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PubMed1993

The efficacy and persistent anthelmintic effect of ivermectin in sheep.

The direct efficacy and the long-term persistent anthelmintic effect of an oral suspension and an injectable formulation of ivermectin at a dose rate of 0.2 mg kg-1 was studied in sheep. Lambs were infected experimentally with Haemonchus contortus, Trichostrongylus vitrinus and Cooperia curticei. After 3 weeks they were treated with an oral suspension or with an injection, and reinfected with the same dose of larvae 3, 6 or 10 days after treatment. Post-mortem worm counts showed no persistent effect of the oral suspension. The injectable formulation showed an excellent persistent effect for up to 10 days against H. contortus. Reinfection with C. curticei 3 days after treatment resulted in a 64% reduction of the worm burden, but reinfection after 6 and 10 days was 100% reduced. The reduction of T. vitrinus was 46% after 3 days and 92% after 6 and 10 days.

Administration, Oral↗
PubMed1993

Model predictions for anthelmintic resistance amongst Haemonchus contortus populations in southern Brazil.

A computer model developed to study Ostertagia circumcincta resistance to anthelmintics in UK sheep flocks has been adapted for use with Haemonchus contortus under southern Brazilian conditions. The model simulates the effect of different anthelmintic control regimens on the year-to-year pattern of resistance in breeding ewes. The nematode control regimen most used by Brazilian sheep farmers was found to increase the frequency of genes which confer resistance from approximately 3% to 14% in an H. contortus population over a 20 year period. The effect of early versus late season anthelmintic treatment was investigated. This indicated that early season treatment would select for resistance rapidly, whereas late season treatments would not, owing to large numbers of untreated parasites accumulating at the beginning of the season. A model which can predict the development of anthelmintic resistance in parasites of ewes is a valuable tool in the understanding of the effect of different strategies on nematode control programmes and merits further consideration.

Animals↗
PubMed1993

Notes on necropsy and herbage processing techniques for gastrointestinal nematodes of ruminants.

Necropsy techniques for the digestive tract of ruminants used at the University of Utrecht differ from those used elsewhere in three respects: (1) the abomasum is opened immediately after slaughter and the "contents" are treated separately from the "washings"; (2) the first 10 m of the small intestine are treated separately from the remainder of the intestine; (3) the aliquots are coloured with iodine before being examined for worms. The majority of the worms are found in the washings of the abomasum and the first part of the small intestine, whereas the contents of the abomasum and the remainder of the small intestine contain the bulk of the digesta. Because inhibited stages of Ostertagia, Haemonchus and, particularly, the very small third stage larvae (L3) of Trichostrongylus can be overlooked easily in digesta, these methods imply a more rapid and accurate enumeration of worms. This is more important in small ruminants than in cattle because a much higher proportion of the inhibited larvae will be washed out of the mucosa and because Trichostrongylus is more important in small ruminants. Herbage sampling methods for monitoring gastrointestinal nematode infections on cattle pastures in northwest Europe should also be suitable for lungworm. The agar-bile technique of Jørgensen is an elegant method, but disadvantages are that many gastrointestinal nematode larvae exsheath, resulting in identification difficulties, and recovery of lungworm larvae decreases as a result of ageing. A simple sucrose flotation method, based on the principle that a sucrose solution does not mix easily with water containing nematodes, has been tested at our laboratory.(ABSTRACT TRUNCATED AT 250 WORDS)

Abomasum↗
PubMed1993

The role of inhibited development in the epidemiology of Ostertagia infections.

Seasonal patterns of inhibited larval development have been described for Ostertagia spp. from many parts of the world; winter inhibition is found in areas where transmission of infections occurs mainly in summer and summer inhibition in areas where transmission is mainly from autumn to spring. There is no fixed regional seasonal inhibition pattern. Depending on weather and farm management, the timing and level of inhibition will vary from year to year. Moreover, differences in the propensity for inhibition have been observed between field strains of Ostertagia in cattle in Australia and in the Netherlands. Simultaneous resumption of development of large numbers of inhibited larvae can result in Type II ostertagiasis, usually in only part of the heard. For reasons as yet unknown, there appear to be differences between regions in the prevalence of this disease. Development of immunity is also involved in the onset of inhibition and the occurrence of two separate inhibited populations in one host population, "seasonal" and "immunological", has been suggested. Seasonal fluctuations in the proportion of inhibition in naturally infected animals do not necessarily imply that the main trigger for inhibition is environmental conditioning, because infection levels and thus the degree of immunity will also fluctuate seasonally. In some Ostertagia field populations during late autumn in the Netherlands, worm burdens of permanently grazed calves consist mainly of inhibited larvae, but burdens of tracer calves consist of adults. Inhibited larvae may also be involved in the development of immunity. Some protection against reinfection with Haemonchus contortus has been demonstrated in barren ewes infected 6 months earlier with a single dose of 15,000 inhibition-conditioned larvae. Such an immunogenic role may be more important in Ostertagia, because inhibited larvae are found deeper in the mucosa than those of Haemonchus.

Animal Husbandry↗
PubMed1993

Lamb serum recognition of infective larvae and adult Haemonchus contortus antigens.

Sixteen- to eighteen-week-old lambs were infected with 2500 3rd stage larvae (L-3) of Haemonchus contortus or kept as uninfected controls. Two months later all animals were challenged with 5000 L-3 of this parasite. Soluble antigens of H. contortus L-3 and adult worms were analyzed by SDS-PAGE and Western blotting during experimental infection and challenge. Antigens from both sources, particularly of low molecular weight under reducing conditions, were recognised by the pooled sera of infected lambs. No single L-3 antigen was recognised by all infected lambs, whereas two peptides having around 25 and 26 kDa from adults were recognised by infected animals during the patency and could be of potential use in the diagnosis of lamb haemonchosis.

Animals↗
PubMed1993

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: screening studies.

Ninety-four species of fungi with known nematophagous activity were tested for their ability to reduce the number of infective larvae of sheep nematodes in faecal cultures, and also for their ability to produce nematode-attractant and nematocidal substances against these free-living stages under in vitro conditions. Reductions of infective larval numbers exceeding 80% were consistently recorded when 100-250 conidia g-1 faeces of various species from the genera Arthrobotrys, Geniculifera and Monacrosporium were used. Even concentrations as low as 10 conidia g-1 faeces resulted in a significant reduction in infective larval numbers compared to control cultures. This study demonstrates that whilst many fungal species exhibit nematophagous activity against a variety of free-living nematodes, few show efficient activity against the free-living stages of parasitic nematodes in the sheep faecal environment. For the most active, there were six species of Arthrobotrys, two species of Geniculifera and two species of Monacrosporium which showed comparable activity to the extensively studied species A. oligospora.

Analysis of Variance↗
PubMed1993

Establishment of camel isolates of Haemonchus longistipes and Trichostrongylus colubriformis in goats.

Two main nematode parasites, Haemonchus longistipes and Trichostrongylus colubriformis, have been reported to cause morbidity and mortality in camels. Although goats are usually reared with camels in the combined animal husbandry system prevailing in Northern India, these parasites have not been reported in goats. Therefore, it was planned to conduct an experimental cross-transmission study of H. longistipes and T. colubriformis isolated from camels and transferred to young goats. Twelve healthy kids (5-6 months) were divided into three groups of four each. Groups I and II were infected orally with third stage infective larvae of H. longistipes and T. colubriformis cultured in the laboratory from faecal isolates from camels, at the rate of 50,000 and 100,000 larvae, respectively; group III comprised uninfected healthy controls. Daily clinical and faecal examinations were made. Body weights and blood haematological indices were measured at weekly intervals. The infection became established in both infected groups, and the animals started passing ova 17 days postinfection. Egg counts varied from 275.00 +/- 248.74 to 6150 +/- 2830.63 eggs g-1. Animals were killed 28 days postinfection. On postmortem examination mature as well as immature worms were recovered from the abomasum and intestine with typical postmortem changes seen in both the groups. Clinical manifestations were weakness and loss of body weight but no diarrhoea. There was a marked fall in haemoglobin and packed cell volume, indicating anaemia in both infected groups.

Abomasum↗
PubMed1993

Detection of Haemonchus contortus surface antigen in faeces from infected sheep.

An antigen capture enzyme-linked immunosorbent assay (ELISA) has been developed that could identify Haemonchus contortus antigens in dilute suspensions of worm homogenates and in faeces from sheep naturally infected with moderate burdens of the parasite. The ELISA is based on a polyclonal (rabbit or sheep) antibody coated solid-phase that captures parasite antigen from a suspension of worms or faeces. The captured antigen is detected by a mouse monoclonal antibody (MAb E2) that is reactive with a cuticle surface antigen of H. contortus. Binding of MAb E2 was shown to be specific for H. contortus and the ELISA was able to detect this antigen in faeces of some infected sheep. Characterisation of the antigen reacting with MAb E2 indicates it to be a collagenase and protease resistant surface protein of H. contortus that under reducing conditions in SDS-polyacrylamide gel electrophoresis exists as polypeptides of molecular weight 122, 56 and 49 kDa.

Animals↗
PubMed1995

Strongyle infections in sheep and goats under the traditional husbandry system in peninsular Malaysia.

Faecal egg counts were used to study patterns of trichostrongyle infections in sheep and goats according to season, age, pregnancy and lactation on traditional farms in west Malaysia. Haemonchus contortus and Trichostrongylus spp. were the most important strongyles in sheep and in goats, H. contortus, Trichostrongylus spp. and Oesophagostomum spp. were most prevalent. The faecal egg counts of sheep and goats were apparently not influenced by the small seasonal climatic variations. Strongyle infections were acquired at an earlier age in sheep than in goats. Mean faecal egg counts decreased from the age of 8 months onwards in sheep while in goats this occurred from 12-18 months onwards. A periparturient rise in strongyle egg counts was observed in both animal species. Haemonchus contortus was mainly responsible for this rise in faecal egg counts. The results are discussed with reference to control of gastrointestinal strongyle infections in sheep and goats.

Aging↗
PubMed1995

Dry areas: an example of seasonal evolution of helminth infection of sheep and goats in southern Mauritania.

A total of 647 faecal egg counts and 53 necropsies were performed on sheep and goats originating from three sites of a Sahelian region of Mauritania (Gorgol) over a period of 2 years (1990-1992). Haemonchus contortus, Oesophagostomum columbianum and Stilesia globipunctata were the most prevalent species. The seasonal pattern was characterized by long survival of adults and high percentages of arrested fourth-stage larvae in the dry season, suggesting that two different strategies were used to survive from one rainy season to the next. Sheep and goats were equally infected, except for Stilesia globipunctata, which was found more often in sheep. The influence of age was limited, although kids and lambs born in the beginning of the dry season did not become infected until their first grazing in the rainy season.

Analysis of Variance↗
PubMed1995

Isotype-specific serum antibody responses of sheep to Haemonchus contortus antigens.

In total, 19 8-month-old Texel sheep were used to study the isotype-specific serum antibody responses against infective larvae and adult worms of Haemonchus contortus. Group Group 1 sheep (n = 7) were infected with 20,000 L3 larvae (Week 0), treated with ivermectin 6 weeks post-infection and subsequently challenged at Week 10 of the experiment. This challenge consisted of a trickle infection of 10,000 L3 larvae per week for 5 weeks. Group 2 sheep (n = 7) received a single infection at Week 10 of the experiment, and Group 3 (n = 5) served as a non-infected control group throughout the entire experiment. Individual blood and faeces samples were collected at weekly intervals. The immune responses were monitored by ELISA and Western blotting. The secondary immune response coincided with a significant reduction of the Haemonchus egg output and reduction of worm counts. Both primary and challenge infections induced humoral immune responses, and ELISA revealed that the most dominant serum antibody responses belong to the IgG1 isotype and to a lesser extent to IgG2. IgM and IgA responses were less dominant. Western blotting experiments demonstrated that many antigens were commonly recognized by antibodies from both primary and challenge infected animals. However, sera of immune animals specifically reacted with low molecular weight proteins. In particular, a 24 kDa antigen present in adult worms appeared to be specifically recognized.

Abomasum↗
PubMed1995

Comparison of two enzyme immunoassays for the detection of Haemonchus contortus infections in sheep.

Two enzyme-linked immunosorbent assays (ELISA) using either excretory/secretory (ES) products or crude somatic antigens (CSA) of adult Haemonchus contortus were compared for their ability to detect antibodies against H. contortus in sheep. Serum samples obtained from a group of 32 H. contortus mono-infected sheep were tested in the two ELISAs and the obtained data were compared with the results of the faecal examinations of these sheep. The first sheep became patent 3 weeks post infection (p.i.) and all sheep had positive egg counts at week 5 p.i. The first antibodies against H. contortus were detected 1 week p.i. and all sheep were found positive by both ELISAs at week 4 p.i. Using sera from a large number of H. contortus-infected sheep a difference in sensitivity between the ES ELISA (97.7%) and the CSA ELISA (89.2%) was found. The specificity of each assay was determined by testing sera obtained from sheep with mono-infections of H. contortus, Trichostrongylus colubriformis, Trichostrongylus vitrinus, Ostertagia circumcincta, Nematodirus battus, Cooperia curticei, Fasciola hepatica, Taenia ovis or Eimeria spp. The specificity of the ES ELISA was 87.2%, whereas the specificity of the CSA ELISA was 82.7%.

Animals↗
PubMed1995

Efficacy of pyrantel tartrate against experimental infections with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis in goats.

The efficacy of pyrantel tartrate was evaluated in goats against induced infections with Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis. All the strains were of sheep origin and tested for susceptibility to pyrantel tartrate in sheep at the standard dose rate (20 mg kg-1) prior to the infection of goats. Fifteen French Alpine female goats were inoculated with the three nematode species. On Day 25 post-infection, goats were randomized into an untreated control group and two pyrantel treatment groups (20 mg kg-1 bodyweight once, and 40 mg kg-1 bodyweight as two doses 24 h apart). The goats were killed and processed for worm recovery 10 days after treatment. The two dose rates achieved high and similar levels of efficacy (> 96%) against Haemonchus contortus and Teladorsagia circumcincta. Against Trichostrongylus colubriformis, however, pyrantel tartrate was less effective at both dose rates as worm reductions ranged from 55 to 62%.

Animals↗
PubMed1995

Haemonchus placei in calves: effects of dietary protein and multiple experimental infection on worm establishment and pathogenesis.

An experiment was conducted to examine the influence of dietary protein and immunisation on parasite establishment and pathogenesis of Haemonchus placei in calves. Four groups of 4-6-month-old worm-free calves (n = 4) were given a low protein diet (LP) containing 213 g crude protein (CP) per head per day or a high-protein diet (HP) containing 469 g per head per day CP. Five weeks later, calves in one of the two groups of each dietary treatment were given 50,000 H. placei infective larvae (L3). Twenty-five days later, infection in these groups was terminated by dosing with oxfendazole. This immunisation process was repeated 4 days later. Four days after termination of the second immunisation all calves were challenged with 100,000 L3. Five weeks later, all calves were slaughtered for abomasal worm counts. Worm establishment was lower in the immunised groups; however, only the HP-I group showed a significant reduction (P < 0.05). All calves gained weight during the first 13 week period, and after challenge the non-immunised groups lost weight, independent of the level of protein in the diet (P < 0.05). Packed cell volume values for all treatments only dropped after challenge (P < 0.05) and the HP-immunised group presented values significantly higher when compared with the other treatments. All calves were hypoproteinaemic and hypoalbuminaemic at the end of the experiment, regardless of the treatment. Immunised calves showed a normocytic normochromic anaemia, while the non-immunised groups presented a microcytic normochromic anaemia.

Animals↗
PubMed1995

A comparison of the responses to repeated experimental infections with Haemonchus contortus among Scottish Blackface lambs.

Twenty helminth-naive Scottish Blackface lambs were given three infections with 10,000 infective larvae of Haemonchus contortus at 8 week intervals. An additional six lambs served as uninfected controls and eight lambs were infectivity controls. The lambs were 7 months old at the start of the infection. Four of the 20 lambs developed severe haemonchosis and were put down during the experiment. The remaining 16 lambs plus uninfected controls were necropsied 8 weeks after the third infection. The mean faecal egg count peaked 6-8 weeks after the first infection, gave a second smaller peak 6-8 weeks after the second infection but produced no peak after the third infection. Mean red blood cell counts fell rapidly during the first infection, then rose gradually during the second and third infections. The mean values suggested that two infections were sufficient to produce effective immunity in the sheep population but they masked considerable individual variation. Eleven animals appeared relatively resistant following the first infection, while two animals were relatively susceptible to even the third infection. The repeatability of mean faecal egg counts or mean red blood cell counts for each animal during the replicate infections were very high, because the rankings of the individual sheep remained remarkably stable. Faecal egg counts were very strongly correlated with red blood cell counts. Multiple regression analysis showed that four factors--faecal egg counts, red blood cell counts, weight and sex--accounted for essentially all of the observed variation in worm burdens among the lambs. Therefore, under these controlled experimental conditions, additional markers appear unnecessary for the detection of resistance status.

Analysis of Variance↗
PubMed1994

Anthelmintic resistance in Haemonchus contortus from sheep in Malaysia.

Albendazole, oxfendazole, fenbendazole, levamisole, closantel, ivermectin and febantel were administered to sheep on four farms and their efficacy assessed by faecal egg count reduction test. High level of resistance of Haemonchus contortus was found to benzimidazoles (albendazole, oxfendazole, fenbendazole) on all farms and to febantel on the one farm where it was tested. No resistance to closantel and levamisole was observed. Resistance to ivermectin was absent on the three farms examined under this study, but has been reported on the fourth farm in earlier work. It is concluded that anthelmintic resistance to benzimidazoles and the probenzimidazole, febantel, is a serious and widespread problem in H. contortus in sheep in Malaysia.

Animals↗
PubMed1994

Rotational grazing for control of gastrointestinal nematodes of goats in a wet tropical environment.

A preliminary experiment involving contamination of pasture plots with eggs of Haemonchus contortus, Trichostronglyus colubriformis and Oesophagostomum columbianum every month for a year established that in the tropical environment of the Pacific island of Tongatapu, hatching and development of all species was rapid and continuous, with a short survival on pasture (3-7 weeks) of the resulting infective larvae. These results indicated that a rotational grazing system consisting of ten paddocks grazed in sequence for 3.5 days at a time may permit a reduction in the frequency of anthelmintic treatment of goats. In comparison with an adjacent set-stocked flock which required treatment on three occasions during the year when mean flock egg counts exceeded 2000 eggs per gram (EPG), rotationally grazed goats generally maintained mean egg counts of less than 1000 EPG. Anthelmintic treatment was only given to rotationally grazed goats individually as they kidded, and there were indications that even this precaution was unnecessary. Because of the expense of frequent anthelmintic treatment and the resulting selection of strains of anthelmintic-resistant nematodes, rotational grazing of small ruminants through fencing, tethering or herding deserves further investigation as a nematode control option in wet tropical environments.

Animal Husbandry↗
PubMed1994

Resistance to benzimidazole anthelmintics by Haemonchus contortus in goats in peninsular Malaysia.

A previous study had suggested that local strains of goat trichostrongyles, comprising largely Haemonchus contortus, might have developed resistance to benzimidazole anthelmintics. A trial involving 18 goats was conducted to confirm this. There was a significant (P < 0.01) reduction in worm burdens in goats given levamisole, but this was not so for those animals given albendazole, fenbendazole, oxfendazole and mebendazole (P > 0.05).

Albendazole↗