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PubMed1992

Growth and development of Haemonchus contortus in jirds, Meriones unguiculatus.

Growth and development of Haemonchus contortus were examined in jirds and were compared to these processes in lambs. Number, sex, size, and stage of development were determined for worms recovered at necropsy at various times postinoculation (PI) from immunosuppressed jirds inoculated with approximately 1,000 exsheathed infective larvae (L3) of H. contortus. In addition, gastric tissue samples from jirds were examined histologically. Parallel studies were done in lambs inoculated with approximately 7,500 L3. Typically, 5-30% of the inoculum established and survived in jirds at reasonably stable numbers to day 14 PI. By day 21 PI, worm numbers in jirds decreased dramatically. Although the parasite was similar in size and development on day 4 PI in jirds and lambs, from day 7 PI on, worms were significantly smaller and less developed in jirds. On histological examination, the parasite was found only in the glandular portion of the stomach of jirds (anatomically similar to its predilection site in the abomasum of lambs), and histological changes were consistent for both host species. Although growth and development of H. contortus are slower and incomplete in jirds, the parasite establishes, grows, and develops (at anatomically comparable sites in both hosts) in this model. Thus, the model appears to provide a useful laboratory host to study H. contortus.

Abomasum↗
PubMed1977

Development of Haemonchus contortus in vitro and the stimulus from the host.

Infective larvae of Haemonchus contortus which have been exposed for about 9 hr to relatively high partial pressures of carbon dioxide at near-neutral pH, as they might be in the rumen, develop slowly to the fourth stage or not at all. But following this treatment, exposure to lower partial pressures of carbon dioxide and higher concentrations of hydrogen ions, such as might be encountered in the abomasal mucosa, brings about development at a rate comparable with that in the sheep.

Animals↗
PubMed2006

Influence of sex on the resistance of sheep lambs to an experimental Haemonchus contortus infection.

36 intact male and 69 female lambs of two breeds (n = 63 Merinoland; n = 42 Rhön) aged 12 weeks were orally infected with 5000 infective-stage larvae, L3, of the nematode Haemonchus contortus. After 4 and 8 weeks faecal egg counts (FEC), haematocrit values and plasma testosterone levels were determined. All lambs were slaughtered at 20 weeks of age. The gastrointestinal tracts were examined for the presence of adult stages of H. contortus. Male lambs showed significantly higher log FEC (p < 0.001), higher mean establishment rates (p < 0.05), higher worm burdens (p < 0.01) and lower haematocrit values (p < 0.001) when compared with female lambs. Correlations between economically important traits (body weight, daily weight gain) and parasitological parameters were significantly higher in male animals. Testosterone level was 4 weeks after infection significantly positive correlated with worm burden. The results suggest that female lambs are more resistant against an experimental H. contortus infection when compared with male lambs. Testosterone seems to play an important role in resistance. This approach can be of importance if parasite resistance is incorporated into breeding programs and the estimated breeding values for rams are only based on male offspring information. Therefore male breeding values are probably not representative for the whole population.

Animals↗
PubMedDate not supplied

[Evaluation of nematode predacious fungus Duddingtonia flagrans on infective Haemonchus contortus and Strongyloides papillosus larvae of goats].

One brazilian isolate of nematode-trapping fungus Duddingtonia flagrans AC 001 was evaluated regarding the capacity of supporting passage through the gastrointestinal tract of goats without losing the ability to entrap infective Haemonchus contortus and Strongyloides papillosus larvae (L3). Ten saneen goats of eight months old, males and infected naturally were divided in two groups of five animals. In the group 1, the animals received orally 20 g of pellets of the D. flagrans. In the group 2 (control), the animals received orally 20 g of pellets without fungi. Fecal Samples were collected at 14, 20, 24, 36 and 46 hours after the treatments and were allocated in fecal cultures at 25 degrees C during fifteen days. There was significant reduction (p<0.05) of the average number of S. papillosus larvae recovered of the fecal cultures in the animals treated with fungus when compared with the control animals at 14 and 46 hours, in the end of the experiment, this difference was 82.3%. There was significant reduction (p<0.05) of the average number of H. contortus larvae recovered of the fecal cultures in the animals treated with fungus when compared with the control animals at 14, 20 and 46 hours, in the end of the experiment, this difference was 59.3%. Such evidences confirm the transit of these fungi pellets by the digestive tract of the goats without loss of the predatory viability on L3 of H. contortus and S. papillosus.

Animals↗
PubMed2005

Haemonchus contortus: parasite problem No. 1 from tropics - Polar Circle. Problems and prospects for control based on epidemiology.

There is no doubt that on a global basis, Haemonchus contortus is by far the most important parasite of small ruminants (sheep and goats). This is particularly more so now, with the development of high levels of resistance to both the broad and narrow spectrum anthelmintic drugs in H. contortus throughout the world. Epidemiological studies describe the lower environmental limits for haemonchosis to occur in sheep, as being a mean monthly temperature of 18C and approximately 50mm rainfall. Thus it has been generally recognised that H. contortus is a problem parasite restricted to the warm, wet countries where sheep and goats are raised. However, recent evidence shows that this parasite is apparently common even in northern Europe. Thus the need for sustainable control strategies for H. contortus is becoming much more pressing. This report highlights two examples of sustainable and highly efficient control programmes for H. contortus, that can be implemented in regions at the extremes of its geographic range (Malaysia and Sweden), where the authors have had direct involvement.

Animal Husbandry↗
PubMed1991

[Development and survival of Haemonchus contortus isolated from sheep on a pasture at Bunia (Itiri, Zaire)].

Development and survival of Haemonchus contortus larvae were studied from December 1987 to November 1988 during three different periods (dry season, first and second rainy seasons) on an experimentally infected pasture at Bunia (Ituri, Zaïre). Whatever the season, eggs developed into infective larvae within six days and the largest number of larvae on the herbage occurred between the 12th and the 18th day post deposition. However, the two rainy seasons were the most favourable for transmission because of the high number of larvae on the pasture and the increased survival of these larvae after 4 weeks.

Animals↗
PubMed1990

Effect of Nilzan and albendazole on the absorptive surfaces of Haemonchus contortus (Nematoda)--a histoenzymic study.

Haemonchus contortus, incubated in 10 micrograms/ml and 50 micrograms/ml concentrations of Nilzan and albendazole in Tyrode solution were stained for histoenzymatic demonstration of various phosphatases, oxido-reductases and esterases. The intestine showed major alterations after drug treatments. The alkaline phosphatases (AkPase), adenosine triphosphatase (ATPase), glucose-6-phosphatase, succinic dehydrogenase (SDH), glutamate dehydrogenase (GDH), reduced nicotinamide adenine dinucleotide phosphate diaphorase and reduced nicotinamide adenine dinucleotide diaphorase showed a decreased activity in intestine after Nilzan treatment, whereas lactic dehydrogenase (LDH), glucose-6-phosphate dehydrogenase (G-6-PD) and monoamine oxidase resisted increased reaction. The albendazole treatment resulted in altered distribution pattern of the AkPase, ATPase, SDH, and GDH; while LDH, G-6-PD, and non-specific esterases exhibited slightly enhanced activity in the epithelium. The functional significance of these changes has been fully discussed.

Absorption↗
PubMed1991

Utility of a Haemonchus contortus/jird (Meriones unguiculatus) model for studying resistance to levamisole.

Trichostrongylid nematodes of sheep commonly are identified as exhibiting resistance to levamisole. In vitro assays have been developed to study levamisole resistance for Haemonchus contortus, but no in vivo model has been identified for this species. To determine the utility of a H. contortus/jird (Meriones unguiculatus) model for examining levamisole resistance, immunosuppressed jirds were inoculated with approximately 1,000 exsheathed infective larvae of H. contortus (resistant or susceptible to levamisole), treated per os on day 10 postinoculation (PI) with levamisole hydrochloride or analogs of the drug, and killed on day 13 PI. Stomachs were removed, opened longitudinally, incubated in distilled water at 37 C for 5 hr, fixed in formaldehyde solution, and stored for subsequent microscopic examination. Doses of levamisole and its analogs, which elicited percentage clearances of greater than or equal to 93.5 for the susceptible strain, cleared less than or equal to 68.9% of the resistant worms. These data are consistent with activities for the drugs against wild-type and levamisole-resistant strains of Caenorhabditis elegans. Thus, the H. contortus/jird model provides a useful in vivo tool to study resistance to levamisole and possibly other anthelmintics.

Animals↗
PubMed1990

Tyrosine-derived cross-linking amino acids in the sheath of Haemonchus contortus infective larvae.

The sheath or second-molt cuticle (2M) was isolated from in vitro exsheathed Haemonchus contortus infective larvae (L3[2M]). Acid hydrolysates of 2-mercaptoethanol (2ME)-soluble and 2ME-insoluble cuticular proteins were analyzed by high performance liquid chromatography for tyrosine-derived cross-linking amino acids. Dityrosine and isotrityrosine were identified by their chromatographic behavior, absorbance spectra, and other chemical characteristics in both the 2ME-soluble and 2ME-insoluble fractions. Dityrosine and isotrityrosine were found in greater amounts in the 2ME-insoluble proteins. When intact 2M cuticles were labeled with 125I prior to acid hydrolysis, radiolabel was recovered in tyrosine but not dityrosine or isotrityrosine indicating that the tyrosine cross-links are not susceptible to iodination in the intact protein. The results are consistent with a hypothesis that tyrosine-derived cross-links are important components of H. contortus 2M cuticular proteins.

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

Scanning electron microscopy of the sheathed infective larva and parasitic third-stage larva of Haemonchus contortus (Nematoda: Trichostrongyloidea).

Scanning electron microscopy was used to describe the infective and parasitic third-stage larvae of Haemonchus contortus, the large stomach worm of ruminants. Infective larvae are ensheathed in the cuticle of the second stage, so the descriptions are of the second- and third-stage cuticles. Both larval stages had an inner circle of 6 labial papillae, an outer circle of 6 labial papillae and 4 somatic papillae, and lateral amphidial pits. Infective larvae (cuticle of the second stage) had the 6 internal labial papillae on prominent bluntly rectangular lappets in a star-shaped arrangement around a large triradiate mouth, small triangular or round amphidial pits, flattened ribbonlike lateral alae, and phasmidial apertures opening on the ventral surface of the lateral alae. Parasitic third-stage larvae had the 6 internal labial papillae on small elevations without lappets around a small mouth; large, oval amphidial pits; ribbonlike lateral alae for most of their length, but with the anterior 30-40 microns of the alae cordlike; and phasmidial apertures on the body cuticle ventral to the lateral alae.

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

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↗
PubMed1988

Evaluation of Haemonchus contortus infections in sexually intact and ovariectomized ewes.

Three experiments were conducted to investigate experimentally the occurrence of periparturient nematode egg rise in ewes and the hormonal modulation of Haemonchus contortus infections. In the first experiment, fall-bred and winter-bred pregnant (n = 4 and 14, respectively) and nonpregnant (n = 5 and 29, respectively) ewes were treated with anthelmintic and were pastured together on fields that were contaminated with H contortus. Three weeks before lambing, all ewes were placed in concrete pens; fecal egg counts for the winter-bred group were obtained on alternate days. Pregnant and lactating ewes had significantly larger numbers (P less than 0.01) of H contortus eggs than did the nonpregnant controls 1 week before and after lambing. Lactating, fall-bred ewes had significantly (P less than 0.01) more adult worms in their abomasum through natural acquisition than the nonpregnant controls. In the second experiment, fall-bred and winter-bred, helminth-free, pregnant (n = 4 and 8, respectively) and nonpregnant (n = 3 and 15, respectively) ewes were inoculated on 5 alternate days, beginning 70 days after breeding with 20,000 infective H contortus larvae. The ewes were maintained on concrete pens throughout pregnancy. Fecal egg counts were significantly (P less than 0.05) greater in pregnant ewes, beginning 1 week before lambing until 1 week after lambing. Abomasums of lactating ewes from both lambing seasons yielded significantly (P less than 0.01) more adult worms at necropsy than nonpregnant ewes. In the third experiment, ewes were ovariectomized (n = 15) or sham-operated (n = 9); half of the control ewes were bred.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Size of inoculum dose regulates in part worm burdens, fecundity, and lengths in ovine Haemonchus contortus infections.

Density-dependent factors frequently have been shown to regulate population parameters of free-living and parasitic helminths. To test the effects of various infection levels of Haemonchus contortus on fecundity and worm size, lambs were inoculated with 3,000, 10,000, and 30,000 infective larvae. Daily eggs per gram (epg) and daily total fecal production per lamb were monitored continuously. Worms were collected from abomasa on 6, 15, 22, and 30 days postinfection (PI). Female worms were smaller on each day in the high-dose group when compared to female worms from the low-dose group; males in the high-dose group were smaller from days 15 through 30 PI. The high- and medium-dose groups had higher mortality rates on day 30 PI, and fecundity (eggs/female/day) was 78% lower. Daily epg and daily total eggs/lamb/day were lower in the high-dose group. Fecundity and worm size were correlated with the log-transformed dose level but not with adult worm number. Early parasite and/or host responses apparently exert long-term negative effects on growth and reproduction relative to the size of the establishing population of H. contortus.

Abomasum↗
PubMed1988

In vitro response of Haemonchus contortus larvae harvested during different times of the patent period to anthelmintics.

Three commercially available ruminant anthelmintics and an investigational drug were evaluated for effects on the motor function/motility of third stage (ensheathed) Haemonchus contortus. Helminth ova were collected at one, five, nine and 13 weeks during the patent period, cultured to the third larval stage and assayed for sensitivity to four different drugs. All four drugs (100 and 10 micrograms ml-1) significantly affected the motility of third stage H contortus larvae cultured from eggs passed at each of the times examined. However, the investigational drug (p-toluoyl chloride phenylhydrazone, 10 micrograms ml-1) had a significantly greater effect on the motility of larvae harvested at 13 weeks than those cultured at nine weeks (32 per cent difference). No other significant differences in the motility response during the patent period were observed.

Albendazole↗