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Concept: Haemonchus contortus


BACKGROUND: Resistance against benzimidazoles (BZ) has recently been detected in Norwegian sheep flocks through a large scale prevalence survey based on the faecal egg count reduction test (FECRT). The use of this test in combination with bulk larval culture only gives an indication of which gastrointestinal nematodes genera that are involved and these results have to be confirmed by a controlled efficacy test (CET) to get accurate information about resistant nematodes populations at species level. A CET was therefore performed with larvae from two flocks where BZ resistance was previously detected through FECRT. RESULTS: The latter test confirmed the previous results in both flocks. In flock A, the BZ resistant nematode population consisted solely of Haemonchus contortus, whereas H. contortus and Teladorsagia circumcincta comprised the resistant worm population in flock B. CONCLUSIONS: Some discrepancies that have been recorded between FECRT and CET results regarding time for post-treatment coproscopical examination and a temporary suppression of faecal egg excretion are discussed.

Concepts: Parasites, Biology, Insect, Nematode, Nematodes, Annelid, Norway, Haemonchus contortus


Ethanol extracts of 25 plant species were screened for anthelmintic effects against Haemonchus contortus. Ethanol extracts of each plant were used at various concentrations (10, 20 and 30%) to treat 10-day faecal cultures, incubated at 27°C with control cultures which were treated with ethanol for 48 h. Five plants with high efficacies (Ananas comosus, Aloe ferox, Allium sativum, Lespedeza cuneata and Warburgia salutaris) were selected from the first screening for further investigation using ethanol, dichloromethane and water extracts at four concentrations (2.5, 5, 10 and 20%). Ethanol was the most effective solvent. Larval counts decreased with increasing extract concentrations, of which 10 and 20% had similar effects. Lespedeza cuneata caused more than 70% mortality at all concentrations. However, there remains a need to assess in vivo efficacy of these plants.

Concepts: Water, Effectiveness, In vivo, In vitro, Efficacy, Medicinal plants, Ananas, Haemonchus contortus


SUMMARY Ivermectin (IVE), one of the most important anthelmintics, is often used in the treatment of haemonchosis in ruminants. The objective of our work was (1) to find and identify phase I and II metabolites of IVE formed by the Barber’s pole worm (Haemonchus contortus), and (2) to compare IVE metabolites in helminths with IVE biotransformation in sheep (Ovis aries) as host species. Ultrahigh-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) was used for this purpose. During in vitro incubations, microsomes (from adult worms or from ovine liver) and a primary culture of ovine hepatocytes were incubated with IVE. In the ex vivo study, living H. contortus adults were incubated in the presence of 1 μM IVE for 24 h. The results showed that the H. contortus enzymatic system is not able to metabolize IVE. On the other hand, 7 different phase I as well as 9 phase II IVE metabolites were detected in ovine samples using UHPLC/MS/MS analyses. Most of these metabolites have not been described before. Haemonchus contortus is not able to deactivate IVE through biotransformation; therefore, biotransformation does not contribute to the development of IVE-resistance in the Barber’s pole worm.

Concepts: Metabolism, In vivo, Domestic sheep, Haemonchus contortus, Ovis, Sheep, Mouflon, Barber's pole


The sensitivity of larval paralysis assay (LPA) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide-formazan (MTT-formazan) assay was compared to evaluate the anthelmintic activity of plant extracts. In this study, the methanolic extract of Azadirachta indica (neem) was evaluated for its activity against the infective-stage larvae (L(3)) of susceptible and resistant Haemonchus contortus strains using the two aforementioned assays. In both in vitro assays, the same serial concentrations of the extract were used, and the median lethal concentrations were determined to compare the sensitivity of both assays. The results revealed a significant difference (P < 0.05) in the sensitivity of the LPA and the MTT-formazan assay. The MTT-formazan assay is more feasible for practical applications because it measured the L(3) mortality more accurately than LPA. This study may help find a suitable assay for investigating the anthelmintic activity of plant extracts against trichostrongylid nematodes.

Concepts: Parasites, Nematode, Nematodes, Annelid, Haemonchus contortus, Neem, Meliaceae, Azadirachta


The resistance of gastrointestinal nematodes to anthelmintics has increased the need to evaluate natural products that can replace or assist current strategies to control gastrointestinal nematodes. The objective of this study was to evaluate the effect of decoctions of Lantana camara (DLc), Alpinia zerumbet (DAz), Mentha villosa (DMv) and Tagetes minuta (DTm) on Haemonchus contortus by two in vitro tests. The effects of increasing concentrations of lyophilized decoctions (0.31 to 10mg/ml) were assessed using the egg hatch test (EHT). The decoctions were then tested in the larval artificial exsheathment assay. H. contortus third stage larvae (L3) were exposed to 0.31mg/ml A. zerumbet and M. villosa decoctions and 0.62mg/ml T. minuta and L. camara decoctions for 3h and then exsheathment procedure at 10min intervals. An inhibitor of tannins, polyvinyl polypyrrolidone (PVPP), was used to study if tannins were responsible for the inhibitory effect on hatching and exsheathment of larvae. A. zerumbet, M. villosa and T. minuta showed a dose-dependent effect in the EHT, which did not disappear after the addition of PVPP. No effect was observed for L. camara in the EHT. However, the decoctions inhibited the process of larval exsheathment, which may be related to tannin action because the addition of PVPP reversed the inhibitory effect. A. zerumbet, M. villosa and T. minuta decoctions showed inhibitory activity on H. contortus larvae hatching and exsheathing. The decoctions of these plants could be used to control gastrointestinal nematodes following confirmation of their anthelmintic activity in vivo.

Concepts: Nematode, In vivo, In vitro, Haemonchus contortus, Zingiberaceae, Alpinia, Alpinia zerumbet, Tagetes minuta


A molecular procedure was developed to detect and quantify larvae of different strongylid parasite species recovered from pasture samples. Two lamb flocks (L and S) grazed separate paddocks with different natural larvae challenges (one low [Paddock L] and one high [Paddock S] challenge) on a commercial farm in Western Australia. Pasture samples were collected and analysed for larvae on 9 separate occasions from each paddock. Pregnant Merino ewes were sampled on 3 separate occasions (2 pre-partum and 1 post-partum). Following lambing, 203 female crossbred lambs were identified, from which faecal samples were collected across five separate samplings. Lamb production and faecal attributes were recorded. Genomic DNA was extracted directly from lamb faeces, in addition to the genomic DNA extracts from strongylid larval species recovered from pastures. Faecal worm egg counts (FWECs) were undertaken. Species-specific qPCRs and conventional PCRs (ITS-2 nuclear ribosomal DNA) were used to screen samples for strongylid species (Teladorsagia circumcincta, Trichostrongylus spp., Haemonchus contortus, Chabertia ovina and Oesophagostomum venulosum). Negative correlations (r(2)>0.91) were found between qPCR C(q) values and log-transformed pasture larval counts for Trichostrongylus spp. and T. circumcincta. Moderate levels of agreement between pasture larval counts and qPCR results were observed (67%). A clear difference in pasture larval challenge levels was observed between the two flocks using both qPCR and conventional pasture larval counts. It is difficult to draw conclusions on the production performances of lambs from the two experimental flocks, as no further replicates were able to be conducted following this experiment. Flock L had higher dressing percentages than Flock S (P=0.038), along with significantly higher faecal consistency and breech fleece faecal soiling scores at successive samplings. The molecular procedures utilised in this study have the potential to be beneficial for livestock grazing management strategies and parasite surveillance, however further investigation is necessary before they can become part of routine diagnostics.

Concepts: Pasture, Field, Farm, Livestock, Grazing, Domestic sheep, Haemonchus contortus, LaMB


This study aimed to identify regions of the genome affecting resistance to gastrointestinal nematodes in a Creole goat population naturally exposed to a mixed nematode infection (Haemonchus contortus, Trichostrongylus colubriformis and Oesophagostomum columbianum) by grazing on irrigated pasture. A genome-wide quantitative trait loci (QTL) scan was performed on 383 offspring from 12 half-sib families. A total of 101 microsatellite markers were genotyped. Traits analysed were faecal egg count (FEC), packed cell volume (PCV), eosinophil count and bodyweight (BW) at 7 and 11 months of age. Levels of activity of immunoglobulin A (IgA) and activity of immunoglobulin E (IgE) anti-Haemonchus contortus L3 crude extracts and adult excretion/secretion products (ESPs) were also analysed. Using interval mapping, this study identified 13 QTL for parasite resistance. Two QTL linked with FEC were found on chromosomes 22 and 26. Three QTL were detected on chromosomes 7, 8 and 14 for eosinophil counts. Three QTL linked with PCV were identified on chromosomes 5, 9 and 21. A QTL for BW at 7 months of age was found on chromosome 6. Lastly, two QTL detected on chromosomes 3 and 10 were associated with IgE anti-L3, and IgE anti-ESP was linked with two QTL on chromosomes 1 and 26. This study is the first to have identified regions of the genome linked with nematode resistance in a goat population using a genome scan. These results provide useful tools for the understanding of parasite resistance in small ruminants.

Concepts: Immune system, Genetics, Bacteria, Caenorhabditis elegans, Nematode, Model organism, Nematodes, Haemonchus contortus


The availability of effective vaccines would add a valuable tool to the management of gastrointestinal nematode infections in livestock. While some experimental vaccines have shown protection in laboratory trials, few have been tested in the field. In the present study, eight month old sheep kept on pasture were treated with anthelmintic 8weeks before vaccination with a larval surface antigen of the nematode parasite, Haemonchus contortus, under a commercially acceptable protocol, i.e. 2 immunizations using a commercial adjuvant; they were then given a controlled challenge infection 4weeks later in indoor pens. Vaccination of sheep with 4 increasing doses of antigen resulted in significant reductions of 61% and 27% in cumulative faecal egg counts in the two highest dose groups, and a 69% reduction in worm burden in the highest dose group. Blood loss, as determined by packed cell volume, was also significantly reduced in the highest dose group of sheep. One outlier sheep showed an unusual increase in egg count without a concomitant increase in worm burden compared to the control sheep, indicating a vaccine-induced stress response. Antigen-specific serum antibody levels steadily increased in sheep while on pasture and decreased when transported to indoor pens. No difference in antibody levels could be detected between vaccinated and unvaccinated sheep, but all showed increased antibody levels compared to uninfected control sheep kept in indoors pens for 2-3months, suggesting sheep were sensitized to the larval antigen either from low dose pasture contamination or cross reaction with pasture-related antigens. The results of these studies confirm the protective properties of the larval surface antigen and its protective effect when vaccinations are performed in the field.

Concepts: Immune system, Vaccine, Vaccination, Nematode, Antigen, Haemonchus contortus


Haemonchus contortus is a highly pathogenic nematode parasite of sheep and goats. This work was conducted to investigate the population and host variations of the parasitic nematode H. contortus of sheep and goats from Malaysia and Yemen. Eight morphological characters were investigated, namely the total body length, cervical papillae, right spicule, left spicule, right barb, left barb, gubernaculum and cuticular ridge (synlophe) pattern. Statistical analysis showed the presence of morphological variation between populations of H. contortus from Malaysia and Yemen, with minor variation in the synlophe pattern of these isolates. Isolates from each country were grouped together in the scatterplots with no host isolation. Body, cervical papillae and spicule lengths were the most important characters that distinguished between populations of the two countries. This variation between Malaysia and Yemen may be attributed to geographical isolation and the possible presence of a different isolate of this worm in each country.

Concepts: Parasites, Statistics, Arthropod, Nematode, Nematodes, Sheep and goats diseases, Goat, Haemonchus contortus


Parasitic nematodes of humans and livestock cause extensive disease and economic loss worldwide. Many parasitic nematodes infect hosts as third-stage larvae, called iL3s. iL3s vary in their infection route: some infect by skin penetration, others by passive ingestion. Skin-penetrating iL3s actively search for hosts using host-emitted olfactory cues, but the extent to which passively ingested iL3s respond to olfactory cues was largely unknown. Here, we examined the olfactory behaviors of the passively ingested murine gastrointestinal parasite Heligmosomoides polygyrus. H. polygyrus iL3s were thought to reside primarily on mouse feces, and infect when mice consume feces containing iL3s. However, iL3s can also adhere to mouse fur and infect orally during grooming. Here, we show that H. polygyrus iL3s are highly active and show robust attraction to host feces. Despite their attraction to feces, many iL3s migrate off feces to engage in environmental navigation. In addition, H. polygyrus iL3s are attracted to mammalian skin odorants, suggesting that they migrate toward hosts. The olfactory preferences of H. polygyrus are flexible: some odorants are repulsive for iL3s maintained on feces but attractive for iL3s maintained off feces. Experience-dependent modulation of olfactory behavior occurs over the course of days and is mediated by environmental carbon dioxide (CO2) levels. Similar experience-dependent olfactory plasticity occurs in the passively ingested ruminant-parasitic nematode Haemonchus contortus, a major veterinary parasite. Our results suggest that passively ingested iL3s migrate off their original fecal source and actively navigate toward hosts or new host fecal sources using olfactory cues. Olfactory plasticity may be a mechanism that enables iL3s to switch from dispersal behavior to host-seeking behavior. Together, our results demonstrate that passively ingested nematodes do not remain inactive waiting to be swallowed, but rather display complex sensory-driven behaviors to position themselves for host ingestion. Disrupting these behaviors may be a new avenue for preventing infections.

Concepts: Carbon dioxide, Parasites, Coprophagia, Caenorhabditis elegans, Nematode, Nematodes, Mouse, Haemonchus contortus