The effect of phenothiazine treatment on arrested Haemonchus contortus larvae in sheep

An experimental infection of freshly cultured Haemonchus contortus larvae was given to housed, non-pregnant sheep in October. Phenothiazine was administered to all animals shortly after patency, but the egg output remained negative until mid-April indicating that removal of adult worms from the abomasum did not stimulate the resumption of development of arrested larvae. Worm burdens at post mortem suggest that adults were not being expelled to any great degree during the winter from the host, but this information is clouded by the difference in numbers of both adult worms and arrested larvae in sheep of different haemoglobin type. The results suggest that haemoglobin type may also be a factor in arrest of larvae as it is in the resistance of sheep to adult H. contortus.     

Feline gingivitis

AIM: To discover whether cross infection between red deer (Cervus elaphus) and cattle is possible with either a bovine isolate of the cattle lungworm, Dictyocaulus viviparus, or with a cervine isolate of the lungworm, Dictyocaulus eckerti.

METHOD: Twelve cattle and 12 red deer were reared parasitefree from birth. At 3–4 months of age, half of each group (n=6) were experimentally infected with D. viviparus and the other half with D. eckerti. The course of infection was monitored for 34 days, after which the animals were slaughtered and the lungs removed to assess levels of infection.

RESULTS: Faecal larval counts demonstrated that patent Dictyocaulus infections occurred in all groups. At necropsy, adult worms were found in the lungs in all groups except the cattle that were infected with D. eckerti. The largest numbers of adult worms were found in the lungs of the red deer infected with D. eckerti.

CONCLUSION: It was demonstrated that both cattle and red deer could be infected with either D. viviparus or D. eckerti. However, D. eckerti larvae that originated from deer established more successfully in deer and D. viviparus larvae that originated from cattle established more successfully in cattle.     

Predicting resistance of sheep to Haemonchus contortus infections

In vitro cultures of lymphocytes from worm-free sheep responded to larval and adult H. contortus antigens by undergoing blast transformation. The level of response varied considerably between animals but was heritable and positively correlated with resistance to subsequent primary, secondary and trickle infection by the parasite, but not with age of the sheep older than 5 months. Lymphocyte responses to phytohaemagglutinin and H. contortus antigens were not present at birth in lambs but developed during the first 5 months in the absence of infection. The proportion of the infecting dose of larvae which was inhibited at the early fourth stage correlated with age of the sheep and with the increase in lymphocyte response to H. contortus antigens during primary infections with H. contortus. Sheep which were most susceptible to infection had the lowest lymphocyte responses to H. contortus antigens but had the highest rate of weight gain during infection. It is suggested that man has selected the most productive animals at the expense of resistance to H. contortus. The definition of genetically controlled markers on lymphocytes is seen as a means by which disease resistant strains of animals may be selected.     

Resistance dynamics of calves to infection with Trichostrongylus axei

Calves were immunized with 10 000 infective larvae each of Haemonchus contortus, Ostertagia ostertagi, and Trichostrongylus axei and challenged with 100 000 of each species. When compared with nonimmunized controls, the immunized calves had 95% fewer H. contortus, 10% fewer O. ostertagi, and 20% fewer T. axei; the latter two reductions were not significant. In four other experiments single or multiple immunizing inoculations of T. axei followed by challenge at various intervals after immunization failed to result in significant resistance measured by the number of worms of the challenge inoculation that became established, by post-challenge fecal egg count, and by gross pathologic alterations of abomasa at necropsy.     

Morphological changes in trichostrongylid eggs after treatment with fenbendazole

The influence of daily doses of 0.05–0.1 mg fenbendazole/kg body weight on egg development was tested in twenty-seven lambs artificially infected with Haemonchus contortus plus Trichostrongylus colubriformis or Ostertagia circumcincta, as well as in two additional sheep naturally infected with Nematodirus spp.Atypical eggs were detected before a reduction in the number of eggs. Atypical eggs had blastomeres of different sizes and shapes; knot-like, crater-like or bubble-like. In isolated cases eggs with atypical first larvae were recognizable. Morphologically changed eggs occurred in the reproductive organs of female O. circumcincta worms.None, or only a very small number of third stage larvae, could be cultured from the faeces of treated sheep.     

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 1. Patterns of seasonal development

Abstract

AIM: To describe the seasonal pattern of development of third-stage infective larvae (L3) from eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus on pasture in the North Island of New Zealand.

METHODS: Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28–31 days after deposition on 13–18 occasions, between January 2005 and July 2006. Analysis of the number of larvae recovered used a mixed model including number of eggs deposited, weight of faeces recovered (an assumed indicator of earthworm activity), site, contamination date, and position of deposited faeces, i.e. on the surface or buried.

RESULTS: There was a significant effect of contamination date on development of all three species, with maximum numbers ofL3 developing between late spring (November) and early autumn (March), and minimum numbers in June and July. There were large differences between species, with H. contortus exhibiting a long period (April to October) where development was close to zero, whereas T. circumcincta developed to some extent all year round. Development of T. colubriformis was intermediate between the other two species.

Burying faeces containing nematode eggs increased the number of L3 recovered compared with surface deposition (p≤0.001), although there were a small number of exceptions involving only T. colubriformis. The weight of faeces recovered at harvest, which was assumed to be an indication of earthworm activity, was correlated with the number of L3 recovered for all species (p<0.001). In a separate analysis, earthworms were assumed tohave been active if <5 g faeces remained at harvest. Where this occurred, the number of L3 of T. colubriformis and T.circumcincta recovered was reduced by 56% and 58%, respectively (p<0.001).

CONCLUSIONS: A marked seasonal pattern of development was observed for all three species, with the most larvae developing in spring-early autumn and the least in winter. This seasonal pattern was most pronounced in H. contortus and least obvious in T. circumcincta. Burying faeces containing eggs generally resulted in more L3 being recovered, whilst the apparent activity of earthworms resulted in fewer larvae being recovered.     

CRITICAL AND CONTROLLED LABORATORY TRIALS IN SHEEP WITH TETRAMISOLE

Critical and controlled anthelmintic tests were carried out using tetramisole hydrochloride per os against adult and immature gastro-entestinal nematodes of sheep. The drug was highly effective against adult Haemonchus contortus, Ostertagia spp, Trichostrongylus axei, intestinal Trichostrongylus spp, Nematodirus spp, Oesophagostomum columbi-anum and Chabertia ovina, and against 5th stage worms of the two latter species, at 10 mg/kg bodyweight and above. Efficiency against Trichuris ovis ranged from 67 to 100% at 20 mg/kg. A dose rate of 10 mg/kg was 98 to 100% effective against 14-day old H. contortus and T. axei, and against both 7-day and 14-day old intestinal Trichostrongylus spp infections, but a rate of 15 mg/kg was required for high activity against 14-day old Ostertagia spp. Seven-day old infections of H. contortus, T. axei and particularly Ostertagia spp were more resistant, and drug activity was variable at a dose rate of 15 mg/kg. Tetramisole would appear to have good activity against 7-day and 14-day old larvae of O. columbianum at 15 mg/kg in lambs in which the development of this species tended to be retarded.     

Anthelmintic efficacy of hydro-methanolic extracts of Larrea tridentata against larvae of Haemonchus contortus

An in vitro study was conducted to determine the anthelminthic activity of hydro-methanolic extracts of Larrea tridentata on sheathed and exsheathed larvae of Haemonchus contortus. Larvae of the parasite were incubated at 20–25 °C in hydro-methanolic extracts at concentrations of 12.5, 25, 50, 100, and 200 mg/mL for 24, 48, or 72 h. Ivermectin and water were the positive and negative controls, respectively. Total phenolic compounds of leaves of L. tridentata were 97.88?±?10.45 mg/g of dry matter. Other compounds detected in this shrub by HPLC-mass spectrometry were sesamin, galocatechin, peonidin 3-O rutinoside, methyl galangin, epigallocatechin 7-O-glucuronide, and epigalocatechin. Mortality rate of sheathed and exsheathed H. contortus was low (16–34%) with doses ≤?100 mg/mL of the extracts. At 200 mg/ml, the hydro-methanolic extracts of L. tridentata killed 32.1 and 68.4% of sheathed and exsheathed larvae, respectively, regardless of incubation time. The effective concentration of the L. tridentata extract for 50% larvae mortality (EC₅₀) after 24 h of incubation was 36 mg/mL (CI?=?6–94). Microscopic observations revealed damage to the cuticle of this parasite exposed to extracts of L. tridentata. These in vitro results provided evidence that L. tridentata extracts possess anti-Haemonchus contortus properties, particularly during the exsheathed stage of this nematode. It would be necessary to assess the safety of this shrub in vivo and also to carry out in vivo efficacy studies.

     

Seasonal Fluctuations of Nematode Populations in Breeding Ewes and Lambs

The seasonal changes in nematode populations of a flock of sheep in the Montreal area were determined using serial fecal egg counts, fecal culture of larvae and necropsy worm counts. It was found that Ostertagia spp.,Nematodirus spp., Trichostrongylus agei, Trichostrongylus spp. and Chabertia ovina over-wintered on pasture and could initiate patent infections the following spring. The development of populations of H. contortus was typical of that seen with most of the other species and was characterized by the following series of events. In early winter when the study was started with stabled pregnant ewes, most of the populations were immature and the egg counts were low and remained so throughout the entire winter. However, in the spring, following lambing, large numbers of adult worms were seen with a consequent decrease in immatures and a sudden increase in egg counts. When the ewes and lambs were pastured together, the egg counts in ewes dropped consequent to “self-cure”, the “spring-rise” providing the major source of overwhelming infections for lambs with deaths by the end of July. As the season progressed larvae taken in by both ewes and lambs did not mature, and by early fall, most of the worm population consisted of immature forms. It appeared that H. contortus could not have more than two generations in ewes or lambs in a single grazing season.     

Systemic responses to challenge infection withHaemonchus contortus in immune Merino sheep

Some systemic responses to single-dose infection with 10 000Haemonchus contortus infective larvae were examined in sheep already shown to have protective immunity against the parasite. The major haematological finding was a neutrophil leukocytosis that occurred after the infections became patent but not during the pre-patent period. There was no definitive eosinophilia and no discernible change in the erythrocyte parameters. Systemic hyperthermia was not conclusively evident during the pre-patent period. Enzyme-linked-immunosorbent assays (ELISA) were used to measure the secondary anti-helminth antibody response in serum during the pre-patent period when the establishment of patent infection is resisted. These ELISAs employed preparations from adult worms to represent the parasitic stages of the worm, preparations from infective larvae to represent the pre-parasitic stages of the worm, and exsheathing fluid, which is the soluble material obtained whenH. contortus larvae undergo ecdysis and transform from the pre-parasitic to the parasitic phase. Antibody responses to the three preparations differed qualitatively, indicating the presence of three different but perhaps overlapping sets of antigens. The three peaks in antibody against exsheathing fluid may reflect the pulses of antigen delivered to sheep as the parasite undergoes its three moults within the host.Abbreviations ELISA enzyme-linked immunosorbent assay - EDTA ethylene diamine tetraacetate     

Synergistic action of mebendazole and levamisole in the treatment of a benzimidazole-resistant Haemonchus contortus in sheep

One-year old worm free, merino wethers, were each infected with 5000 H. contortus larvae of a strain resistant to mebendazole at a rate of 52 mg/kg body weight of sheep. After 21 days, they were assigned to two trials. The preliminary trial showed that mebendazole and levamisole acted synergistically on the H. contortus infection. In the second trial, sheep were treated with 0.35 mg/kg levamisole (one seventh the minimum effective dose against susceptible worms) or 40 mg/kg mebendazole (40 times the minimum effective dose against susceptible worms). In each case the anthelmintics did not reduce worm burdens, although mebendazole depressed egg production. However, when mebendazole and levamisole, at the above dose rates, were administered simultaneously, total worm counts in sheep were reduced by almost 60%. Similar results were obtained when the levamisole was administered 8 h or 14 h after mebendazole treatment. The implications of these observations for the treatment of benzimidazole-resistant haemonchiasis in sheep are discussed.     

A Preliminary Study on the Anthelmintic Activity of Calotropis procera Latex against Haemonchus contortus Infection in Najdi Sheep

The anthelmintic activity of Calotropis procera latex was investigated in sheep that had been infected with single oral doses of 12 000 infective Haemonchus contortus larvae. Inappetence, dullness, erosive abomasitis, decreased haemoglobin concentration and increased eosinophils were the main features of haemonchosis in the sheep. In the sheep treated with single oral doses of 0.01 ml or 0.02 ml/kg body weight of C. procera latex, egg production was significantly reduced, but not completely suppressed, and fewer adult Haemonchus worms were found in the abomasum. Although the appetite improved, the haemoglobin concentration and serum copper, iron and zinc levels were still reduced after therapy with Calotropis latex. Calotropis latex showed a concentration-dependent larvicidal activity in vitro within 20 min of application.     

Verminous Pneumonia in Adult Dairy Cows in Southern Ontario due to Dictyocaulus viviparus

An outbreak of verminous pneumonia due to Dictyocaulus viviparus in a herd of mature, lactating, dairy cows in southern Ontario is described. The fact that the herd had been closed to new additions for ten years and had never experienced clinical disease due to D. viviparus in the past makes the occurrence of this herd problem difficult to explain. Correlation of fecal Baermann analysis for D. viviparus larvae with the progress of anthelmintic treatment is discussed. It is suggested that certain climatological variations in combination with unique, immunological aspects of D. viviparus infection may have contributed to the development of clinical disease in this herd.     

Use of disophenol for the control ofHaemonchus contortus in sheep in west java,Indonesia

Summary The result of a field trial investiguting the anthelmintic effect of disophenol againstH. contortus in sheep raised under Asian small farming practice is reported. It was clearly shown that a single injection of disophenol suppressed the numbers ofH. contortus to very low levels for periods up to 3 months despite the presence of large populations ofH. contortus infective larvae available on pasture and herbage grasses.

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Uso Del Disofenol Para El Control DeHaemonchus Contortus En Ovejas En El Oeste De Java, Indonesia

Resumen Se describen los resultados de un trabajo de campo, en donde se investigó el efecto anti helmíntico del disofenol contra elH. contortus, en ovejas criadas en minifundios.Se demostró claramente que, una sola inyección de disofenol, redujo sensiblemente el número deH. contortus por períodso de 3 meses, a peser del gran número de larves infectivas presentes en el pasto.

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Le Disophenol Dans La Lutte ContreHaemonchus Contrortus Chez Le Mouton A L'est De Java, En Indonesie

Résumé Les résultats obtenus lors d'essais expérimentaux sur l'effet anthelminthique du Disophenol contreH. contortus chez des moutons élevés suivant les formules des petits élevages asiatiques sont rapportés.Il a été clairement démontré qu'une seule injection de Disophenol ramène le nombre deH. contortus à de très bas niveaux pendant une période de 3 mois en dépit de la présence de nombreuses populations de larves infectieuses deH. contortus présentes dans les pâturages et plantations fourragères.

     

Effect of plant trichomes on the vertical migration of <Emphasis Type="Italic">Haemonchus contortus</Emphasis> infective larvae on five tropical forages

The influence of trichomes on vertical migration and survival of Haemonchus contortus infective larvae (L3) on different forages was investigated. Four different forages showing different distributions of trichomes (Brachiaria brizantha cv. Marandu, Brachiaria brizantha cv. Xaraes, Andropogon gayanus, and Stylosanthes spp.), and one forage species without trichomes (Panicum maximum cv. Tanzania), were used. Forages cut at the post-grazing height were contaminated with faeces containing L3. Samples of different grass strata (0–10, 10–20, >20 cm) and faeces were collected for L3 quantification once per week over four weeks. In all forages studied, the highest L3 recovery occurred seven days after contamination, with the lowest recovery on A. gayanus. In general, larvae were found on all forages’ strata. However, most of the larvae were at the lower stratum. There was no influence of trichomes on migration and survival of H. contortus L3 on the forages.     

Spread of lungworm (Dictyocaulus viviparus) infection by Pilobolus fungi among stabled calves

Pilobolus kleinii spores isolated from cattle faeces were administered daily by the oral route to two donor calves excreting Dictyocaulus viviparus larvae in their faeces.Faeces were collected at daily intervals from the donor calves, and on each day a pooled sample of 500 g was placed outside a pen containing two parasite-free experimental calves. A wire screen prevented the experimental calves from coming into contact with the artificially deposited faecal portions.Pilobolus kleinii fruit bodies were observed on the faecal surface in large numbers 5–10 days after deposition.Sporangial discharge was observed to be directed against a window which served as the only light source. Sporangia were found up to 110 cm away from the faeces, and it was estimated that at least 29% of them had been transmitted to a feeding trough placed close to the wire screen. Infective D. viviparus larvae were observed on some of the discharged sporangia.The experimental calves started excreting low numbers of D. viviparus larvae in their faeces 40–49 days after the first portions were deposited. These results indicate that P. kleinii was reponsible for the infection of the experimental calves with D. viviparus, through the discharge of sporangia carrying infective lungworm larvae.     

Effect of selenium and vitamin E on oxidative stress in lambs experimentally infected with <Emphasis Type="Italic">Haemonchus contortus</Emphasis>

The objective of this study was to evaluate oxidative stress in lambs experimentally infected with Haemonchus contortus and supplemented with selenium and vitamin E. Twenty male Corriedale lambs were divided into four experimental groups with five animals each: G1 consisted of animals infected and supplemented with 0.2 mg/kg of live weight (LW) sodium selenite by intramuscular injection (IM); G2 consisted of animals infected with larvae and supplemented with 0.2 mg/kg LW sodium selenite IM and 2000 IU per animal of Vitamin E IM; G3 consisted of animals infected with larvae and supplemented with 2000 IU per animal of Vitamin E IM; and G4 consisted of animals infected with larvae. The animals were infected orally with 500 H. contortus larvae (L3) every 48 hours for 20 days. For biochemical analyses and eggs per grams of feces (EPG) evaluation, blood and feces were both collected at zero (T0), 20 (T1), 40 (T2) and 60 (T3) days. The weight of the animals was also measured at these times. Lower TBARS values were observed in the supplemented animals compared to the control group. The groups supplemented with Selenium exhibited blood GSH-Px activity higher than that of non-supplemented animals. Supplementation with selenium provided greater antioxidant protection against oxidative stress generated from experimental infection of lambs with H. contortus.     

Selective and on-demand drenching of lambs: Impact on parasite populations and performance of lambs

AIM: To determine whether drenching regimes for lambs by which a proportion (10%) of the heaviest animals was selectively left untreated, or animals are only drenched ‘on demand’ when faecal nematode egg counts (FEC) exceeded a threshold level, would result in measurable increases in parasite larval challenge in the autumn and/or decreases in the performance of lambs.

METHODS: A replicated study compared three drenching strategies in which mobs of lambs (n=360 in total) received either: a five-drench preventive programme, administered to all animals (Treatment 1); a five-drench preventive programme, but the 10% heaviest animals left untreated each time (Treatment 2); or drench treatments administered only when FEC exceeded 500 eggs per gram of faeces (epg) (Treatment 3). After the five-drench programme, animals in Treatments 1 and 2 were treated according to FEC as for Treatment 3. A triple-combination drench containing ivermectin, oxfendazole and levamisole, administered orally, was used for all treatments. There were nine farmlets, allowing three replicates of each treatment, in a completely randomised design. Parasite infestations on pasture were measured in autumn by pasture plucks, and worm burdens were monitored in tracer lambs, while the performance of lambs was assessed by liveweight gains, fleece weights, and body condition and dag scores.

RESULTS: Increased numbers of Haemonchus contortus and Trichostrongylus colubriformis larvae on pasture were found in the autumn on farmlets treating selectively or on-demand (Treatments 2 and 3). No differences were detected in other parasite species. Mean liveweight gains did not differ between treatments but some differences were detected between drenched and undrenched lambs in Treatment 2. Mean body condition and mean dag scores of lambs in Treatment 3 tended to be lower and higher, respectively, than those of lambs in Treatment 1; Treatment 2 was generally intermediate.

CONCLUSIONS: Drenching strategies for lambs designed to slow the development of anthelmintic resistance, by increasing the pool of susceptible worms available to dilute resistant survivors after treatment, resulted in increased numbers of H. contortus and T. colubriformis but not other species of parasite on pasture. The increased parasite challenge to lambs in the autumn was associated with small production losses, which may be acceptable to farmers wishing to implement such strategies. It is clear that further work is required on the interaction between management practices and the population dynamics of parasites, especially with regard to creating pools of susceptible genotypes to slow the development of drench resistance.     

The therapeutic efficacy and prophylactic activity of doramectin against Dictyocaulus viviparus in cattle

SUMMARY Three groups of 8, 4-month-old male Jersey or Jersey-cross calves were infected with 2400 Dictyocaulus viviparus L₃ larvae and either left untreated or injected subcutaneously with 200 μg/kg doramectin 5 or 25 days after infection (DAI). Lungworms were found in all untreated cattle (geometric mean = 49) at necropsy 39 or 40 DAI. None was found in any of the treated cattle. In a second experiment, groups of 6, 8-month-old calves were untreated or injected with 200 μg/kg doramectin 28, 21 or 14 days before each calf was challenged with 2700 D viviparus larvae. Lungworms were recovered at necropsy 32 to 34 DAI. The geometric mean worm burden in the untreated cattle was 550. This was reduced by 100%, 99.5% and 94.1% in calves treated with doramectin 14, 21 or 28 days, respectively, before infection. It was concluded that doramectin is a highly effective anthelmintic against D viviparus adult or L₄ infections of cattle, and that reinfection of treated cattle will be significantly reduced for at least 28 days after treatment.