Anthelmintic resistance amongst sheep and goats in Kenya

Faecal egg count reduction tests (FECRT) and larval cultures were used to assess the prevalence of anthelmintic resistance amongst sheep and goats on farms served by Kenya's five regional Veterinary Investigation Laboratories. Twenty-four out of 42 farms tested (57%) showed resistance to at least one anthelmintic group. Resistance to levamisole was found in nine out of 35 sheep farms tested (26%) and 12 out of 24 goat farms (50%). Resistance to benzimidazole drugs was found in 10 out of 28 sheep farms (36%) and six out of 20 goat farms (30%). Larval cultures of post-treatment faecal samples showed resistance to be predominantly due to Haemonchus contortus. Twelve farms were routinely using substandard products which appeared to have no anthelmintic activity.     

Multiple anthelmintic resistance and the possible contributory factors in Beetal goats in an irrigated area (Pakistan)

This paper presents the first report of multiple anthelmintic resistance in the gastrointestinal nematodes of goats and its possible contributory factors in an irrigated area (Pakistan). A total of 18 privately owned Beetal goat flocks were selected in order to determine the anthelmintic resistance against commonly used anthelmintics. Forty to 48 animals from each flock were selected according to their weight and egg count. The three anthelmintics viz., oxfendazole, levamisole and ivermectin, were given to three groups at manufacturer’s recommended dose while one group was kept as untreated control. Anthelmintic resistance was determined through faecal egg count reduction and egg hatch tests while assessment of the contributory factors of anthelmintic resistance was measured through the rural participatory approach. Faecal egg count reduction test revealed high prevalence of anthelmintic resistance (83.3%) and it was either single (levamisole) or multiple (oxfendazole and levamisole). Egg hatch test confirmed the resistance against oxfendazole as detected with faecal egg count reduction test. None of the goat flocks was resistant to ivermectin. Copro-cultures revealed that Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta were the most common species exhibiting resistance to levamisole and oxfendazole. Step-wise logistic regression of the data on worm control practices revealed significant role of under-dosing, low-protein diets, healthcare supervision by the traditional healers and mass treatments.     

Detecting benzimidazole resistance with faecal egg count reduction tests and in vitro assays

Composite strains of Trichostrongylus colubriformis and Ostertagia spp consisting of 0, 1, 10, 25, 50, 75, 90, and 100% of known resistant strains were prepared and tested for benzimidazole resistance using faecal egg count reduction tests, in vitro egg hatch assays and tubulin binding assays. All tests detected resistance where the proportion of the resistant strain in the composite was 50% or more, whereas none of the tests unequivocally detected resistance below 25%. Egg count reduction tests were no less sensitive than the in vitro tests in detecting low levels of resistance but the egg hatch and tubulin binding assays provided a better quantitative estimate of moderate to high levels of resistance. Faecal egg count reduction therefore, provides a suitable means of detecting resistance in the field but tests, more sensitive to low levels of resistance are required. Results indicate that the use of post-treatment counts alone provides an adequate indication of anthelmintic efficiency.     

Multiple resistance in goat-derived Ostertagia and the efficacy of moxidectin and combinations of other anthelmintics

Faecal egg count reduction tests were used to identify a strain of Ostertagia circumcincta/trifurcata complex in goats which was resistant to: ivermectin (at 0.2 mg/kg and 0.4 mg/kg orally), oxfendazole (at 5 mg/kg orally), levamisole (at 12 mg/kg orally) and fenbendazole (at 5 mg/kg orally) combined with levamisole (at 9.4 mg/kg orally). The percentage reductions achieved in these faecal egg count reduction tests were respectively 27%, 83%, 82%, 79% and 82%. Moxidectin (at 0.2 mg/kg by subcutaneous injection), fenbendazole (at 10 mg/kg orally) combined with levamisole (at 18.8 mg/kg orally), ivermectin (at 0.4 mg/kg orally) combined with oxfendazole (at 10 mg/kg orally) and ivermectin (at 0.4 mg/kg orally) combined with levamisole (at 12 mg/kg orally) were effective in removing these nematodes in goats as determined by faecal egg count reduction tests. These drenches achieved reductions of 100%, 100%, 98% and 100% respectively.     

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.     

An introductory survey of helminth control practices in south africa and anthelmintic resistance on Thoroughbred stud farms in the Western Cape Province

Fifty-one per cent of 110 questionnaires, designed for obtaining information on helminth control practices and management on Thoroughbred stud farms in South Africa, were completed by farmers during 2000. The number of horses per farm included in the questionnaire survey ranged from 15 to 410. Foals, yearlings and adult horses were treated with anthelmintics at a mean of 7.3 +/- 3.0, 6.6 +/- 2.7 and 5.3 +/- 2.3 times per year, respectively. An average of 3.4 different drugs were used annually, with ivermectin being used bymost farmers during 1997-2000. On 43% of farms the weights of horses were estimated by weigh band and 45% of farmers estimated visually, while both were used on 7% of farms and scales on the remaining 5%. Doses were based on average group weight on 50% ofthe farms and on individual weights on 46%. Forty-three per cent of farmers performed faecal egg count reduction tests (FECRT). Most farmers rotated horses between pastures and treated new horses at introduction. Faecal removal was practiced on 61% of farms and less than 50% of farmers used alternate grazing with ruminants. Faecal egg count reduction tests were done on 283 horses, using oxibendazole, ivermectin and moxidectin on 10,9 and 5 farms, respectively, in the Western Cape Province during 2001. While the efficacy of oxibendazole was estimated by FECRT to range from 0-88% and moxidectin from 99-100%, ivermectin resulted in a 100% reduction in egg counts. Only cyathostome larvae were recovered from post-treatment faecal cultures.     

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.     

Anthelmintic resistance and sheep management practices in south western Victoria

Twenty-eight farms in 7 shires in south western Victoria were selected and tested for presence of benzimidazole-resistant nematodes between November 1979 and June 1981. Mean faecal egg counts of sheep were less than 100 strongyloid eggs/g on 11 farms. Faecal egg count reduction tests were conducted on the remaining 17 farms and thiabendazole was less than 90% efficient in reducing egg counts in sheep from 5 (29%) of these farms. Thiabendazole-resistant Teladorsagia circumcincta were identified at necropsy of experimentally infected treated sheep. In further studies a survey of 104 farms was conducted in the Mount Rouse and Dundas shires of western Victoria in 1981 and 1982 respectively to determine the prevalence of anthelmintic resistance in these shires. Mean faecal egg counts among weaner sheep in the winter-spring of both years were less than 100 eggs/g which indicated low levels of parasitic nematode populations. A faecal egg count reduction test was conducted on 10 farms and thiabendazole was less than 90% efficient on 3; levamisole was greater than 90% efficient in all 10 tests. Most of the surveyed farms carried Merino or Merino crossbred sheep at 10 to 15 dry sheep equivalents per ha and weaners were treated with anthelmintics 3 to 6 times per year. Management procedures based mainly on anthelmintic therapy were effective in controlling nematode populations in weaner sheep, although many producers alternated between different groups of anthelmintics within the same year contrary to current recommendations for long-term preservation of anthelmintic efficacy. It was concluded that anthelmintic resistance was not of practical importance to the majority of sheep producers in the region.     

Naphthalophos combinations with benzimidazoles or levamisole as effective anthelmintics for sheep

Objective: To investigate the relative efficacy and safety of the anthelmintic naphthalophos in sheep, either given alone or in combination with benzimidazole (fenbendazole and albendazole) or levamisole anthelmintics.
Design: A parasitological study using faecal egg count reduction tests, a validating slaughter trial and field safety trials.
Procedure: Faecal egg count reduction tests were carried out on 13 farms. Naphthalophos and combinations of naphthalophos with levamisole and fenbendazole were included in the drench tests. On one property a controlled efficacy study was carried out to validate faecal egg count reduction test findings. In this trial, sheep were slaughtered 10 days after treatment and the remaining parasites recovered from the gastro-intestinal tract. Safety trials were carried out on eight farms where approximately 50 000 sheep were treated with naphthalophos and albendazole that were tank mixed in the backpack.
Results: The efficacy of naphthalophos alone in faecal egg count reduction tests ranged from 59 to 98% with one test showing 95% reduction. The efficacy of naphthalophos and levamisole ranged from 74 to 100%, with 5 farms showing 95% reduction. The efficacy of naphthalophos and fenbendazole ranged between 88 and 100% with 95% reduction achieved on 10 farms. The controlled efficacy study showed a good correlation between the faecal egg count reduction tests and numbers of parasites recovered, except for Nematodirus where the faecal egg count reduction tests overestimated efficacy. The mortality rate in the safety trials was 0.05%, with most fatalities occurring on one farm.
Conclusion: The combination of naphthalophos and fenbendazole was more effective than a combination of naphthalophos and levamisole, and will provide a sufficiently safe drench rotation option.     

Seasonal variations in the numbers of trichostrongylid nematode eggs and their larvae in the faeces of farmed goats in Malaysia.

Faecal worm egg counts of goats from two farms in Penang Island, West Malaysia, were monitored over a period of 14 months. The faecal egg count pattern followed that of total rainfall. The humid tropical environment was favourable for the development of various species of trichostrongylid nematodes, namely Haemonchus contortus, Trichostrongylus spp., Oesophagostomum spp. and Cooperia spp. Generally, H. contortus was observed to be the predominant species, more so in the monsoon months of the year.     

Use of two in vitro methods for the detection of anthelmintic resistant nematode parasites on Slovak sheep farms

A survey of the prevalence of anthelmintic resistant nematode populations was conducted on 32 sheep farms in the Slovak Republic. In vitro egg hatch test and larval development tests were used for the detection of resistance to benzimidazole anthelmintics and they were compared with in vivo faecal egg count reduction tests. There was agreement in the declaration of resistance between the faecal egg count reduction test and both in vitro tests. The presence of resistant populations was determined on two farms using egg hatch test. In both farms, the LD(50) values were higher than 0.1 microg TBZ/ml, indicating resistance. By using LD(99) values it might be possible to reveal relatively small proportion of resistant larvae in the population. The prevalence of benzimidazole resistance has not change on Slovak sheep farms during last decade.     

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.     

Resistance of Teladorsagia circumcincta in goats to ivermectin in the Netherlands

Resistance of Teladorsagia circumcincta in goats to ivermectin In 2005, suspected ivermectin resistance of gastrointestinal nematodes was investigated in 17 goats on a farm in the Netherlands, using a faecal egg count reduction test combined with faecal larval cultures. Eight goats were treated orally with 0.2 mg/ kg ivermectin on 1 August 2005 and the other nine goats served as untreated controls. Faeces were collected from all goats on 1 August and on 12 August. Faecal egg counts were reduced by 80.6% in goats receiving ivermectin. On the basis of faecal larval cultures and the egg counts, ivermectin was found to be 100% effective against Haemonchus contortus, 15.0% effective against Teladorsagia circumcincta, and 93.3% effective against Trichostrongylus spp. The effect of levamisole and oxfendazole on gastrointestinal nematodes was also evaluated. Nine goats were treated subcutaneously with 5 mg/kg levamisole and seven goats orally with 4.5 mg/kg oxfendazole on 12 September On the basis of faecal egg counts performed on 12 and 22 September, levamisole reduced the total egg count by 95.4% and oxfendazole reduced the egg count by 85.8%. Differentiation of pooled faecal larval cultures revealed that levamisole was 99.9% effective against H. contortus, 81.9% effective against T. circumcincta, and 99.5% against Trichostrongylus spp. Oxfendazole was 75.5% effective against H. contortus, 33.2% effective against T. circumcincta, and 100% effective against Trichostrongylus spp. On 28 October the nine goats that were still present on the farm were orally treated with 0.4 mg/kg ivermectin. Faecal egg counts and differentiation of pooled larval cultures of faecal samples collected on 28 October and 9 November, respectively, revealed that total egg counts were reduced by 93.1%. Ivermectin was 49.1% effective against T. circumcincta but 100% effective against H. contortus and Trichostrongylus spp. Thus H. contortus appears to be resistant to oxfendazole and T. circumcinta appears to be resistant to oxfendazole and ivermectin. This is the first documented case of ivermectin resistance of a gastrointestinal nematode of small ruminants in the Netherlands.     

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 of nematode parasites of small ruminants in eastern Ethiopia: exploitation of refugia to restore anthelmintic efficacy

Faecal egg count reduction tests (FECRT) were conducted in May 2003 to determine the efficacy of anthelmintics used for treatment against nematode parasites in separately managed sheep and goat flocks at Alemaya University in eastern Ethiopia. These tests revealed high levels of anthelmintic resistance to albendazole, tetramisole, the combination of these two drugs, and to ivermectin in the goat flock (predominantly infected by Haemonchus contortus and Trichostrongylus spp.), whereas all drugs were highly efficacious in the sheep flock. A second FECRT confirmed these observations. Following this, a new management system was implemented on the goat flock for a period of 9 months (January-September 2004) in an attempt to restore the anthelmintic efficacy. This involved a combination of measures: eliminating the existing parasite infections in the goats, exclusion from the traditional goat pastures, and introducing communal grazing of the goats with the university sheep flock and livestock owned by neighbouring small-holder farmers. A second series of FECRTs (Tests 3 and 4) conducted 7 months after this change in management, showed high levels of efficacy to all three drugs (albendazole, tetramisole and ivermectin) in the goat flock. This is the first field study to demonstrate that anthelmintic efficacy in the control of nematode parasites of small ruminants can be restored by exploiting refugia.     

Composite faecal egg count reduction test to detect resistance to triclabendazole in Fasciola hepatica

A faecal egg count reduction test, using composite samples, was developed in order to assess the efficacy of the flukicide, triclabendazole (TCBZ) on commercial sheep farms in England and Wales. First, a comparison between individual counts and composite counts was conducted using sheep on two farms with different levels of infection. Faecal samples were collected from 50 sheep on each farm at the time of TCBZ treatment and 21 days later. The results showed that a composite fluke egg count (CFEC) was as sensitive as using individual samples, and the test was subsequently validated on an additional 18 sheep farms. The pre- and post-treatment CFECs using five composite samples were subjected to bootstrap analysis. The variance in fluke egg counts of composite samples was high, but analyses indicated that 20 individual samples analysed as two composites was as sensitive as using five composites. The two-composite assay was evaluated on another five farms. On seven out of 25 farms sampled, egg counts either did not decrease significantly or increased following treatment, suggesting TCBZ resistance on these farms. This assay represents a practical field test that can be used in the first instance to evaluate the efficacy of TCBZ on sheep farms where resistance is suspected.     

Total Anthelmintic Failure to Control Nematode Parasites of Small Ruminants on Government Breeding Farms in Sabah,East Malaysia

Government-owned small-ruminant breeding farms in Malaysia provide the source of sheep and goats to smallholder farmers in the country. In the eastern Malaysian state of Sabah, high-level stock losses have been recorded on these farms for several years, frequently accompanied by clinical signs indicating pathogenic levels of infections with the nematode parasite Haemonchus contortus. This suggests that their dependence on chemotherapy to control parasite infections had failed. Accordingly, tests for anthelmintic efficacy using the faecal egg count reduction test (FECRT) on the range of drugs used to control nematode parasites were carried out on the five government small-ruminant breeding farms in Sabah. These tests showed a total failure of the benzimidazole, imidothiazole, macrocyclic lactone and salicylanilide groups of anthelmintics to control H. contortus infections of sheep and goats on all farms. Drastic changes in animal management need to be made in an attempt to deal with this situation, for which suggestions are made.     

A comparison of in vitro tests and a faecal egg count reduction test in detecting anthelmintic resistance in horse strongyles.

This study reports a comparison between faecal egg count reduction test (FECRT), egg hatch assay (EHA) and larval development assay (LDA) for detecting anthelmintic resistance in equine strongyles. Resistance to benzimidazoles was demonstrated in 33 of 42 (79%) farms tested by FECRT and in 32 (62%) of the 52 farms tested by EHA. As the reference strain used was not fully susceptible to benzimidazoles it was not possible to determine the level of resistance by LDA. Pyrantel resistance was indicated on three of 15 farms by faecal egg count reduction. Resistance was also indicated by LDA for one of these farms. In addition resistance was indicated by LDA on two more farms that were not tested by FECRT. Further testing is needed to confirm if these findings are truly indicative of resistance. Generally, correlations between the tests were poor and it was not possible to use the outcome of one test to predict the outcome of another.     

Multiple anthelmintic resistance on a goat farm in Hawassa (southern Ethiopia)

A study was conducted to determine the presence of anthelmintic resistance on Hawassa University goat farm in southern Ethiopia. The 180 goats were stratified by age and sex and randomly assigned to treatment groups (albendazole, tetramisole and ivermectin and untreated control). Each treatment group included 15 goats and treatments were administered according to weight of each goat with 7.5 mg/kg bw albendazole, 22.5 mg/kg bw tetramisole and 0.2 mg/kg bw ivermectin dose rates recommended by scientists. Faecal samples were collected on day 0 before treatment, and again on day 12 post treatment. Efficacy of all the drugs was assessed on day 12 post treatment by faecal egg count reduction test (FECRT). Multiple anthelmintic resistance in Haemonchus spp. against albendazole, tetramisole and ivermectin was recorded in all age categories of the goats. Likewise, Trichostrongylus/Teladorsagia spp. showed resistance against ivermectin. Coprocultures from all pre- and post-treatments revealed the predominance of Haemonchus spp. Resistance against anthelmintics is attributed to the high frequency of treatment and low dosage of treatment practices on the farm. Large scale studies, however, are needed to assess the current status of anthelmintic resistance against the most commonly used anthelmintics in different agroecology, species of animals and management systems in Ethiopia.     

Field studies investigating anthelmintic resistance in young cattle on five farms in New Zealand

AIM: To investigate the efficacy of pour-on anthelmintics against field strains of parasitic nematodes in young cattle on five farms in New Zealand. METHODS: Faecal nematode egg count (FEC) reduction (FECR) tests were carried out on five calf-rearing farms using pour-on formulations of levamisole, ivermectin, eprinomectin, and the simultaneous administration of levamisole and ivermectin. Faecal samples were collected per rectum before treatment and about 7, 14, 21 and 28 days after treatment, for FEC and faecal nematode larval culture. RESULTS: Resistance (i.e. <95% reduction in FEC) of Cooperia oncophora to ivermectin and eprinomectin was identified on all five farms. There was limited evidence of possible emerging resistance in Ostertagia spp to ivermectin but not eprinomectin, in short-tailed larvae of Cooperia spp to ivermectin and eprinomectin, and in Trichostrongylus spp to ivermectin, eprinomectin and levamisole used separately. Levamisole was effective against C. oncophora, but had variable efficacy against Ostertagia spp in the calves in this study. Simultaneous treatment with levamisole and ivermectin pour-on formulations were effective against all genera on all farms. CONCLUSIONS: To effectively manage roundworm parasites in their calves farmers need to be aware of the resistance status of the parasites on their farms. Levamisole is likely to be an effective anthelmintic on most farms at times of the year when the impact of Ostertagia spp is not high. Simultaneous administration of levamisole and ivermectin pour-on anthelmintics to cattle is likely to control both ML-resistant C. oncophora and stages of Ostertagia spp that are not controlled by levamisole alone.