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)     

Effects of exogenous progesterone and/or prolactin on Haemonchus contortus infections in ovariectomized ewes

Reproduction can alter the course of ovine nematodiasis; fecal nematode egg concentrations often increase near lambing and throughout lactation, a phenomenon referred to as the periparturient rise. To identify the host mechanisms that might link these disparate events, i.e. lactation and the fecundity of gastrointestinal trichostrongyles, ovariectomized ewes were injected daily with progesterone and/or prolactin, or saline. Progesterone treatment commenced 20 days before inoculation with Haemonchus contortus and prolactin was administered throughout the 30-day infection period. Ovariectomized ewes receiving prolactin during the experimental infection maintained higher daily fecal egg concentrations than the progesterone, progesterone/prolactin, or the control treatment groups. However, ovariectomized ewes that received 20 days of pre-inoculation exposure to progesterone, as well as prolactin during the infection, had greater numbers of nematodes that were larger than the other treatment groups. Thus, the sequential delivery of these hormones that are associated with the reproductive cycle in ewes produced some of the same results that occur during periparturient rise.     

Physiological responses to water restriction in dry and lactating Awassi ewes

The effect of water restriction in Awassi ewes was assessed under two physiological conditions: lactating and dry, over a 3-week-period (August–September, 2002). Eight dry and eight lactating Awassi ewes (with their lambs) were assigned to one of two watering regimes: watered once every three days and daily watering, respectively. Weather data, body weight and rectal temperature were recorded. Venous blood was sampled on the watering day of the water-restricted group, and subjected to haematological, biochemical and electrolytes analysis. Ewes under water restriction lost more weight and had higher packed cell volume, haemoglobin, serum cholesterol, urea, creatinine, total protein and albumin as compared to daily-watered animals. However, lactation seemed to have no significant effect on these serum components. As for blood pH and electrolytes, Na⁺ and Cl⁻ were significantly higher under water restriction; whereas significantly lower K⁺ and Ca⁺⁺ but higher pH and Cl⁻ were observed in lactating animals. Finally, lower cortisol concentrations were observed in water-restricted animals, warranting further studies on the hormonal adaptation to long term water stress. It was concluded that water restriction induces similar changes in blood physiological indicators in dry and lactating Awassi ewes; while lactation beyond the first month post partum seems to mostly affect blood electrolytes.     

Serum and abomasal antibody response of sheep to infections with Haemonchus contortus

Serum and abomasal IgA, IgG and IgM antibody response against adult worm, L3 and egg antigens of Haemonchus contortus was monitored by the ELISA technique after one or two infections with this nematode. Following the first infection, antibody levels in serum did not change materially. After administration of a challenge dose of infective larvae, antibodies of the three immunoglobulin classes in infected animals rose slightly, but this rise appeared later than the fall in the faecal egg counts. In contrast, in abomasal mucosa, IgA anti-larval antibody levels, which did not increase materially after the primary infection, rose rapidly after a transient inhibition when sheep were challenged. A close temporal relationship was observed between the rise in local anti-worm IgA antibodies and the self-cure reaction, but antibody levels fell rapidly after worm diminution. The local antibody response was thus considered to be related to immunity of sheep to H. contortus.     

The interaction of Trypanosoma congolense and Haemonchus contortus infections in trypanotolerant N'Dama cattle.

The interactions between Trypanosoma congolense and Haemonchus contortus infections were studied in N'Dama calves. A total of 38 N'Dama bulls was divided into four groups and each group infected either with H. contortus 1 week after infection with T. congolense or with T. congolense 4 weeks after infection with H. contortus, or with either infection singly. Parasitological (faecal egg counts, parasitaemia), haematological (packed cell volume, white blood cell counts, albumin) and clinical parameters (body weight change, mortality rate) were compared among the various groups. The results showed a reduced prepatent period and a markedly increased pathogenicity of H. contortus infections in animals with a concurrent T. congolense infection. The most harmful combination was a H. contortus infection 1 week after the T. congolense infection which resulted in a progressive and severe anaemia, accompanied by hypoalbuminaemia, increased weight loss and high mortality. The anaemia induced by dual infections showed a low responsiveness to chemotherapy and in several cases supportive treatment did not help recovery. The results also showed that animals with a concurrent T. congolense and H. contortus infection ran a higher risk of succumbing during the infection, and also during 10 weeks following treatment. Although infections with T. congolense alone produced no clinical signs, they were found to significantly reduce the ability of infected animals to mount a normal response to a subsequent H. contortus infection. It was concluded that the increased H. contortus egg excretion observed in animals infected with both parasites might significantly increase the risk of nematode infections and that the reduced prepatent period might necessitate more frequent anthelmintic treatments. These interactions should, therefore, be considered wherever attempts are made to control these two diseases.     

Evaluation of copper supplementation to control Haemonchus contortus infections of sheep in Sweden

A pen study was conducted to assess the effect of providing daily copper mineral supplement, or copper wire particle (COWP) capsules, on established or incoming mixed nematode infections in young sheep. For lambs with established (6 week old) infections, COWP resulted in 97% and 56% reduction of the adult and early L4 stages of H. contortus, respectively, compared with controls (p<0.001). Additionally there was a 74% reduction in Teladorsagia circumcincta infections in the COWP lambs compared with controls (p<0.01). However, no effect was observed when COWP were given at the commencement of a larval dosing period of 6 weeks. There was no significant effect of copper mineral supplement (given at the recommended rate to prevent Cu deficiency) on either established, or developing parasite infections. In addition, a field trial was conducted on a commercial farm to assess the effects of COWP in the management of recurrent H. contortus infections, but lack of parasites during the grazing season prevented an adequate assessment from being made. These results indicate that there is little, if any, benefit from a parasite control standpoint in recommending copper therapy, specifically to control parasites in Swedish sheep flocks.     

Periparturient and seasonal rise in the trichostrongylid egg output of infected ewes during the dry season in Northern Nigeria

The faecal parasite egg output of lambing and non-lambing ewes in two sheep flocks in the dry season of 1975/1976 and 1976/1977 was determined. Ewes wormed at the end of the rainy season showed a very low parasite egg output during the dry season of 1975/ 1976. No periparturient rise of parasite eggs was detectable in the ewes which lambed in December or January. Towards the end of the dry season the parasite egg counts in the faeces increased and the highest counts were observed in lactating ewes.The parasite egg output at the beginning of the dry season was apparently due to recently acquired infections, mainly Trychostronglus sp. The increase in egg output at the end of the dry season was related to the development of inhibited larvae mainly of Haemonchus sp. This development was detectable from the end of February onwards.The differences in parasite egg output during the two seasons was associated with different rainfall patterns during 1975 and 1976.     

Evaluation of ivermectin against experimental infections of Haemonchus contortus and Trichostrongylus colubriformis in goats.

Fourteen nematode parasite-na?ve kids were given a mixed larval inoculum (approximately 17,250 infective larvae) via stomach tube. Twenty-two days after infection, the kids were randomly assigned to control and treatment groups of seven animals each. Mean eggs per gram for control and treatment groups were 4304 and 5315, respectively. Kids in the treatment group were given ivermectin (0.2 mg kg-1) administered by subcutaneous injection. At necropsy, the mean numbers of Haemonchus contortus and Trichostrongylus colubriformis for control and treatment groups were 2259 and 0, and 3033 and 773, respectively. This reduction was significant (P less than 0.05) for both species, resulting in an efficacy of 100.0% and 74.5%, respectively. The lower efficacy against T. colubriformis may be a sign of resistance, a reduced effectiveness due to route of administration, or a higher dose may be required with subcutaneous administration, as has been observed previously.     

The intensity of resistance by mature Merino ewes against Haemonchus contortus and Tichostrongylus colubriformis in single-species and combined-species infection

Three-year-old, non-lactating and non-pregnant Merino ewes, raised on pasture under a program of strategic treatment with anthelmintic and found to be extremely resistant to "trickle" infection with Haemonchus contortus, were given single-dose infections with either H. contortus or Trichostrongylus colubriformis or both species together. The purpose was to ascertain the intensity of protective immunity against the 2 parasites in sheep with immunity acquired from a presumably slight exposure to infection. To provide a criterion, some infected ewes were immunosuppressed with corticosteroid, dexamethasone. Untreated ewes were extremely resistant to challenge infection with either 15,000 or 150,000 H. contortus or 15,000 T. colubriformis. Surprisingly, when mixed infection was given, egg counts for H. contortus were significantly elevated compared with infection by that species alone. Antibody to antigens from infective larval and adult H. contortus was measured in serum by enzyme-linked-immunosorbent assay (ELISA) during the course of infection. Serum titres against larval antigens were significantly depressed when infections with either H. contortus or T. colubriformis were permitted by immunosuppression with dexamethasone, whereas those against adult antigen were depressed when infection with T. colubriformis was permitted.     

The abomasal histology of worm-free sheep given primary and challenge infections of Haemonchus contortus

The histological changes in the abomasal mucosa of pairs of worm-free ewes and lambs were compared at various stages after infection and reinfection with 350 Haemonchus contortus L3 per kg bodyweight. In terms of worm burdens the ewes were relatively resistant to reinfection compared with the lambs and the histological changes in the abomasum at most stages after infection were more marked in the adult animals. These included increases in the numbers of mast cells, globule leucocytes, eosinophils and IgA plasma cells in the mucosa.     

Resistance of St. Croix lambs to Haemonchus contortus in experimentally and naturally acquired infections.

Parasitological and immunological parameters of experimental or naturally acquired infections with Haemonchus contortus were compared in St. Croix and Dorset lambs. In experimental infections, St. Croix lambs developed significantly greater levels of resistance to H. contortus, following primary exposure, as compared with Dorset lambs. This resistance was influenced both by age and by prior exposure to parasites. In grazing experiments on H. contortus-infected pasture, St. Croix lambs shed significantly fewer eggs as early as 5 weeks following initial exposure. Further, St. Croix lambs had more than 99% fewer worms in the abomasum at necropsy compared with age-matched Dorset lambs. Lymphoproliferative assays using peripheral blood mononuclear cells and antigen-specific serological tests demonstrated only minor differences in immune responsiveness between the two breeds despite the dramatic parasitological differences. Similarly, abomasal mucus from both breeds had elevated levels of parasite-specific antibodies and contained substances mediating larval paralysis. In contrast, St. Croix lambs which had become resistant to nematode infection had dramatically higher numbers of globule leukocytes in the abomasal mucosa compared with Dorset lambs.     

The establishment and development of Haemonchus contortus in goats

Twelve goats were inoculated with 40,000 third-stage Haemonchus contortus larvae and two were killed on each of Days 4, 7, 11, 14, 18 and 21 after inoculation (DAI). The number of worms that established, and the site of development were recorded. More worms established in the fundic, than in the middle or pyloric thirds of the abomasum. Early development occurred within the mucosa; emergence into the lumen started between 7 and 11 days after infection. By 4 DAI, all worms had completed the third moult to the L4 stage. At 11 DAI the majority of the worms were adults. A mean of 13.2% of the female worms had eggs in their uteri at 18 DAI; by 21 DAI more than half of the female worms had eggs in their uteri. The development of H. contortus was essentially similar to that described in sheep.     

The effect of oxfendazole terminated infections with Haemonchus contortus on the development of immunity in sheep

The relative contribution of third (L3), fourth (L4) or adult stages of Haemonchus contortus to the development of immunity was evaluated in three groups of sheep subjected to infections terminated by oxfendazole treatments at the L3, L4 or adult stage. A control group did not receive immunising infections. All the groups were challenged with 5000 L3, to evaluate the protection provided by the different protocols. All sheep were necropsied at the end of the experiment to count the abomasal worm burdens. A marked reduction in egg counts after challenge infection was only observed in sheep in which the infection was terminated in the adult stage (Group 4). A significant reduction in worm burden was also observed in Group 4. The immunising infections and/or the challenge infection resulted in moderately elevated IgG antibody levels against L3, L4 and adult somatic antigens in all the groups. In contrast, a strong IgG response against H. contortus excretory/secretory (ES) antigens was observed in the groups in which the immunising infection was terminated in the L4 and the adult stage. An elevated lymphocyte proliferation response against Haemonchus ES antigens was found only in the group that had their immunising infection terminated at the adult stage. The combined data suggest that exposure to and elicited immunological responses to ES antigens are important for the development of immunity against H. contortus.     

Serial passage of Haemonchus contortus in resistant and susceptible sheep

A recently isolated field strain of Haemonchus contortus was passaged through resistant (repeatedly reinfected) and susceptible (immunosuppressed) sheep for six and nine generations, respectively. Infectivity of the resulting serially passaged strains was not significantly different when tested in groups of 1-year-old susceptible sheep.     

捻转血矛线虫Hc-TTR-51蛋白的定位及功能

捻转血矛线虫(Haemonchus contortus)是最重要的家畜寄生虫之一。已报道秀丽隐杆线虫(Caenorhabditis elegans)转甲状腺素蛋白(transthyretin,TTR)参与虫体细胞间的相互作用。目前捻转血矛线虫转甲状腺素蛋白(Hc-TTR-51)的定位及功能尚未见报道。研究首先克隆捻转血矛线虫Hc-ttr-51基因,然后分析其蛋白在捻转血矛线虫、HEK 293T细胞内的定位情况,最后RNA干扰Hc-ttr-51基因分析对秀丽隐杆线虫生长发育的影响,从而对其功能进行预测分析。结果表明,捻转血矛线虫Hc-ttr-51基因在虫体各发育阶段均有表达,与其他发育期虫体相比,L1、L3、雄成虫该基因的转录水平显著上升。在L3期虫体体内该蛋白广泛表达,L4期和成虫体内该蛋白特异性表达于性腺。在HEK 293T细胞中,该蛋白在细胞质中呈明显的点状分布。RNA干扰秀丽隐杆线虫Hc-ttr-51基因表达后,虫体产卵量极显著下降,体长体宽显著缩短,咽泵率显著下降。以上研究为捻转血矛线虫生长发育特性、疫苗研究等提供依据。     

欧洲盘羊捻转血矛线虫感染的诊断及病理学观察

对1只急性死亡的幼年欧洲盘羊进行剖检观察,皱胃内可见大量粉白色线虫,采用形态学及分子生物学相结合的方法对虫体进行鉴定,诊断为捻转血矛线虫;对虫体寄生部位的病理学进行观察,在皱胃黏膜间及黏膜固有层内均可见虫体及虫卵。