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PubMed1995

Characterization of local antibody responses to the gastrointestinal parasite Haemonchus contortus.

The ability to identify antigens associated with an infection has generally relied on the use of serum antibodies produced by infected or previously exposed individuals. A major drawback with the use of serum is that it does not necessarily reflect the local antibody response at mucosal tissue sites. This study describes an approach that allows the use of antibodies generated close to the infection site to detect the transient expression of stage-specific antigens during infection with the gastrointestinal parasite Haemonchus contortus. This was achieved by infecting immune sheep with H. contortus larvae and removing the abomasal lymph nodes draining the infection site shortly after the challenge infection. Antibody-secreting cell (ASC) probes were generated from these lymph nodes after short-term in vitro culture of cell suspensions, which allowed the accumulation of antibodies secreted by in vivo-induced ASC into the culture supernatant. Lymph node culture supernatants (= ASC probes) from immune sheep challenged 5 days previously were used to probe Western blots of third and fourth stage larval preparations, and revealed distinct reactivity to larval antigens. No antibody reactivity to larval antigen preparations was detected in sheep that were not challenged. The number of antigens identified using ASC probes was significantly restricted compared to either pre- or post-challenge sera. In contrast to the variability of the serum response, the specificity of ASC probes was highly repeatable between different sheep. ASC probes were also used to purify a H. contortus larval antigen by affinity chromatography, which allowed limited biochemical studies to be undertaken. The antigen(s) recognized by the ASC probes were shown to be expressed on the surface of the larvae. These studies illustrate the use of a novel means of studying the local antibody response close to a mucosal infection site in order to identify and isolate stage-specific antigens expressed during infection.

Animals↗
PubMed1994

Sublateral hypodermal chords in Haemonchus (Nematoda: Trichostrongyloidea): description and potential as a systematic character.

Prominent sublateral hypodermal chords (SHC) are described in Haemonchus spp. Four large SHC are located 1 muscle cell away from the lateral chords from the level of the middle of the esophagus to midbody. The SHC are largest in midbody and merge with the lateral chords at about 65% of the body length from the anterior end. With the aid of transmission electron microscopy, a band of nerve tissue was located parallel and medial to the SHC. Haemonchus spp. and Mecistocirrus digitatus have SHC that are so large they can be identified in thick freehand midbody cross sections cut with a cataract knife. Because SHC have not been described in other Trichostrongylidae, their presence in members of the Haemonchinae may have value as a systematic character.

Animals↗
PubMed1993

Monoclonal antibody to CD4+ T cells abrogates genetic resistance to Haemonchus contortus in sheep.

The roles of CD4+ and CD8+ T cells in genetically determined resistance of sheep to Haemonchus contortus (a natural host-parasite relationship) was investigated by selectively depleting genetically resistant merino lambs of their CD4+ or CD8+ T cells by treatment with mouse monoclonal antibody (mAb) specific for the appropriate determinant before and during challenge infection. Administration of anti-CD4 mAb to genetically resistant lambs completely abrogated their expression of genetic resistance as indicated by significantly higher faecal egg output and worm burdens found in the CD4+ T-cell-depleted lambs compared with those of controls. Host responses associated with resistance to H. contortus including mucosal mast cell hyperplasia and tissue eosinophilia were also significantly suppressed in CD4-depleted lambs. The development of anamnestic anti-parasite antibody responses were also significantly inhibited by anti-CD4 mAb. Furthermore, anti-CD4 mAb abolished differences in host responses between genetically resistant and random-bred (susceptible) lambs. In contrast, depletion of CD8+ T cells had no effect on genetic resistance; faecal egg output, worm counts, mast cells and eosinophil responses in CD8-depleted lambs were not significantly different from those in controls. Together, these results suggest that CD4+ T cells play a pivotal role in mediating genetic resistance to H. contortus, and in the generation of mucosal mast cell hyperplasia, tissue eosinophilia and anti-Haemonchus antibody. CD8+ T cells appear to play no protective role. The possible mechanisms by which CD4+ T cells might mediate anti-parasite resistance are discussed.

Animals↗
PubMed1993

[The behavior of hematological parameters (hemoglobin, hematocrit, leukocyte count) and clinicochemical values in plasma (glucose, total proteins, alpha-amino-N, urea, pepsinogen, ascorbic acid, Fe, Cu, Zn) and the content of ascorbic acid in liver, spleen and adrenal glands in healthy lambs and lambs infected with Haemonchus contortus and Trichostrongylus colubriformis].

In 8 healthy, noninfected lambs with an initial body weight (b. w.) of 24.79 +/- 1.16 kg as well as in 3 groups of lambs (n = 8 per group) of a similar body weight after an inoculation with 3rd stage larvae of Haemonchus contortus (2500) and Trichostrongylus colubriformis (10,000) analyses of the blood plasma were performed for 45 days thereafter. On the 37th day after infection ivermectin (0.2 mg/kg b. w.) was administered per os respectively subcutaneously to the lambs of 2 groups. After 7 and 8 days the content of ascorbic acid in the liver, the spleen and the adrenals as well as that of vitamin A in the liver was analysed. The behaviour of the values influenced by a moderate infection with trichostrongylid nematodes is discussed.

Animals↗
PubMed1993

Consequences of dose-dependent immunosuppression by progesterone on parasitic worm burdens in lambs.

Eighteen female lambs with prior exposure to Haemonchus contortus infections were ovariectomized and assigned to 1 of 3 replacement regimens: 0, 25, or 250 mg of progesterone/d delivered IM. After 3 weeks of hormonal treatment, all lambs were inoculated with 100,000 infective larvae of H contortus. After 8 weeks of hormonal treatment, a blastogenic assay was performed on blood lymphocyte populations, and the abomasum from each lamb was obtained for larval and adult worm recoveries of H contortus. Lambs of the 25 mg of progesterone group had significantly (P < 0.05) reduced blastogenic response to concanavalin A and greater adult and larval populations, compared with controls. Lambs of the 250 mg of progesterone group had worm burdens and lymphocyte blastogenesis values intermediate between those of the other treatment groups.

Animals↗
PubMed1993

Comparison of the effects on milk production of concurrent infection with Haemonchus contortus and Trichostrongylus colubriformis in high- and low-producing dairy goats.

The impact of nematode parasitism of the digestive tract on milk output and milk quality was examined in dairy goats. In addition, the consequences of worm infection were compared in goats with different lactation performance (ie, with initial high or low milk production). Forty-eight goats in the second month of lactation were allotted equally to 2 groups. The first group was given 5,000 Haemonchus contortus and 20,000 Trichostrongylus colubriformis larvae. The 24 additional goats remained free of parasites. Parasitologic, serologic, and milk data were collected every 2 weeks for 5 months, and body condition of the goats was scored throughout the study. Results of strongyle egg count in feces, increase in pepsinogen values, and reduction in RBC count, PCV, and serum inorganic phosphate concentration indicated subclinical infection. This subclinical parasitism induced a decrease in body condition scoring and led to persistent decrease in milk yield, ranging from 2.5 to 10% reduction from control values. Changes in fat and protein contents were not detected. In contrast, the consequences of infection were more severe in the 6 goats with the highest milk production at the start of the study. Decrease in milk output ranged between 13.0 to 25.1%, and was associated with decrease in fat content. Comparison of the response to parasitism in the 6 goats with the highest lactation performance and the 6 goats with the lowest performance indicated differences between both subgroups. According to parasitologic and pathologic data, high-producer goats had less resistance and/or resilience to infection associated with more severe consequences on milk production.

Animals↗
PubMed1994

New morphological characters for identifying individual specimens of Haemonchus spp. (Nematoda: Trichostrongyloidea) and a key to species in ruminants of North America.

The large stomach worms Haemonchus contortus, Haemonchus placei, and Haemonchus similis are important pathogens of cattle and sheep. This paper describes characteristics of surface cuticular ridges (synlophe), which for the first time provide morphological criteria for identifying individual adult specimens of either sex. The diagnostic patterns of the synlophe on the anterior half of specimens can be observed at 400x in temporary mounts on glass slides. The synlophe can be studied in cleared preserved specimens or in living or freshly thawed frozen specimens mounted in water. The synlophe of H. contortus has 30 ridges in the region of the posterior half of the esophagus, 4 fewer than H. placei and H. similis. The 4 extra ridges of H. placei and H. similis are consistently located bilaterally to the 3 ventralmost and the 3 dorsalmost ridges. The 4 extra ridges of H. similis extend to the end of the synlophe posterior to midbody, but in H. placei they extend posteriorly only to the end of the anterior quarter of the nematode. A key is included to the 3 species of Haemonchus parasitic in domestic sheep and cattle using characteristics of spicules, female reproductive system, female tail, and the synlophe.

Animals↗
PubMed1993

The pattern of faecal egg output in lambs infected with a multiple resistant strain of Haemonchus contortus after treatment with albendazole.

Worm-free lambs (n = 6) were infected with 5,000 L3 of an ivermectin/benzimidazole/closantel resistant strain of Haemonchus contortus. On Day 21 post infection animals were allocated, according to worm egg counts, to 2 groups of 3 animals each and on Day 29 one group was treated with albendazole at 3.8 mg kg-1, while animals in the other group remained untreated as controls. All animals were slaughtered on Day 44 when the treated group was found to have 2,083 +/- 1,718 worms and the controls 2,783 +/- 633, a reduction of 25.2% in worm burdens. The pattern of egg output was monitored and it was found that 2 d after dosing, worm egg counts had been suppressed by 89% in the treated group; thereafter the egg counts increased, but never returned to the pretreatment levels and by Day 15 post treatment, they were still 41.1% lower in the treated group than in the controls.

Albendazole↗
PubMed1993

Efficacy of moxidectin against a strain of Haemonchus contortus resistant to ivermectin, a benzimidazole and a salicylanilide.

The efficacy of moxidectin at 0.2 mg kg-1 live body mass against the multiple anthelmintic resistant White River Krtz strain of H. contortus was determined and compared to that of ivermectin, a benzimidazole, a salicylanilide and levamisole. Moxidectin and levamisole were effective against this strain of H. contortus and reduced the arithmetic mean burdens of this parasite in the sheep by 99.98% and 99.59%, respectively, while the efficacy of ivermectin, albendazole and closantel was only 29.1%, 33.75% and 78.3%, respectively.

Albendazole↗
PubMed1993

Controlled tests of activity of several antiparasitic compounds against natural infections of Haemonchus contortus and other helminths in lambs from a flock established in 1962.

Antiparasitic activity of several compounds was evaluated over a long period (about 25 years) in the same flock of sheep. Haemonchus contortus was of special interest, including its relation to drug resistance, especially to thiabendazole and other benzimidazoles, in addition to phenothiazine. Eleven compounds were evaluated in 15 controlled tests, done between 1966 and 1989 in naturally infected lambs (n = 145) born and raised on the same pasture. Sheep were first placed on the pasture in 1962, and a few more were added thereafter. Internal parasites in these sheep were classified in 3 general categories: indeterminate exposure to parasiticides; H contortus, resistant to thiabendazole; and H contortus, resistant to phenothiazine. The parasitic infections probably became more homogeneous after several years because of few introductions of outside sheep after initial establishment of the flock. Activity against naturally acquired internal helminths was evaluated for cambendazole (CBZ: dosage, 20 mg/kg of body weight), fenbendazole (FBZ: 5 or 7.5 mg/kg), mebendazole (MBZ: 10 mg/kg); oxfendazole (OFZ: 3.5 or 10 mg/kg), oxibendazole (OBZ: 10 mg/kg); parbendazole (PBZ: 15 mg/kg), phenothiazine (PTZ: 550 mg/kg); pyrantel pamoate (PRT: 25 mg base/kg), tetramizole (TET: 15 mg/kg); thiabendazole (TBZ: 30 or 44 mg/kg), and trichlorfon (TCF: 100 mg/kg). Thiabendazole was used more often (9 tests) than the other compounds. Thiabendazole was more active against mature H contortus in later years than when first used in 1966, although it was never 100% effective. Efficacy against immature H contortus for TBZ did not exceed 86%. Activity against immature and mature stages of this parasite was good overall for the other benzimidazoles.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Selection for a strain of Haemonchus contortus that exhibits periparturient egg rise in sheep.

Periparturient egg rise (PPR) is a principal means for some nematode parasites to survive over winter and to provide transmission of infective larvae from ewes to lambs during the spring. Routine laboratory propagation techniques probably have selected for those characteristics that would not promote PPR in conventional laboratory strains of Haemonchus contortus. An established isolate of H. contortus (BPL) was the source of the initial inoculum to select for a strain that readily exhibits characteristics of PPR. The selection process included inoculation of helminth-free pregnant ewes during mid-gestation, collection of nematode eggs during lactation, and storage of infective larvae at 4 C for 4 mo. After 10 generations, the 2 strains, BPL and PPR from lambs and pregnant ewes were compared for reproductive, morphological, and population differences in lambs and pregnant ewes. After lambing, ewes inoculated with the PPR strain had significantly higher fecal egg concentrations. Lambs inoculated with the PPR strain had higher egg concentrations, higher total daily egg production, fewer adult worms, larger female worms, and higher fecundity. Repeated selection in the appropriate host, after prolonged storage of the inoculum, produced a PPR strain of H. contortus morphologically and reproductively distinct from the initial source isolate.

Animals↗
PubMed1977

"Spring rise" in fecal nematode egg counts in sheep in Maine.

A "spring rise" in fecal nematode egg counts occurred in Maine sheep housed under conventional conditions during 2 years. Nematodes causing this increase were Haemonchus contortus in one year and Ostertagia sp in the other. The increase in egg counts was greater in sheep that lambed than in unbred sheep. Most of the eggs in the spring rise were probably produced by worms that passed the winter in developmental arrest in the sheep. Some of the female worms probably came from contaminated bedding and developed in the sheep without arrest in growth. Acquisition from contaminated bedding, therefore, should be considered as an additional factor in the epizootiologic character of the condition in Maine.

Animals↗
PubMed1977

Helminths of wild ruminants introduced into Czechoslovakia.

The paper contains results of helminthological studies on ruminants introduced into Czechoslovakia from other regions and continents. It is pointed out that introduction of wild ruminants is not only of theoretical importance in the adaptation of parasites to a new environment, but also of practical consequence in the mutual exchange of parasites between the imported and autochthonous game animals.

Animals↗
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↗
PubMed1995

Effectiveness of the ivermectin sustained-release bolus in the control of bovine nematodosis.

OBJECTIVE: To evaluate the nematocidal effectiveness of the ivermectin sustained-release bolus throughout its 135-day delivery period. DESIGN: Twenty-four naturally infected calves were randomly allocated to 1 of 3 equivalent experimental groups: group-T1 calves were untreated controls, group-T2 calves each received a sustained-release bolus on trial day 0, and group-T3 calves were rendered nematode-free and used at 35-day intervals during the study as tracers. One contaminated pasture was used for all principal calves for the 135-day grazing interval of the study. Calves of groups T1 and T2 were also artificially administered mixed infective nematode larvae at intervals during the grazing period, after which, all calves were confined to concrete for 21 days prior to necropsy. ANIMALS: All calves were approximately 6 months old on trial day 0, weighed from 136 to 216 kg, and were of mixed breeding and sex. PROCEDURE: At intervals during the study, feces from all calves were analyzed for nematode egg counts, and all calves were weighed and examined for bolus retention (T2 calves only). For nematode recovery, all calves were necropsied 21 to 22 days after removal from the contaminated pasture. RESULTS: Parasitic populations of Haemonchus, Ostertagia, Trichostrongylus, Cooperia, Bunostomum, and Oesophagostomum spp were significantly reduced in cattle treated with the ivermectin sustained-release bolus. CONCLUSION: The nematocidal activity of the ivermectin sustained-release bolus proved highly effective, with > 98% efficacy for all nematode species present.

Ancylostomatoidea↗
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↗