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.     

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.     

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.     

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.     

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.     

The influence of a heavy infection with sensitive and resistant strains of Ostertagia circumcincta and with Trichostrongylus colubriformis on the pharmacokinetics of febantel in lambs

Plasma concentrations of febantel and its major metabolites, fenbendazole, oxfendazole and fenbendazole sulphone, were determined after oral administration of 7.5 mg/kg febantel in lambs before and 28 days after infection with 100,000 L3 larvae of a benzimidazole (BZ)-sensitive or BZ-resistant strain of Ostertagia circumcincta or with 75,000 L3 larvae of a BZ-sensitive Trichostrongylus colubriformis strain. The febantel concentrations were always low, and in only a few samples were higher than the limit of detection. A mean decrease in the area under the curve (AUC) for the three metabolites of 10.2%, 16.4% and 4.9% in lambs infected, respectively, with BZ-sensitive O. circumcincta, BZ-resistant O. circumcincta and T. colubriformis was observed. The Cmax for all the metabolites was higher in the BZ-sensitive O. circumcincta group than in the naive sheep, while the Tmax occurred earlier. The Cmax and the Tmax values for all the metabolites were lower in the BZ-resistant O. circumcincta group than in their own naive controls. In the T. colubriformis group the Cmax values of the metabolites were lower and the Tmax occurred much later.     

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.     

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.     

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.     

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.     

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.     

Parasite spectrum and seasonal epidemiology of gastrointestinal nematodes of small ruminants in The Gambia

One hundred and four post mortem examinations of randomly selected sheep (52) and goats (52) were carried out weekly from March 1990 to February 1991. Gastrointestinal parasites were identified and counted. A large spectrum of 16 helminth species was found in 101 (97%) infected animals. The nematodes infecting small ruminants were, in order of predominance: Trichostrongylus colubriformis (96% of all animals), Oesophagostomum columbianum (82%), Haemonchus contortus (67%), Strongyloides papillosus (55%), Gaigeria pachyscelis (38%), Cooperia spp. (49%) and Trichuris ovis (12%). Forty-five (43%) necropsies revealed an infection with Moniezia benedeni, Avitellina centripunctata or Stilesia globulosa. Infections with Schistosoma bovis and Paramphistomum spp. were rarely seen. Goats carried significantly lower worm burdens than sheep and were less often infected by tapeworms. Nematode worm burdens followed a similar seasonal pattern in both host species. While Trichostrongylus colubriformis was also recovered in high numbers in the mid dry season, other species such as H. contortus, Strongyloides papillosus and Oesophagostomum columbianum reached distinct peaks in the rainy season (July-October). Different survival strategies for the prolonged dry season were observed. Haemonchus contortus outlived the unfavourable climatic conditions as inhibited larvae in the abomasal mucosa, while the other nematode species survived as adults with a reduced fecundity. Egg production per adult worm specimen was found to depend heavily on the season and egg counts in the dry season (November-June) did not correspond to the size of worm burdens. Unexpectedly high worm burdens were recovered from adult and old animals. Investigations of young animals indicated that no reinfection can occur during the dry season. The findings are discussed with regard to their relevance for strategic control of gastrointestinal nematodes in small ruminants.     

Reduced egg counts in mixed infections with Oestrus ovis and Haemonchus contortus: influence of eosinophils?

In all, 2 groups of lambs were infected either with Oestrus ovis first-instar larvae or with 10,000 third-stage larvae (L3) of Haemonchus contortus. Another group of lambs was infected with both parasites. Fecal nematode egg counts, plasma pepsinogen concentrations, specific O. ovis enzyme-linked immunosorbent assay (ELISA) antibodies, and blood eosinophil counts were monitored and compared to with the values recorded for a control group of uninfected lambs. There was no significant difference between the burden of H. contortus found in mixed and single infections. However, the nematode egg production was significantly depressed in mixed infections. O. ovis affects the population of H. contortus at least by decreasing the parasite egg output. This effect may be mediated through the increase in eosinophil production stimulated by the presence of O. ovis.     

Effect of plant species on the larvae of gastrointestinal nematodes which parasitise sheep

Faeces containing Trichostrongylus colubriformis and/or Ostertagia circumcincta eggs were used to provide four contaminations in each of 2 years on plots of browntop, Yorkshire fog, ryegrass, tall fescue, lucerne, chicory, cocksfoot, white clover, and prairie grass and in the second year a mixed sward of ryegrass/white clover. Third stage larvae were recovered from faeces and from four strata of herbage, 0-2.5, 2.5-5, 5-7.5 and > 7.5 cm above the soil surface at 2, 4, 6, 8, 11, and 14 weeks after faeces were deposited on the swards. Herbage species had a significant (P < 0.0001) effect on the number of larvae recovered. Greatest numbers of larvae, as indicated by ranking analysis, were recovered from Yorkshire fog, ryegrass, and cocksfoot and lowest numbers from white clover and lucerne. The difference between herbages in numbers of larvae recovered was due to the "development success", the ability of larvae to develop to the infective stage and migrate on to herbage, rather than "survival", the rate of population decline once on the herbage. Faecal degradation was most rapid from white clover and browntop, intermediate from tall fescue, lucerne, prairie grass, cocksfoot, and ryegrass, and slowest from Yorkshire fog swards. The numbers of larvae recovered from herbages were related (r2 = 0.59, P < 0.05) with the faecal mass remaining. A greater proportion of the total larvae recovered from the herbage was recovered from the bottom stratum of Yorkshire fog and prairie grass than from white clover, with the other herbages intermediate, indicating that larvae had greater difficulty migrating up Yorkshire fog and prairie grass than the other herbage species. In most herbage species, despite more larvae being recovered from the lowest stratum, larval density (L3/kg herbage DM) was highest in the top stratum. This study has demonstrated that herbage species can have a significant impact on the population dynamics and vertical migration of T. colubriformis and O. circumcincta larvae.     

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.     

Prevalence and epidemiology of trichostrongylids in Wyoming cattle with consideration of the inhibited development of Ostertagia ostertagi

During 1988, monthly collections of abomasa and the cranial portion of the small intestine of 208 native Wyoming cattle were examined for adult and larval helminth parasites. Egg counts were performed on colonic faecal specimens. The animals ranged from 7 months to 8 years of age and were sampled at slaughter houses or diagnostic laboratories from five different counties in the State. Most of the cattle had ranged for a long time on non-irrigated, high altitude grass plains from about 1250 to 2500 m above sea level. All animals examined were found infected. Nematode genera (and number of species) found included Ostertagia (4), Trichostrongylus (2), Haemonchus (1), Cooperia (4) and Nematodirus (2). One trematode, Fasciola hepatica, and a cestode, Moniezia benedeni, also were found. Trichostrongylus axei, Trichostrongylus longispicularis and Cooperia lyrata were found for the first time in Wyoming, Ostertagia circumcincta was found for the first time in cattle in Wyoming, and Haemonchus placei, tentatively identified in a previous survey, was definitively confirmed. Predominant species (and prevalence) were Ostertagia ostertagi (98%), Cooperia oncophora (60.6%), Ostertagia bisonis (41.8%), Cooperia bisonis (33.6%) and T. Axei (27.9%). One or more of the four species of Ostertagia were found in all animals. Inhibited O. ostertagi and O. bisonis larvae predominated from November to April and reached a peak in January to comprise 88% of the total nematode burden for that month. The adult population of abomasal nematodes peaked in April and predominated thereafter until October. Haemonchus placei also spent the autumn-winter period in an inhibited state of development. Faecal egg counts were lowest during winter months, when the highest number of worms were present as L4 larvae, as determined by luminal and mucosal counts. Nematode populations in the small intestine peaked in June and persisted until November. The results of this study showed the magnitude and species composition of nematode parasitism in cattle raised on high altitude grass plains, underscored the inaccuracy of faecal egg counts as an indicator of worm burden during fall and winter seasons, and provided information on which anthelmintic treatment timing would be most efficacious.     

Comparisons of two polymorphic species of Ostertagia and phylogenetic relationships within the Ostertagiinae (Nematoda: Trichostrongyloidea) inferred from ribosomal DNA repeat and mitochondrial DNA sequences

The first internal transcribed spacer DNA (ITS-1) (rDNA) and the mitochondrial (mt) DNA-derived cytochrome oxidase I gene (COX-1) were enzymatically amplified, cloned and sequenced from 6 nominal species of Ostertagiinae as well as Haemonchus contortus and Haemonchus placei. The portion of the COX-1 gene analyzed was 393 base pairs (bp) in length and contained 33 within species polymorphic base changes at 28 synonymous sites. The ITS-1 rDNA consensus sequences ranged from 392 bp (Ostertagia ostertagi/Ostertagia lyrata, Teladorsagia circumcincta) to 404 bp (H. contortus, H. placei). These data were used both in a distance analysis to assess the concept of polymorphic species within the genus Ostertagia and in parsimony analysis to assess phylogenetic relationships within a limited group of Ostertagiinae. Pairwise similarity scores of both ITS-1 and COX-1 data showed the highest number of conserved sites between the proposed dimorphic species of Ostertagia. The level of similarity was lower in the COX-1 data due to the high number of synonymous base changes. Analysis by maximum parsimony of the same data did not refute O. ostertagi/O. lyrata and Ostertagia mossil/Ostertagia dikmansi as dimorphic species and supported monophyly of these ostertagiines relative to representatives of the haemonchine outgroup. In the single most parsimonious tree from ITS-1 rDNA data, a subclade of Ostertagia spp. included forms possessing parallel synlophes and long esophageal valves that typically occur in cervid hosts.     

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.     

Comparison of six in vitro tests in determining benzimidazole and levamisole resistance in Haemonchus contortus and Ostertagia circumcincta of sheep

Six in vitro methods for the detection of anthelmintic resistance were compared using benzimidazole/levamisole-resistant Haemonchus contortus and benzimidazole/levamisole/ivermectin-resistant Ostertagia circumcincta as well as susceptible strains of both parasite species. The degree of resistance to thiabendazole and levamisole was compared by (1) an egg hatch assay, (2) an egg hatch paralysis assay, (3) a larval development assay, (4) a larval paralysis assay (5) a larval paralysis assay with physostigmine and (6) larval micromotility assay. The degree of resistance for each assay was expressed as resistance factor--RF. For the detection of thiabendazole and levamisole resistance, the larval development test was observed as the most sensitive to measure quantitatively a degree of resistance between susceptible and resistant strains. For this test the RF for thiabendazole and levamisole was 14.3 and >32.5, respectively in H. contortus strains and 21.1 and 3.5 in strains of O. circumcincta. Egg hatch assay was also found to be sensitive and accurate in determining of resistance to benzimidazole. For measurement of levamisole resistance the egg hatch paralysis assay and larval paralysis assay were found to be able to distinguish between strains, but some disadvantages of these techniques make it unsuitable for field detection of levamisole resistance. Other in vitro assays as larval paralysis assay with physostigmine and larval micromotility assay were also investigated. Significant differences in paralysis of the larvae were observed using larval paralysis assay.     

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