Evaluation of the clinical impact of endoscopic ultrasonography in gastrointestinal disease

A total of 120 gastro-intestinal tracts and 960 faecal samples were examined to assess the prevalence and seasonal changes in the gastro-intestinal helminth parasites of Red Sokoto (maradi) goats slaughtered at Ibadan between May 1991 and April 1992. Egg types of strongyles, Strongyloides, Trichuris, Skrjabinema, Dicrocoelium and Moniezia were encountered in 93%, 83%, 44%, 0.9%, 2.3% and 31% of the faecal samples respectively. However, only strongyle, Strongyloides and Trichuris eggs occurred in large numbers and were more common during the rainy season than in the dry season. The parasites recorded and their prevalences were Haemonchus contortus (90.0%), H. ovis (5.0%), Strongyloides papillosus (80.8%), Trichostrongylus colubriformis (78.3%), T. axei (69.2%), Trichuris ovis (72.5%), T. globulosa (38.3%), Oesophagostomum columbianum (67.5%), Cooperia curticei (58.3%) Gaigeria pachyscelis (40.8%), Skrjabinema ovis (5.0%), Nematodirus battus (5.8%), Moniezia expansa (29.2%), M. benedeni (10.0%), Paramphistomum spp. (5.0%) and Cysticercus tenuicollis (33.3%). Haemonchus ovis is reported for the first time in Nigeria. Mixed infections were most prevalent. Young goats were more commonly infected and had higher worm counts than adult goats. Only Haemonchus, Trichostrongylus, Strongyloides and Cooperia spp. occurred in large numbers. Irrespective of the age of the goats, higher worm counts were generally encountered during the rainy season than in the dry season. The results are discussed in relation to the control of helminthiasis in grazing animals in Nigeria.     

Efficacy of an ivermectin controlled-release capsule against nematode and arthropod endoparasites in sheep

Five controlled trials were conducted in Germany or in the United Kingdom, using 74 female sheep of merino or Dorset horn breeds, to evaluate the efficacy of an ivermectin controlled-release capsule against naturally acquired or induced infections of gastrointestinal nematodes, lungworms and nasal bot larvae and against incoming infections with gastrointestinal and pulmonary nematodes. Half of the animals were treated with one ivermectin controlled-release capsule that delivered ivermectin at the rate of 1.6 mg per day for 100 days while the other half remained untreated. Parasites were counted 21, 28, 35 or 56 days after administration of the capsule. The treatment was highly effective (> or = 99 per cent) against established parasites of the following species: Haemonchus contortus (adults and fourth-stage larvae), Ostertagia circumcincta, O pinnata, O trifurcata, Ostertagia species fourth-stage larvae, Trichostrongylus axei, T colubriformis, T vitrinus, Cooperia curticei, Nematodirus battus, N filicollis, Strongyloides papillosus, Chabertia ovina, Oesophagostomum venulosum, Trichuris ovis, Tr skrjabini, Dictyocaulus filaria, Protostrongylus rufescens and Oestrus ovis (larvae). The treatment prevented the establishment of the gastrointestinal nematodes H contortus, O circumcincta, T axei, T colubriformis, C curticei, N battus, N filicollis, Ch ovina, Oe vennulosum and the establishment of the lungworm D filaria by > 99 per cent compared with untreated controls (P < or = 0.01).     

Efficacy of albendazole against gastrointestinal nematodes of cattle

Forty-five calves with artificial and pasture-acquired nematode infections were medicated with albendazole at dose levels of 0, 2.5, 5.0, or 10 mg/kg of body weight. A dose level of 2.5 mg/kg removed at least 99% of adult Trichostrongylus axei, Trichostrongylus colubriformis, Cooperia oncophora, and Bunostomum phlebotomum. Burdens of Haemonchus contortus, Strongyloides papillosus, and Ostertagia ostertagi were reduced 79, 88, and 97%, respectively. At a dose level of 5.0 mg/kg, at least 95% of all adult nematodes were removed; at 10 mg/kg, at least 97% were removed. At least 99% of 4th-stage larvae of O ostertagi, T axei, C oncophora and T colubriformis and 96% of H contortus were expelled at a dose level of 2.5 mg/kg. At 5.0 and 10 mg/kg, 99 to 100% of all species of larvae were removed. Trichuris spp adults were slightly susceptible at all dose levels; larvae were susceptible (83%) only at 10 mg/kg.     

Helminth species of goats in Germany

The helminth fauna of the gastrointestinal tract of 25 and the respiratory organs and the livers of 6 German goats was qualitatively and quantitatively examined. One trematode species (Dicrocoelium dendriticum), 2 species of cestodes (Moniezia expansa and metacestodes of Taenia hydatigena) and 28 species of nematodes (24 in the gastrointestinal tract and 4 in the lungs) were recorded. Two goats were infested with Oestrus ovis larvae. The most prevalent species were Ostertagia circumcincta and Chabertia ovina (84% each), Ostertagia trifurcata and Oesophagostomum venulosum (76% each), Ostertagia pinnata and Trichostrongylus colubriformis (64% each), Trichuris ovis (60%) and Skrjabinema ovis and Trichuris globulosa (56% each). The highest mean worm counts were seen in goats infected with Skjabinema ovis (4003), Ostertagia circumcincta (2501), Trichostrongylus axei (1825), Trichostrongylus colubriformis (1578) and Nematodirus battus (1050). Totally, the goats did harbour more nematodes in the abomasum (3734) than in the small intestine (1707) or the large intestine (2343). The lungs were parasitized by Cystocaulus ocreatus, Muellerius capillaris, Neostrongylus linearis and Protostrongylus rufescens.     

Seasonal pattern of inhibition of Ostertagia ostertagi in calves in northeast Mississippi

The composition of, and seasonal changes in, populations of gastrointestinal parasites of calves in northeast Mississippi were determined for 10 months post-weaning. After weaning on 15 October, 20 mixed breed beef steers were grazed together on a 4 ha fescue/bermudagrass pasture. From November through August of the following year, two of the calves were removed each month for necropsy and counting of gastrointestinal nematodes. Eight species of worms were found: Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, Bunostomum phlebotomum, Cooperia spp., Trichostrongylus colubriformis, Oesophagostomum spp., and Trichuris ovis. During all months, Ostertagia ostertagi and Cooperia spp. combined comprised at least 89% of gastrointestinal nematode burdens. Cooperia spp. represented 92.6% of the total worm burden of calves in November but declined to about 56% in January and February. From March through August, Ostertagia ostertagi comprised at least 79% of the worms from calves. Numbers of inhibited Ostertagia ostertagi increased markedly from February to March and remained at high levels prior to resumption of development in August. The proportion of Trichostrongylus axei remained about 4% throughout the year, but the highest numbers were recorded in the summer months. Other species were minor components of the worm population. These data indicate that with respect to Ostertagia ostertagi, northeast Mississippi can be considered a summer inhibition zone.     

Epidemiology of gastro-intestinal nematodes of sheep in wet tropical conditions in Malaysia

A study on the seasonal variations in the population structure of Haemonchus contortus and Trichostronglyus colubriformis was conducted for a period of 12 months in a typical large scale sheep farm on improved pasture in Peninsular Malaysia which has a wet tropical climate. Successive groups of helminth-free tracer lambs were grazed for 4 weeks together with naturally infected sheep and were necropised for worm counts 2 weeks after their removal from the pasture. The monthly populations of H. contortus fluctuated slightly except in May and August during which more worms were found in the tracer animals. The numbers of T. colubriformis were comparatively high from October to December 1992 and again in March 1993, low during April and June 1992. Small numbers of hypobiotic larvae of H. contortus were detected in the tracer animals. Development and survival of infective larvae of H. contortus and T. colubriformis on pasture were investigated by spreading faeces containing eggs on grass plots in October 1993, February and May 1994. Development of the eggs to the infective larvae occurred within one week and their survival times were 7 weeks in the 3 experiments. The potential for control by rotational grazing is discussed.     

Depression in Parkinson''s disease. Pharmacological characteristics and treatment

An eight-year study was conducted to define the epidemiology of gastrointestinal nematode infection in Suffolk and Gulf Coast Native (Native) breeds of sheep, and to determine if the Native sheep is more resistant to infection. For the initial three years, each breed grazed separate pastures where anthelmintic treatments were administered to individual animals on a salvage basis. For the last five years, both breeds grazed concurrently; anthelmintic treatments were administered to individual animals on a salvage basis for the first three years, and to all animals, when treatment criteria were met, for the last two years. The fecal egg count (FEC) and blood packed cell volume (PCV) were monitored, and tracer lamb nematode burdens were determined. Overall, FEC for both breeds increased in the spring (periparturient rise) for most years and in the summer for all years. Under separate grazing conditions, Native ewes and lambs had consistently lower infection levels than Suffolk ewes and lambs. During the haemonchosis season (June-September) each year, Suffolk ewe and lamb PCV decreased, and Native ewe and lamb PCV remained relatively stable. The salvage treatment protocol resulted in 27 treatments for Suffolk and one for Native ewes; similarly for lambs, 13 for Suffolk and zero for Native. Tracer lambs grazed with their respective breed, and the FEC and mean total nematode burden corresponded with the pattern of infection for their respective breed. The predominant nematodes found in Suffolk and Native tracer lambs were Haemonchus contortus and Trichostrongylus spp., respectively. Under concurrent grazing conditions, the same seasonal repeatable pattern of infection was present and was exhibited by both breeds, with the Native ewes and lambs being consistently and significantly (p < or = 0.05) lower for FEC and higher for PCV. The salvage treatment protocol resulted in 57 and zero treatments for Suffolk and Native ewes, respectively; for lambs, 46 and 11. Tracer lamb nematode burdens again corresponded to their respective breed pattern of infection, with H. contortus and Trichostrongylus spp. being predominant in Suffolk and Native lambs, respectively. Data from all tracer lambs showed a relatively low level of hypobiosis (H. contortus only), and, although there was no consistent hypobiosis season, the tendency was for a higher level to occur in the fall. These results showed that the classic repeatable seasonal pattern of gastrointestinal nematode infection occurred in both breeds of sheep, and that Native sheep were more resistant to infection (specifically H. contortus) than Suffolk sheep.     

The subgenus Persicargas (Ixodoidea: Argasidae: Argas). 26. Argas (P.) arboreus: effect of photoperiod on diapause induction and termination

The anthelmintic efficacy of fenbendazole (methyl 5-(phenylthio)-2-benzimidazole carbamate) was tested in sheep against standardised strains of Hcaemonchus contortus and Trichostrongylus colubriformis, known to be resistant to thiabendazole (LD90 for thiabendazole against H ontortus was 200 mg/kg bodyweight and against T colubriformis was 150 mg/kg). Fenbendazole at dose rates of 5, 10 and 20 mg/kg per os reduced total worm counts in H contortus infected sheep by 66, 90 and 100 per cent respectively, with similar reductions recorded for worm egg outputs. For the thiabendazole resistant strain of T colubriformis, fenbendazole reduced total worm counts in infected sheep by 4, 44 (40-48), 79 (75-83), 96 and 100 per cent at dose rates of 5, 10, 20, 40 and 80 mg/kg per os. Significant suppression of worm-egg production by thiabendazole resistant T colubriformis was obtained with fenbendazole at dose levels of 5 mg/kg and above. The implications of these results are discussed in the light of the increasing occurrence of strains of trichostrongylid nematodes resistant to currently available benzimidazole anthelmintics.     

Some aspects of inhibited development of trichostrongylids in ruminants

Inhibited development is an important aspect of the biology of some gastrointestinal nematodes of ruminants, particularly species of the subfamily Ostertagiinae and Haemonchus spp. There is a seasonality in the occurrence of the phenomenon. It tends to occur predominantly during the unfavourable season for the free-living stages. Thus 'winter' and 'summer-dry season' patterns of inhibition can be observed. Furthermore, the phenomenon is influenced by immunity of the host and by management factors. Different studies show conflicting results on the phenomenon of inhibition. This is examplified by studies related to H. contortus in small ruminants. Other studies indicate that large differences in propensity for inhibition can indeed occur in a single region. However, it has to be stressed that inadequate necropsy techniques can easily result in underestimation of the proportion of inhibited larvae, particularly in Haemonchus spp. in cattle. The macrocyclic lactones are highly effective against inhibited larvae of gastrointestinal nematodes. Treatment may even prevent establishment of inhibited larvae of Ostertagia and Trichostrongylus axei up to 1 month after treatment. The efficacy of benzimidazoles seems to be lower in the middle of the 'inhibition' period than at the beginning or the end. Some studies indicated that the presence of inhibited stages may be important for the build up of immunity. However, removal of high inhibited O. ostertagi burdens at housing does not impair development of immunity. Very little progress has been made on the molecular mechanisms of inhibited development.     

Systematics of gastrointestinal nematodes of domestic ruminants: advances between 1992 and 1995 and proposals for future research

The systematics of trichostrongyloid nematodes of ruminants provides a foundation for diagnostics and responds to the need to identify eggs in feces, free-living larvae from pastures or fecal cultures and larval or adult nematodes collected from hosts. These needs are associated with diagnostic problems or research projects. Difficulties in identifying all developmental stages of trichostrongyloid nematodes of domestic ruminants still severely limit the effective diagnosis and control of these parasites. Phylogenetic hypotheses as the basis for predictive classifications have been developed only for the subfamilies of the Trichostrongylidae. This report briefly describes recent progress in the development of improved tools for identification, phylogenetic analyses and predictive classifications. It also describes future research needed on the identification and classification of trichostrongyloid nematode parasites of domestic ruminants. Nematodes included are species of the super-family Trichostrongyloidea known to be important pathogens of domestic ruminants. The information summarized is presented by nematode developmental stage and by taxonomic groups. Eggs: While eggs of some trichostrongyloid nematode parasites of ruminants can be readily identified to their genus (Nematodirus), and some to species (e.g. Nematodirus battus), most of the important pathogens (including the Ostertagiinae and Haemonchinae) cannot be identified morphologically or morphometrically even to family level. However, DNA technology has been developed for determining not only the presence of specific pathogens in eggs from fecal samples, but also for estimating the percentage of the total eggs that each pathogen comprises. This new method will make possible a rapid determination of which individual animals in a herd should be treated. Larvae: The most commonly-used method for identifying infective larvae is time-consuming (several weeks), unreliable for estimating intensities of individual species as components of mixed populations and requires highly trained specialists. Available identification keys for larvae are not well illustrated and need to be augmented. Adults: Recent advances in the identification of adult trichostrongyloids and their systematics are organized by taxonomic group. Genera included are Ostertagia, Haemonchus, Cooperia, Trichostrongylus and Nematodirus. Recently, the first phylogenetic analysis of the Trichostrongylidae family established monophyly for the family. A similar analysis of the Molineidae is needed. Ostertagia: Several studies of polymorphism summarized the phenomenon and listed 19 polymorphic species in five genera. Two studies of DNA differences within and among polymorphic species of Ostertagiinae supported earlier hypotheses that the species pairs represent polymorphic species. A phylogenetic analysis of the Ostertagiinae and generic concepts are needed. Haemonchus: A key to three species of Haemonchus provides, for the first time, morphological characteristics for the microscopical identification to species of individual adult nematodes of either sex. The Food and Drug Administration is now requiring that results of drug trials include identification of Haemonchus to species. Cooperia: Studies using random amplified polymorphic DNA methods showed a high degree of variation within and among C. oncophora/C. surnabada, but supported a polymorphic relationship for the species pair. A phylogenetic analysis of the Cooperiinae is needed. Trichostrongylus: Restriction Fragment Length Polymorphisms (RFLPs) of genomic DNA of two strains of T. colubriformis indicated a high degree of intra- and inter-strain DNA polymorphism. However, other studies demonstrated expected species level differences between T. colubriformis and T. vitrinus using Random Amplified Polymorphic DNA (RAPD) methods. Sequences of the second Internal Transcribed Spacer Region (ITS-2) ribosomal repeat showed sequence differences of 1.3-7.6% among five     

Efficacy of oxibendazole against adult and larval nematodes of cattle

Calves which were artificially infected with Haemonchus, Ostertagia, Trichostrongylus, Cooperia, and Oesophagostomum but which were also carrying natural infections of Nematodirus and Trichuris were treated with 15.0 mg of oxibendazole (methyl-5-n-propoxy-2-benzimidazole-carbamate)/kg of body weight at 3 days, 7 days, and 42 days after exposure to the infective trichostrongylid and strongylid larvae. Efficacies against adult populations of these genera treated on day 42, except Trichostrongylus, exceeded 98%. The chemical was highly effective against immature nematodes of the genera, except Oesophagostomum (0%). Data were not obtained on Trichostrongylus. The oxibendazole premix was palatable, and toxicosis due to the chemical was not seen in these calves.     

Intestinal nematodes of white-tailed deer in southeastern United States

The small intestine, large intestine, and cecum of 975 white-tailed deer (Odocoileus virginianus) from 83 localities in 13 southeastern states were examined for nematodes. In order of prevalence, the following parasites were found: Capillaria bovis, Eucyathostomum webbi, Monodontus louisianensis, Nematodirus odocoilei, Oesophagostomum venulosum, Trichuris sp, Cooperia punctata, Trichostrongylus longispicularis, Strongyloides sp, Cooperia oncophora, Cooperia spatulata, Cooperia sp, and Trichostrongylus calcaratus. Over one-half of the deer examined were free of intestinal nematodes, and most infected deer harbored few parasites. Of the most prevalent species, C bovis, N odocoilei, O venulosum, and Trichuris sp were widely distributed, whereas M louisianensis and E webbi were restricted in distribution. Severe pathogenicity was associated with only heavy Strongyloides sp infections in 2 penned deer. The findings of this study suggested that white-tailed deer of the Southeast are insignificant in the epizootiology of important intestinal nematodes of domestic livestock.     

Avermectin/milbemycin resistance in trichostrongyloid nematodes

Resistance to levamisole and the benzimidazoles appears to be achieved by one or, at most, two mechanisms in the common trichostrongyloid parasites of sheep. For the avermectin/milbemycin anthelmintic class the picture is more complex. In-vitro assays employing the free-living stages of trichostrongyloid nematodes were used to investigate structure-activity relationships for the avermectins/milbemycins. While avermectin/milbemycin-susceptible isolates of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta were found to differ in their intrinsic sensitivities to avermectin/milbemycin inhibition of larval development and L3 motility, structure-activity profiles against all three species were similar. In-vivo avermectin/milbemycin resistance was associated with a reduced sensitivity to avermectin/milbemycin inhibition of larval motility and/or development in some, but not all, isolates. Where a reduced sensitivity to avermectin/milbemycin inhibition of larval development was observed, different groups of resistant isolates displayed different structure-activity profiles. Many avermectin/milbemycin-resistant isolates showed an increased sensitivity to paraherquamide. These in-vitro data have allowed the classification of avermectin/milbemycin-resistant isolates into a number of distinct types. Study of the inheritance of avermectin/milbemycin resistance in two resistance types suggests that the in-vitro differences between resistant isolates reflect important differences in the mechanism of resistance present. The kinetics of expulsion of H. contortus, T. colubriformis and O. circumcincta from sheep following treatment with ivermectin indicate that, in vivo, the critical action of avermectins/milbemycin against O. circumcincta may be different to that which results in H. contortus and T. colubriformis elimination. This observation provides some explanation for the differences between resistant isolates. If, for different species, the critical event(s) leading to expulsion are different, then it follows that the mechanisms of resistance observed may also differ.     

Urinary deoxypyridinoline is a useful biochemical bone marker for the management of postmenopausal osteoporosis

Fecal nematode egg counts and serum pepsinogen concentrations of cattle were determined in six Provinces of the northern (Chiangrai and Lampang), north-eastern (Khonkaen, Mahasarakham and Nakhonratchasima) and eastern (Chonburi) parts of Thailand in the dry season. Nematode eggs were detected in 82% of animals examined. Serum pepsinogen concentrations ranged from 78 to 2,951 (mean 934) mU tyrosine. Animals in Chonburi Province had higher mean values for both egg counts and serum pepsinogen concentrations than animals in the other Provinces. Two calves in Khonkaen and Mahasarakham Provinces were found to be heavily infected with Strongyloides papillosus, with 10,840 and 9,593 eggs/g feces. The source and route of S. papillosus infections remained unknown.     

Evaluation of olfactory and auditory system effects of the antihyperthyroid drug carbimazole in the Long-Evans rat

Groups of lambs either with or without controlled-release albendazole (ABZ) capsules (CRCs) were challenged twice weekly for 6 weeks with either drug-susceptible or drug-resistant Ostertagia circumcincta and Trichostrongylus colubriformis. Groups with and without CRCs remained unchallenged as controls. There was minimal establishment of drug-susceptible parasites of either species in those lambs with CRCs. However, drug-resistant parasites of both species established adult worm burdens in the presence of the capsules. The humoral immune response, as measured by the serum antilarval (L3) antibody (Ab) titre, was pooled for weeks 4-6 and compared for each group. With the exception of anti-T. colubriformis Ab in group 2, anti-L3 Ab titres were significantly higher in all the parasite-challenged groups as compared to the control animals. Also, with the exception of anti-resistant O. circumcincta Ab levels in the CRC-treated animals (group 5), no significant difference was observed in Ab titres between the four groups challenged with either resistant or susceptible larvae. The results demonstrate the inability of CRCs to prevent establishment of drug-resistant parasites and that immune stimulation is not inhibited by the capsules.     

Cryopreservation of the first-stage larvae of trichostrongylid nematode parasites

First stage (L1) larvae of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia circumcincta can be cryopreserved in the presence of DMSO using a two-step freezing protocol involving an initial period at -80 degrees C prior to transfer to liquid nitrogen. Thawed L1 larvae continue development in vitro producing third stage (L3) larvae that are infective to sheep when dosed per os. Establishment rates for L3 larvae grown from thawed L1 larvae were 40 and 80% for H. contortus and T. colubriformis, respectively. There was no difference in survival or infectivity between benzimidazole (BZ)-susceptible and BZ-resistant H. contortus isolates and cryopreservation caused no shift in their BZ-resistance status as indicated in an in vitro larval development assay. Cryopreservation also had no effect on the sensitivity of these isolates to the avermectins or levamisole in vitro. High survival rates (60-70%), good levels of establishment and the stability of anthelmintic resistance status of isolates indicate that little if any selection occurs during the cryopreservation process. L1 larvae of all 3 species have been successfully recovered after 16 months storage in liquid nitrogen, cultured to the L3 stage and established in sheep.     

Trends and international comparisons in infertility in circumpolar areas

A study was carried out at the International Livestock Research Institute (ILRI) Debre Berhan Research Station in Ethiopia from 1992 to 1995 to compare the peri-parturient rise (PPR) in faecal nematode egg counts (FEC) in ewes of two indigenous sheep breeds. A total of 1439 Menz and 1347 Horro ewes were single sire mated following oestrus synchronization to lamb in the wet and dry season. Three ewe treatment groups were constituted as mated/lactating/undrenched; mated/lactating/drenched; unmated/undrenched for three wet and three dry lambing seasons. All ewes grazed naturally contaminated pasture. Levels of faecal egg output were monitored at mating, 3 months after mating, 2 weeks before lambing, 4, 8 and 12 weeks post-lambing. A significant PPR in FEC occurred 2 weeks before lambing and peaked at 4 weeks post-parturition in ewes lambing just before the beginning of the dry season (October/November). There was no significant increase in FEC when lambing occurred before the onset of the long rainy season (May/June). The PPR in this study was associated with both lactation and seasonal availability of third-stage infective larvae on pasture. There was no consistent breed difference in FEC during the six sampling periods from mating to weaning. Faecal cultures and worm counts from both breeds confirmed the presence of Longistrongylus (Pseudomarshallagia) elongata, Trichostrongylus spp.and Haemonchus contortus. The role of the peri-parturient rise of FEC in ewes in gastrointestinal nematode transmission is discussed.     

Interleukin 4 (IL-4) blocks the IL-2-induced increased in natural killer activity and DNA synthesis of decidual CD16-CD56bright NK cells by inhibiting expression of the IL-2 receptor alpha, beta, and gamma

The complement of beta-tubulin alleles in Trichostrongylus colubriformis populations was examined and found to undergo changes similar to those previously reported for Haemonchus contortus following selection for benzimidazole (BZ) resistance. Genomic DNA from BZ-resistant and -susceptible strains was probed with a series of overlapping fragments derived from a T. colubriformis beta-tubulin gene. A susceptible population showed a high level of polymorphism (detected as RFLPs with several enzymes and directly by sequence analysis) at a locus, tcb-1, which appears to be the homologue of the gru-1 locus in H. contortus. This polymorphism disappeared following selection for BZ resistance, leaving a single tcb-1 allele in the resistant population. The same single allele was present in 2 additional, unrelated resistant populations. These data support the hypotheses that tcb-1 and gru-1 are major determinants of BZ susceptibility and hence a major target of BZ-resistance selection.     

Activity of morantel citrate against strains of benzimidazole-resistant nematodes of sheep in the United Kingdom

The activity of morantel citrate (5.94 mg/kg base) was determined in laboratory tests against field isolates of benzimidazole-resistant nematodes. Its efficacies against adult and seven-day-old worms were 100 per cent and 100 per cent for Cooperia curticei, 95.1 per cent and 69.8 per cent for Haemonchus contortus and 100 per cent and 82 per cent for Ostertagia circumcincta. Morantel citrate was 100 per cent effective against benzimidazole-susceptible Nematodirus battus and Trichostrongylus vitrinus, and it reduced faecal egg counts by 97.9 per cent in sheep infected naturally with benzimidazole-resistant H contortus and O circumcincta.     

FDA: making a difference in women''s health

The resistance status of gastro-intestinal nematodes to anthelmintics was evaluated on 881 sheep farms throughout Australia during 1991-92. Resistance was shown to be widespread. Overall, 85% of farms had sheep infected with nematodes resistant to benzimidazole, 65% to levamisole and 34% to combination (benzimidazole+levamisole) products. Resistance to ivermectin was not detected. On only 9% of farms did all anthelmintic groups reduce egg counts by greater than or equal to 95%. The culture of faeces from untreated sheep showed Telodorsagia circumcincta, Trichostrongylus spp, Chabertia ovina and Haemonchus contortus to be the principal species. The nature and prevalence of resistance was not significantly correlated with stocking rate. However, resistance to combination products was almost twice as prevalent on farms in areas with an average annual rainfall of greater than 500 mm.