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PubMed1984

The prevalence and pathogenesis of naturally-occurring Haemonchus longistipes infection in Sudanese camels.

Camel haemonchosis is prevalent in the Sudan, especially during the rainy season, with a decrease in prevalence in the dry season possibly due to delayed maturation of the worms. The naturally occurring disease in Sudanese camels is characterized by emaciation, anaemia, oedema of the lower parts of the limbs, eosinophilia, hypoproteinaemia, hypoalbuminaemia, hyperglobulinaemia and eosinophilia, as well as elevated blood urea concentrations.

Animal Diseases↗
PubMed1987

Physiological and microbiological changes in the abomasum of sheep infected with large doses of Haemonchus contortus.

The pH, PO2 and the number of viable bacteria per ml of abomasal fluid were recorded before and after administering large doses of infective larvae of H. contortus to sheep. Highly significant increases were observed in the pH, in numbers of viable bacteria and in the proportion of oxygen-sensitive bacteria in the abomasal fluid during the first 10 to 14 days of infection. At the same time a decrease in the abomasal fluid PO2 was recorded. Subsequently a slow recovery of pH, PO2 and bacterial numbers to pre-infection values ensued. The microbiological and physiological changes occurring in the abomasum of sheep after infection with H. contortus are discussed with reference to these results.

Abomasum↗
PubMed1989

Post-mortem changes in the abomasal mucosae of sheep infected with Haemonchus contortus compared with those in uninfected sheep.

Progressive post-mortem changes were observed, with fibre optic endoscopy, in the abomasum of uninfected sheep and sheep infected with H. contortus. Loss of epithelial cells was observed 14 to 16 min after death in the uninfected sheep. The loss exposed the underlying lamina propria. This loss became more widespread as the time after death increased. Epithelial cell loss was observed earlier (as early as 6 min after death) in the infected sheep. Three of the infected sheep also displayed dispersal of alkaline phosphatase activity 30 min after death. The present work shows that post-mortem changes can occur quite quickly in animals, especially infected animals, and emphasizes the importance of rapid removal of tissue from animals after death.

Abomasum↗
PubMed1991

Effect of weaning on antibody responses and nematode parasitism in Merino lambs.

Lambs weaned at eight weeks old were compared with control lambs which remained with their dams; both groups grazed the same pasture. Weaning significantly reduced the growth rate, control lambs being, on average, 6 kg heavier than weaned lambs at 15 weeks old. When contamination of pasture with larval parasites was light, both groups of lambs suffered only modest parasitic infections. When lambs were experimentally infected with 5000 Haemonchus contortus and 10,000 Trichostrongylus colubriformis larvae at eight weeks old, the mean faecal egg count for weaned lambs was twice that for controls at 12 weeks old (P less than 0.001) and weaned lambs suffered a significantly greater decline in packed cell volume than controls over the next four weeks. Antibody responses following immunisation with either ovalbumin or Brucella abortus at four and at eight weeks old, did not differ significantly between control and weaned lambs. In contrast serum antibody responses to H contortus and T colubriformis differed significantly between the two groups, with controls responding earlier and more strongly than weaned lambs. The practical significance of these findings is that up to three months old, suckled lambs, when faced with a substantial parasite challenge, have much better prospects than weaned lambs.

Animals↗
PubMed1991

Post natal ontogeny of immunological responsiveness in Merino sheep.

Sheep in five age groups (two weeks, 10 weeks, 18 weeks, six months and four years old) were immunised systemically, twice, with ovalbumin or Brucella abortus (live or killed) and antibody responses in blood were measured. The animals were also infected with the nematode parasites Trichostrongylus colubriformis and Haemonchus contortus and faecal egg counts and serum antibody responses to larval antigens were measured. The experiments were designed so that, as far as possible, the effect of age per se could be dissociated from the combined effects of age and prior exposure to antigen. The effects of the age of sheep were more marked for antibody responses to Brucella abortus lipopolysaccharide than to ovalbumin. Older animals had much greater resistance to infection with internal parasites, as shown by the magnitude of the faecal egg count. In contrast to older lambs, neonatal lambs (infected with H contortus at two weeks old) had consistently declining concentrations of anti-H contortus antibody in their serum, mounted no detectable autogenous anti-H contortus antibody response in blood and appeared to develop no resistance to the parasite. Post natal ontogeny of immune responses was different for the various antigens/pathogens.

Aging↗
PubMed1991

Disposition of oxfendazole in goats and efficacy compared with sheep.

The disposition of intraruminally administered oxfendazole (OFZ) in goats was studied at 5, 10 and 20 mg kg-1. The area under the plasma concentration with time curve (AUC) increased with increasing dose but at a declining rate. AUC was lower after intra-abomasal compared with intraruminal administration. OFZ was less effective against drug resistant Trichostrongylus colubriformis in goats than in sheep but was of similar efficacy against drug resistant Haemonchus contortus in both host species. In the same experiment peak plasma levels of OFZ in goats were about half those in sheep given the same dose. Of 70 goats tested in the field, total rumen bypass occurred in 12 per cent and partial bypass in 67 per cent. Lower systemic availability due to bypass would be expected to reduce further anthelmintic efficacy in goats. From the results of these experiments a dose rate of 10 mg kg-1 is recommended for goats. When given at this rate as a divided dose at 12 hourly intervals over 24 hours, OFZ was significantly more effective than a single dose in reducing egg counts.

Animals↗
PubMed1992

Effects of dietary molybdenum on nematode and host during Haemonchus contortus infection in lambs.

The addition of molybdenum (0.05 mmol kg-1 dry-matter) to the diet of lambs given a trickle infection of Haemonchus contortus larvae (500 third stage larvae d-1 over six weeks) reduced mean faecal egg counts (epg) from 3952 to 2312 +/- 402 by 32 days (P less than 0.02) and greatly reduced the mean number of worms recovered from the abomasum 14 days after infection ceased (907 compared with 4167: P less than 0.01). Infection reduced haemoglobin concentrations less in lambs given molybdenum although the difference was small relative to the reduction in worm burden. Lambs not given molybdenum had low intraepithelial mast cell counts in the abomasal mucosa and less abomasal hypertrophy than expected from abomasal parasitism. Molybdenum did not consistently reduce the copper status of the host or the parasite. Previous exposure to molybdenum greatly reduced protein but not proteinase activity in, or secreted by, adult worms cultured for eight hours. It is suggested that molybdenum either increased the inflammatory response which preceded worm rejection or that it indirectly enhanced that reaction by reducing the effectiveness of copper-dependent, anti-inflammatory enzymes in the gastrointestinal mucosa.

Abomasum↗
PubMed1993

Protection in lambs immunised with Haemonchus contortus gut membrane proteins.

Substantial protection against Haemonchus contortus was induced in lambs by hyperimmunising them with an integral membrane extract of intestines dissected from adult worms. The procedure was effective in young growing animals but did not afford any cross protection against either Ostertagia circumcincta or Nematodirus battus. A serum transfer experiment suggested that the effector mechanism was serum antibody which bound to the brush border membrane of the parasites intestinal cells. Sheep which had acquired immunity to H contortus by previous exposure to a trickle infection did not recognise the gut membrane proteins, which suggested that these are normally hidden from the host.

Animals↗
PubMed1993

Evaluation of aspects of the protection afforded to sheep immunised with a gut membrane protein of Haemonchus contortus.

Experiments were undertaken to evaluate the type of protection conferred against Haemonchus contortus by immunising sheep with H11, a 'hidden' integral gut membrane protein isolated from this parasite. A serial kill experiment showed that worms began to be lost from immunised lambs between seven and 14 days after challenge with a single dose of larvae and adult female worms were more susceptible than male worms. Seven-day-old juveniles survived immunisation even though their intestinal cells became coated with sheep antibody. Immunisation was equally effective against both benzimidazole-resistant and susceptible strains of H contortus. When immunised lambs were subjected to a trickle infection, they were largely protected against the anaemia and egg output observed in the challenge controls. Moreover, they grew as fast and as efficiently as uninfected lambs fed on the same high protein diet and acquired a natural immunity during the course of the trickle infection.

Animals↗
PubMed1993

Survival and development of ivermectin-resistant or susceptible strains of Haemonchus contortus under field and laboratory conditions.

The free-living development of three strains of Haemonchus contortus was studied in two experiments. Day 21 faecal samples were collected from lambs infected with either a susceptible strain, a laboratory-selected ivermectin (IVM) resistant strain or a South African field strain showing multiple anthelmintic resistance, which included IVM. No eggs hatched in samples cultured at 4 or 10 degrees C. At 22 degrees C the laboratory-selected strain showed the highest rate of development while at 27 degrees C the susceptible strain produced the highest yield of third stage larvae (L3): at both temperatures the field strain showed the lowest percentage development to L3. The second experiment was a field study carried out in southern Brazil. Faeces containing either an IVM-susceptible or an IVM-resistant strain of H contortus were placed in two series of grass plots during each of three summer months. Soil subsequently yielded more larvae than did grass suggesting migration or mechanical transport into the soil. For plots contaminated during the first two months there was no significant difference in recovery rate between the two strains (P > 0.05). When contamination occurred during the third month, the IVM-resistant strain produced significantly higher recovery rates (P < 0.05) from both pasture and soil.

Animals↗
PubMed1993

The same fractions of Haemonchus contortus soluble antigen induce lymphocyte responses in naive lambs and immune sheep.

Soluble antigen extracted from third stage larvae of Haemonchus contortus was divided into fractions based on molecular weight by sodium dodecyl sulphate polyacrylamide gel electrophoresis and electrotransferred to nitrocellulose. Infection immunised adult sheep and H contortus naive lambs were used to examine the lymphocyte responses to these fractions in vitro. The results demonstrate that the same two fractions induced the strongest responses in both groups of animals.

Animals↗
PubMed1993

Immune responsiveness of lambs selected for resistance to haemonchosis.

Several parameters of immune competence were measured in lambs with genetic resistance to Haemonchus contortus and in lambs with average susceptibility to H contortus (random-bred). Increase in skinfold thickness following intradermal injection was greater in resistant lambs for concanavalin A and to a lesser extent for phytohaemagglutinin. Both mitogens induced infiltration of superficial and deep dermis by eosinophils, CD4+, CD8+ and T19+ lymphocytes, though the responses did not differ between groups. Primary but not secondary antibody responses to the T cell-dependent antigen, ovalbumin was greater in resistant lambs. In contrast, antibody responses to the T cell-independent antigen, Brucella abortus lipopolysaccharide, did not differ between groups. Taken together the data suggest that enhanced T lymphocyte function may contribute to the greater resistance to H contortus of genetically resistant lambs.

Animals↗
PubMed1994

Serum antibody responses of Texel sheep experimentally infected with Haemonchus contortus.

The primary and secondary serum antibody responses of Texel sheep to infective larvae (L3) and adult worms of Haemonchus contortus were studied. Ten-month-old sheep were infected with 20,000 H contortus L3, treated with ivermectin seven weeks later and, after four weeks, reinfected with 10,000 L3 once a week for six weeks. Faecal egg counts were significantly lower during the secondary infection than during the primary infection, but both infections induced antibody responses, as demonstrated by an enzyme-linked immunosorbent assay (ELISA). The primary antibody response developed rather slowly, but the secondary response developed more rapidly and the IgA responses against L3 antigens and the IgG1 and IgG2 responses against adult antigens were twice those observed during the primary infection. These accelerated and enhanced responses after the reinfection suggest an immunological memory for H contortus antigens.

Animals↗
PubMed1994

Antibody-containing cells in the abomasal mucosa of sheep with genetic resistance to Haemonchus contortus.

The frequency distribution of parasite-specific antibody-containing cells (ACC) and total immunoglobulin-containing cells (ICC) in the abomasal mucosa was examined in genetically resistant and random-bred sheep, following infection with Haemonchus contortus, to determine whether the two genotypes differed in the development of a local immune response. Immunofluorescence staining was used to detect ACC and ICC of IgA, IgG1, IgG2 and IgM classes. No ACC were found in the abomasum of any of the sheep before infection. ACC were first detected in the abomasal mucosa of both the resistant and susceptible sheep seven days after infection, reached a peak level on day 21 and then declined. At all observation times, the majority of ACC in both genotypes were of the IgA isotype, followed by IgG1 and IgM. The IgG2-ACC response was negligible compared with the IgA and IgG1 response. The comparison of genotypes showed that the resistant sheep had significantly more IgA-ACC on days 14, 21, 28 and 35, and significantly more IgG1-ACC than random-bred sheep on days 14, 21 and 28. The numbers of IgG2- and IgM-ACC did not differ between the genotypes. The abomasal mucosa of the resistant sheep was also found to have significantly more ICC than the mucosa of random-bred sheep; IgA-ICC predominated at all the observation times followed by IgG1 and IgM. These results suggest that IgA and IgG1 antibodies, produced locally in response to infection, may play a role in mediating genetic resistance to haemonchosis in sheep.

Abomasum↗
PubMed1995

Influence of supplementation with dietary soyabean meal on resistance to haemonchosis in Hampshire down lambs.

The influence of dietary protein supplementation on resistance to haemonchosis was examined in Hampshire down lambs fed either a basal diet or a diet supplemented with soyabean. At seven months of age the lambs were challenged with an initial loading dose of Haemonchus contortus, followed by a trickle infection three times a week. Blood and faecal samples were collected three times a week and bodyweights were recorded weekly. After 10 weeks the lambs were slaughtered and their worm burdens and carcase composition determined. Although their mean worm burdens were similar, the lambs given the basal diet had higher faecal egg counts, lower packed red cell volumes and lower concentrations of total plasma protein and plasma albumin than the lambs given the supplemented diet. The dietary supplementation also improved the carcase composition of the lambs.

Animal Feed↗
PubMed1992

Characterisation of ovine mast cells derived from in vitro culture of haemopoietic tissue.

Ovine mast cells generated in vitro from bone marrow (BMMC) were compared with mucosal mast cells (MMC) isolated from parasitised abomasum. Ultrastructurally, the granules of BMMC were partially developed and immature. Both cells types contained beta-hexosaminidase, arylsulfatase, histamine, dopamine and sheep mast cell proteinase (SMCP). Greater amounts of beta-hexosaminidase, but less SMCP, histamine and arylsulfatase were present in BMMC. Stimulation with calcium ionophore A23187 caused the secretion of granule constituents and generation of leukotriene C4 by BMMC in a dose-dependent manner. An additional [3H]diisopropylfluorophosphate-binding 31,500 mol. wt. serine esterase, antigenically related to SMCP (27,000 mol. wt.) was present in cultures of BMMC but was not detected in isolated MMC. Both enzymes were detected in BMMC by Day 7 of culture and were secreted concomitantly following stimulation of BMMC with ionophore.

Abomasum↗
PubMed1992

Induction of tissue eosinophilia by platelet-activating factor in Merino sheep.

A study was undertaken on the capacity of platelet-activating factor (PAF) to induce eosinophil accumulation in the mammary glands of non-lactating sheep. Platelet-activating factor induced dose-dependent accumulation of eosinophils in mammary exudates 24 h after infusion. Infection, by intraruminal injection of 20,000 infective Trichostrongylus colubriformis larvae, did not modify the responsiveness of outbred sheep to intramammary infusion of PAF. Mature ewes from high and low responder lines of a flock of sheep, selected on the basis of their responses to vaccination and experimental challenge with T. colubriformis as lambs, did not differ in the magnitude of the eosinophil responses to doses of PAF from 5 x 10(-13) to 5 x 10(-7) mol per gland. Intramammary infusion of an extract from third stage larvae of Haemonchus contortus elicited inflammatory exudates containing five- to ten-fold more eosinophils than that elicited by the highest dose of PAF tested. The experiments indicate that the eosinophil chemotactic agonist PAF can induce tissue eosinophilia in sheep and thus may play a role in directing the accumulation of eosinophils in tissues during disease states such as gastrointestinal parasitism.

Animals↗
PubMed1992

Localization of immunoglobulin-containing cells in the abomasum of sheep following infection with Haemonchus contortus.

Abomasal cannulation followed by serial collection of biopsies was used to study the kinetics of appearance of IgA-, IgG1-, IgG2- and IgM-containing cells in the abomasum of sheep following infection with Haemonchus contortus. Very few immunoglobulin-containing cells (ICC) were found in the abomasum of sheep before infection. Following H. contortus infection, there were increased numbers of ICC in the submucosa of the abomasum. Seven days after infection, the numbers of IgA-, IgG1- and IgM-containing cells were six times greater than for uninfected control animals. The numbers of ICC continued to rise as the infection progressed, and the peak response was observed between 21 and 28 days after infection. IgA-containing cells (68-84%) were the most frequent cell types at all the observation times, followed by IgG1 and IgM. IgG2-containing cells were minimal throughout the experiment. As there were no significant changes in the numbers of ICC in the abomasum of uninfected controls it is concluded that H. contortus stimulated a local immune response in the abomasum of parasitized sheep.

Abomasum↗