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PubMed2004

Anthelmintic activity of Artemisia brevifolia in sheep.

This paper describes the in vitro and in vivo anthelmintic activity of Artemisia brevifolia in comparison with levamisole. In vitro studies revealed anthelmintic effects of crude aqueous (CAE) and methanol extracts (CME) of Artemisia brevifolia (whole plant) on live Haemonchus contortus as evident from their paralysis and/or mortality at 6 h post exposure. For in vivo studies, the whole plant of Artemisia brevifolia was administered as crude powder (CP), CAE and CME at graded doses (1, 2 and 3 g kg(-1) body weight (b.w.) to sheep naturally infected with mixed species of gastrointestinal nematodes. Maximum reduction (67.2%) in eggs per gram (EPG) of faeces was recorded on day 14 post treatment in sheep treated with Artemisia brevifolia CAE at 3 g kg(-1) b.w. It was found that, although, Artemisia brevifolia whole plant possesses anthelmintic activity against nematodes, it is not comparable with levamisole (99.2% reduction in EPG) at any of the doses tried in this study. However, increase in EPG reduction was noted with an increase in the dose of Artemisia brevifolia administered as CP, CAE and CME. The graded dose response suggested further studies on a larger number of animals on higher doses than those used in the current study.

Administration, Oral↗
PubMed2006

In vitro and in vivo anthelmintic activity of crude extracts of Coriandrum sativum against Haemonchus contortus.

In vitro anthelmintic activities of crude aqueous and hydro-alcoholic extracts of the seeds of Coriandrum sativum (Apiaceae) were investigated on the egg and adult nematode parasite Haemonchus contortus. The aqueous extract of Coriandrum sativum was also investigated for in vivo anthelmintic activity in sheep infected with Haemonchus contortus. Both extract types of Coriandrum sativum inhibited hatching of eggs completely at a concentration less than 0.5 mg/ml. ED(50) of aqueous extract of Coriandrum sativum was 0.12 mg/ml while that of hydro-alcoholic extract was 0.18 mg/ml. There was no statistically significant difference between aqueous and hydro-alcoholic extracts (p>0.05). The hydro-alcoholic extract showed better in vitro activity against adult parasites than the aqueous one. For the in vivo study, 24 sheep artificially infected with Haemonchus contortus were randomly divided into four groups of six animals each. The first two groups were treated with crude aqueous extract of Coriandrum sativum at 0.45 and 0.9 g/kg dose levels, the third group with albendazole at 3.8 mg/kg and the last group was left untreated. Efficacy was tested by faecal egg count reduction (FECR) and total worm count reduction (TWCR). On day 2 post treatment, significant FECR was detected in groups treated with higher dose of Coriandrum sativum (p<0.05) and albendazole (p<0.001). On days 7 and 14 post treatment, significant FECR was not detected for both doses of Coriandrum sativum (p>0.05). Significant (p<0.05) TWCR was detected only for higher dose of Coriandrum sativum compared to the untreated group. Reduction in male worms was higher than female worms. Treatment with both doses of Coriandrum sativum did not help the animals improve or maintain their PCV while those treated with albendazole showed significant increase in PCV (p<0.05).

Albendazole↗
PubMed2006

Ivermectin selection on beta-tubulin: evidence in Onchocerca volvulus and Haemonchus contortus.

Ivermectin resistance is common in trichostrongylid nematodes of livestock, such as Haemonchus contortus. This anthelmintic is the only drug approved for mass administration to control onchocerciasis caused by the nematode parasite, Onchocerca volvulus. In parts of West Africa up to 18 rounds of ivermectin treatment have been administered to communities and there are reports of poor parasitological responses to treatment. Understanding ivermectin resistance and ivermectin selection is an important step to reduce selection pressure for resistance, and to develop molecular markers which can be used to monitor the development of resistance and its spread. Here we report evidence that ivermectin selection changes the frequency of beta-tubulin alleles in both the sheep parasite, H. contortus, and the human parasite, O. volvulus. In O. volvulus we have been able to look at the frequency of beta-tubulin alleles in O. volvulus obtained before any ivermectin was used in humans in Africa, and following its widespread use. In H. contortus, we have been able to look at the frequency of beta-tubulin alleles in a strain which has not seen any anthelmintic selection and in an ivermectin selected strain derived from the unselected strain. We have found ivermectin selects on beta-tubulin in both of these nematode species. In the case of O. volvulus, we had previously reported that ivermectin selects for specific single nucleotide polymorphisms in the O. volvulus beta-tubulin gene. This polymorphism results in three amino acid changes in the H3 helix of beta-tubulin, as well as deletions in an associated intron. We report a simple PCR assay to detect the amplicon length polymorphism, resulting from these intronic deletions, which can be used to monitor the frequency of the beta-tubulin allele selected for by ivermectin in O. volvulus.

Africa, Western↗
PubMed2005

Lack of effects of quebracho and sainfoin hay on incoming third-stage larvae of Haemonchus contortus in goats.

The effects of tannins on adult populations of Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta in goats are characterised mainly by a decrease in egg excretion without any significant changes in worm number. In contrast, the impact of tannins on T. colubriformis or T. circumcincta third-stage larvae (L3) is associated with a significant reduction in worm establishment. The objective of the present study was to examine the effects of quebracho extract tannins on H. contortus L3. The consequences of consumption of sainfoin hay were also examined. Twenty-one naïve kids were divided into three experimental groups. Group Q received quebracho extract and group S received sainfoin hay from days D3 to D5. Group C remained as an infected control group. All kids received 1500 L3 H. contortus on D0, D1 and D2. On D18, post-infection, the kids were slaughtered and the worm populations compared in the different groups. Compared to the control values, the worm counts decreased, respectively, by 33% and 38% in groups Q and S but the differences were not significant. No differences were found in pathophysiological measurements between the three groups. The results confirm differences in tannin effect according to nematode species but not parasitic stage.

Anacardiaceae↗
PubMed2004

Vaccination against the nematode Haemonchus contortus with a thiol-binding fraction from the excretory/secretory products (ES).

Fractionated excretory/secretory products (ES) of adult Haemonchus contortus were evaluated as protective antigens. The proteins were successively eluted from a Thiol Sepharose column using 25 mM cysteine followed by 25 mM Dl-dithiothreitol (DTT). Sheep were vaccinated three times and challenged with 5000 third stage infective larvae (L3) of H. contortus. Highest level of protection was found in sheep vaccinated with the DTT-eluted fraction in which egg output and worm burden were reduced by 52 and 50%, respectively, compared to the adjuvant control group. There was a positive correlation between fecundity (number of eggs per female) and the cumulative EPG or worm burden. Serum and mucus antibody levels of ES-specific immunoglobulins increased after immunizations and after challenge for IgG, IgA and IgE. The harvesting of H. contortus from animals clustered per group revealed the presence of cysteine protease activity in the ES of all groups but in addition to that, metalloprotease activity was also detected in the groups vaccinated with the DTT-eluted fraction, total ES and adjuvant only, in contrast to previous batches of ES (completely inhibited by E64) obtained from non vaccinated animals.

Abomasum↗
PubMed2004

In vivo electroporation improves immune responses to DNA vaccination in sheep.

In vivo electroporation was utilised to enhance plasmid DNA expression in sheep muscle to improve the immune response to DNA vaccination. DNA encoding enhanced green fluorescence protein expressed at higher levels in sheep muscle following in vivo electroporation which caused minimal muscle damage. Groups of seven sheep were then given three intramuscular injections of plasmids encoding two Haemonchus contortus Ag, with and without electroporation at 0, 3 and 7 weeks. Humoral responses were enhanced in electroporated sheep. Four weeks after vaccination, all groups were injected subcutaneously with recombinant Ag formulated in Quil A. Induction of vaccine-specific immune memory was demonstrated in DNA-vaccinated sheep.

Animals↗
PubMed2004

Protection studies in sheep using affinity-purified and recombinant cysteine proteinases of adult Haemonchus contortus.

Vaccination with a membrane-bound thiol Sepharose-binding fraction (TSBP) of adult Haemonchus contortus has been shown to confer significant levels of protection against homologous challenge in sheep. This fraction is greatly enriched for cysteine proteinase activity. Following fractionation of TSBP by anion-exchange chromatography on MonoQ, protection was found to partition with those fractions further enriched for cysteine proteinase activity. In this study, the cysteine proteinases of adult H. contortus TSBP were specifically purified by affinity chromatography using recombinant H. contortus cystatin, a potent cysteine proteinase inhibitor. Although only 1-1.5% of total TSBP bound to cystatin-Sepharose, this fraction contained 100% of the cysteine proteinase activity, as determined by gelatin substrate gel analysis. When used to immunise sheep, less than 3microg per dose of this cysteine proteinase fraction was found to confer a substantial and repeatable level of protection against homologous challenge infection, reducing faecal egg counts by 48 and 28% and worm burdens by 44 and 46% over two trials. Host serum immunoglobulin levels and abomasal mast cell and eosinophil numbers were evaluated, although no correlation with protection was observed. Three cathepsin B-like cysteine proteinases present in TSBP (hmcp1, 4 and 6) have been identified previously by cDNA library immunoscreening. The predicted mature forms of these three cysteine proteinases were expressed in bacteria as insoluble, GST-fusion proteins. Following solubilisation in urea/DTT, the protective capacity of a cocktail of recombinant proteins was evaluated in sheep. Although no reduction in faecal egg counts was observed, sheep vaccinated with recombinant cysteine proteinases showed a highly significant 38% reduction (P <0.01) in worm burdens.

Animals↗
PubMed2005

Production of eosinophil chemoattractant activity by ovine gastrointestinal nematodes.

Eosinophilia is a well documented feature of helminth infections but the precise nature of the interaction between parasite and eosinophil remains an enigma. This paper describes experiments demonstrating that ruminant gastrointestinal trichostrongyles produce potent chemoattractant activity for ovine bone marrow-derived eosinophils in vitro. This activity was initially identified as a constituent of whole worm extracts of third and fourth larval (L3, L4), and adult stages of Teladorsagia circumcincta, and adult Haemonchus contortus. Similar activity was detected in excretory/secretory (E/S) material derived from live T. circumcincta L3. Subsequently, by adapting the assay technique to incorporate live worms directly into the system, it was shown that L3 of both T. circumcincta and H. contortus produced eosinophil chemoattractant activity. In contrast, neither whole worm extracts, or E/S preparations from mixed stages of the free-living nematode Caenorhabditis elegans contained eosinophil chemoattractant activity, and there was no evidence of chemoattractant production by live C. elegans. The results described are challenging to the traditional dogma that eosinophils are host-protective effector cells, and raise the intriguing possibility that ovine nematodes actively encourage recruitment of eosinophils. Local eosinophil-mediated mucosal damage, comparable to that seen in the asthmatic lung, may then provide a permissive local microenvironment for the parasite. Moreover, if they prove important for pathogenicity, nematode chemoattractants could offer future potential as novel therapeutic targets.

Animals↗
PubMed2005

Cells, cytokines and other molecules associated with rejection of gastrointestinal nematode parasites.

Infections with gastrointestinal nematodes represent a major problem for human health and animal health and production. The physical size of the parasite, its changing life-cycle stages and the relative inaccessibility to host cells pose unique challenges to the immune system, which has evolved specialized strategies for parasite control. This paper reviews the work performed in the authors' laboratories to identify components that are involved in the natural rejection response against ruminant gastrointestinal nematode parasites, in particular Haemonchus contortus in sheep. The results of these studies indicate that stage-specific antibodies act in concert with effector cells, in particular globular leukocytes (intraepithelial mast cells) and eosinophils, appropriately activated/primed by type 2 (T2) cytokines, to initiate different mechanisms of parasite expulsion and killing. In addition, other molecules, in particular carbohydrate binding galectins, may be involved in strengthening the final effector phase of the rejection response.

Animals↗
PubMed2003

Ovicidal and larvicidal activity in vitro of Spigelia anthelmia Linn. extracts on Haemonchus contortus.

The rapid development of anthelmintic resistance, associated with the high cost of the available anthelmintic drugs, had limited the success of gastrointestinal nematodiasis control in sheep and goats and thus awakened interest in the study of medicinal plants as alternative sources of anthelmintics. Spigelia anthelmia extracts obtained with hexane, chloroform, ethyl acetate or methanol, were tested on Haemonchus contortus eggs and larvae via egg hatch and larval development tests. The extracts were evaluated at five concentrations: 3.1, 6.2, 12.5, 25.0 and 50.0 mg ml(-1). At 50.0 mg ml(-1), the ethyl acetate extract inhibited 100% of the egg hatching and 81.2% of the larval development. In a similar way the methanolic extract inhibited 97.4% of the egg hatching and 84.4% of larval development. These results suggest that utilization of S. anthelmia extracts may be useful in the control of sheep and goats gastrointestinal nematodes.

Animals↗
PubMed2003

The anthelmintic efficacy of five plant products against gastrointestinal trichostrongylids in artificially infected lambs.

Forty-eight helminth-free lambs were divided into eight groups (A-H) of six animals. Groups A-G were infected artificially with 10,000 third stage larvae of Haemonchus contortus and 20,000 third stage larvae of Trichostrongylus colubriformis, whereas group H remained uninfected. Thirty days post-infection the lambs were treated orally with a single dosage of one of the following products: group A with 3 mg/kg body weight (BW) of an aqueous ethanol extract (70%, v/v) of the seeds of Azadirachta indica A. Juss syn. Melia azedarach L. (Meliaceae); group B with 1 g/kg BW of a raw powder of the leaves of Ananas comosus (L.) Merr. (Bromeliaceae); group C with 0.3 mg/kg BW of an aqueous ethanol extract of a 1:1 mixture (g/g) of Vernonia anthelmintica (L.) Willd. (Asteraceae) seeds and Embelia ribes Burm (Myrsinaceae) fruits; group D with 183 mg/kg BW of an aqueous ethanol extract of the whole plants of Fumaria parviflora Lam. (Fumariaceae); group E with 28 mg/kg BW of an aqueous ethanol extract of the seeds of Caesalpinia crista L. (Caesalpiniaceae); group F with 25 mg/kg BW of pyrantel tartrate and group G with 50% ethanol. Group H remained untreated. Only the ethanol extract of F. parviflora caused a strong reduction of the faecal egg counts (100%) and a 78.2 and 88.8% reduction of adult H. contortus and T. colubriformis on day 13 post-treatment. The extract was as effective as the reference compound pyrantel tartrate. Therefore, the ethanol extract itself or single constituents of F. parviflora could be a promising alternative source of anthelmintic for the treatment of gastrointestinal trichostrongylids in small ruminants.

Administration, Oral↗
PubMed2004

High genetic correlation between resistance to Haemonchus contortus and to Trichostrongylus colubriformis in INRA 401 sheep.

To compare the protection acquired by infection with Haemonchus contortus or Trichostrongylus colubriformis, successive cross infections with the two species were conducted in two genetically similar groups of 150 ewe lambs from 30 sires of INRA 401 breed. At 6 and 7.5 months of age, each group received two doses of 10000 L3 separated by a treatment of one of the species, followed by a similar infection with the second species at 9 and 11.5 months. Faecal egg counts (FECs) were done 28 and 35 days after each dose. There were very high genetic correlation within and between species suggesting that the environmental conditions were very similar. The heritability of FEC of H. contortus ranged from 0.39 to 0.48 and the genetic correlations between FEC after the first and second infections with the same or different species were all near 1. Selection against this species could be done on the response to only one dose. For T. colubriformis, only the response to challenge infection had a similar heritability (0.47); the genetic correlations within and among species were also near one. These results will assist the selection of sheep resistant to nematode parasites.

Animals↗
PubMed2003

Efficiency of feeding Duddingtonia flagrans chlamydospores to grazing ewes on reducing availability of parasitic nematode larvae on pasture.

Gastrointestinal nematodes are of concern in sheep production because of production and economic losses. Control of these nematodes is primarily based on the use of anthelmintic treatment and pasture management. The almost exclusive use of anthelmintic treatment has resulted in development of anthelmintic resistance which has led to the need for other parasite control options to be explored. The blood sucking abomasal parasitic nematode Haemonchus contortus causes severe losses in small ruminant production in the warm, humid sub-tropic and tropics. This study evaluated the effectiveness of a nematode trapping fungus, Duddingtonia flagrans, in reducing availability of parasitic nematode larvae, specifically H. contortus, on pasture. Chlamydospores of D. flagrans were mixed with a supplement feed which was fed daily to a group of crossbred ewes for the duration of the summer grazing season. A control group was fed the same supplement feed without chlamydospores. A reduction in infective larval numbers was observed in fecal cultures of the fungus-fed group. Herbage samples from the pasture grazed by the fungus-fed group also showed a reduction in infective larvae. There were no significant (P > 0.05) differences in overall fecal egg count, packed cell volume or animal weight between fungus-fed and control groups. Tracer animals were placed on the study pastures at the end of the study to assess pasture infectivity. Although tracer animals were only two per group, those that grazed with the fungus-fed group had substantially reduced (96.8%) nematode burdens as compared to those from the control group pasture. Results demonstrated that the fungus did have activity against nematode larvae in the feces which reduced pasture infectivity and subsequently nematode burdens in tracer animals. This study showed that D. flagrans, fed daily to grazing ewes, was an effective biological control agent in reducing a predominantly H. contortus larval population on pasture.

Animal Feed↗
PubMed2004

Effect of dexamethasone treatment on the immune response of Gulf Coast Native lambs to Haemonchus contortus infection.

Neonatal and weaner Gulf Coast Native (Native) lambs were studied to determine whether an immunological basis underlies their natural resistance to Haemonchus contortus infection. Neonatal Native lambs (n = 8) and weaner Native lambs (n = 15) were randomly assigned to a treatment or a control group. Lambs in the treatment group received dexamethasone by intramuscular injection three times a week for 10 weeks (neonatal) and 15 weeks (weaners). All lambs were monitored for fecal egg count (FEC), blood packed cell volume (PCV), and white blood cell differential counts on a weekly basis for the duration of the studies. Neonatal lambs were kept on pasture with their dams and weaner lambs were dewormed at weaning and kept in pens where they received trickle infections. Serum antibody titers to H. contortus whole worm antigen (WWA) were determined using ELISA. Lymphocyte proliferation assays on peripheral blood mononuclear cells (PBMC) were done to assess lymphocyte function. All lambs were vaccinated with killed Brucella abortus strain 19 to assess the effect of dexamethasone treatment on antibody response. All lambs were necropsied at the end of each study to recover the contents of the gastrointestinal tract for nematode enumeration and identification. The results showed that mean FEC and mean PCV of the treatment group was significantly higher and lower, respectively, than in the control group in both neonatal and weaner lambs from weeks 6 and 5, respectively. At necropsy, total nematode count was significantly higher in treatment groups than in the control groups. Serum antibody titers to H. contortus WWA were significantly lower in treated groups than in control groups. Treatment groups showed a consistent depression in lymphocyte percentage being significantly lower from week 6 in both neonatal and weaner lambs. No differences were found in the response of PBMC to mitogen stimulation between the groups. Lambs in the control groups showed strong positive brucellosis card tests and the treatment groups did not. Dexamethasone treatment resulted in depression of the immune response and loss of natural resistance of Native lambs to H. contortus infection. The results of these studies suggest that some aspects of the immune response may underlie the natural resistance of Native sheep to H. contortus infection.

Animals↗
PubMed2004

Field studies on the biological control of nematode parasites of sheep in the tropics, using the microfungus Duddingtonia flagrans.

Long-term field studies were conducted on two government managed small ruminant research farms, located in different geo-climatic regions and approximately 300 km separate from each other, on Peninsula Malaysia. The Infoternak trial (48 weeks) and the Chalok trial (43 weeks) each compared nematode parasite control in separately managed groups of young sheep, either short-term rotationally grazed around a suite of 10 paddocks in addition to receiving a daily supplement of Duddingtonia flagrans spores (Fungus Group); or similar groups of sheep being rotationally grazed alone (Control Group). The prevailing weather conditions at Infoternak farm were of below average rainfall conditions for the most of the trial. As a consequence, only very low worm infections (almost exclusively Haemonchus contortus) were acquired by the 17 sets of tracer lambs that grazed sequentially with the experimental lambs. However on all except 2 occasions in the early part of the trial, the mean tracer worm burdens were significantly lower (P < 0.05) and the experimental lambs grew significantly better (P = 0.054) in the Fungus Group. Rainfall at Chalok farm during the course of the trial was also below average. As a consequence infectivity of pastures was assumed to be relatively low based on faecal egg counts (epg) of the experimental sheep, which following an anthelmintic treatment prior to allocation, remained very low in both treatment groups. Faecal egg counts of undosed replacement lambs in the latter half of the Chalok study, showed a progressive increase in the Control Group to levels exceeding 3000 epg, whereas the Fungus Group remained static at approximately 500 epg. These results show that the deployment of the nematophagous fungus, D. flagrans, can improve the level of parasite control of sheep in the tropics above that which can be achieved by the short-term rotational grazing strategy alone.

Animal Husbandry↗
PubMed2004

Variability in the resistance of the Nigerian West African Dwarf goat to abbreviated escalating trickle and challenge infections with Haemonchus contortus.

The West African Dwarf (WAD) goat is known to be relatively resistant to infection with Haemonchus contortus. An experiment was carried out to assess variability in resistance under escalating trickle and single pulse challenge infection protocols. Thirty two 7-8 month old goats were subjected to trickle infection beginning with a thrice weekly dose of 100 L3 and increasing to 500 L3 by week 5, the last dose being administered on D30. Infection was abbreviated with fenbendazole on D32 and the animals challenged with 4000 L3 (=404-741L3/kg body weight) on D46 and necropsied on D81. The goats exhibited marked individual variability in faecal egg counts (FEC) and worm burdens (Wb). For convenience, we arranged the goats into FEC classes 1, 2 and 3, corresponding to peak counts of <1000, 1000-2500 and >2500 epg and Wb classes 1, 2 and 3, with counts of <50, 50-100 and >100 worms, respectively, broadly reflecting relatively resistant, intermediate and poorly resistant response phenotypes. Wb classes broadly reflected the FEC phenotypes and although there were no significant differences between the Wb of the FEC classes at necropsy, significant differences in FEC were detected when analysis was carried out only on Wb classes. There was also a significant positive correlation between FEC class on each of the days of challenge (D67 to D80) and worm burden at necropsy. In general, the goats showed strong resistance/tolerance to challenge, with more than 80% having Wb not exceeding 5% of the challenge dose, and only in class three goats were weight loss and anaemia detected in some animals. PCV and weight changes also closely reflected the FEC and Wb classes, with a significant negative correlation between each and Wb. Infection level did not significantly affect the sizes of either male or female worms and no significant difference was detected between the levels of circulating eosinophils in any FEC or Wb class. Overall, the data are consistent with the existence of a range of response phenotypes, which reflect variations in resistance of WAD goats to H. contortus infection, the genetic basis of which will be explored in future experiments.

Animals↗
PubMed2004

The epidemiology of abomasal nematodes of sheep in Sweden, with particular reference to over-winter survival strategies.

In May 2002, studies on the seasonal patterns of nematode infection of sheep were undertaken on four commercial sheep farms in southern Sweden, which had previously reported problems with nematode parasitism, especially due to Haemonchus contortus. One farm was used for intensive investigation. This entailed the establishment of two replicate groups of sheep, each consisting of 20 ewes and their lambs, on adjacent pasture paddocks. The seasonal patterns of nematode infection were followed by regular (approximately monthly) sampling of both ewes and lambs for nematode faecal egg counts and larval differentiation, and the sequential use of replicate groups of tracer lambs. H. contortus and Teladorsagia circumcincta were the most abundant nematode species, with the former most prevalent in the post-parturient faecal egg counts of ewes. Tracer worm counts showed almost 100% arrested development in the early fourth larval stage for H. contortus as early as mid-summer and the numbers of parasites progressively increased during the season. T. circumcincta also showed high levels of arrested development, but not as early, or as absolute, as for H. contortus. Tracers allocated to the paddocks at the time of turn-out following winter in May 2003, showed virtually a total absence of H. contortus in contrast to exceedingly high infections with T. circumcincta. Results of the three additional monitoring flocks supported these findings. It can be concluded that under Swedish sheep farming conditions, H. contortus has evolved to survive the long, cold winters entirely within the host as the arrested larval stage, relying on the lambing ewe to complete its life cycle. The peri-parturient relaxation of resistance in the ewes triggers the resumption of development to the adult egg-laying parasites to result in pasture contamination and the completion of just one parasite generation/year. In contrast, T. circumcincta can survive well over-winter, both on pasture and within the host.

Animals↗
PubMed2004

Resistance to benzimidazole and macrocyclic lactone anthelmintics in cattle nematodes in Argentina.

In April 2003, persistent scouring and ill-thrift that was reported in calves form an intensive beef rearing operation in central Argentina despite treatments with benzimidazole and ivermectin. In order to conduct a controlled faecal egg count reduction test on this herd, 40 calves 5-8-months-old were selected on the basis that they had a nematode eggs per gram (epg) of faeces count greater than 150. Animals were divided into four groups (1-4) of 10 calves. Calves of groups 1-3 were treated, respectively, with subcutaneous injection of ivermectin (200 mcg/kg), ricobendazole (4 mg/kg) and levamisole (7.5 mg/kg), while calves of group 4 remained as untreated controls. The egg count reductions carried out 10 days later were lower than 15% in calves treated with ivermectin and ricobendazole, but 100% in animals receiving levamisole. Pooled post-treatment faecal cultures showed larval percentages of 92 and 95 for Haemonchus and 8 and 5 for Cooperia in the faeces of calves treated with ivermectin and ricobendazole, respectively. This is the first reported case of Haemonchus parasiting cattle showing simultaneous resistance to avermectins and benzimidazole type anthelmintics.

Albendazole↗