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PubMed1988

The effect of selenium supplementation on immunity, and the establishment of an experimental Haemonchus contortus infection, in weaner merino sheep fed a low selenium diet.

Immunity in 12 weaner Merino sheep fed a low selenium (Se) diet (low Se sheep) was compared with that in 10 matching sheep fed the same diet but each given an intraruminal Se pellet (high Se sheep), while the sheep were housed in individual, sheltered pens. All sheep were challenged with killed Brucella abortus cells (days 0 and 28), rabbit red blood cells (days 0, 7 and 28) and corynebacterium pseudotuberculosis toxoid (days 0 and 28), and serum antibody titres were measured weekly for 8 weeks from day 0. The sheep were then experimentally infected with Haemonchus contortus, and slaughtered 8 weeks later. The mean antibody titre to B. abortus, measured by 4 different tests, was significantly higher in the high Se sheep on occasions during the primary immune response phase (Rose Bengal test - day 21 (p less than 0.05), day 28 (p less than 0.025); complement fixation - day 7 (p less than 0.05); enzyme-linked immunosorbent assay - day 14 (p less than 0.01); serum agglutination - no differences), but not during the secondary phase. The mean antibody titre to rabbit red blood cells, measured by haemagglutination test, was marginally higher in the high Se sheep on day 49 (p = 0.049). The mean antibody titre to C. pseudotuberculosis, measured by enzyme-linked immunosorbent assay, was not significantly different between the groups at any time during the trial. In addition, the mean in-vitro responsiveness of peripheral blood lymphocytes to stimulation with phytohaemagglutinin in the high Se sheep was significantly greater than that in 10 sheep from the low Se group on day 22 (p less than 0.01), but not day 50.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

The effect of level of nutrition on the development of resistance to Haemonchus contortus in sheep.

Merino wether weaners, 5-months old at the start of the experiment and fed lucerne-based pellets at 600 g per head per day, developed resistance to Haemonchus contortus given as a continuous or "trickle" infection at the rate of 500 larvae 3 times per week over a period of 17 weeks. By contrast, the development of resistance was impaired in weaners fed pellets at 400 g per head per day. Low food intake and protein-energy deprivation, therefore, have a major effect in impairing the development and expression of host-protective immunity against haemonchosis. The point at which low food intake causes outbreaks of haemonchosis in sheep at pasture is critical in determining procedures for prevention and control of the disease.

Animal Feed↗
PubMed1993

Factors affecting the prevalence and severity of footrot in a merino flock selected for resistance to Haemonchus contortus.

An outbreak of virulent footrot occurred in three lines of sheep selected for different levels of resistance to Haemonchus contortus, providing an opportunity to examine the factors affecting footrot severity. The selection lines did not differ significantly in average footrot score, but various other factors were found to have an effect. In breeding ewes, the average score was 10.2 (maximum possible score 20) and the prevalence of footrot was 96%. There was a significant age effect, with average score increasing from 9.1 +/- 0.8 in 2-year-old ewes, to 13.4 +/- 0.9 in 7-year-old ewes. Ewes that lost their lambs tended to have higher scores than those that either failed to lamb or successfully reared their litter. Significant differences in footrot score were caused by the lambing paddock in which the ewes had been, during the period seven weeks to one week before infection. Among lambs, aged about 20 weeks, the average footrot score was lower (5.0), as was the prevalence (75%). The score increased by an average of 0.09 +/- 0.03 per day of age and the prevalence increased by an average of 0.6% +/- 0.3% per day of age. Lambs born and reared as twins had significantly lower scores than singles, and progeny of maiden dams had lower scores than progeny of older ewes. There was no significant difference because of the sex of the lamb.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1995

Duration of the persistent activity of moxidectin against Haemonchus contortus in sheep.

Weaned lambs were infected with Haemonchus contortus 35, 28, 21, 14 and 7 days after treatment with moxidectin at 0.2 mg/kg and 35 and 14 days after treatment with ivermectin at the same dose rate. Worm counts 14 days after infection showed that moxidectin prevented the establishment of over 99% of infective larvae for 28 days and reduced the establishment rate at 35 days by 96%, relative to ivermectin. There was no difference in the protective efficacy of ivermectin at 14 or 35 days. The persistence of moxidectin is likely to provide advantages in nematode control, particularly when used as a strategic early summer treatment or as a pre-lambing treatment to ewes. Implications of the persistent activity of moxidectin for the development of resistance during the decay phase are discussed.

Animals↗
PubMed1990

The localization of somatostatin-like immunoreactivity in the alimentary tract of the sheep with observations on the effect of an infection with the parasite Haemonchus contortus.

Cells containing somatostatin immunoreactivity were localized in the alimentary tract of parasite-free sheep by indirect immunocytochemistry, using an antiserum raised to ovine somatostatin. Nerve fibres showing somatostatin-like immunoreactivity were identified in the oesophagus, reticulum wall and groove, rumen pillar and wall, omasum sulcus and abomasum. Varicose fibres were found in the myenteric plexuses of the duodenum, jejunum, ileum and colon. The greatest distribution of endocrine cells (99 cells mm-2) was found in the antrum of the abomasum with 47, 29, 12 and 6 cells mm-2 respectively in the fundus, the first part of the duodenum, mid-jejunum and ileum. Some of the parasite-free sheep which had never experienced infection with larvae of the abomasal nematode, Haemonchus contortus, were paired with similar sheep in an experiment to investigate the effect of parasitism on nitrogen metabolism in the small intestine. The protocol of this experiment required observations before and after parasite infection, with final observations 2 weeks after removal of the infection by treatment with an anthelmintic drug. The sheep were then killed and tissues taken from each paired animal. Tissues from the recently parasitized sheep showed increases of D cells in the fundus and antrum of the abomasum. At present it is not clear if these increases were related to parasitism, per se, or were the post-treatment indicators of healing and recovery from infection with parasite larvae.

Animals↗
PubMed1978

The influence of breed on the susceptibility of sheep and goats to a single experimental infection with Haemonchus contortus.

Four breeds of sheep and three breeds of goats, maintained on both high and low planes of nutrition were given a single infection of 350 Haemonchus contortus larvae per kg. Although animals on a low protein diet had much higher faecal egg counts than those on the high protein diet the pattern of relative susceptibility was similar in both cases. It would appear that the nutritional status of the host influences its resistance to H contortus infection. Of the breeds studied the indigenous Red Masai was the most resistant breed of sheep while the exotic Saanen was more resistant than the the two indigenous breeds of goats.

Animals↗
PubMed1991

Effectiveness of clean grazing strategies in controlling Haemonchus contortus infections in sheep in the United Kingdom.

The effectiveness of clean grazing systems for controlling the sheep abomasal parasite Haemonchus contortus under experimental conditions was monitored for a grazing season in ewes and lambs carrying either benzimidazole-susceptible or resistant populations of the parasite. Both preventive and evasive strategies failed to give effective control of H contortus. Lambs grazing with ewes that had received no anthelmintic showed clinical signs of haemonchosis by early July. Lambs from ewes dosed with a benzimidazole (mebendazole) before turn out, developed clinical signs of haemonchosis later in the season. The presence of anthelmintic resistant genotypes had a significant effect on the appearance of clinical signs, and on the epidemiology and control of disease. It was concluded that alternative worm control strategies will be required for the effective control of H contortus in the United Kingdom.

Abomasum↗
PubMed1991

Effectiveness of strategic anthelmintic dosing in controlling Haemonchus contortus infections in sheep in the United Kingdom.

The strategic use of anthelmintics in the control of infections of Haemonchus contortus in ewes and lambs, was investigated in a series of paddock trials. The levels of infection and clinical signs associated with the presence of either benzimidazole-resistant or benzimidazole-susceptible strains of H contortus in lambs were controlled by regular drenching with levamisole or mebendazole, respectively, or by the strategic use of closantel in combination with mebendazole. In the latter case, control was achieved by dosing either the ewes in the early part of the grazing season, or the lambs from June onwards. It was concluded that worm control strategies based on closantel could provide effective control of both benzimidazole-susceptible and benzimidazole-resistant strains of H contortus on farms in the United Kingdom.

Animals↗
PubMed1994

Effect of subclinical Eimeria species infections in tropical goats subsequently challenged with caprine Haemonchus contortus.

Fourteen goat kids of the local indigenous breed naturally infected with Eimeria species were divided into two equal groups. The first group was superinfected with 500,000 Eimeria species oocysts and the second group was treated with amprolium. Sixty days later both groups were infected with 5000 third-stage caprine Haemonchus contortus larvae. The goats experimentally superinfected with eimeria shed more H contortus eggs and gained weight more slowly.

Amprolium↗
PubMed1980

Haemonchus contortus resistance in straightbred and crossbred Barbados Blackbelly sheep.

Resistance to Haemonchus contortus infection was studied in two experiments conducted with 52 lambs of widely different genetic background. Breed groups compared were: Dorset (D), Barbados Blackbelly (B), Dorset x Blackbelly (D x B), Suffolk x Blackbelly (S x B), Suffolk x Dorset x Blackbelly (S x D x B,[1/4 B]) and nonBlackbelly (NB, D and S). In each experiment, lambs were raised on concrete from birth and were essentially parasite free until infective larvae were administered. In Exp. 1, D x B, S x D x B and D wether lambs approximately 3 months old were infected with a standard dose of invective larvae estimated to be 98% H. contortus. D x B lambs had a longer (P < .05) prepatency period and, at necropsy 17-day postinfection, had a higher (P < .05) percentage of female parasites classified as immature than did the other breed groups. These data showed that the development of H. contortus larvae was inhibited in D x B host animals. In Exp. 2, B, D x B, S x B and NB ewe and wether lambs approximately 4 months old were treated with three sensitizing doses of H. contortus larvae. These were followed by a challenge infection. On the basis of fecal egg counts (eggs per gram feces, EPG), there was no evidence that the challenge infection induced a self-cure reaction in any breed group. All lambs with B breeding had significantly higher Hb levels at the end of the experiment than did NB lambs. b and S x B lambs had higher (P < .05) Hb levels than the D x B lambs, and B lambs had the highest (P < .05) mean corpuscular hemoglobin concentrations. Five days after the challenge infection, B, D x B and S x B lambs also had significantly higher white blood cell levels than did NB lambs. Significant sex differences were also observed in Exp. 2. Ewe lambs had lower final EPG levels, higher preinfection and postinfection Hb levels and higher maximum postinfection cosinophil levels. Breed x sex interactions for these parameters were not significant.

Abomasum↗
PubMed1981

Studies on cross-transmission and pathogenicity of Haemonchus contortus in white-tailed deer, domestic cattle and sheep.

Experiments were conducted to compare the relative pathogenicity and infectivity of deer- and cattle-derived Haemonchus contortus for three hosts, viz., white-tailed deer, cattle and domestic sheep. Parameters evaluated for all animals were: general physical condition, basic hematologic values, fecal egg counts and parasite infectivity rates. Clinical signs attributable to H. contortus infections were not observed in any of the experimental animals. Deer harboring H. contortus burdens greater than 70 worms/kg body weight had decreased packed cell volume, hemoglobin and total serum protein values. Statistical analyses indicated there was not a significant difference (P greater than .05) in infectivity of deer-derived H. contortus in these hosts. No significant difference (P greater than .05) in infectivity for deer was noted between deer-derived H. contortus and cattle-derived H. contortus. Morphometric comparisons of helminths recovered indicated that parasites of deer and cattle origin were both compatible with the description for H. contortus. Results suggest that cross-transmission of H. contortus occurs between deer and domestic livestock.

Animals↗
PubMed1975

The resistance of a field strain of Haemonchus contortus to five benzimidazole anthelmintics in current use.

Using artificially infected sheep, the response of a laboratory strain of Haemonchus contortus, which had not been subjected to anthelmintics for three years, was compared with that exhibited by a parbendazole resistant field strain following treatment with each of seven anthelmintics, the laboratory strain proved fully susceptable to thiabendazole, parbendazole, cambendazole, mebendazole, fenbandazole, levamisole and haloxon, in contrast to the field strain which showed a moderate to marked resistance to all five benzimidazoles, but was fully susceptible to levamisole and haloxon.

Animals↗
PubMed2006

[A new control method for Haemonchus contortus: FAMACHA].

FAMACHA is a method that has been developed against Haemonchus contortus which causes anemia in sheep and goats especially in tropical and subtropical areas. The basic principle of the method is the detection of the color changes in the mucous membrane of the eye that is caused by anemia. According to the FAMACHA Anemia Guide, (FAG), the mucous membranes of the eyes of animals are inspected for color differences at two or three week intervals. The criteria are used for treating the animals. Thus FAG provides practical diagnosis and treatment of animals that are actually affected by H. contortus. Avoiding unnecessary treatment prevents the formation of drug resistance. The method is effective only if it is used with an effective Trichostrongylidae control program. The FAMACHA method can be tested in Turkey where H. contortus is a problem; especially in mild and rainy areas. Furthermore, the method maybe modified for other parasites causing anemia.

Anemia↗
PubMed1991

Concurrent infections with the ruminant nematodes Haemonchus contortus and Trichostrongylus colubriformis in jirds, Meriones unguiculatus, and use of this model for anthelmintic studies.

Haemonchus contortus- and Trichostrongylus colubriformis-infected jirds (Meriones unguiculatus) are useful for anthelmintic studies. With concurrent infections of these parasites established in the jird, questions of not only anthelmintic activity, but to some extent spectrum, could be assessed in a single model system. This report outlines a model using immunosuppressed (0.02% hydrocortisone in feed) jirds concurrently infected with H. contortus and T. colubriformis. Immunosuppressed jirds were inoculated with approximately 1,000 exsheathed infective larvae of each species, treated per os on day 10 postinoculation (PI), and killed on day 13 PI. Stomachs and small intestines were removed, opened longitudinally, incubated in distilled water at 37 C for 5 hr, fixed in formaldehyde solution, and stored for subsequent examination. Contents of both organs were examined using a stereomicroscope (15-45 x). Various standard anthelmintics were 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 comparable to those required for efficacy against these parasites in ruminants. This model, using worms of 2 genera living in distinct sites, allows preliminary evaluation of anthelmintic activity and spectrum for experimental compounds in a single cost- and resource-efficient experiment.

Animals↗
PubMed1990

Effect of Haemonchus contortus infection on the clearance of antipyrine, sulfobromophthalein, chloramphenicol, and sulfathiazole in lambs.

A study was made to determine the effect of Haemonchus contortus parasitic infection in lambs on the clearance of several IV administered drugs. Clearance of sulfobromophthalein or sulfathiazole from the plasma of lambs was unaffected by infection with H contortus. Clearance of antipyrine was enhanced by the infection, and thiabendazole treatment did not alter this effect. Clearance of chloramphenicol (CAP), administered as the succinate ester (CAPS), was not changed by the infection, but it was increased after treatment with thiabendazole. Changes in the mean body residence time and initial plasma concentration of CAPS and CAP after treatment with thiabendazole indicate that hydrolysis of CAPS to CAP was reduced. High concentrations of CAPS apparently enhanced its own elimination directly rather than via the expected sequence involving hydrolysis, glucuronidation, and excretion of CAP-glucuronide. Enhanced clearance of antipyrine following infection of lambs with H contortus can be explained in at least 2 ways. First, it is possible that the lambs did not have mature amounts of hepatic drug metabolizing enzyme activity as reported by other investigators, which may be explained by breed differences or animal husbandry practices. Second, infection of lambs by H contortus may have triggered an inductive response in hepatic cytochrome P-450-mediated activities, which might result via a generalized enhancement in hepatic protein synthesis associated with the physiologic response to replace plasma proteins and other blood components lost through gastrointestinal hemorrhage caused by the active feeding of adult worms. Other phase-II reactions such as acetylation, glucuronidation, and glutathione-S-transferase apparently were not affected.

Animals↗
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↗