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PubMed1999

Nematode burdens and cellular responses in the abomasal mucosa and blood of Florida Native, Rambouillet and crossbreed lambs.

This experiment was carried out to compare the worm burden and cellular responses in the abomasal mucosa and blood of Florida Native and Rambouillet lambs and also in animals produced by crosses of these two breeds (generations F1 and F2). Animals were exposed to infection by gastrointestinal nematodes on three different occasions. The first infection was natural, occurring while they were suckling lambs. After weaning, they were kept indoors for 53 days and then were allowed to graze a contaminated pasture for 50 days for a second natural infection. The third infection was an artificial challenge with 6000 Haemonchus contortus infective larvae. The highest mean fecal egg counts (FEC) values were found in Rambouillet lambs followed in decreasing order by F1, F2 and Florida Native lambs. Throughout the trial, most of the high mean packed cell volumes and plasma protein levels were recorded in the F2 lambs; in contrast, most of the low values were found in the Rambouillet lambs. During the natural infection period, the highest percentages of larvae in the fecal cultures of the lambs were Haemonchus. However, high percentages of Trichostrongylus larvae were found particularly in Florida Native lambs. The mean number of blood eosinophils increased after the artificial challenge, reached a peak 21 days after infection and then declined. The highest and lowest blood eosinophil means were recorded in F2 and Florida Native lambs, respectively. The H. contortus burden was significantly higher in Rambouillet and in F1 lambs than in Florida Native and F2 lambs (p < 0.05), while no significant differences were recorded among eosinophil, mast cell and globule leucocyte counts in the abomasal mucosa (p > 0.05). The highest correlation coefficient recorded at the end of this study was between FEC and worm burden (r = 0.7). These two parameters showed a moderate negative correlation with PCV, plasma protein and mast cell counts in the abomasal mucosa. The results obtained in this study indicate that crossbreeding Florida Native and Rambouillet sheep can be a rapid way to combine and improve the characteristics of these two breeds. The parasitological results were promising, however, more studies will be necessary to verify the impact of crossbreeding in other traits.

Abomasum↗
PubMed1999

Serum antibody response of Castellana sheep to Haemonchus contortus infection and challenge: relationship to abomasal worm burdens.

Primary and secondary serum antibody responses to Haemonchus contortus were studied in Castellana sheep. Ten-month-old sheep were infected (200 L3/kg live weight (lw)) and challenged (400 L3/kg lw) or uninfected and equally challenged with H. contortus. Primary infections induced a partially protective response upon challenge, characterized by higher serum protein levels, longer prepatent periods, lower fecal egg counts, and significant reduction in the establishment rate of the parasite and abomasal adult and L4 worm burdens. The resistant status of the infected and challenged sheep was not clearly related either to the serum specific antibody levels (IgG: IgG1, IgG2; IgM; IgA) estimated by ELISA or to immunodetection patterns in the Western blots.

Abomasum↗
PubMed1999

Further studies on anthelmintic resistance in sheep at an organised farm in arid region of Rajasthan.

Faecal egg count reduction test (FECRT) and in vitro egg hatch assay (EHA) was performed on Indian Karakul (3/4 crosses of Karakul with Malpura, Marwari and Sonadi) transported from arid region campus, Bikaner, where resistance was reported in 1996. FECRT revealed that fenbendazole and levamisole were 100% effective in reducing the egg counts. LC50 value on EHA was 0.074 +/- 0.015 microg thiabendazole ml(-1). The faecal culture examination revealed the presence of Haemonchus contortus only. It was concluded that H. contortus was fully susceptible to both benzimidazole and levamisole.

Animals↗
PubMed1999

The distribution of pepsinogen within the abomasa of cattle and sheep infected with Ostertagia spp. and sheep infected with Haemonchus contortus.

The effect of nematode infections on the production of pepsinogen by ruminants was investigated immunohistochemically and biochemically. Abomasal tissues were collected from parasite-naive cattle and sheep, from sheep infected with predominantly Ostertagia circumcincta, sheep infected experimentally with Haemonchus contortus and cattle infected with Ostertagia ostertagi. Pepsinogen was also assayed biochemically in homogenates of fundic mucosae from sheep infected with predominantly O. circumcincta. Infection with Ostertagia spp. parasites was associated mainly with nodular hyperplasia, resulting in increased numbers of cells that produce both pepsinogen and mucus. Measured biochemically, nodules contained more pepsinogen than adjacent more normal mucosa (p < 0.05), and this effect was largely attributable to the greater mass of nodules. Infection of sheep with H. contortus was associated with generalised hyperplasia, characterised by increased numbers of mucopeptic cells and in at least one animal with reductions in parietal cell numbers. At the same time, the zymogen granule content of chief cells was reduced. Similar changes were occasionally seen in sheep infected predominantly with O. circumcincta. Generalised hyperplasia is likely to be indicative of the presence of ambulatory parasitic stages as opposed to those confined to nodules. The potential for the enhanced production of pepsinogen by increased numbers of cells with a joint mucous cell and zymogenic cell phenotype may offset decreases in the numbers of chief cells or reductions in chief cell activity.

Abomasum↗
PubMed1999

Anthelmintic resistance in sheep and goat farms on Peninsular Malaysia.

The faecal egg count reduction test (FECRT) was conducted on 39 sheep farms and 9 goat farms located in Peninsular Malaysia. The anthelmintic groups used in these tests were the benzimidazoles, levamisole, the benzimidazole/levamisole combination, macrocyclic lactones and closantel. Results indicated that the prevalence of resistance to the benzimidazole group was high, with approximately 50% of the sheep farms and 75% of the goat farms having resistant nematode parasite populations present. Resistance to levamisole, closantel and ivermectin was also detected. Differentiation of the infective larvae derived from faecal cultures indicated that by far the most predominant parasite species was Haemonchus contortus.

Animal Husbandry↗
PubMed1999

Chemo- and thermosensory neurons: structure and function in animal parasitic nematodes.

Nematode parasites of warm-blooded hosts use chemical and thermal signals in host-finding and in the subsequent resumption of development. The free-living nematode Caenorhabditis elegans is a useful model for investigating the chemo- and thermosensory neurons of such parasites, because the functions of its amphidial neurons are well known from laser microbeam ablation studies. The neurons found in the amphidial channel detect aqueous chemoattractants and repellants; the wing cells-flattened amphidial neurons-detect volatile odorants. The finger cells-digitiform amphidial neurons-are the primary thermoreceptors. Two neuron classes, named ADF and ASI, control entry into the environmentally resistant resting and dispersal dauer larval stage, while the paired ASJ neurons control exit from this stage. Skin-penetrating nematode parasites, i.e. the dog hookworm Ancylostoma caninum, and the threadworm, Strongyloides stercoralis, use thermal and chemical signals for host-finding, while the passively ingested sheep stomach worm, Haemonchus contortus, uses environmental signals to position itself for ingestion. Amphidial neurons presumably recognize these signals. In all species, resumption of development, on entering a host, is probably triggered by host signals also perceived by amphidial neurons. In the amphids of the A. caninum infective larva, there are wing- and finger-cell neurons, as well as neurons ending in cilia-like dendritic processes, some of which presumably recognize a sequence of signals that stimulate these larvae to attach to suitable hosts. The functions of these neurons can be postulated, based on the known functions of their homologs in C. elegans. The threadworm, S. stercoralis, has a complex life cycle. After leaving the host, soil-dwelling larvae may develop either to infective larvae (the life-stage equivalent of dauer larvae) or to free-living adults. As with the dauer larva of C. elegans, two neuron classes control this developmental switch. Amphidial neurons control chemotaxis to a skin extract, and a highly modified amphidial neuron, the lamellar cell, appears to be the primary thermoreceptor, in addition to having chemosensory function. The stomach worm, Haemonchus contortus, depends on ingestion by a grazing host. Once ingested, the infective larva is exposed to profound environmental changes in the rumen. These changes stimulate resumption of development in this species. We hypothesize that resumption of development is under the control of the ASJ neuronal pair. Identification of the neurons that control the infective process could provide the basis for entirely new approaches to parasite control involving interference with development at the time and place of initial host-contact.

Ancylostoma↗
PubMed1999

The effects of urea supplementation on production and parasitological responses of sheep infected with Haemonchus contortus and Trichostrongylus colubriformis.

Merino wether lambs were individually confined and fed a basal diet of oaten chaff containing essential minerals which was untreated or contained 3% urea. Within each dietary group animals were orally infected with either 200 H. contortus (H), 1000 T. colubriformis (T) or both species (H + T) thrice weekly or remained uninfected (C). Weight gain, wool production, and parasite burden were measured over a 19-week period. Sheep on the diet containing urea gained more weight, consumed more feed and grew more wool of higher fibre diameter than their counterparts given no urea. On both diets uninfected sheep consumed more feed than infected sheep and the sheep given no urea and infected with both H and T worm species consumed the least feed. Parasitised sheep gained less weight than uninfected control sheep. Sheep with urea in their diet had lower faecal egg counts when infected with H alone or with H and T but there was no effect of urea on egg count of sheep infected with T alone. In contrast, T numbers after slaughter were reduced in sheep fed diets containing urea whereas H numbers were not affected by diet. It was concluded that supplementation with urea can increase resilience to parasitism thereby improving production and also enhance resistance mechanisms against worms in young sheep on low quality roughage diets. These responses can be partly attributed to stimulation of feed intake, presumably due to enhanced ruminal digestion, but also to elevated rumen NH3-N levels which would be expected to have increased rumen microbial protein synthesis and availability to the intestines.

Abomasum↗
PubMed1999

Comparison of naturally acquired parasite burdens among Florida native, Rambouillet and crossbreed ewes.

The response to natural infection by gastrointestinal nematodes was evaluated in three groups of lambing mature ewes: 16 Florida Native; 21 Rambouillet; and 18 1/2 Florida Native x1/2 Rambouillet (F1 generation). Fecal egg counts (FEC), packed cell volume (PCV) and plasma protein levels were determined periodically through a one-year period. The highest FEC was recorded in Rambouillet ewes, with most of the means higher than 1000 eggs per gram (EPG). Florida Native and F1 ewes showed similar trends in FEC, with most of the means below 500 EPG. The highest mean PCV values were recorded in Florida Native ewes, followed in decreasing order by F1 and Rambouillet ewes. F1 ewes showed the lowest plasma protein levels and Florida Natives the highest. Fecal cultures revealed the highest percentages of Haemonchus larvae in Rambouillet ewes (>64%) and the lowest percentages in Florida Native ewes. Florida Native and F1 ewes were more resistant to gastrointestinal nematode infections than were Rambouillet ewes. High negative correlation coefficients between FEC x PCV and FEC x plasma protein levels coincided with peaks in mean FEC of Rambouillet (May and July), Florida Native and F1 ewes (October). This study showed that crossbreeding Rambouillet and Florida Native sheep resulted in the production of F1 ewes resistant against gastrointestinal nematode infections.

Animals↗
PubMed1999

Decreased ivermectin and moxidectin sensitivity in Haemonchus contortus selected with moxidectin over 14 generations.

Ivermectin resistance in the nematode Haemonchus contortus has been reported in many parts of the world and many ivermectin resistant isolates have been found to have reduced sensitivity to moxidectin. However, it is unclear whether parasites that are selected with moxidectin would demonstrate reduced sensitivity to ivermectin. In this study, the effects of moxidectin and ivermectin on an unselected strain and a strain of H. contortus derived from the unselected strain but selected over 14 generations with moxidectin, were compared in jirds. The recovery of adult worms and fourth stage (L4) larvae following treatment were compared between strains and anthelmintics. Moxidectin-selected H. contortus showed reduced sensitivity to ivermectin as well as to moxidectin. Doses of 0.1 mg/kg of moxidectin and 0.4 mg/kg of ivermectin were necessary to obtain an efficacy of 95% or above against the moxidectin-selected strain of H. contortus compared with 0.025 mg/kg for moxidectin and 0.1 mg/kg for ivermectin required for a similar efficacy in the unselected strain.

Animals↗
PubMed1999

Persistent activity of doramectin injectable formulation against experimental challenge with Haemonchus placei in cattle.

Two studies were conducted in North America to evaluate the persistent activity of doramectin injectable formulation against experimental challenge with Haemonchus placei. In both studies, calves were randomly assigned to 1 of 4 treatment groups (n = 10 per group) or a larval viability group (n = 2). Calves were treated subcutaneously in the lateral midline of the neck with saline (1 ml/50 kg) on Day 0, or with doramectin (200 mg/kg = 1 ml/50 kg) on Day 0, 7, or 14. Animals used to assess larval viability did not receive any treatment. Beginning on Day 14 and continuing through Day 28, each of the 40 treated calves were given approximately 300 infective larvae of H. placei per os. The two larval viability animals received approximately 10,000 larvae as a single dose on Day 28. Approximately two weeks later, all animals were slaughtered and the abomasum from each calf processed for nematode recovery. A 2% aliquot of abomasal contents plus wash was examined for enumeration and identification of nematodes. Geometric mean H. placei counts were calculated from the log (H. placei count +1) and used to estimate percentage reduction. Overall, doramectin was > or =96.9% efficacious in reducing infection with H. placei when challenged daily 14-28 days after treatment.

Abomasum↗
PubMed2000

Multiple anthelmintic resistance in a goat herd.

Anthelmintic resistance was monitored over a 30 month period within a goat herd in eastern Virginia, USA. Resistance to ivermectin, levamisole and benzimidazole drugs was detected in Haemonchus contortus using the fecal egg count reduction test (FECRT). When levamisole use was discontinued for 1 year, susceptibility to levamisole appeared to return. Although a single treatment with fenbendazole was able to reduce fecal egg counts by only 50%, two doses administered in a 12 h interval increased efficacy to 92%, however, confidence intervals indicated that resistance was still present. When fecal egg counts were determined the following year after several treatment using this protocol, the efficacy of fenbendazole had fallen again to 57% reduction in fecal egg counts. The predominant genus present in cultured composite fecal samples was Haemonchus. Trichostrongylus, Cooperia and Teladorsagia were also present in smaller numbers.

Administration, Oral↗
PubMed2000

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.

Abomasum↗
PubMed2000

The efficacy of levamisole, and a mixture of oxfendazole and levamisole, against the arrested stages of benzimidazole-resistant Haemonchus contortus and Ostertagia circumcincta in sheep.

Sheep were allowed to graze pasture that had been seeded with benzimidazole-resistant Haemonchus contortus and Ostertagia circumcincta in order to acquire a burden of arrested larvae. Following housing, sheep were dosed orally with either oxfendazole at a dose rate of 4.7 mg/kg (to confirm the benzimidazole-resistant status of the species of nematode), levamisole at a dose rate of 7.5 mg/kg, or an oxfendazole/levamisole mixture at a dose rate of 4.6 mg/kg oxfendazole and 8.1 mg/kg levamisole. The efficacies of the treatments were assessed by estimation of the arrested larval burden in the abomasum of each sheep, either at 10 or 11 days (oxfendazole and oxfendazole/levamisole mixture), or 12 or 13 days (levamisole), after treatment. Compared to the untreated controls, the protection afforded by a single dose of either levamisole or the oxfendazole/levamisole mixture was >99% against the arrested stages of both Haemonchus contortus and Ostertagia circumcincta. Treatment with oxfendazole confirmed the benzimidazole-resistance status of the two species.

Abomasum↗
PubMed2000

Variability of resistance in goats infected with Haemonchus contortus in Brazil.

The variability between and within breeds with respect to nematode egg counts (EPG), packed cell volume (PCV) and hemoglobin (Hb) was studied in 36 yearling female goats of the Caninde (15), Bhuj (6) and Anglo-Nubian (15) breeds, exposed to Haemonchus contortus. Nematode-free goats were turned to a contaminated paddock in late February. From then on, fecal egg per gram counts (EPG), packed cell volume (PCV) and hemoglobin (Hb) were determined at 2-week intervals up to Week 18. The EPG, transformed as [log(EPG + 75)], varied (P < 0.01) between goats within breeds and between weeks of exposure, but not between goat breeds (P > 0.05). PCV and Hb were affected by goat breeds (P < 0.05), by goats within breeds (P < 0.01) and by weeks of exposure (P < 0.01). Anglo-Nubians had higher (P < 0.01) PCV and Hb than Caninde; Bhuj had intermediate values. There were two EPG rises; one between Weeks 6 and 10 and the other between Weeks 14 and 16. The within breed variability was marked during the EPG rise on Week 6, when individual egg counts ranged from 130 to 2500. The EPG rises coincided with drops in Hb. PCV presented a similar trend, though not as marked. Haemonchus was responsible for more than 95% of nematode eggs counted. Considering the goat as experimental unit, the correlation coefficients (r) were: -0.45, P = 0.0064, between log(EPG + 75) and PCV; and -0.53, P = 0.0009, between log(EPG + 75) and Hb. The negative correlation between egg counts and blood values suggested breed differences in PCV and Hb were related to resistance to H. contortus infection and/or to its effects.

Animals↗
PubMed2000

Vaccination of calves with Haemonchus placei intestinal homogenate.

The ability of adult Haemonchus placei intestinal homogenate to confer protection against homologous challenge infection was evaluated. Calves were immunized twice with 100 microg H. placei intestinal protein in 5% dextran-sulfate/PBS (vaccinates) or PBS alone (controls) and were challenged with approximately 3300 infective H. placei larvae. There was no significant difference between groups in the total number of nematodes recovered but significantly fewer (p < 0.001) adult females were recovered from vaccinates. The proportion of fourth-stage larvae in vaccinates was significantly greater (p < or = 0.05) than in controls. Lengths of adult male and female nematodes were significantly shorter (p < 0.001) in vaccinated calves, and the numbers of eggs present in the uteri of female nematodes from vaccinates were significantly decreased (p < 0.001). Counts of nematode eggs per gram of feces (EPG) of vaccinates were significantly less than that for controls on Days 29-49 post-challenge (p < or = 0.05). Vaccinates had significant increases in serum IgG1 and IgG2 log(10) titers (p < or = 0.05) but not in serum IgM. EPG, numbers of females, and size of males and females were negatively correlated with increased mean post-challenge IgG1 and IgG2 titers. Reduction in binding of periodate-treated gut homogenate by immune serum indicated a carbohydrate specific component in the immune response.

Animals↗
PubMed1997

Cortisol as an indicator of severity of parasitic infections of Haemonchus contortus in lambs (Ovis aries).

Two experiments were conducted with lambs to examine the effects of experimental infections of Haemonchus contortus on circulating cortisol levels. In both experiments, naive lambs were divided into three groups based on inoculum doses of 0 (control), 2000 (low dose) and 20,000 (high dose) infective larvae. In experiment 1, the lambs were sampled once daily from day 1 post-inoculation (p.i.) until day 39 p.i. Lambs from the high-dose group had significantly higher sustained levels of cortisol throughout the course of the infection than either the low-dose group or control lambs. In experiment 2, blood was sampled at 30-min intervals for 4 hr on day 21 p.i. The high-dose group also had highest cortisol levels. The consequences of chronic stress and the resultant elevated cortisol concentrations potentially could compromise animal health and animal well-being.

Animals↗
PubMed2002

Anthelmintic activity of preparations derived from Myrsine africana and Rapanea melanophloeos against the nematode parasite, Haemonchus contortus, of sheep.

Myrsine africana L. and Rapanea melanophloeos L. belong to the plant family Myrsinaceae. Various rural communities in Kenya, such as smallholder farmers and pastoralists, use them to treat their livestock. The anthelmintic effects/activities of leaves and fruits of M. africana and fruits of R. melanophloeos were tested in sheep experimentally infected with the nematode parasite Haemonchus contortus. Male lambs were infected with 3000-5000 third stage larvae of H. contortus and treated 28 days after inoculation with concoctions made from leaves or fruits of the plants. No significant reduction in faecal nematode egg counts was observed with any of the concoctions at any of the doses tested. Packed red cell volume decreased and live weight increased at similar rates in treated and control groups, thus there was no significant effect of treatment. The results showed that the tested extracts of the M. africana and R. melanophloeos were not efficacious against H. contortus in sheep.

Animals↗