Resistance of young lambs to Haemonchus contortus infection, and its loss following anthelmintic treatment
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Keywords:
Ostertagia
Trichostrongylus
Summary Ten controlled tests were done between 1972 and 1989, in lambs on pasture, evaluating activity of fenbendazole ( fbz ; 5 mg/kg of body weight), oxfendazole ( ofz ; 3.5 and 10 mg/kg), oxibendazole ( obz ; 10 mg/kg), pyrantel pamoate ( prt ; 25 mg of base/kg), and thiabendazole ( tbz ; 44 and 50 mg/kg) against natural infections of helminths, with emphasis on 2 strains (A and B) of Haemonchus contortus . Strain A was phenothiazine-susceptible and strain B was phenothiazine-resistant when isolated in 1955. For approximately 10 years prior to these tests, sheep infected with both strains had been treated periodically each year with several compounds, including thiabendazole, which was used many more times than the other drugs. For this study, 4 ( fbz , ofz , obz , and prt ) of the 5 compounds were evaluated in either 1 or 2 controlled tests. The fifth compound, tbz , was used for 5 tests. Strain A H contortus was resistant to tbz for all years tested, but more susceptible to fbz , ofz , obz , and prt . Overall, strain B was susceptible to tbz (with a few exceptions), and also to fbz , ofz , obz (activity less on immature forms), and prt . Other abomasal parasites (2 species of Ostertagia and 3 of Trichostrongylus ) were found in low numbers, but removal overall was good for the compounds tested. Trichostrongylus axei, found in higher numbers than species of Ostertagia and other species of Trichostrongylus , were effectively removed by all compounds in most cases. Activities of tbz and prt were also evaluated against several species of intestinal helminths, most of which were found in low numbers. Cooperia curticei were inconsistently removed by tbz , but activity of prt was effective. Both compounds were active on mature Nematodirus sparger, but tbz had variable activity on immature forms. Strongyloides papillosus were effectively removed by tbz . Other parasites found in lower numbers than the aforementioned 3 species were Capillaria spp, Trichuris spp, and Oesophagostomum columbianum ; removal was variable for both drugs.
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Nematode populations is stabled ewes of the Rimouski region were studied by means of fecal worm egg counts, fecal culture of larvae, and worm counts at necropsy. It was found that during the winter strongyle egg counts were low, Trichostrongylus eggs being most numerous, The stronglye egg counts increased following lambing and reached peak in June. Ostertagia spp was the principal contributor to this "spring-rise", with substantial contribution from Trichostrongylus and Haemonchus contortus. The bulk of adult worm populations in winter, however, was made up of Trichostrongylus, whereas the great majority of the populations of Ostertagia spp, H. contortus and Nematodirus spp were inhibited in development at the fourth larval stage. All the worms recovered at necropsy in spring were adults, coinciding with the "spring-rise".
Nematodirus
Ostertagia
Trichostrongylus
Ostertagia ostertagi
Eggs per gram
Trichuris
Oesophagostomum
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The activity of tetramisole has been demonstrated against Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus spp., Oesophagostomum columbianum, Gaigeria pachyschelis, Nematodirus spp., Trichuris spp., and Chabertia ovina in three series of experiments involving 70 sheep. Tests against Dictyocaulus filaria were carried out on 25 young sheep. Doses were varied from 5-15 mg/kg to establish the optimum oral dose.
Nematodirus
Ostertagia
Trichostrongylus
Trichuris
Oesophagostomum
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The seasonal incidence of helminth infestation on a farm in the Transvaal Highveld was determined by the slaughter of tracer lambs exposed on pasture for periods of approximately 6 weeks. Haemonchus contortus, the most prevalent nematode, was recovered in the greatest numbers from January--May 1974. Peak counts of Ostertagia circumcincta were made during March and April 1974 and in January 1975, while Trichostrongylus spp. were mainly encountered from March--June. Cooperia spp. were generally recovered from November--May and Moniezia expansa from October--April. H. contortus, O. circumcincta and Cooperia spp. all exhibited increasing degrees of arrested development in the 4th larval stage from February--June.
Trichostrongylus
Ostertagia
Nematodirus
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The activity of ivermectin against common nematode parasites of sheep was examined in 2 experiments. In the 1st experiment, 14 sheep with naturally acquired infections were assigned to 2 groups of 7 sheep each. Sheep in 1 group were treated with 200 micrograms of ivermectin/kg of body weight and the remainder served as nontreated controls. In the 2nd experiment, 15 sheep with experimentally supplemented infections (including a benzimidazole-resistant strain of Haemonchus contortus) were assigned to 3 groups of 5 each. The 1st group was treated with 200 micrograms of ivermectin/kg, the 2nd was treated with 88 mg of thiabendazole/kg, and the 3rd served as nontreated controls. Ten to 12 days after treatment, all sheep were euthanatized and necropsied, and the parasites they harbored were recovered and identified. Efficacy of ivermectin was excellent (greater than 96%) against Dictyocaulus filaria, H contortus, Ostertagia circumcinta, Marshallagia marshalli, Trichostrongylus axei, T colubriformis, and T vitrinus. Treatment was not as uniformly effective for Nematodirus spathiger (73% to 85%), N filicollis (80% to 96%), Cooperia curticei (92% to 100%), immature nematodes (92% to 100%), and early 4th-stage larvae (46% to 100%). Efficacy of thiabendazole was poor for H contortus (42%) and early 4th-stage larvae in the abomasum (52%), but approached 100% for most of the other parasites.
Ostertagia ostertagi
Ostertagia
Mebendazole
Trichostrongylus
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The gastrointestinal nematodiosis represents one of the main health problems of goats reared under grazing, and in Haemonchus contortus and Trichostrongylus colubriformis species it is the most responsible for economic losses of goat. The diagnosis of parasitic animal must be grounded in clinical evaluations and results of tests used, including the pasture. The degree of parasitic infection in animal and pasture contamination assist in the adoption of measures of grazing management (forage, height of grazing, pasture rotation and stocking rate) and anthelmintic treatment suitable for each system created in different geographic regions. This article was written according to the health and economic importance of gastrointestinal helminthiasis caused by nematodes in goats subjected to grazing.
Trichostrongylus
Animal health
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Forty-five ram lambs uniformly exposed to natural infections of various helminths were assigned to 5 groups of 9 lambs each and used to conduct controlled anthelmintic trials. One group of lambs served as unmedicated controls, and 4 groups were treated as follows: (1) thiabendazole 50 mg/ kg; (2) thiabendazole 100 mg/kg; (3) levamisole 8 mg/kg; (4) parbendazole 15 mg/kg. All lambs were necropsied 4 to 6 days posttreatment for residualworm counts. Both mature and immature stages of several parasite species were recovered from the unmedicated control lambs; Haemonchus contortus was the most numerous. For the medicated groups 1, 2, 3, and 4 above, the calculated efficacies of the treatments against all stages of parasites were, respectively, H. contortus 48, 88, 99, and 79%; Ostertagia spp. (mainly 0. circumcincta) 94, 99, 76, and 99%; Trichostrongylus spp. (T. axei, T. vitrinus, and T. colubriformis) 99, 100, 99, and 100%; Nematodirus spathiger 90, 100, 96, and 83%; Oesophagostomum venulosum 98, 100, 100, and 99%. The data indicate the H. contortus strain in these lambs was somewhat resistant to thiabendazole and parbendazole. Fourth-stage larvae were recovered only of H. contortus, Ostertagia spp., and N. spathiger, and generally were not removed as effectively as 5th-stage parasites. However, levamisole was highly effective against 4th-stage H. contortus and N. spathiger, and 100 mg/kg of thiabendazole removed all 4th-stage N. spathiger. The 3 anthelmintics significantly reduced strobilar volume of Moniezia expansa, but had no activity against the scoleces. During the last decade, three new broadspectrum anthelmintics, viz., thiabendazole, tetramisole, and parbendazole, have shown considerable promise against helminths, particularly gastrointestinal nematodes of sheep and other domestic animals. The effective action of thiabendazole [2-(4'thiazolyl)-benzimidazole] against a wide variety of nematode parasites of various animals was first reported by Brown et al. (1961). Since that time a substantial literature (see Gibson, 1965, 1969; Levine, 1968) has accumulated supporting the original findings. Recently, however, Theodorides et al. (1970) and Colglazier et al. (1970a) summarized a number of published reports pertaining to strains of Haemonchus contortus that were resistant to the drug. Thienpont et al. (1966) first reported on the anthelmintic activity of dl-tetramisole [2,3,5,6tetrahydro-6-phenyl-imidazo (2,1-b) thiazole hydrochloride] in man and animals. Subsequently, Bullock et al. (1968) separated the dextro and levo isomers of the drug, and showed that the anthelmintic action was attribReceived for publication 3 September 1970. * National Animal Parasite Laboratory, Veterinary Science Research Division. t Animal Science Research Division, ARS, USDA, Beltsville, Maryland 20705. utable primarily to the levo form. Considerable published data have now accumulated which attest to the broad-spectrum activity of this chemical, and to the fact that the levo isomer (levamisole) is about twice as active as the dl compound (Walley, 1966; Fitzsimmons, 1966; Forsyth, 1966, 1968; Gibson, 1966; Gibson et al., 1968a, b; Hart and Curr, 1968; Hart et al., 1969; Lyons et al., 1968; Pankhurst and Sutton, 1966; Pretorius, 1967; Ross, 1966; Shone and Philip, 1967; Colglazier et al., 1969, 1970b). In 1967, Actor et al. published the first report on another promising livestock anthelmintic, parbendazole [5(6)-butyl-2-benzimidazole carbamate], a benzimidazole compound related chemically to thiabendazole. Parbendazole had an anthelmintic spectrum similar to that of thiabendazole, but it was active at lower dose level. Several studies on the activity of parbendazole against gastrointestinal nematodes of sheep and goats have been reported which essentially confirm and extend the earlier findings, viz., Bennett (1968), Danek et al. (1969), Johns and Mendel (1969), Lammler et al. (1969), Luque Forero et al. (1969), Ross (1968), Theodorides et al. (1968, 1969). Theodorides et al. (1970) also reported that a number of thiabendazole-resistant strains of H. contortus were also cross-resistant to parbendazole.
Levamisole
Nematodirus
Ostertagia
Trichostrongylus
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Calves experimentally infected with Haemonchus, Ostertagia, and Cooperia, and to lesser degrees with Trichostrongylus, Oesophagostomum, Nematodirus, and Bunostomum were used in a controlled experiment to record the anthelmintic efficacy of a benzimidazole compound methyl 5-(phenylthio)-2-benzimidazolecarbamate at dosage levels of 3.5, 5, and 7.5 mg/kg bodyweight. With the 3 dosages, reductions of Haemonchus were 96.7, 99.2, and 99.8%; of Ostertagia, 97.2, 97.2, and 99.5%; and of Cooperia, 99.9, 99.9, and 99.9%. Pronounced reductions were also recorded for Trichostrongylus, Nematodirus, Oesophagostomum, Trichuris, and Capillaria, but these populations were too numerically small or too unevenly distributed within the control groups to be given much emphasis. The experimental parasitic populations which developed in the 10 control calves amounted to 91, 763 worms (total).
Oesophagostomum
Nematodirus
Trichostrongylus
Ostertagia
Trichuris
Ostertagia ostertagi
Benzimidazole
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Benzimidazole resistance involving several gastrointestinal nematode genera on a single sheep farm in New Zealand is reported for the first time. A controlled slaughter trial showed that at the recommended dose rate of 12.5 mg/kg, mebendazole had efficacies of 0, 60, 66, 90, 54 and 38% against Haemonchus contortus, Ostertagia spp., Nematodirus spp., intestinal Trichostrongylus spp., Strongyloides spp. and Oesophagostomum venulosum, respectively. The relevance of such multigeneric resistance to possible future options for controlling anthelmintic resistant sheep trichostrongylids is briefly discussed.
Mebendazole
Nematodirus
Ostertagia
Trichostrongylus
Benzimidazole
Oesophagostomum
Ostertagia ostertagi
Strongyloides
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In two successive years, separate phalaris-subterranean clover pasture plots near Canberra were contaminated with nematode eggs by grazing with naturally infected sheep in each of the summer months (December, January, February) and the first month of autumn (March). At intervals until mid- to late winter, the availability of infection on pasture was estimated by grazing with worm-free 'tracer' lambs which were subsequently slaughtered for worm counts. Summer rainfall in both years was above average. Tracer counts of Haemonchus contortus and Ostertagia, Trichostrongylus and Nematodirus spp. per l08 eggs per hectare remained high during summer, with evidence that migration of larvae to the herbage could continue for at least 2 months after contamination. Rates of decline in tracer worm counts over the autumn and winter did not differ between years, and from an assumed maximum 2 months after contamination in each of the summer months, were fastest from December and slowest from February contamination. These rates were similar for all genera on December-contaminated plots, but on January and February plots, Ostertagia spp. declined more slowly. H. contortus numbers fell sharply in early autumn to be low by the end of May. By mid July there would be few larvae of all genera available on pastures contaminated in December and January, but this is less certain on February-contaminated pastures, especially for Ostertagia spp. Implications for the control of nematode infections in sheep by anthelmintic treatment and grazing management are considered.
Ostertagia
Trichostrongylus
Nematodirus
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