Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Haemonchiasis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed1990

Efficacy of ivermectin against benzimidazole-resistant nematodes of sheep.

Two trials involving a total of 36 Dorset horn lambs were conducted to assess the anthelmintic efficacy of ivermectin against experimental infections of benzimidazole-resistant strains of Haemonchus contortus and Ostertagia circumcincta. Two resistant strains of each of the two species were used and in each trial the lambs were allocated to three groups. One group was given 200 micrograms ivermectin/kg bodyweight orally, the second group was given 5 mg oxfendazole/kg bodyweight orally and the third group remained untreated as controls. Fourteen days after treatment the lambs were necropsied. Ivermectin was found to be more than 99 per cent to 100 per cent effective against all four benzimidazole-resistant strains, whereas oxfendazole was 78.6 per cent and 83.8 per cent effective against the H contortus strains, and 25.6 per cent and 39.8 per cent effective against the O circumcincta strains.

Animals↗
PubMed1990

[The nematode Haemonchus contortus: antigenic characterization and immune response in rabbits and sheep].

In the first part of the study, various tissues of L3 larvae and adult Haemonchus contortus were examined by indirect fluorescence to investigate their antigenicity. L3 larvae were studied in immunoblots as well. The following tissues contained antigens: the sheath and cuticle of L3 larvae; and the cuticle, muscles, epithelium and glandular tissue of the oesophagus and sheath of the spicules of adult nematodes. On the cuticle of exsheathed L3 larvae, we detected by light-microscope slightly raised patches: places where the cuticle differs from the surrounding cuticular morphology. We suggest that the patches are comparable to those found on exsheathed L3 larvae of the horse. Whether the patches produce excretory or secretory antigens or both is unknown, however. Somatic soluble extracts of L3 and adult worms were found to be complex mixtures of proteins by polyacrylamide gel electrophoresis. Results in immunoblots of L3 larvae suggested that the region between the 42 kDa protein and the 18 kDa protein may contain antigens specific for H. contortus. We injected rabbits with the 42-25 kDa fraction of the L3 larvae. The rabbit sera were probed in immunoblots with the total somatic soluble L3 extract for the presence of antibodies. Antibodies reacted with antigens in the 42-25 kDa fraction, however, cross-reactions occurred with antigens in the L3 fractions that were not injected into the rabbits. We found that antibodies against phosphorylcholine were induced and suggest that these cause some of the cross-reactions. In the second part of the study sheep were infected orally with H. contortus and their lymphocyte responses towards L3 antigen and mitogen were measured in a lymphocyte stimulation test. Lymphocyte responses to L3 antigen are expressed in a stimulation index. Two groups of worm-free raised sheep were inoculated (sheep older than 1 year and lambs that were 4 to 6 months old) as well as a group of hyperimmunized sheep. Some sheep were inoculated only once; others were inoculated and then challenged. Lymphocytes of sheep that were hyperimmunized replicated rapidly in the test resulting in significantly higher stimulation indices than those recorded for the lymphocytes of all other sheep. After inoculation the enhanced response further increased. We explain these lymphocyte responses as a result from the immunological memory induced during the hyperimmunization. Lymphocytes of sheep over 1 year old only respond in the test when sheep are infected.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1990

Influence of dietary protein on the immune responsiveness of sheep to Haemonchus contortus.

Twenty helminth-free lambs were fed diets containing either 169 g crude protein (CP) kg-1 dry matter (DM) or 88 g CP kg-1 DM from the age of seven months. One month later five lambs from each dietary group were vaccinated against Haemonchus contortus by the oral administration of 10,000 irradiated larvae on two occasions, four weeks apart. Four weeks following the administration of the second dose of irradiated larvae both the vaccinated and unvaccinated lambs were exposed to an experimental infection of 10,000 non-irradiated H contortus larvae Faecal egg output and haematological changes were monitored throughout the study. The lambs were slaughtered 28 days after challenge when worm burdens were assessed. Vaccination was equally successful in inducing a strong resistance to the challenge infection regardless of dietary status. It was concluded that dietary protein does not influence the response to vaccination with irradiated H contortus larvae of lambs more than seven months old.

Abomasum↗
PubMed1990

Pepsinogen types in worm-free sheep and in sheep infected with Ostertagia circumcincta and Haemonchus contortus.

Pepsinogen isolated from the plasma of Dorset wethers with abomasal burdens of Ostertagia circumcincta was found to have the same proportions of three zymogen subtypes as that isolated from the plasma of Merino wethers with abomasal burdens of Haemonchus contortus. It appears that the underlying pathophysiological response which causes increased plasma pepsinogen concentrations during abomasal parasitism may be the same irrespective of the breed of sheep or species of parasite.

Abomasum↗
PubMed1990

A novel anthelmintic model utilizing jirds, Meriones unguiculatus, infected with Haemonchus contortus.

Currently, no in vivo laboratory model is available for evaluating anthelmintics against the important ruminant helminth Haemonchus contortus. This report outlines a novel anthelmintic assay utilizing immunosuppressed (0.02% hydrocortisone in feed) jirds, Meriones unguiculatus, infected with H. contortus. Immunosuppressed jirds were inoculated with approximately 1,000 exsheathed infective larvae of H. contortus, treated per os on day 10 postinoculation (PI), and necropsied on day 13 PI. Each stomach was removed, opened longitudinally, incubated in distilled water at 37 C for 5 hr, fixed in formaldehyde solution, and stored for subsequent examination. Stomach contents were examined using a stereomicroscope (15-45x). A variety of standard anthelmintics has been evaluated in the model; modern broad-spectrum ruminant anthelmintics (benzimidazoles, febantel, ivermectin, levamisole hydrochloride, and milbemycin D) are active uniformly and in most cases at doses (mg/kg) comparable to those required for efficacy against H. contortus in ruminants. This model provides an important new tool to assess preliminarily the activity of experimental drugs against H. contortus in vivo prior to studies in ruminants and also may provide a useful tool for studying host-parasite interactions for H. contortus.

Animals↗
PubMed1979

The influence of breed on the susceptibility of sheep of Haemonchus contortus infection in Kenya.

The relative resistance of six breeds of sheep to Haemonchus contortus infection was investigated under field conditions on two stations situated in a semi-arid zone in Kenya. As judged by faecal egg counts, monitored throughout a two-year period, it was found that there were consistent differences between the breeds. The breeds studied in order of increasing susceptibility were Red Masai, Blackhead Persian, Merino, Dorper, Corriedale and Hampshire. Post mortem findings confirmed that the differences in faecal egg count were related to the establishment of worms rather than larval inhibition or the suppression of worm egg production. There was also evidence that the Red Masai showed self-cure more frequently than the other breeds.

Animals↗
PubMed1979

The influence of haemoglobin phenotype on the susceptibility of sheep to Haemonchus contortus infection in Kenya.

Two flocks of Merino sheep were set-stocked on pastures known to be endemic for Haemonchus contortus. Both flocks included sheep with the three common haemoglobin types (HbAA, HbAB, HbBB). The results of regular monitoring over a two-year period showed a clear relationship between haemoglobin types and susceptibility to haemonchosis. The HbAA sheep experienced fewer deaths, had consistently lower egg counts and exhibited a more frequency and effective self-cure than the HbAB or the HbBB types. Post mortem findings demonstrated that this phenomenon was due to differences in the establishment of adult H contortus and not to suppression of egg laying capacity or an alteration of male to female adult worm ratio.

Animals↗
PubMed1989

[Haemonchosis in camels].

Over the last thirty years, several surveys referring to the gastrointestinal parasites in the dromedary have shown high infestation rates by Haemonchus longistipes. Certain other studies have pointed out the economic and clinical importance of the camel haemonchosis. The author presents an overview of established knowledge on this major disease for the dromedary, which has hitherto been underestimated. The known features belonging either to this species or inferred from sheep haemonchosis, as a much better studied illness, are then presented. They refer to the parasite and to its cycle, to epidemiology, pathogeny, symptoms, lesions, diagnosis and treatment not forgetting feasible prophylactic measures as a conclusion. The author insists upon the season characteristic of the disease, the factors favouring infestations, and the more or less severe anaemia/cachexy syndrome, according to the observed forms of the affection. Differential diagnosis is often difficult to ascertain and several effective drugs available for treatment are reviewed. Finally, the control of this illness needs to take into account the specific features of the dromedary rearing together with a necessary involvement of the camel owners.

Animals↗
PubMed1989

South African field strains of Haemonchus contortus resistant to the levamisole/morantel group of anthelmintics.

A strain of Haemonchus contortus from the Pietermaritzburg district of Natal was found to be resistant to levamisole (geometric mean efficacy 76.5%), morantel (41.9%), the benzimidazoles (oxfendazole: 33.7%) and rafoxanide (82.0%), but apparently fully susceptible to closantel and disophenol. In the case of ivermectin, a mean of 5.2% of the H. contortus was not removed at a dosage of 200 micrograms kg-1 live mass. A second strain of H. contortus, from Amsterdam in the south-eastern Transvaal, showed reduced susceptibility to levamisole (80.8%) and morantel (46.2%), the only 2 drugs tested. This is apparently the first report of resistance to the levamisole/morantel group of anthelmintics in sheep in South Africa.

Animals↗
PubMed1989

The problem of escalating resistance of Haemonchus contortus to the modern anthelmintics in South Africa.

During the past decade in South Africa there has been a continual increase in sheep of strains of gastrointestinal helminths resistant to the modern anthelmintics. Five strains of Haemonchus contortus are described in this paper. Despite the fact that 2 of the 5 strains were tested for susceptibility only to ivermectin, a total of 10 instances of resistance were found. Four of the 5 strains were resistant to ivermectin, 2 to closantel, 2 to rafoxanide and 2 to the benzimidazoles. One of these strains was concurrently resistant to 3 different anthelmintic groups, namely, the ivermectins, the benzimidazoles and the salicylanilides. Resistance to ivermectin developed in 2 strains of H. contortus after a history of only 3 treatments with this compound in one instance and 11 treatments in the other. In the latter case drenching with ivermectin was well interspersed with that of other anthelmintics. This rapid development of resistance suggests that there may be cross-resistance between ivermectin and another anthelmintic group. Two of the ivermectin resistant strains were recovered from separate properties in the south-western Cape Province, where Ostertagia circumcincta, which is usually the dominant parasite in this region, was virtually eliminated by the anthelmintic treatment. On each of these properties it was apparently replaced by a resistant strain of H. contortus. A serious threat to control is the dissemination of worm strains with multiple resistance to anthelmintics. The strain of H. contortus resistant to 3 anthelmintic groups has already been widely dispersed, as the farmer concerned suddenly decided to give up farming with sheep and to sell his flock.

Animals↗
PubMed1989

Efficacy of levamisole against immature and mature nematodes in goats with induced infections.

Anthelmintic efficacy of levamisole against induced infections with 7- and 21-day-old Haemonchus contortus, Ostertagia circumcincta, Trichostrongylus axei, and T colubriformis was evaluated as an oral drench in goats. Group 1 (n = 8) was not treated, group 2 (n = 8) was given 3.96 mg of levamisole/kg of body weight, group 3 (n = 8) was given 7.92 mg of levamisole/kg, and group 3 (n = 7) was given 11.88 mg of levamisole/kg. Efficacy against all worms was low in goats given 3.96 mg of levamisole/kg, but was high against adult H contortus (99%) and adult T colubriformis (99.7%) in goats given 7.92 mg of levamisole/kg. Although efficacy against adults of all species was high in goats given 11.88 mg of levamisole/kg, some immature worms of all species remained in the abomasa of goats.

Animals↗
PubMed1989

Lack of reversion of a benzimidazole resistant strain of Haemonchus contortus after six years of levamisole usage.

The resistance level of Haemonchus contortus was studied on a farm where benzimidazole resistance had been detected in 1980 and where, since 1982, only levamisole had been used for worm control. Egg development tests gave LD50 values of 0.18, 0.19 and 0.21 microgram ml-1 thiabendazole for samples taken from ewes in 1988 compared with 0.21 microgram ml-1 in 1981. Studies on sheep experimentally infected with larvae cultured from the faeces of these ewes confirmed the continued resistance of H contortus to benzimidazoles, and demonstrated the absence of benzimidazole resistance in other nematode species together with the susceptibility of all species to levamisole.

Animals↗
PubMed1985

Early changes in plasma pancreatic polypeptide, somatostatin, gastrin and motilin levels induced by H. contortus infection in lamb.

Plasma levels of pancreatic polypeptide (PP), somatostatin (GH-RIH), gastrin and motilin were measured during 6-7 h after oral infection with 25 000 infective (3rd stage) larvae of H. contortus in lambs or after intravenous injection of larvae or worm antigenic (Ag) extracts. A 3-fold increase in plasma gastrin was observed during the first 60 min after infection and GH-RIH increased significantly (P less than 0.01) 180 min later whereas both PP and motilin remained unchanged. An early (60 to 120 min) increase in GH-RIH and a late (5 to 7 h) increase in PP plasma levels were observed after both worm and larvae antigenic extracts whereas plasma motilin was unaffected. Plasma gastrin was significantly (P less than 0.01) increased during 3-4 h following the injection of worm but not of larvae antigenic extract. It was concluded that the immediate hypergastrinemia following H. contortus infection is not the consequence of a general immune response of the host and is probably related to the release of unknown substance(s) by the infective larvae into the abomasum or to mucosal inflammation due to a local immune response; in contrast, the increase in plasma GH-RIH levels appeared to be the result of antigenic reactions. The other hormonal changes observed after Ag injections may be the consequence rather than the reason of changes in abomasal secretory pattern.

Animals↗