experiment lasting 4 years, changes in the Teladorsagia circumcincta and Trichostrongylus colubriformis populations were compared in lambs and adult sheep with differing resistance statuses. Two flocks of 30 rams (resistant R and susceptible S) grazed separate pastures and 8 rams were slaughtered in the middle and at the end of each grazing season. Five groups of tracer lambs were added each year to estimate the pasture infectivity and were killed for worm counts.