Benzimidazole resistance in equine cyathostomes in Slovakia

The present study included 19 stud farms, including 243 horses, that were investigated for the occurrence of anthelmintic resistant cyathostomes. The number of horses on the farms varied from nine to more than 100, and horses of all ages were included. A minimum of seven horses were used for faecal egg count reduction (FECR) tests. The anthelmintics included were: fenbendazole (paste formulation), ivermectin (paste formulation) and pyrantel (powder). Resistance to benzimidazoles was detected on 14 farms, with FECR values ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment revealed exclusively cyathostome larvae. Ivermectin was tested on eight farms and proved to be effective on all. Pyrantel was tested on two farms and FECR test indicated high efficacy (92-97%). Egg hatch assay (EHA) results showed that mean concentrations of thiabendazole that inhibited hatching in 50% of the eggs (ED(50)) in resistant populations were over 0.1 microg ml(-1). The results of our study suggest widespread resistance to fenbendazole in equine cyathostomes in Slovakia, and possible strategies to delay anthelmintic resistance are discussed briefly.     

Cases of reduced cyathostomin egg-reappearance period and failure of Parascaris equorum egg count reduction following ivermectin treatment as well as survey on pyrantel efficacy on German horse farms

In 2003 and 2004, on a total of 63 different German horse farms, a survey using the faecal egg count reduction (FECR) test was performed to investigate the efficacy of ivermectin (IVM, Ivomec) and pyrantel (PYR, Banminth) treatment against gastro-intestinal nematodes in a total of 767 horses. IVM treatment resulted in 100% reduction of the cyathostomin egg production 14 and 21 days post-treatment (d.p.t.) on 37 farms. On the remaining five farms, the mean faecal egg count reduction ranged between 97.7 and 99.9%. The mean cyathostomin FECR following PYR treatment ranged between 92.2 and 100% on the 25 farms tested. Therefore, based on the 90% FECR threshold suggested for detection of anthelmintic resistance in horses, neither IVM nor PYR anthelmintic resistance was detected. However, if the thresholds recommended for the detection of resistance in small ruminants were applied, on one and four farms signs of reduced IVM and PYR efficacy, respectively, were observed. In 2005, to further investigate these findings, the cyathostomin egg-reappearance period (ERP) following IVM treatment was examined on six selected farms, two of which were found to show less than 99.8% FECR in the previous survey. On these two latter farms, the ERP was less than 5 weeks, while on the other four it was at least 8 weeks. Earlier investigations described IVM cyathostomin ERP of at least 9 weeks. The efficacy of IVM to reduce Parascaris equorum egg excretion was also studied. On one farm in 2 consecutive years, IVM treatment did not lead to a significant reduction in P. equorum faecal egg counts in one and five young horses, respectively.     

Occurrence of anthelmintic resistant equine cyathostome populations in central and southern Italy

In the present survey, 276 horses bred on 16 farms located in central and southern Italy were investigated for the presence of drug resistant cyathostomes by a Fecal Egg Count Reduction Test (FECRT). Sixteen to 20 animals were selected on each farm and randomly assigned to one of four equally sized treatment groups. Groups were treated with fenbendazole, pyrantel pamoate, ivermectin or moxidectin. Resistance to fenbendazole was declared on six farms (37.5%) and suspected in two farms (12.5%), with FECR values ranging from 41% to 88.3%. Resistance to pyrantel was found in two farms (12.5%) and was suspected in one case (6.2%), with FECR values ranging from 43% to 85.4%. Macrocyclic lactones remained effective on all farms. Only cyathostome third stage larvae (L3) were found in fecal cultures after treatment. This paper reports the first wide survey conducted in Italy for anthelmintic resistance in equine cyathostomes. The results indicate that multiple drug resistant equine cyathostomes are present in the central and southern regions of Italy. These data call for a geographically and numerically broader investigation of horse farms in all regions and for the development and implementation -among veterinarians, owners and managers of a plan to reduce the expansion of these anthelmintic resistant populations and control these important parasites.     

Anthelmintic resistance in cattle nematodes in northwestern São Paulo State, Brazil

The present study was carried out in the northwestern region of S?o Paulo State, Brazil, to determine the anthelmintic resistance status in cattle naturally infected with gastrointestinal nematodes. The anthelmintics tested were levamisole phosphate (Ripercol, Fort Dodge), albendazole sulphoxide (Ricobendazole, Fort Dodge), ivermectin (Ivomec, Merial) and moxidectin (Cydectin, Fort Dodge), administered at the doses recommended by the manufacturers. From April 2002 to May 2004, 25 cattle farms were evaluated. On each farm, steers were divided into treatment and control (not treated) groups based on fecal egg counts (FEC). Between 7 and 10 days after the anthelmintics administration, fecal samples were collected from each animal for post-treatment FEC. Fecal cultures from each group were also prepared for larval identification. After treatment, mean FEC reduction (FECR) in treatment groups (compared with control groups) was assessed on each farm. FECR was lower than 90% on 23 farms after ivermectin treatment. On 19 farms, FECR of 100% was recorded following moxidectin treatment; on the remaining 6, FECR ranged from 90% to 97.2%. After albendazole treatment, FECR was higher than 90% on 20 farms and ranged from 47.4% to 84.6% on other 5. After levamisole treatment, FECR was higher than 90% on 23 farms and equal to 47.4% and 73.7% on other 2 farms. Results indicated the presence of resistant Cooperia spp. and Haemonchus spp., especially to ivermectin; on some farms, resistance to albendazole and levamisole was also observed.     

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers' opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef-cattle rearing farms in the North Island of New Zealand. METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age. RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8-12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levamisole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased. CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers' opinions were divided on many issues and the overall impression was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.     

A Field Study on the Effect of Some Anthelmintics on Cyathostomins of Horses in Sweden

The objective of the study was to investigate different aspects on the efficacy of three anthelmintics on cyathostomin nematodes of Swedish horses. A faecal egg count reduction (FECR) test was performed on 26 farms. Horses were treated orally with recommended doses of ivermectin, pyrantel pamoate or fenbendazole. Faecal samples were collected on the day of deworming and 7, 14 and 21 days later. No resistance was shown against ivermectin; the FECR was constantly >99%. The effect of pyrantel was assessed as equivocal in 6 farms 14 days after treatment; the mean FECR was 99%. As many as 72% of the fenbendazole-treated groups met the criteria for resistance; the mean FECR was 86%, ranging from 56% to 100%. A re-investigation of two farms where pyrantel resistance had been suspected clearly revealed unsatisfactory efficacy of pyrantel on one of these farms; the FECR varied from 72% to 89%. Twenty-six of the horses previously dosed with pyrantel or fenbendazole, and which still excreted ≥150 eggs per gram of faeces 14 days after treatment, were dewormed with ivermectin and fenbendazole or pyrantel in order to eliminate the remaining cyathostomins. A total of 13 cyathostomin species were identified from horses that initially received fenbendazole and seven species were identified from pyrantel-treated individuals. The egg reappearance period (ERP) following treatment with ivermectin and pyrantel was investigated on two farms. The shortest ERP after ivermectin treatment was 8 weeks and after pyrantel was 5 weeks. We conclude that no substantial reversion to benzimidazole susceptibility had taken place, although these drugs have scarcely been used (<5%) in horses for the last 10 years. Pyrantel-resistant populations of cyathostomins are present on Swedish horse farms, but the overall efficacy of pyrantel is still acceptable.     

Anthelmintic resistance and management of nematode parasites on beef cattle-rearing farms in the North Island of New Zealand

AIM: To provide information on current farmers’ opinions and farming practices thought to be related to anthelmintic resistance, and to test for associations between the presence of anthelmintic resistance and management practices on beef cattle- rearing farms in the North Island of New Zealand.

METHODS: A study using an interview-based questionnaire about management of internal parasites was conducted on 62 beef cattle-rearing farms in the North Island of New Zealand, using case-control analyses to test for associations between management practices and the presence or absence of resistance to ivermectin or albendazole. Resistance was inferred from faecal nematode egg count (FEC) reduction (FECR) tests (FECRTs) when there was <90% reduction in FEC 7-10 days after treatment of calves <12 months of age.

RESULTS: Of the 59 farmers who completed the questionnaire, most (n=40) ranked parasites highly, and at about the same level as quality and quantity of feed, as important production-limiting factors for their enterprises. In contrast, anthelmintic resistance was not perceived to be a problem on 13 farms, and its importance was rated low on 24, moderate on 15, and high on only six farms. Despite all farms having planned parasite control programmes, there was heavy reliance on clinical signs of parasitism to determine frequency of treatments. About one in three farmers with beef breeder cows routinely treated their calves at marking, one in five treated mixed-age cows, and almost half treated rising 2-year-old cows before calving. One in four farmers used anthelmintics on calves on 8–12 occasions in their first year of life. Co-grazing with other species was rare, but follow-on grazing within 3 months after older cattle or sheep was common. On most farms, grazing cattle was restricted to part of the farm, a finding with implications for parasite control and persistence of larvae in refugia. Macrocyclic lactone (ML) anthelmintics or their combinations with other action families were currently, and for the past 5 years, used more frequently than benzimidazoles and levamisole, and benzimidazole-levami- sole combinations. The prevalence of resistance to ivermectin was high (82%) and no plausible model of associations could be constructed from the data. The prevalence of resistance to albendazole was 60%, and the risk of resistance increased as the number of rising 1-year-old cattle present mid-winter increased, and decreased as the number of breeding cows >2 years old present mid-winter increased.

CONCLUSION: It is clear that in practice anthelmintic resistance is a secondary consideration to obtaining productivity advantages from the use of anthelmintics in beef cattle. Farmers’ opinions were divided on many issues and the overall impres- sion was of confused and diverse thinking regarding the principles of the use of anthelmintics. The overall outlook regarding anthelmintic resistance in cattle is bleak unless the need for integrated and long-term research activities is acted upon soon.     

Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random sample of beef cattle herds in the North Island of New Zealand. METHODS: A cross-sectional prevalence study was conducted using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, levamisole and albendazole on 60 calves on each of 62 farms in the North Island chosen at random from farms that conformed with the selection criteria. Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident. RESULTS: Of the farms that completed the FECRT, 4/61 (7%) showed > or =95% reduction in FEC for all anthelmintics tested. Resistance to ivermectin was evident on 56/61 (92%) farms, to albendazole on 47/62 (76%) farms, and to both ivermectin and albendazole on 45/61 (74%) farms. Resistance to levamisole was evident on only 4/62 (6%) farms. The parasites most prevalent in resistant populations cultured were Cooperia spp. On 45/61 (74%) farms where Cooperia spp were present in sufficient numbers, resistance to both ivermectin and albendazole was evident. No cases of levamisole-resistant Cooperia spp were detected. Resistance of Ostertagia spp to ivermectin was evident on 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, and to levamisole on 4/46 (9%) farms. CONCLUSION: Anthelmintic resistance in parasitic nematodes of cattle is common in the North Island of New Zealand. Beef farmers need to be aware of the risks posed by anthelmintic resistance, and routine FECR testing is recommended to ensure optimal productivity and to guide decision-making when purchasing anthelmintics to be used on-farm.     

Anthelmintic resistance in cyathostomins of brood horses in Ukraine and influence of anthelmintic treatments on strongylid community structure

In 2004-2006, 322 brood horses from 11 horse farms were examined using the faecal egg count reduction test (FECRT) to determine the presence and distribution of anthelmintic resistance in strongylids in Ukraine. The anthelmintic drugs "Albendazole-7.5" (7.5mg of albenazole, Ukraine) at a dose of 5mg per kg body weight and "Univerm" (0.2% aversectin C, Russia) at a dose of 0.5mg per kg body weight were used. Seventy-one horses from six farms were examined in vivo to investigate the influence of anthelmintic treatment on the gastrointestinal strongylid community structure. Horses were treated with anthelmintics; faecal sampling (200 g in each sample) for strongylid expulsion was performed 24, 36, 48 and 60 h after treatment; and all strongylids expelled (25,292 specimens) were collected and identified. Fourteen horses from the Dubrovsky horse farm were also examined to determine the benzimidazole-resistant cyathostomin species; 5208 specimens of benzimidazole-resistant cyathostomins were collected and identified. According to the FECRT data, benzimidazole resistance in strongylids was observed only at the Dubrovsky horse farm (FECRT=68.7%). No resistance to macrocyclic lactones in strongylids or in Parascaris equorum was observed. Twenty-nine strongylid species were found in horses from six horse farms. The number of species per horse ranged from 4-9 (5.8+/-1.5) to 10-20 (14.4+/-2.9) and depended on horse anthelmintic treatment strategies. From 4 to 13 strongylid species predominated (prevalence>66.7%) in the strongylid community. Eleven cyathostomin species (Cylicocyclus nassatus, C. ashworthi, C. leptostomum, Cyathostomum catinatum, C. pateratum, Cylicostephanus calicatus, C. longibursatus, C. goldi, C. minutus, Coronocyclus coronatus and C. labiatus) were found to be resistant to benzimidazoles at the Dubrovsky horse farm. Ten of these were the dominant species in the strongylid community; only C. labiatus was a rare species (prevalence 29.4%). Species richness and species diversity were significantly higher in horses from farms without treatment or with occasional treatments than from farms with regular treatments. The shape of the prevalence frequency distribution of strongylid species from farms with regular treatments was bimodal ("core" and "satellite" mode). This distribution was multimodal at farms without treatment or with occasional anthelmintic treatments. The results of the current study indicated the possibility of the further spread of anthelmintic resistance on horse farms in Ukraine and the necessity of monitoring the development of resistance in horse parasitic nematodes.     

Endoparasite control management on horse farms – lessons from worm prevalence and questionnaire data

Reasons for performing study: Increasing prevalence of anthelmintic resistance in equine nematodes calls for a reexamination of current parasite control programmes to identify factors influencing control efficacy and development of resistance. Objectives: To investigate if associations occur between prevalence of parasitic nematodes and management practices. Methods: German horse farms (n = 76) were investigated in 2003 and 2004. Information on farm and pasture management with respect to endoparasite control measures obtained using a questionnaire survey. Faecal examinations were performed in parallel. Results: Horses (n = 2000) were examined by faecal nematode egg counts, grouped into foals, yearlings and mature individuals for statistical analyses. Farms were categorised into 3 types, riding, stud farms and small holdings. Count regression models were used to analyse strongyle faecal egg count data. Following dichotomisation of faecal egg count (FEC) data, prevalence of strongyle and Parascaris equorum infections were assessed by logistic regression models as a function from various management factors. Yearlings on stud farms showed a 2‐fold higher risk of being positive for strongyle FEC, higher (i.e. ≥3 per year) anthelmintic drug treatment frequencies were associated with reduced strongyle infection rates only in mature individuals but not in foals or yearlings, foals on farms fertilising pastures with horse manure had a significantly higher risk of being P. equorum FEC positive and yearlings on stud farms were more often showing incomplete FECR following anthelmintic treatment compared to yearlings on other farm types. The mean yearly treatment frequencies per age group were: foals 4.52, yearlings 3.26 and mature horses 2.72 times, respectively. Conclusion and potential relevance: To delay the development of anthelmintic, resistance management should include additional nonchemotherapeutic parasite control strategies, FEC‐monitoring, controlled quarantine treatment of new arrivals and control of efficacy by the faecal egg count reduction test on a regular basis.     

Anthelmintic resistance in South Africa: surveys indicate an extremely serious situation in sheep and goat farming

Surveys to determine the prevalence and degree of resistance of Haemonchus spp. of sheep and goats to the available anthelmintics in South Africa indicate that small ruminant production is entering a crisis situation. Three surveys employing the faecal egg count reduction (FECR) test to determine resistance were conducted in some of the main sheep-producing areas in the summer rainfall region of South Africa, where H. contortus is the principal worm species in sheep. After analyzing the data recorded in the surveys by six different methods, including the RESO test at two different levels of confidence, the results obtained in the least stringent one (geometric mean reduction of the worm egg counts of drenched, vs untreated group of sheep) are reported in this paper, so that if any bias was obtained it would be in the favour of the anthelmintic. In Mpumalanga and KwaZulu-Natal there was anthelmintic resistance in Haemonchus spp. on all the 52 farms surveyed. Sixteen percent of the strains of H. contortus were < 60% susceptible to three of the four anthelmintics tested, and 8% of the strains were < 40% susceptible to all four of the anthelmintics. FECR tests of sheep in six localities in the Lebowa district of Northern Province indicated that even in previously disadvantaged communities where anthelmintic treatment is less intensive, anthelmintic resistance is developing, and is possibly at the level at which the situation on commercial sheep and goat farms in South Africa was 25 years ago. From the data it appears that the level of anthelmintic resistance of H. contortus in South Africa is possibly the highest that has so far been recorded in the world and that strains of it are emerging that may soon not be controllable by treatment with any of the existing anthelmintics. Farmers in the summer rainfall region, if not the whole country, must be alerted to the immediate need for testing the parasite burdens of their sheep for susceptibility to preparations in all four groups of anthelmintic compounds currently available. Alternative methods of integrated worm control, including biological, must be sought and implemented with urgency, to reduce further selection for resistance and to induce reversion of the resistance that has already developed.     

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.     

A survey of equine parasite control practices in Tennessee

A weighted, random sample of 130 horse owners in Tennessee was selected from subscribers to an equine newsletter published by the Agricultural Extension Service. Data about the participants' farms, horses, parasite control practices, and sources of information regarding equine parasite control were obtained through a telephone survey. The response rate was 98%. The typical respondent kept 4 horses on 2 pastures totaling 15 acres, and did not rotate pastures as a parasite control measure. The majority (83%) of horse owners indicated that they administered anthelmintics according to a regular schedule; 9% delayed deworming until the onset of weight loss. Proportions of owners deworming the various classes of horses at least 1, 2, 3, or 4 times annually were as follows: foals (0 to 6 months) 100, 60, 15, and 0%, respectively; weanlings (6 to 12 months) 100, 91, 32, and 0%, respectively; yearlings (1 to 2 years) 100, 100, 86, and 51%, respectively; and adults (greater than 2 years) 100, 94, 56, and 24%, respectively. Median treatments of yearlings and adults were evenly spaced at 6-, 4-, or 3-month intervals when the owners dewormed 2, 3, or 4 times annually, respectively. Mean intervals between treatments of foals and weanlings were less regular. Of the horse owners who dewormed 2 or more times annually, most (53 to 80%) used the same product exclusively for all treatments. In all age classes of horses, ivermectin paste (46 to 63%) was the most common product used, followed by tube deworming (23 to 38%) and use of benzimidazoles (4 to 16%).(ABSTRACT TRUNCATED AT 250 WORDS)     

A combination treatment strategy using pyrantel pamoate and oxibendazole demonstrates additive effects for controlling equine cyathostomins

Anthelmintics of the avermectin/milbemycin class continue to demonstrate the highest efficacy against cyathostomin nematodes; however, over‐reliance on these drugs is increasing the likelihood that recent emerging resistance to these drugs will worsen. Use of benzimidazole and pyrantel compounds given concurrently may provide sufficiently high efficacy to serve as a viable treatment alternative to the avermectin/milbemycin drugs, thus reducing the selective pressures for resistance development. The study was conducted to determine if oxibendazole (OBZ) and pyrantel pamoate (PYR) would have greater efficacy when used in combination vs. what either drug could achieve individually, and to determine if the combination protocol would consistently achieve faecal egg count reduction (FECR) rates >90%, the general threshold for acceptable efficacy. Horses of various ages and breeds on 11 horse farms were assigned randomly to treatment with OBZ (n = 34), PYR (n = 35), or a combination of both (n = 61). A faecal egg count was performed for each horse prior to treatment and 9–14 days post treatment. Mean FECR percentages were calculated for each treatment group on individual farms, and for each treatment group across all farms. Combination treatment achieved >90% mean FECR on all 11 farms, and >95% on 9 of the 11 farms. Overall arithmetic mean FECR rates were 90.03%, 81.10% and 96.35% for horses treated respectively with OBZ, PYR, and the 2 drugs in combination. Combination treatment with OBZ and PYR demonstrated an additive effect whereby horses given both anthelmintics concurrently had mean FECR percentages that were significantly greater than in horses given either drug alone. Combination treatment with OBZ and PYR can be an efficacious and viable treatment choice for controlling cyathostomins, thereby reducing the over‐reliance on avermectin/milbemycin drugs.     

Prevalence of anthelmintic resistance on 62 beef cattle farms in the North Island of New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on a random sample of beef cattle herds in the North Island of New Zealand.

METHODS: A cross-sectional prevalence study was conducted using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, levamisole and albendazole on 60 calves on each of 62 farms in the North Island chosen at random from farms that conformed with the selection criteria. Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident.

RESULTS: Of the farms that completed the FECRT, 4/61 (7%) showed ≥95% reduction in FEC for all anthelmintics tested. Resistance to ivermectin was evident on 56/61 (92%) farms, to albendazole on 47/62 (76%) farms, and to both ivermectin and albendazole on 45/61 (74%) farms. Resistance to levamisole was evident on only 4/62 (6%) farms. The parasites most prevalent in resistant populations cultured were Cooperia spp. On 45/61 (74%) farms where Cooperia spp were present in suffi cient numbers, resistance to both ivermectin and albendazole was evident. No cases of levamisole-resistant Cooperia spp were detected. Resistance of Ostertagia spp to ivermectin was evident on 4/45 (9%) farms, to albendazole on 15/46 (35%) farms, and to levamisole on 4/46 (9%) farms.

CONCLUSION: Anthelmintic resistance in parasitic nematodes of cattle is common in the North Island of New Zealand. Beef farmers need to be aware of the risks posed by anthelmintic resistance, and routine FECR testing is recommended to ensure optimal productivity and to guide decision-making when purchasing anthelmintics to be used on-farm.     

Prevalence of anthelmintic resistance on sheep farms in New Zealand

AIM: To establish the prevalence of anthelmintic resistance in parasitic nematodes on sheep farms in New Zealand. METHODS: A cross-sectional prevalence study was conducted, using a standardised faecal nematode egg count (FEC) reduction (FECR) test (FECRT) for ivermectin, at a full (0.2 mg/kg) and half (0.1 mg/kg) dose rate, and albendazole, levamisole and albendazole-levamisole in combination, on 60 lambs (n=10 per group) on farms selected from throughout New Zealand. Farms that conformed with selection criteria were chosen at random (n=80) or with a history of suspected resistance to macrocyclic lactone (ML) anthelmintics (n=32). Resistance to an anthelmintic was inferred when there was <95% reduction in FEC 7-10 days after treatment. Larval cultures were performed for all control groups and for treated groups for which resistance was evident. RESULTS: Of the farms randomly selected, 36% showed > or =95% FECR for all anthelmintics tested; resistance to ivermectin at 0.1 and 0.2 mg/kg liveweight was evident on 36% and 25% of these farms, respectively. Resistance to both ivermectin (0.2 mg/kg) and levamisole was evident on 8/80 (10%) farms, to ivermectin and albendazole on 10/80 (13%) farms, and to ivermectin, levamisole and albendazole on 6/80 (8%) farms. The prevalence of resistance to a half dose of ivermectin tended to be more prevalent on farms with a history of suspected ML resistance (p=0.06). Resistance to albendazole was seen across all the main parasite genera, and to levamisole in Nematodirus, Ostertagia (= Teladorsagia) and Trichostrongylus species. Resistance to ivermectin was dominated by Ostertagia spp, although Cooperia, Nematodirus and Trichostrongylus species were also implicated. CONCLUSION: Anthelmintic resistance in parasitic nematodes of sheep is common in New Zealand. Not only was resistance to albendazole and levamisole common, but resistance to the ML, ivermectin, was at a higher prevalence than expected. Sheep farmers and advisors in New Zealand need to re-evaluate the way they manage parasites, and more research is urgently needed if the steady decline in anthelmintic susceptibility is to be halted.     

Impaired efficacy of ivermectin against Parascaris equorum, and both ivermectin and pyrantel against strongyle infections in trotter foals in Finland

In order to assess the resistance situation against macrocyclic lactones in Parascaris equorum and against tetrahydropyrimidine derivatives in strongyles in Finnish trotter horses, 112 foals on 18 farms, mostly 1 year old, were examined for these parasites with a modified McMaster faecal flotation method. P. equorum positive foals (n=24) were given ivermectin orally at a dose of 200 μg/kg b.w., while strongyle positive but P. equorum negative foals (n=38) received pyrantel embonate orally at a dose of 19 mg/kg. Sixteen P. equorum infected foals, treated with ivermectin, also harboured strongyles. During the anthelmintic treatment visit to the farm, Faecal Egg Count Reduction Test (FECRT) reference (first) samples were collected. Fourteen days later, the second sampling (reduction samples) was done. The FECR was calculated for each foal/parasite combination. The reduction efficacies of ivermectin against P. equorum (mean 52%, calculated from the individual egg count reductions) and pyrantel against strongyles (43%) were strongly indicative of widespread resistance. Also indication of ivermectin resistance among strongyles was seen. The widespread use of anthelmintics for Finnish horses obviously has resulted in resistance, as has happened elsewhere, too.     

Equine strongyles II. Occurrence of anthelmintic resistance in Switzerland

The occurrence of anthelmintic resistance in strongyles was investigated in 440 horses on 90 farms in Switzerland. The egg hatch assay suggested that benzimidazole (BZ)-resistance was present in 40 of 82 farms (49%). Faecal egg count reduction after pyrantel-treatment was above 96% in 14 of 15 farms. In the remaining farm the efficacy was only 80%. Ivermectin efficacy was investigated on 5 farms and the efficacy was recorded at 98-100%. Faecal cultures undertaken after treatment revealed almost exclusively larvae of the family Cyathostominae. Data about management practices, pasture hygiene and anthelmintic usage were obtained with a questionnaire. Horses were treated on average 3.5 times per year. In 75% of the farms BZ were a component of the seasonal treatment schedule. Only the use of BZ had a significant correlation with the presence of BZ-resistance (P < 0.01). Recommendations for the control of equine strongyles should include measures that minimize the risk of resistance developing against remaining effective anthelmintics.     

Searching for ivermectin resistance in Dutch horses

A study was conducted to evaluate the occurrence of resistance against, in particular, ivermectin in cyathostomins in the Netherlands. Seventy horse farms were visited between October 2007 and November 2009. In initial screening, faecal samples were collected 2 weeks after deworming with either ivermectin, moxidectin or doramectin. Pooled faecal samples from a maximum of 10 horses were examined for worm eggs using a modified McMaster technique and for worm larvae after faecal larval cultures. In total 931 horses were involved. On 15 of 70 farms eggs and/or larvae were found. On 8 of these 15 farms a FECRT with ivermectin was performed on 43 horses. Efficacy of ivermectin against cyathostomins of 93% was found in one animal on one farm. Additionally, the strategies and efforts of the horse owners to control cyathostomins, as well as risk factors for the development of macrocyclic lactone resistance were evaluated with a questionnaire. Strikingly, many responders indicated that the control of cyathostomins in horses is achieved through very frequent deworming. Fourteen percent of these owners deworm seven times per year or more. On 34% of the 70 farms treatment was repeated within the Egg Reappearance Period of a product.     

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.