Characterisation of two triple resistant field isolates of Teladorsagia from Scottish lowland sheep farms

The anthelmintic resistance status of two field isolates derived from farms (farm A and B) located near Edinburgh were examined using both controlled efficacy tests (CET) and faecal egg count reduction tests (FECRT). Efficacies against fenbendazole (FBZ), levamisole (LEV) and ivermectin (IVM) and, for one isolate, against combinations of these anthelmintics and moxidectin were determined in na?ve lambs, artificially infected with the isolates and treated with the compounds at the manufacturers recommended dose rates. (FBZ, 5mg/kg bodyweight (BW); LEV, 7.5mg/kg BW; IVM, 0.2mg/kg BW; Moxidectin (MOX) 0.2mg/kg BW). In both field isolates, the predominant species found pre-treatment and the only species found post-treatment was Teladorsagia circumcincta. Resistance to FBZ, LEV and IVM was confirmed in CET and FECRT on farm A and to the latter two compounds on farm B, which had a history of benzimidazole resistance and where TBZ resistance was also demonstrated using an egg hatch assay (EHA). For the farm A isolate CET efficacies against FBZ; IVM; LEV; FBZ + IVM; FBZ + LEV; FBZ, LEV + IVM and MOX were 59, 60, 88, 94,93, 92 and 98%, respectively. The CET efficacies for the farm B isolate were 51% and 72% for LEV and IVM, respectively.     

Further characterisation of a triple resistant field isolate of Teladorsagia from a Scottish lowland sheep farm

Anthelmintic efficacies against juvenile developing populations of Teladorsagia species that were known to be resistant to anthelmintics from all three broad spectrum families were examined using a controlled efficacy test. Fenbendazole (FBZ), levamisole (LEV), ivermectin (IVM), combinations of these anthelmintics and moxidectin (MOX) were assessed in parasite na?ve lambs artificially infected with 8,000 third stage larvae (Tci5) and treated orally 8-day post-infection with the compounds at the manufacturers recommended dose rates, FBZ, 5 mg/kg body weight (BW); LEV, 7.5 mg/kg BW; IVM, 0.2 mg/kg BW; MOX (0.2 mg/kg BW). The lambs were slaughtered 14-day post-treatment. The arithmetic mean worm burden reductions resulting from oral treatments with FBZ; IVM; LEV; FBZ+IVM; FBZ+LEV; FBZ, LEV+IVM or MOX were 36%, 82%, 38%, 86%, 60%, 88% and 97%, respectively. The results illustrate that combination treatments showed improved efficacies against the juvenile population compared to individually administered treatments but that these improvements were not wholly effective. Moxidectin was the only treatment that was over 95% effective, though caution should be noted when advising the use of MOX prophylactically since 3% of the infection still survived this treatment. Treatments directed at juvenile stages of Tci5 were less effective, with the exception of IVM, compared to a similar trial using Tci5 where the same treatments were directed against a predominantly adult population. No interaction was detected comparing the timings of treatments and its effectiveness with the exception of IVM (two-way ANOVA, p < 0.05). These findings suggest that, on the whole, the selection processes for anthelmintic resistance (AR) may occur at an early stage of development within the parasites, having severe implications for the early detection of AR.     

Evaluation of a larval development assay (DrenchRite) for the detection of anthelmintic resistance in cyathostomin nematodes of horses

A larval development assay (LDA, DrenchRite) was evaluated to determine the effectiveness of this method in detecting anthelmintic resistance in cyathostomin nematodes of horses. A total of 15 horse farms from Georgia and South Carolina (USA) and Population S ponies from the University of Kentucky (USA) were included in this study. Nematode eggs were extracted from pooled fecal samples and placed into the wells of a DrenchRite plate for testing against thiabendazole (TBZ), levamisole (LEV) and 2 ivermectin (IVM) analogs (IVM-1, IVM-2). After a 7-day incubation larvae in each well were counted and data were analyzed by logistic regression. Resistance status of each farm for different drugs was determined in a separate study using a fecal egg count reduction test. LDA were performed on the 15 farms once, however, the Population S cyathostomins were assayed on 3 separate occasions to estimate the consistency of results between assays. Mean TBZ LC50 for oxibendazole resistant, suspected resistant and sensitive farms were 0.2015, 0.1625, and 0.1355 microM, respectively. For LEV, mean LC50 for PYR resistant, suspected resistant and sensitive farms were 1.590, 1.8018 and 1.4219 microM, respectively. All 15 farms had worms susceptible to IVM; mean LC50 for IVM-1 and for IVM-2 were 7.5727 and 87.9718 nM, respectively. A linear mixed model was fitted to the data to determine the relationship between LC50 and LC95 and resistance status for each farm. No meaningful relations were found. Consistency of assays varied between drugs, being best for TBZ and worst for LEV and IVM-1. All farms in this study had benzimidazole-resistant nematodes; therefore usefulness of DrenchRite for discriminating susceptibility versus resistance to this drug class could not be accurately assessed. Moreover, since all farms tested were sensitive to IVM and resistance to this drug class has not yet been reported in cyathostomins, it is not possible to assess accurately the usefulness of DrenchRite LDA for detecting IVM resistance at this time. Assay results for LEV suggest that LEV in a LDA does not yield data that is useful in estimating PYR efficacy in vivo. Based on results for PYR/LEV, the current high prevalence of benzimidazole resistance, no known cases of IVM resistance, and the sometimes extreme variation in results seen in many of the assays, DrenchRite LDA cannot be considered a useful tool for the diagnosis of resistance in cyathostomins of horses at present.     

Comparing different formulae to test for gastrointestinal nematode resistance to benzimidazoles in smallholder goat farms in Mexico

The objective was to examine the coincidence in the prevalence of benzimidazole (Bz) resistance in smallholder goat herds, as determined by three average-based and two individually-based faecal egg count reduction (FECR) tests. Nineteen smallholder goat herds with more than 30 animals were selected from 84 herds in Yucatan. Animals shedding 150 eggs/g of faeces (EPG) on day zero were randomly divided into two groups. The control group did not receive treatment and the treated group received fenbendazole (10mg/kg body weight per os). Feed was withdrawn for 16 h before treatment. Ten days after treatment, both groups were sampled to determine their FEC. Faecal cultures and identification of infective larvae were performed for estimating the proportions of genera of gastrointestinal nematodes (GIN) present. Presence of resistant GIN was determined with three different average-based FECR (FECR(1), FECR(2) and FECR(3)) and two individually-based FECR (iFECR(1) and iFECR(2)). The prevalence of herds with Bz resistant nematodes (and 95% confidence interval (95% CI)) was calculated using each formula. Coincidence among formulae was estimated with Kappa values. The prevalence (+/- 95% CI) of Bz resistance calculated with FECR(1) (57.89 +/- 22.20) had a high coincidence with iFECR(1) and iFECR(2) (Kappa values of 0.86 and 0.79, respectively). The prevalence with FECR(2) (31.58 +/- 20.90) and FECR(3) (21.05 +/- 18.33) had a low coincidence with FECR(1) (Kappa < 0.50). Trichostrongylids found on Bz resistant farms were mainly Haemonchus spp., however, some Trichostrongylus spp. and Oesophagostomum spp. were found too. The high coincidence between the standard average-based FECR(1) and the individually based formulae is encouraging and may suggest that either formula could be applied to smallholder farmers. Further laboratory studies are needed to confirm the resistance status in the herds.     

A field evaluation of anthelmintics for control of cyathostomes of horses in Brazil

The anthelmintic efficacy of ivermectin (IVM), piperazine citrate (PPZ) and fenbendazole (FBZ) alone, and combinations of FBZ with varying dosages of PPZ, was evaluated for the control of strongyles of Mangalarga equids. In all cases of positive strongly egg counts per gram of faeces (EPG) before and after treatment, pure populations of cyathostome larvae with eight gut cells were consistently observed in faecal cultures. The faecal egg count reductions (FECR) were evaluated between Day 7 and Day 56 post-treatment. Significant differences (P less than or equal to 0.05) were found between Day 7 and Day 49 when comparing the mean EPG values of IVM with those of the other anthelmintics. PPZ alone and the combination of FBZ (7.5 mg kg-1) and PPZ (55 mg base kg-1) did not show significant differences during the trial; both groups exhibiting an FECR of greater than 90% between Day 7 and Day 30. Horses treated with the combinations of FBZ (7.5 mg kg-1) and PPZ at either 40 or 25 mg base kg-1, and with FBZ alone at either 7.5 or 15 mg kg-1, showed an FECR of less than 90% 2 weeks after treatment. The emergence of a degree of resistance of strongyles to FBZ and PPZ in a segment of the cyathostomes in this population is suggested.     

Efficacy of albendazole, levamisole and fenbendazole against gastrointestinal nematodes of cattle, with emphasis on inhibited early fourth stage Ostertagia ostertagi larvae.

An experiment was conducted to compare the anthelmintic efficacy of albendazole (ABZ), levamisole (LEV) and fenbendazole (FBZ) against inhibited early fourth stage larvae (EL4) of Ostertagia ostertagi during April in Louisiana. Forty cross-bred beef heifers (average weight 165 kg) were acquired during winter and grazed on pastures contaminated with O. ostertagi and other nematodes until early April. The cattle were weighed and randomly allotted into four groups of ten animals on 6 April and treatments were administered on 7 April. Experimental groupings were: Group 1, non-treated controls; Group 2, ABZ by oral drench at 10 mg kg-1; Group 3, LEV by topical, pour-on administration to back midline at 10 mg kg-1; Group 4, FBZ by oral drench at 10 mg kg-1. Equal numbers of cattle from each group were slaughtered daily between 10 and 13 days after treatment. Mean numbers of O. ostertagi developmental stages present in untreated controls were: adults, 13,714; developing L4 (DL4), 6487; inhibited EL4, 21,719. The mean percentage of inhibited EL4 was 51.8. Smaller numbers of Haemonchus placei, Trichostrongylus axei and Cooperia spp. were recovered uniformly in control cattle. Percentage reduction values for the three compounds against O. ostertagi adults, DL4 and EL4, respectively, were: ABZ, 99.0, 95.3, 84.9; LEV, 1.0, 21.8, 32.1; FBZ, 99.2, 97.2, 97.5. Differences between ABZ and LEV EL4 counts were not significant, but in all other cases worm counts in ABZ and FBZ-treated cattle were significantly lower (P less than or equal to 0.05) than in LEV-treated and control cattle. Both ABZ and FBZ were 98-100% effective against Haemonchus adults and L4, T. axei adults, and Cooperia spp. adults and L4. LEV was 100% effective against Haemonchus adults and L4, 85.6% against T. axei, and 94.6% and 89.59% effective against Cooperia spp. adults and L4, respectively.     

Effect of strategic gastrointestinal nematode control on faecal egg count in traditional West African cattle

This paper reports on the effect of strategic anthelmintic treatments and other determinants on faecal egg counts (FEC) of Trichostrongyles in N'Dama cattle of a west African village. Initially, 527 animals from 13 private N'Dama cattle herds were monitored in a longitudinal study from October 1989 to December 1994. Each herd was stratified by age and animals were sequentially allocated to two groups with similar age distributions. One group received a single anthelmintic treatment of fenbendazole (7.5 mg/kg BW), in October 1989 (n = 250), whereas the other group remained untreated (n = 277) throughout the study. In the next rainy season (June to October), the treated animals were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until December 1994. Biannual anthelmintic treatments decreased the level of FEC between 31% (late dry season) and 57% (rainy season), when compared to untreated controls. The highest levels of FEC were found during the rainy season from June to October. FEC levels decreased until 4 years of age, after which they remained on a constant low level. The variability of returns to anthelmintic treatments between herds did not seem to be influenced by FEC at the herd level. The financial evaluation of anthelmintic interventions cannot be predicted from FEC and must necessarily rely on the direct monitoring of livestock productivity parameters.     

A survey of anthelmintic resistance on ten goat farms in the Manawatu region in 1988

A survey of anthelmintic resistance on ten goat farms was carried out. The criterion for resistance was a faecal egg count reduction (FECR) of <90 percent based on arithmetic means of 11 to 19 goats per group. It was found that nine of the ten farms harboured nematodes resistant to oxfendazole when used at 5mg/kg although on two of these, the FECR's were 89.2 percent and 89.8 percent. Post treatment larval cultures indicated Haemonchus, Ostertagia and Trichostrongylus were the resistant genera involved. On none of the ten farms was resistance to oral ivermectin at 0.2mg/kg detected.     

A comparison of two integrated approaches of controlling nematode parasites in small ruminants

Control of gastrointestinal nematodes (GIN) in small ruminants in regions of the world where anthelmintic resistance is prevalent must rely on more than just chemical deworming strategies. The objective of this experiment was to compare two integrated treatment protocols for control of GIN (primarily Haemonchus contortus in this region) using anthelmintics, copper oxide wire particles (COWP) and FAMACHA(?), compared to traditional anthelmintic use only. Three separate trials were conducted on mature ewes, weaned goats, and weaned lambs in which three deworming management strategies were applied: 1) all animals were dewormed with levamisole at four week intervals (LEV), 2) individual animals were dewormed with moxidectin when scored≥4 (ewes) or ≥3 (kids and lambs) using FAMACHA(?) (FAM/MOX), 3) all animals were dewormed with moxidectin initially and again with COWP (2g) when group mean FEC exceeded 500 (ewes), 3000 (kids), or 1000 (lambs) eggs/g (MOX/COWP). In this final group, during periods between group treatments, individual animals were dewormed with albendazole and levamisole according to FAMACHA(?) score. Fecal egg counts (FEC) and blood packed cell volume (PCV) were determined every 7 days and body weight every 28 days for 30, 20, or 16 weeks in ewes, goats, and lambs, respectively. Efficacy of levamisole was 83.4-86.4%, efficacy of moxidectin was 93.5-100%, and efficacy of COWP was 10.8-98.1% among the three trials. The mean number of deworming treatments per animal that occurred for the LEV, FAM/MOX, and MOX/COWP groups, respectively, was 7.9, 0.6, and 2.5±0.4 (P<0.001) for ewes, 5.2, 1.6, and 3.4±0.3 (P<0.001) for goats, and 4.0, 1.7, and 3.6±0.2 (P<0.001) for lambs. Production (body weight of lambs weaned from ewes or final body weight of kids and lambs) was similar among management strategy groups for ewes and kids, but FAM/MOX lambs were lighter by the end of the trial (P<0.003). While more time and labor was required to use the FAMACHA(?) system, a more conservative use of anthelmintics occurred in the FAM/MOX group.     

Efficacy of some anthelmintics on an ivermectin-resistant strain of Haemonchus contortus in sheep

Following evidence of reduced efficacy of ivermectin in a field population of Haemonchus contortus in Brazil, this strain of the parasite was submitted to a controlled anthelmintic test. Eighty worm-free lambs were randomly split into two groups of 40. Each lamb in the first group was infected with 5000 third stage larvae (L3) of the ivermectin-resistant strain; the remaining 40 lambs were each infected with 5000 L3 of a H. contortus strain of known susceptibility to the major groups of anthelmintic compounds used in sheep. On Day 28 post-infection, each group was subdivided according to egg counts and at random into four sub-groups of ten lambs, each of which was treated with albendazole (ABZ) at 3.8 mg kg-1, levamisole (LEV) at 7.5 mg kg-1 or ivermectin (IVM) at 0.2 mg kg-1, or was left as untreated control. At slaughter, 7 days later, all the anthelmintics reduced worm burdens in animals infected with the susceptible strain (ABZ 98.9%, LEV and IVM 100%). By contrast, in the lambs infected with the ivermectin-resistant strain, LEV was 99.8% effective, but ABZ reduced worm counts by only 14.7% and IVM by only 10.4%. Interestingly at necropsy on Day 7 post-treatment, the egg counts in the resistant strain treated with ABZ had been reduced by 92.5%, although worm counts were reduced by only 14.7%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Efficacy of major anthelmintics against horse cyathostomins in France

This paper reports a survey conducted in France during 2011 to evaluate the efficacy of commonly used anthelmintics against horse cyathostomins. A total of 40 farms and 1089 horses were screened for the presence of cyathostomins. All farms but one were positive, with an overall animal infection rate of 53.7%, ranging from 9% to 83% on individual farms. On 445 horses from 30 of these farms, a faecal egg count reduction test (FECRT) was performed to evaluate the efficacy of oral formulations of fenbendazole (FBZ), pyrantel embonate (PYR), ivermectin (IVM) and moxidectin (MOX). Calculation of the mean FECR and 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. Resistance to FBZ was found on 17 of 18 farms investigated, with a mean reduction of 57% (95% CI: 38.5-71.2%). Suspected resistance for PYR was found on 6 of 30 farms, and confirmed on another 3 of 30 farms, with a mean reduction for PYR of 94.7% (95% CI: 88.9-98.5%). Reduced efficacy simultaneously of FBZ and PYR was found in 7 farms. Reduced efficacy of IVM was found in one animal on one farm and of MOX in one animal on another farm, and was combined with resistance against FBZ and/or PYR. These results indicate that single and multiple drug resistance and reduced efficacy in equine cyathostomins is present in France. Macrocylic lactones proved to be highly effective compounds against cyathostomins, with reduced efficacy for IVM and MOX in two farms only. These results extend present knowledge on the occurrence of drug resistant cyathostomins in Europe, and illustrate the necessity to use anthelmintics in appropriate worm control programmes.     

Evaluation of tests for anthelmintic resistance in cyathostomes

Resistance, especially to the anthelmintic benzimidazoles (BZ), has been reported in horse cyathostomes world-wide. Diagnosis of resistance has traditionally been made by faecal egg count reduction (FECR) trials, however, this technique has limitations. Some of the shortcomings may be resolved by refining the test or by using an in vitro test. FECR tests and the larval development assay (LDA) were performed on adult horses held on 15 different horse properties across a wide geographical area of NSW, Australia. FECR were measured before and 10-14 after days treatment with oxibendazole (OBZ), morantel (MOR) or ivermectin (IVM) at recommended dose rates. Eight properties were rejected following low pre-treatment egg counts, leaving seven in the study. On these, the majority of larvae recovered from faecal cultures were cyathostomes. Using a definition of resistance as a FECR of <90%, resistance to OBZ was present on six properties and to MOR on two properties. Resistance to IVM was not detected. An alternative method of calculating FECR based on individual horse egg counts pre- and post-treatment was developed and results from the same properties compared with the results of the LDA. For example, for the BZ, correlation coefficients of values of lethal concentration to kill 50% of population (LC50) on LDA and FECR percentages were -0.536 before and -0.704 after OBZ treatment. We conclude that the LDA has the potential to be a single visit test for detection of anthelmintic resistance in horse cyathostomes but requires further investigation and standardisation.     

Anthelmintic resistance of nematodes in communally grazed goats in a semi-arid area of South Africa

A survey was conducted on the occurrence of anthelmintic resistance of nematodes in communally grazed goats in a semi-arid area in South Africa. In herds belonging to 10 small-holder goat farmers, the efficacies of fenbendazole, levamisole and rafoxanide were tested by faecal egg count reduction (FECR) tests. Efficacies of 80% were considered a threshold for anthelmintic resistance. The FECR tests showed that all drugs tested more than 80% effective in most instances, but there were notable exceptions. In 1 case, rafoxanide was only 31% effective and in another case fenbendazole was only 47% effective. The occurrence of anthelmintic resistance in this farming sector is of concern. Steps should be taken to prevent its further spread and to avoid the development of a situation as on numerous commercial sheep farms in South Africa where resistance is very common.     

Comparative plasma disposition of fenbendazole, oxfendazole and albendazole in dogs

The plasma disposition of fenbendazole (FBZ), oxfendazole (OFZ) and albendazole (ABZ); and the enantiospecific disposition of OFZ, and ABZSO produced were investigated following an oral administration (50 mg/kg) in dogs. Blood samples were collected from 1 to 120 h post-administration. The plasma samples were analysed by high performance liquid chromatography (HPLC). The plasma concentration of FBZ, OFZ, ABZ and their metabolites were significantly different from each other and depended on the drug administered. The sulphone metabolite (FBZSO2) of FBZ was not detected in any plasma samples and the parent molecule ABZ did not reach quantifiable concentrations following FBZ and ABZ administration, respectively. OFZ and its sulphone metabolite attained a significantly higher plasma concentration and remained much longer in plasma compared with FBZ and ABZ and their respective metabolites. The maximum plasma concentrations (Cmax), area under the concentration time curve (AUC) and mean residence time (MRT) of parent OFZ were more than 30, 68 and 2 times those of FBZ, respectively. The same parameters for ABZSO were also significantly greater than those of FBZSO. The ratio for total AUCs of both the parent drug and the metabolites were 1:42:7 for following FBZ, OFZ and ABZ administration, respectively. The enantiomers were never in racemic proportions and (+) enantiomers of both OFZ and ABZSO were predominant in plasma. The AUC of (+) enantiomers of OFZ and ABZSO was, respectively more than three and seven times larger than that of (-) enantiomers of both molecules. It is concluded that the plasma concentration of OFZ was substantially greater compared with FBZ and ABZ. The data on the pharmacokinetic profile of OFZ presented here may contribute to evaluate its potential as an anthelmintic drug for parasite control in dogs.     

Dairy goat demography and Q fever infection dynamics

Between 2007 and 2009, the largest human Q fever epidemic ever described occurred in the Netherlands. The source was traced back to dairy goat farms, where abortion storms had been observed since 2005. Since one putative cause of these abortion storms is the intensive husbandry systems in which the goats are kept, the objective of this study was to assess whether these could be explained by herd size, reproductive pattern and other demographic aspects of Dutch dairy goat herds alone. We adapted an existing, fully parameterized simulation model for Q fever transmission in French dairy cattle herds to represent the demographics typical for Dutch dairy goat herds. The original model represents the infection dynamics in a herd of 50 dairy cows after introduction of a single infected animal; the adapted model has 770 dairy goats. For a full comparison, herds of 770 cows and 50 goats were also modeled. The effects of herd size and goat versus cattle demographics on the probability of and time to extinction of the infection, environmental bacterial load and abortion rate were studied by simulation. The abortion storms could not be fully explained by demographics alone. Adequate data were lacking at the moment to attribute the difference to characteristics of the pathogen, host, within-herd environment, or a combination thereof. The probability of extinction was higher in goat herds than in cattle herds of the same size. The environmental contamination was highest within cattle herds, which may be taken into account when enlarging cattle farming systems.     

Risk factors for Brucella seropositivity in goat herds in eastern and western Uganda.

Cross-sectional prevalences and risk factors for Brucella seropositivity in goats in eastern and western Uganda were investigated. Serum was collected from 1518 goats randomly selected from 145 herds which had been identified using multistage sampling. The brucellosis card test (CT) and the Brucella melitensis tube-agglutination test (TAT) were used in parallel to detect antibodies against B. abortus and B. melitensis, respectively. Interviewer-administered questionnaires were used to collect information on goat health and management. This information was used in multivariable logistic-regression models to determine the risk factors for Brucella seropositivity in goat herds. For each analysis, a herd was considered positive if at least one goat in the herd tested positive for antibodies against Brucella and negative if none was positive.Four percent (55/1480) of the goats screened with the CT had antibodies against Brucella. The reactors were distributed in 13% (19/145) of the herds. The most-important herd-level risk factors identified were use of a hired caretaker as the primary manager of the operation compared to owner/family members (adjusted odds ratio (OR)=8.1; 95% CI 1.6, 39.7), keeping sheep in addition to goats (OR=6.0; CI 1.5, 23.7) compared to having no sheep, and free browsing (OR=4.7; 95% CI 1.0, 20.7) when compared to tethering or zero-grazing.Using the TAT, 10% (141/1446) of the goats tested positive. The positives were distributed in 43% (63/145) of the herds. Free browsing (OR=6.7; 95% CI 2.7, 16.9) when compared to tethering or zero-grazing and lack of veterinary care (OR=2.9; CI 1.3, 6.7) were the most-important factors identified in the multivariable model for B. melitensis herd seropositivity.To explore/reduce the risk of misclassification in a secondary analysis, herds were reclassified as positive if at least one goat tested positive on both tests and negative if none of the goats was positive on any of the two tests. Using this classification, 2% (30/1320; 95% CI 2, 3%) of the goats tested positive resulting in 13% (12/93) of the herds being positive. The distribution of the above risk factors by brucellosis herd-status (as defined by the second criterion) is also presented.     

Anthelmintic resistance in cattle nematode in the western Pampeana Region of Argentina

During the past three years there have been several reports of cattle anthelmintic resistance (AR) in Argentina. Twenty-five cattle herds in the west fattening area of the Pampeana Region were surveyed to assess the prevalence of AR and the species of nematode involved. The survey involved fattening and cow-calf systems with a mean of 6760 bovines. Resistance was determined in vivo by a faecal egg count reduction test (FECRT). Efficacies from the World Association for the Advancement of Veterinary Parasitology (WAAVP) formula were compared with those obtained from the Abbott formula. Sixty 6-12-month-old calves were selected from each property and divided into four groups, namely, IVM (ivermectin, 0.2mg/kg), BZD (fenbendazole, 5mg/kg or albendazole 7.5mg/kg), LVM (levamisole, 7.5mg/kg) and Control (untreated group). Nematode larvae were identified by four pooled faecal cultures for each group. Cooperia and Ostertagia were the predominant nematode larvae in pre-treatment cultures. The mean FECRT efficacies for IVM, BZD and LVM were 81.0+/-21%, 93.3+/-8% and 97.6+/-4%, respectively. AR was detected in 16 (64%) herds. IVM resistance was present in 15 herds and BZD resistance in eight herds (32%). Resistance to both ivermectin and fenbendazole was present in seven herds. LVM resistance was not detected. Cooperia was the predominant post-treatment nematode in all the herds with IVM resistance. In one herd with IVM resistance, Ostertagia counts were slightly increased over pretreatment counts. Ostertagia was the prevalent post-treatment genera in herds with BZD resistance. A high level of resistance to ivermectin was recorded in this fattening region of Argentina. Also several herds with resistance to benzimidazole were observed. These results show the importance of AR in Argentinian cattle production. High correlation between WAAVP and Abbott formulae was observed. However, under some uncertain diagnosis, both formulae could be applied as complementary to help result interpretations.     

Assessment of anthelmintic resistance in nematode parasites of sheep and goats owned by smallholder farmers in eastern Ethiopia

The anthelmintic resistance status was investigated of nematode parasites of sheep and goats owned by smallholder farmers in communities that received breeding stock from a source where a high level of anthelmintic resistance has been reported. The investigation used the faecal egg count reduction technique, whereby suitable animals within each of eight separate communities were pooled to achieve the numbers required to conduct separate tests for both sheep and goats. Anthelmintics tested were albendazole (ABZ), tetramisole (TET), a combination (ABZ $+$ TET) and ivermectin (IVM), at the manufacturers' recommended dose rates. Results showed that there was no evidence of anthelmintic resistance in nematode parasites of either sheep an goats in any community. This indicates that dilution of resistant parasites imported with introduced breeding stock, and the low selection pressure imposed by the smallholder farmers themselves, has prevented anthelmintic resistance from emerging in nematode parasites of small ruminants in these communities.     

Larval development assay for detection of anthelmintic resistance in cyathostomins of Swedish horses

The aim of this study was to investigate the suitability of a larval development assay (LDA) for the determination of anthelmintic resistance in cyathostomin nematode populations of the horse. In addition, comparison of results between geographic regions, types of horse establishment, and the use of anthelmintics in Sweden, was established. Seventy horse herds from different parts of Sweden were sampled, and strongyle eggs from the faeces of 54 of those were investigated by an LDA (DrenchRite). The following anthelmintics were tested: thiabendazole (TBZ), levamisole (LEV), ivermectin monosaccharide (IVM-MS), ivermectin aglycone (IVM-AG) and pyrantel (PYR). The LC50 values for TBZ and LEV were generally lower than those previously reported in other LDA studies on horse nematodes. This could be related to the infrequent use of these compounds for the past 20 years in Sweden. In this study, there was a great variation within and between assay plates that could not be explained. Still the LC50 values differed significantly between the regions for all anthelmintics, except for pyrantel. The highest LC50s were observed in parasite populations from the south of Sweden. There were no significant differences between riding schools and studs. Limitations of this technique exist, namely the lack of established cut-off values for susceptible and resistant populations and interpretation problems related to multi-species infections. Although there are advantages with LDA such as the possibility of testing several compounds simultaneously without interference with the deworming programmes on the farms, we conclude that LDA currently is not a reliable alternative to the faecal egg count reduction test (FECRT).     

A survey of nematode control measures used by milking goat farmers and of anthelmintic resistance on their farms

Forty-seven milking goat herds, located throughout New Zealand, were surveyed for anthelmintic usage and for gastrointestinal nematodes resistant to anthelmintics. Most farmers (62%) followed a predetermined drenching programme and usually (68%) had a policy of alternating between drench families. Alternation was generally within the farming year. Kids were on average being drenched 12.5 times during their first year (range 2-34). Does aged greater than one year were all being drenched at the same frequency (average 13.4, range 2-34) irrespective of age. On each of the 47 farms, a group of goats was treated with a benzimidazole (BZ) drench (oxfendazole, OFZ, at 4.5 mg/kg on 36 farms and thiabendazole, TBZ at 66 mg/kg on 11 farms); a second group was treated with a "cell membrane depolarizing" (CMD) drench (levamisole, LEV, at 8 mg/kg on 35 farms and morantel citrate, MOR, at 10 mg/kg on 12 farms); a third group remained untreated as controls. Faecal egg counts and larval cultures were done before dosing and one week later. Faecal egg count depressions of <80% were taken as being suggestive of anthelmintic resistance. On this basis resistance was found on 79% of farms surveyed. Resistance to BZs alone occurred on 36% of farms, resistance to CMDs alone on 4% and resistance to both on 38% of farms. On 23% of farms one or other of the drenches was without any apparent effect and on one farm both of the drenches tested failed to reduce the egg counts. Post-drenching larval cultures showed Trichostrongylus, Haemonchus and Ostertagia to be the most prevalent genera remaining after drenching with BZ on 14,11, and 8 farms, respectively. After drenching with LEV Ostertagia was the dominant species on 10 farms, Trichostrongylus on 2 and on one farm the two genera were equally common. Following treatment with MOR Trichostrongylus was the dominant species on 3 farms, Haemonchus on 2 and on one farm Trichostrongylus and Ostertagia were equally common. There was a positive association between drenching frequency and the presence of resistance on farms. Possible interpretations of this association are discussed.