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PubMed1995

Experimental study of survival strategy of Haemonchus contortus in sheep during the dry season in desert areas of the Mauritania.

The survival of the most common worm of sheep and goats of desert areas, Haemonchus contortus, during the dry season is of the utmost importance. It may be achieved through long survival of adult worms that may preserve their ability to excrete viable eggs or to inhibited development in host and survival as a larval stage. Twelve lambs were experimentally infected with larvae obtained at the end of the rainy season. The resulting adult worms were able to survive and maintain their ability to produce viable eggs that developed into infective larvae up to 50 wk after infection. It is concluded that survival of adults during the dry season played a major role in transmission from 1 rainy season to the next, rather than inhibited development and survival as a larval stage.

Animals↗
PubMed1996

Developmentally regulated zinc metalloproteinases from third- and fourth-stage larvae of the ovine nematode Haemonchus contortus.

Parasitic third-stage larvae of the sheep abomasal nematode Haemonchus contortus develop and molt in vitro to the fourth stage (L4) in 48-72 hr, at which time they begin feeding. Coincident with the third molt, larvae begin to secrete significant amounts of protein into culture fluids, including a zinc metalloproteinase. This culture-derived zinc metalloproteinase differs from a previously described metalloproteinase from infective third-stage larvae (L3[2M]), which mediates the ecdysis process. These differences include time of expression, molecular mass, and substrate specificity. The purified proteinase, from cultures of L4, has a molecular weight of approximately 46 kDa, functions as an endopeptidase, and digests several native proteins of host origin including fibrinogen and fibronectin.

Amino Acid Sequence↗
PubMed1996

Viability of infective larvae of Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus colubriformis following exsheathment by various techniques.

Various techniques were examined to determine optimum conditions for exsheathing infective larvae of 3 important ruminant parasites (Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus colubriformis). In repeated experiments, aliquots of 10(5)-10(6) infective larvae, 1-2 mo old, of each parasite were incubated in each of 4 exsheathing media (distilled water, Earle's balanced salt solution + carbon dioxide, nematode washing buffer + carbon dioxide, or sodium hypochlorite) for 1 or 18 hr. In each case, the percentage of larvae exsheathed and infectivity for jirds was determined. Results of these studies indicate that no single exsheathing technique of those studied is optimum for every parasite. In addition, caution must be used in drawing conclusions from in vitro studies using exsheathed larvae because techniques that routinely provide high percentages of exsheathment also appear to reduce viability.

Animals↗
PubMed1996

Extracellular matrix degradation by Haemonchus contortus.

To better understand the in vivo function of secreted cysteine proteases of Haemonchus contortus, the ability of live parasites to degrade connective tissue was investigated using [3H]proline-labeled extracellular matrix produced by smooth-muscle cells (R22). The matrix was composed of glycoprotein(s) (34%), elastin (49%), and collagen (15%) in an insoluble, multilayered, cross-linked structure. No degradation of the extracellular matrix by third-stage larvae (L3) (10,000/ml) occurred during 24-hr in vitro incubation. In contrast, fourth-stage larvae (L4) (1,000/ml) degraded 42% of the matrix, whereas adults (100/ml) degraded the entire matrix. The presence of Z-phe-ala-FMK (100 microM), a specific cysteine protease inhibitor, during incubation of adults, reduced matrix degradation to 30% without affecting parasite motility. Isolated adult excretory/secretory products (ESP) (0.1 mg protein/ml) degraded 64% of the total matrix; specific degradation consisted of 80.3% of the glycoprotein, 67.1% of the elastin, and 27.6% of the collagen matrix components. Degradation of the matrix by ESP was stimulated by dithiothreitol (2 mM) and inhibited by Z-phe-ala-FMK. Thus, the secretory cysteine proteases of H. contortus are active under physiological conditions and able to degrade the major components of connective tissue in an in vitro model system that simulates their structure in vivo. These data strengthen the proposed role of these enzymes in the breakdown of host tissue.

Animals↗
PubMed1977

Anti-larval antibodies in the serum and abomasal mucus of sheep hyperinfected with Haemonchus contortus.

A radioimmunoassay technique was used to follow the anti-larval antibody response in the serum of sheep subjected to repeated dosing with Haemonchus contortus. The response was found to develop slowly and seemed to decline as soon as the sheep stopped receiving larvae. No immunological memory was observed after the sheep were challenged with 4000 larvae nine weeks after daily dosing was stopped. Examination of abomasal mucus collected from the sheep at slaughter revealed the presence of IgA and IgG antibodies. It is suggested that most of this mucus IgG was derived from blood whereas the IgA was locally produced.

Abomasum↗
PubMed1977

Developmental arrest of Haemonchus contortus larvae in lambs given larval inoculum exposed to different temperatures and storage conditions.

The temperature (15 or 30 C) at which Haemonchus contortus larvae were allowed to develop to the infective (3rd) stage and the temperature at which they were subsequently stored (4, 15, or 30 C) had no effect on the occurrence of developmental arrest (larval impasse) of the larvae in infected lambs. If a large inoculating dose (10,000 larvae) was given to the lambs, a smaller percentage of nematodes was retained (14.2%) then if a small dose (1,000 larvae, 25.8% retention) was given, but the percentage of larvae in developmenttal arrest was greater (7.7% of the retained nematodes vs 0.02%). The temperatures of larval development and storage had no effect on the sex ratio of the adults that developed (46.3% male nematodes).

Animals↗
PubMed1996

Radiolabelled adult Haemonchus contortus obtained from eggs voided in the faeces of a sheep injected with 59Fe.

The infective larvae of Haemonchus contortus (L3) obtained from an artificially infected sheep injected with 125 microCi of 59Fe, incorporated the isotope and retained it in sufficient quantities to be detectable by autoradiography in the adult worms which developed. This is apparently the first report of incorporation of 59Fe into adult helminths, of which the L3 originated from an animal that was injected with the isotope.

Animals↗
PubMed1996

In vitro effects of anthelmintics on the histochemistry of Haemonchus contortus and Trichuris globulosa.

In vitro incubation of Haemonchus contortus (RUD., 1803) and Trichuris globulosa (v. LINSTOW, 1901) were proformed for 10-12 h in Tyrode's solution and 10 and 50 micrograms/ml concentrations each of albendazole (ABZ), fenbendazole (FBZ), thiophenate (TP), dl-tetramisole and oxyclozanide (TO), dl-tetramisole HCI (TMS) and levamisole HCI (LMS) to study morphological and histochemical alterations. The major structural changes observed after treatment with all the drugs were vacuolation in the intestine of H. contortus except with TP treatment and disruption of the epithelium in T. globulosa except with TMS treatment. The other major alteration in T. globulosa was the loss of muscle striations after TP, TO, TMS and LMS treatments. All the six anthelmintics reduced the quantity of neutral mucopolysaccharides in the intestine of H. contortus and T. globulosa except with TMS and LMS treatments in the latter. Acidic mucopolysaccharides detected in the microvilli of the intestine of H. contortus were lost after TO and ABZ treatments. The loss of lipids from the intestine was evident after TO, ABZ, FBZ and TP treatments in H. contortus and by all the drugs in T. globulosa. LMS treatment caused accumulation of very large lipid droplets in the intestine of H. contortus.

Animals↗
PubMed1997

Enhanced ability of third-stage larvae of Haemonchus contortus to withstand drug exposure following chemically induced exsheathment.

Normal (ensheathed) and exsheathed third-stage larvae of Haemonchus contortus were exposed in vitro to various concentrations of levamisole or ivermectin. Exsheathment was induced by brief exposure to sodium hypochlorite. When observed approximately 2 min after immersion in levamisole at 0, 5, 10, and 100 micrograms/ml (3 trials), the mean percentage motility (to nearest whole number) of normal larvae was 84, 43, 37, and 15, respectively. However, the mean percent motility of exsheathed larvae was 77, 78, 79, and 72, respectively. When observed 55 min after immersion in levamisole at the same concentrations, the mean percent motility of normal larvae was 76, 4, 3, and 0, respectively, whereas that for exsheathed larvae was 72, 75, 68, and 0. When observed 45 min after initial exposure to ivermectin at 0, 8, 80, and 160 micrograms/ml, the mean percent motility of normal larvae was 87, 6, 3, and 3, respectively, whereas the mean percent motility of exsheathed larvae was 94, 75, 29, and 14, respectively. Thus, both drugs were effective against both kinds of larva; but the time and concentration required for efficacy were markedly affected by the presence or absence of a sheath or by unknown effects of the exsheathment process. For both levamisole and ivermectin, exsheathed larvae had a much greater ability than normal larvae to withstand drug exposure.

Animals↗
PubMed1976

Effect of temperature on survival of free-living stages of Haemonchus contortus.

One percent or more unembryonated eggs of Haemonchus contortus survived in sheep fecal pellets less than 0.5 hour at -95 C, 2 hours at -28 C, 1 hour at -10 C, 4 days at 4 C, and 1 hour at 45 C. One percent or more embryonated eggs survived 1 hour at -95 and -28C, 12 hours at -10 C, 64 days at 4 C, and 12 hours at 45 C. Over half the unembryonated and embryonated eggs survived only 1 and 4 days, respectively, at 4 C. One percent or more 1st-stage larvae did not survive 0.5 hour at -95 C but did survive 0.5 hour at -28 C, 8 hours at -10 C, 16 days at 4 C, and 1 hour at 45 C. Less than 1% of 2nd-stage larvae survived up to 2 days at -95 C; all were dead by 4 days. Second-stage larvae survived 32 days at -28 C, 8 days at -10 C, 64 days at 4 C, and 2 hours at 45 C. One percent or more 3rd-stage larvae survived 256 days at -95 C, 16 days at -28 C, 32 days at -10 C, more than 256 days at 4 C, 128 days at 20 C, 64 days at 25 and 35 C, and 4 days at 45 C. Thus, the increasing order of survival was unembryonated eggs, 2nd-stage larvae, 1st-stage larvae, embryonated eggs, and 3rd-stage larvae.

Animals↗
PubMed1998

Effects of macrocyclic lactones on ingestion in susceptible and resistant Haemonchus contortus larvae.

The effects of ivermectin and ivermectin aglycone on pharyngeal uptake of a carbohydrate substrate (3H-inulin) were measured in larvae of a macrocyclic lactone (ML)-susceptible isolate and 2 ML-resistant isolates of Haemonchus contortus. The resistant isolates showed a tolerance (in terms of the concentration of compound required to reduce feeding to 50%) toward ivermectin of approximately 4.5- and 9-fold and toward ivermectin aglycone of approximately 14-fold, compared to the susceptible isolate. This indicates that susceptible and resistant isolates can be readily distinguished on the basis of the sensitivity of pharyngeal uptake to MLs. The use of various metabolic inhibitors in this assay system did not reveal the nature of the resistance mechanism. Pretreatment of resistant larvae with inhibitors of multidrug resistance mechanisms (P-glycoprotein and multidrug resistance protein) and detoxification enzymes (monooxygenases, esterases, and glutathione transferases) did not reduce their level of tolerance to the ivermectin aglycone.

Animals↗
PubMed1979

The response of Awassi and Merino sheep to primary infection with Haemonchus contortus.

The possible existence of breed differences in the response of sheep to primary infection with Haemonchus contortus was examined by comparing worm establishment and pathogenic effects of the parasite in Awassi and Merino sheep of haemoglobin type B infected with 500 third stage H. contortus larvae per kg body weight. The results showed that the Merino sheep had lower faecal egg counts and worm burdens and suffered less severe clinical disturbances than sheep of the Awassi breed. This suggests that genetic resistance operates primarily at the level of worm establishment.

Animals↗
PubMed1996

Comparative efficacies of closantel, ivermectin, oxfendazole, thiophanate and levamisole against thiabendazole resistant Haemonchus contortus in sheep.

Forty-nine sheep artificially exposed to a thiabendazole (TBZ) resistant isolate of Haemonchus contortus were assigned to 7 groups of 7 animals each and used to conduct a controlled anthelmintic trial. One group of sheep served as untreated infected controls and 6 groups were treated as follows: closantel, 5.0 mg kg-1; ivermectin, 0.2 mg kg-1; oxfendazole, 5.0 mg kg-1; thiophanate, 50 mg kg-1, levamisole, 7.5 mgkg-1 and thiabendazole, 66 mg kg-1. Eggs per gram of faeces were determined on days 21, 24 and day 34 (10 days post-treatment) after infection and all animals were necropsied for residual worm counts. The calculated efficacies of the treatments against H. contortus as indicated by worm reduction were closantel (100%), ivermectin (99.3%), oxfendazole (35.2%), thiophanate (56.7%), levamisole (98.6%) and thiabendazole (24.3%). The data therefore indicate that the TBZ-resistant isolate of H. contortus used was highly resistant to the 2 benzimidazole (BZ) anthelmintics, oxfendazole and thiophanate. This is the first report in Kenya of a field strain of H. contortus resistant to thiophanate.

Animals↗
PubMedDate not supplied

Changes in liveweight gain, blood constituents and worm egg output in goats artificially infected with a sheep-derived strain of Haemonchus contortus.

Two groups of goats were dosed with 10,000 and 20,000 sheep-derived strain (SDS) larvae of Haemonchus contortus respectively. Over a period of 42 days goats dosed with 20,000 larvae lost more weight than those dosed with 10,000 larvae. Infected goats showed anaemia from about 2 weeks after infection as well as reduced levels of total serum proteins and albumins.

Animals↗
PubMedDate not supplied

Infection of goats with Haemonchus contortus and Trichostrongylus colubriformis: histopathology and pH changes.

Two groups of goats were experimentally infected with Haemonchus contortus and Trichostrongylus colubriformis, and killed at various days after infection (DAI). The percentage of worms that established in the abomasum and the small intestine was low. At necropsy, abomasums from infected goats had thickened walls and oedematous folds. At 7 DAI there was an initial infiltration of eosinophils and some neutrophils which tend to increase with age of infection. The mean pH of the abomasum in goats infected with H. contortus was 5.43 (range 5.3-5.7), while that of the control goats was 3.30 (range 2.8-3.7).

Abomasum↗
PubMed1989

No association between the ovine leucocyte antigen (OLA) system in the Australian merino and susceptibility to Haemonchus contortus infection.

A genetic analysis has been made of the Ovine Leucocyte Antigenic (OLA) system in Australian merinos. The animals consisted of sires, dams and their progeny. The typing data were consistent with previous findings of a high degree of polymorphism. At least two closely linked loci with several alleles at each are necessary to explain the data. No evidence was found for an association between OLA types and three measures of susceptibility to infection by the blood-sucking parasite Haemonchus contortus. Attention is drawn to the utility of half-sib data for analysis of the genetic control of resistance to parasites in sheep and other animals with a similar breeding structure.

Animals↗
PubMed1989

Cross-immunity between Haemonchus contortus and Trichostrongylus colubriformis in sheep.

Cross-protective immunity between the nematode parasites, Haemonchus contortus and Trichostrongylus colubriformis, was examined in sheep vaccinated with irradiated larvae of either species. Secondary immunological responsiveness stimulated in this manner protected only against challenge infection with the species used for vaccination. Significant cross-protective immunity was not observed. Titres of serum antibody to an extract of adult but not infective larval T. colubriformis reflected the specificity for protective immunity. Immediate hypersensitivity skin reactions to nematode extracts did not reflect the antigen-specificity for protective immunity.

Animals↗
PubMed1990

Response to helminth infection of sheep selected for resistance to Haemonchus contortus.

Lines of Merino sheep selected for increased (IRH) and decreased (DRH) resistance to Haemonchus contortus were compared with an unselected (CH) line, after approximately four generations of selection. Measurements were recorded on 69 IRH, 47 DRH and 84 CH animals. Following artificial challenge with H. contortus, the IRH line had significantly (P less than 0.001) lower faecal egg counts than the CH and DRH lines (2730, 12,720 and 17,400 epg, respectively). Significant differences (P less than 0.05) were found between all lines in the minimum packed cell volumes during artificial infection (25.7, 22.0 and 20.3%) and in faecal egg counts after natural infection (140, 3590 and 8750 epg). Differences were also recorded (P less than 0.05) following artificial challenge with Trichostrongylus colubriformis (490, 840 and 1340 epg). On a percentage basis, faecal egg counts in the IRH line deviated less from the CH line following artificial infection with T. colubriformis (42%) than with H. contortus (79%). The reverse was true for the DRH line (60 and 37%, respectively). Differences in egg output of this magnitude should have a marked effect on requirements for anthelmintic treatment, rate of development of drug resistance and level of pasture contamination when the lines are grazed separately.

Animals↗