Determination of anthelmintic efficacy against equine cyathostomins and Parascaris equorum in France

This article reports the results of a faecal egg count reduction test on 4 farms in France, as an integrated part of the routine deworming strategy against horse cyathostomins and Parascaris equorum. Treatment with fenbendazole (FBZ) or ivermectin (IVM) was evaluated in yearlings on Farms 1 and 2 and treatment with pyrantel embonate (PYR) was tested on Farms 3 and 4. Calculation of the arithmetic mean faecal egg count reduction and the 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. For equine cyathostomins, resistance to FBZ was found with an arithmetic mean reduction of 48.8% (95% CI: 1.9–69.3%). On Farms 1 and 2, horses with reduced efficacy were identified. PYR was found to be effective against cyathostomins, with an arithmetic mean reduction of 95.3% (95% CI: 84.6–99.8%), as well as IVM (100%). For P. equorum, both FBZ and PYR were effective (100% reduction). The efficacy of IVM, however, was low (45.5%; 95% CI: 0–96.3%). These results confirm that FBZ resistance in equine cyathostomins is present in France and that anthelmintic resistance to IVM is present in P. equorum. This study underlines the necessity to evaluate the efficacy of horse deworming strategies on a regular basis under field conditions.     

Effects of fecal collection and storage factors on strongylid egg counts in horses

Fecal analyses are becoming increasingly important for equine establishments as a means of parasite surveillance and detection of anthelmintic resistance. Although several studies have evaluated various egg counting techniques, little is known about the quantitative effects of pre-analytic factors such as collection and storage of fecal samples. This study evaluated the effects of storage temperature, storage time and airtight versus open-air storage on fecal egg counts. The experimental protocols were replicated in two study locations: Copenhagen, Denmark and Athens, Georgia, USA. In both locations, the experiment was repeated three times, and five repeated egg counts were performed at each time point of analysis. In experiment A, feces were collected rectally and stored airtight at freezer (−10 to −18 °C), refrigerator (4 °C), room (18–24 °C), or incubator (37–38 °C) temperatures. Egg counts were performed after 0, 6, 12, 24, 48, and 120 h of storage. In experiment B, feces were collected rectally and stored airtight or in the open air in the horse barn for up to 24 h. Egg counts were performed after 0, 3, 6, 12, and 24 h of storage. In experiment A at both locations, samples kept in the refrigerator showed no decline in egg counts, whereas storage in the freezer and incubator led to significantly declining egg numbers during the study. In contrast, storage at room temperature yielded marked differences between the two study locations: egg counts remained stable in the U.S. study, whereas the Danish study revealed a significant decline after 24 h. In experiment B, the Danish study showed no differences between airtight and open-air storage and no changes over time, while the U.S. study found a significant decline for open-air storage after 12 h. This difference was attributed to the different barn temperatures in the two studies. To our knowledge, this is the first study to evaluate the pre-analytic factors affecting egg counts in horses using an experimental protocol replicated in two contrasting geographic and climatic locations. Our results demonstrate that refrigeration is the best method for storage of fecal samples intended for egg count analysis, but that accurate results can be derived from fecal samples collected from the ground within 12 h of passage.     

Daily Variability of Strongyle Fecal Egg Counts in Horses

Strongyle parasites are ubiquitous in grazing horses and constitute a potential threat to equine health. Feces were collected from six horses four times daily over a period of 5 days. Fecal egg counts (FECs) were performed to identify any diurnal rhythms in strongyle egg shedding and to quantify variability at the different levels: individual horses, repeated counts, repeated subsamples, different time points, and different days. No significant differences in FECs were found between the different time points (P = .11). The variables—horse, day, subsample, and egg count—accounted for a variance of 104.83, 0.10, 7.24, and 5.61, respectively. The apparent lack of additional variability between the four different time points suggests that time of the day chosen for collecting fecal samples does not constitute a source of error in field studies. The majority of variability exists between different subsamples and repeated egg counts on the same subsamples, whereas the variability of FECs between following days can be considered negligible. The findings of this study have implication for designing and performing field surveillance of strongyle FEC levels and applying the FEC reduction test for evaluating anthelmintic efficacy.     

Accuracy and Precision of Mini-FLOTAC and McMaster Techniques for Determining Equine Strongyle Egg Counts

The use of fecal egg count techniques to indirectly assess intestinal parasite burdens and determine anthelmintic efficacy is common in parasitological research and veterinary practice. The McMaster method is one of the most widely used techniques in veterinary practice, but recently, the Mini-FLOTAC technique has been introduced as a possible alternative. Studies comparing the two methods in precision and accuracy are needed. This study aimed at evaluating the Mini-FLOTAC technique for determining equine strongyle egg counts through a two-part procedure. First, a set of fecal counts was executed using both methods. Next, blind counts were performed on spiked fecal samples with true egg counts at 0, 5, 50, 500, and 1,000 eggs per gram. All counts were performed in triplicates, and each sample was counted using both methods. Mini-FLOTAC and McMaster had 83.2% and 53.7% precision, respectively. The accuracy was found to be 42.6% and 23.5% for Mini-FLOTAC and McMaster, respectively. In conclusion, this study found that Mini-FLOTAC exhibited both higher precision and accuracy than the McMaster technique and appears to be a more reliable alternative. Using a more precise egg-counting method can help assure that changes in egg counts before and after treatment reflect a genuine reduction and are not due to chance variability.     

Comparison between methods for measuring fecal egg count and estimating genetic parameters for gastrointestinal parasite resistance traits in sheep

Fecal egg count (FEC) is an indicative measurement for parasite infection in sheep. Different FEC methods may show inconsistent results. Not accounting for inconsistencies can be problematic when integrating measurements from different FEC methods for genetic evaluation. The objectives of this study were to evaluate the difference in means and variances between two fecal egg counting methods used in sheep—the Modified McMaster (LMMR) and the Triple Chamber McMaster (LTCM); to estimate variance components for the two FEC methods, treating them as two different traits; and to integrate FEC data from the two different methods and estimate genetic parameters for FEC and other gastrointestinal parasite resistance traits. Fecal samples were collected from a commercial Rideau-Arcott sheep farm in Ontario. Fecal egg counting was performed using both LMMR and the LTCM methods. Other parasite resistance trait records were collected from the same farm including eye score (FAMACHA), body condition score (BCS), and body weight (WT). The two FEC methods were highly genetically (0.94) and phenotypically (0.88) correlated. However, the mean and variance between the two FEC methods were significantly different (P < 0.0001). Therefore, re-scaling is required prior to integrating data from the different methods. For the multiple trait analysis, data from the two fecal egg counting methods were integrated (LFEC) by using records for the LMMR when available and replacing missing records with re-standardized LTCM records converted to the same mean and variance of LMMR. Heritability estimates were 0.12 ± 0.04, 0.07 ± 0.05, 0.17 ± 0.06, and 0.24 ± 0.07 for LFEC egg count, FAMACHA, BCS, and WT, respectively. The estimated genetic correlations between FEC and the other parasite resistance traits were low and not significant (P > 0.05) for FAMACHA (r = 0.24 ± 0.32) and WT (r = 0.22 ± 0.19), and essentially zero for BCS (r = −0.03 ± 0.25), suggesting little to no benefit of using such traits as indicators for LFEC.     

Lack of Cyathostomin sp. reduction after anthelmintic treatment in horses in Brazil

The increase of anthelmintic resistance in the last years in the nematode population of veterinary importance has become a major concern. The objective of the present study was to evaluate the efficacy of the main anthelmintic drugs available in the market against small strongyles of horses in Brazil. A total of 498 horses from 11 horse farms, located in the states of Paraná, São Paulo, Rio de Janeiro and Minas Gerais, in Brazil, were treated with ivermectin, moxidectin, pyrantel and fenbendazole, orally at their recommended doses. The fecal egg count reduction test (FECRT) was used to determine the product's efficacy and fecal culture was used to determine the parasite genus. Reduction on anthelmintic efficacy was found for fenbendazole in all horse farms (11/11), pyrantel in five yards (5/11) and ivermectin had low efficacy in one of the yards studied (1/11). Multidrug resistance of up to 3 drugs classes was found in one of the tested farms (1/11). Cyathostomin were the most prevalent parasite. The results showed that resistance to fenbendazole is widespread; the efficacy of pyrantel is in a critical situation. Although the macrocyclic lactones compounds still showed high efficacy on most farms, suspected resistance to macrocyclic lactones is of great concern.     

A Field Survey on Anthelmintic Resistance in Equine Small Strongyles in Norway

A field survey at 17 stables involving 221 horses was performed to evaluate the presence of anthelmintic resistance in the equine small strongyles (cyathostomes). The horses were allocated into treatment groups, and resistance to fenbendazole (FBZ), pyrantel pamoate (PYR) and ivermectin (IVM) was tested by the faecal egg count reduction test (FECR-test). Faecal samples were collected at the time of treatment, 14 days post treatment and 90 days post treatment.Resistance to FBZ, which was defined as a faecal egg count reduction <95%, was found in 14 out of 17 stables. In 2 of the 14 stables the egg reductions were close to the limit of 95%, 91 and 93%, respectively. In 1 stable the egg reductions indicated resistance to PYR as well as detection of resistance to FBZ, 94% reduction for PYR and 85% for FBZ. No signs of resistance were detected to IVM.The investigation was performed in late autumn and winter, and due to the climatic conditions and cleaning procedures in the stables no reinfection took place during this period. The faecal egg count reduction from treatment till day 90 post treatment was used as an expression of the effect of PYR and IVM on the early stage (hypobiotic), late third stage and fourth stage larvae in the gut wall. This was justified because there was no reinfection and because the 14 day post treatment egg counts were zero or close to zero for the PYR and IVM treatment groups. The effects of PYR and IVM on the larval stages were compared and no statistically significant differences were found.     

Effectiveness of current anthelmintic treatment programs on reducing fecal egg counts in United States cow-calf operations

During the United States Department of Agriculture (USDA) National Animal Health Monitoring System’s (NAHMS) 2007–2008 beef study, producers from 24 states were offered the opportunity to evaluate their animals for internal parasites and for overall responses to treatment with anthelmintics. A lapse of 45 d was required between initial sampling and any previous treatments. Choice of anthelmintic (oral benzimidazoles, and both injectable and pour-on endectocides) was at the discretion of the producer so as not to alter the local control programs. Fresh fecal samples were collected from 20 animals, or from the entire group if less than 20, then randomly assigned to 1 of 3 participating laboratories for examination. Analyses consisted of double centrifugation flotation followed by enumeration of strongyle, Nematodirus, and Trichuris eggs (the presence of coccidian oocysts and tapeworm eggs was also noted). Where strongyle eggs per gram (epg) exceeded 30, aliquots from 2 to 6 animals were pooled for egg isolation and polymerase chain reaction (PCR) analysis for the presence of Ostertagia, Cooperia, Haemonchus, Oesophagostomum, and Trichostrongylus. Results from 72 producers (19 States) indicated that fecal egg count reductions were < 90% in 1/3 of the operations. All operations exhibiting less than a 90% reduction had used pour-on macrocyclic lactones as the anthelmintic treatment. While some of these less than expected reductions could have been the result of improper drug application, PCR analyses of the parasite populations surviving treatment, coupled with follow-up studies at a limited number of sites, indicated that less than expected reductions were most likely due to anthelmintic resistance in Cooperia spp. and possibly Haemonchus spp.     

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.     

Faecal worm egg count analysis for targeting anthelmintic treatment in horses: Points to consider

Equine gastrointestinal nematodes are ubiquitous; in horses that graze contaminated pasture and that are not treated appropriately, large numbers of worms can accumulate, which can lead to serious clinical disease. Nematode control has traditionally followed interval treatment regimens, which involve regular anthelmintic administration to all horses based on the strongyle egg reappearance periods of each drug, usually defined around the time of licensing. Interval treatment programmes have resulted in substantial reductions in large strongyle disease, but have made major contributions to the development of anthelmintic resistance, particularly in cyathostomins. Cyathostomin resistance to 2 of the 3 available anthelmintic classes is widespread, and resistance to both classes in single populations is not uncommon. Reduced efficacy of the most commonly used macrocyclic lactone anthelmintics, as measured by shortened egg reappearance periods after treatment, is emerging in cyathostomins. Macrocyclic lactone resistance is also now commonly reported in Parascaris equorum on stud farms. Faecal worm egg counts (FWEC) are increasingly being used as part of targeted approaches to parasite control, whereby only those horses with moderate to high FWEC within a group are treated with an anthelmintic. The objective of this approach is to reduce environmental contamination, while leaving a proportion of the worm population in some horses unexposed to selection pressure for anthelmintic resistance. This article reviews recent findings in equine parasitology research that will underpin guidelines for control, with a particular focus on how to optimise the value of FWEC methodologies and anthelmintic efficacy analyses.     

Resistance to benzimidazole anthelmintics in small strongyles (Cyathostominae) of horses in Denmark.

This study was undertaken to establish whether anthelmintic resistance was present in nematode parasites of horses in Denmark. Sixteen horse farms were selected for faecal egg count reduction (FECR) tests to measure the efficacy of the anthelmintic used. Resistance to benzimidazole anthelmintics was found on 13 of the 16 farms, with FECR values ranging from 80.0% to -101.3%. On the remaining 3 farms FECR was 100.0%, 99.3% and 97.2%. Results of a questionnaire study on anthelmintic usage, parasite control measures and management practices showed that horses in this study were treated on average 7.1 times/year. Horse owners changed between preparations of drugs but almost only within the same class of anthelmintics. Nine owners gave an anthelmintic treatment to purchased horses before they were introduced on the farm. On 14 farms, the same paddock was grazed every year and the average stocking rate was estimated to be 2.4 horses/ha. Strategies to avoid development of anthelmintic resistance are discussed and recommendations of parasite control on horse farms are presented.     

河北省坝上地区绵羊消化道线虫对丙硫苯咪唑抗药性的检测

目的　为了查明绵羊消化道线虫对丙硫苯咪唑的抗药性。方法　应用粪便虫卵减少试验 (FECRT)对河北省坝上地区绵羊消化道线虫的抗药性进行了检测。结果　应用 5 m g/ kg丙硫苯咪唑对 5组绵羊进行驱虫的虫卵减少率分别为 4 3.9% ,38.4 6 % ,4 9.0 9% ,37.6 3%和 4 3.35 % ,驱净率分别为 2 0 % ,15 % ,15 % ,2 5 %和 10 %。结论　根据 FECRT 95 %置信域小于 90 % ,表明试验羊对该药有抗药性     

Frequent deworming in horses; it usually does not do any good, but it often harms

Due to excessive and inappropriate use of dewormers anthelmintic resistance has developed as a significant problem in horse parasites in the Netherlands. Since it is unlikely that new classes of anthelmintics against horse nematodes will be introduced in the near future, it is important to use the present drugs wisely. Veterinarians should advice horse owners about worm control programs with a more targeted approach. The number of anthelmintic treatments should be reduced and, through selective anthelmintic treatments, further development of anthelmintic resistance should be delayed. Preferably, horses with a low faecal egg count should not be treated at all to ascertain a reduction of the selection pressure for anthelmintic resistance. The propensity for low faecal egg counts is hereditary. This implies that mature horses with consistent low egg counts can be detected by faecal examination and that it is not necessary to repeat faecal examination each time in these animals. New horses on the farm should always be dewormed on arrival and should be introduced only after the efficacy of treatment has been determined. Anthelmintic resistance can also be introduced with the arrival of a new animal that is infected with drug-resistant parasites.     

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.     

Resistance to thiabendazole, fenbendazole and levamisole in Haemonchus and Trichostrongylus species in sheep on a Kenyan farm

Resistance to thiabendazole (TBZ), fenbendazole (FBZ) and levamisole (LVM) in naturally acquired gastrointestinal nematode parasites in sheep was investigated on a farm where anthelmintic resistance was suspected. This was measured by both the in vitro egg hatch assay, and reductions in faecal egg and worm counts in treated animals. In the egg hatch assay, nematode eggs were incubated in various concentrations of either TBZ or LVM. The level of resistance was expressed as the drug concentration inhibiting 50% of the eggs from hatching (LC50). The nematode population had LC50 values of 0.26 microgram ml-1 TBZ and 3.12 micrograms ml-1 LVM. In the faecal egg and worm count reduction test, naturally infected sheep were treated with either TBZ (88 mg kg-1), FBZ (10 mg kg-1) or LVM (15 mg kg-1). Faecal egg and total worm counts from these sheep were then compared with counts from untreated sheep. TBZ, FBZ and LVM failed to reduce the faecal egg counts and total worm counts by more than 90%. Based on the identification of larvae from faecal cultures, the most predominant nematode species in the resistant population were Haemonchus (62%) and Trichostrongylus (28%). TBZ reduced faecal egg counts for both species by less than 90%. FBZ and LVM also reduced Haemonchus spp. eggs by less than 90%. Other nematode species numbers did not satisfy criteria for the determination of efficacy.     

The efficacy of a combined oral formulation of derquantel-abamectin against anthelmintic resistant gastro-intestinal nematodes of sheep in the UK

The objective of the present studies was to evaluate the efficacy of a combined formulation (Startect(?) Dual Active Oral Solution for Sheep, Pfizer Animal Health) of derquantel (DQL) and abamectin (ABA) for the treatment of: (1) sheep experimentally infected with a moxidectin (MOX)-resistant isolate of Teladorsagia circumcincta, and (2) multi-drug resistant gastrointestinal nematode parasites under UK field conditions. In the first study, a total of 40 animals were allocated into 4 treatment groups, and were either left untreated or treated with DQL+ABA, MOX or ABA. Faecal samples were collected on days 1-5 and on day 7 after treatment to examine the reduction in faecal egg excretion and to evaluate the egg viability. On day 14 post treatment all animals were euthanised for abomasal worm counts. There was a 100% reduction in geometric mean worm counts for the DQL+ABA treated animals compared to the untreated control animals (P<0.0001), whereas the percentage reduction in worm counts for the MOX- (P>0.05) and ABA-treated (P=0.0004) animals was 12.4% and 71.8%, respectively. The data from the egg hatch assay (EHA) indicated that in the MOX-treated and the ABA-treated animals, the majority of the eggs hatched after treatment. In the field study, performed on four farms, animals were allocated into 6 groups of 11-15 animals each in order to conduct a faecal egg count reduction test (FECRT), based on arithmetic mean egg counts. One group of animals remained untreated, whereas the other animals were treated with DQL+ABA, MOX, fenbendazole (FBZ), levamisole (LV) or ivermectin (IVM). On each of the farms the reduction in egg excretion after treatment with FBZ, LV or IVM was below 95.0%, indicating anthelmintic resistance. The efficacy of DQL+ABA ranged from 99.1 to 100%, yielding significantly lower egg counts compared to the untreated control group (P≤0.003). For MOX the egg counts were significantly (P≤0.003) lower compared to the untreated group at each farm, with reductions varying from 98.2 to 100%. The post-treatment copro-cultures for larva identification indicated that T. circumcincta was the most abundant worm species after treatment (52-99% of the larvae). The results of these studies confirm the high efficacy of the DQL+ABA combination formulation against anthelmintic resistant nematodes in the UK.     

Statistical and biological considerations in evaluating drug efficacy in equine strongyle parasites using fecal egg count data

Anthelmintic resistance (AR) is a serious problem for the control of equine gastrointestinal nematodes, particularly in the cyathostomins. The fecal egg count reduction test (FECRT) is the most common method for diagnosing AR and serves as the practical gold standard. However, accurate quantification of resistance and especially accurate diagnosis of emerging resistance to avermectin/milbemycin (A/M) drugs, is hampered by a lack of accepted standards for study design, data analysis, and data interpretation. In order to develop rational evidence-based standards for diagnosis of resistance, one must first take into account the numerous sources of variability, both biological and technical, that affect the measurement of fecal egg counts (FECs). Though usually ignored, these issues can greatly impact the observed efficacy. Thus, to accurately diagnose resistance on the basis of FECRT data, it is important to reduce levels of variability through improved study design, and then deal with inherent variability that cannot be removed, by performing thorough and proper statistical analysis. In this paper we discuss these issues in detail, and provide an explanation of the statistical models and methods that are most appropriate for analyzing these types of data. We also provide several examples using data from laboratory, field, and simulation experiments illustrating the benefits of these approaches.     

A survey on anthelmintic resistance in nematode parasites of sheep in the Slovak Republic

The prevalence of anthelmintic resistance on 27 sheep farms in Slovakia was investigated in 2003 and 2004 using the faecal egg count reduction test (FECRT) according to the WAAVP guidelines. Resistance to albendazole was detected on one farm (3.7%) and suspected on two farms (7.4%) out of 27 sheep flocks. Resistance to ivermectin was tested on 26 farms. On six (23.1%) farms, results indicated the presence of ivermectin resistance. Resistance to ivermectin was suspected on eight farms (30.8%). However, it is also possible that generic ivermectin anthelmintics used in survey have a lower efficacy against sheep nematodes.     

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.     

Evaluation of the efficacy of anthelmintics sold on Ethiopian markets against <Emphasis Type="Italic">Haemonchus contortus</Emphasis> in experimentally infected Sheep

A total of 54 lambs, aged between 6–8 months were experimentally infected with Haemonchus contortus to evaluate the efficacy of different anthelmintic brands sold on Ethiopian markets using the faecal egg count reduction test (FECRT) and controlled anthelmintic efficacy trial. Accordingly four different albendazole (Alzole®, Analgon-300®, Albenjung_s® and Ahshialben-300®), two tetramisole (Tetsole® and Ashitetra 600) and two tetramisole-oxyclozanide (Tetraclozan sheep® and Tetraclozash 900®) brands were evaluated at the dosage rates recommended by the manufacturers. Animals were allocated into nine groups of six animals each, and balanced for faecal egg counts (FEC), based on their pre-treatment FEC and treatments were randomized among the groups. One group was kept untreated as a control. Faecal egg count was conducted on day 30 post-infection (day of treatment) and on the 10th day post-treatment. Evaluation of anthelmintics based on FECRT revealed high efficacy (99.55–100% reduction in FEC) for all anthelmintic brands tested against H. contortus. The worm count reduction test using controlled anthelmintic efficacy trial also supported the above finding with 99–100% efficacy of the tested anthelmintics. Therefore, the suspicion on the anthelmintic products as being substandard in quality is not credible, at least, for the brands investigated in this study and it might rather be attributed to under dosing. The need for a good extension system for livestock producers with regard to good anthelmintic usage practices, in light of the inevitable development of anthelminitic resistance, is emphasized. Regular surveillance and laboratory quality evaluation of the anthelmintic products in Ethiopia is indicated.