Comparative efficiency of moxidectin gel or ivermectin paste for cyathostome control in young horses

Thirty-six young horses were allocated to three similar groups. Horses in Group 1 were treated with moxidectin gel on Days 0, 90, and 180, Group 2 horses received ivermectin paste on Days 0, 60, 120, and 180, and horses in Group 3 were untreated controls. All horses were maintained on a common pasture for the first 180 days. Immediately after the final scheduled deworming, each group was moved to a separate, clean pasture where it remained until Day 360. At monthly intervals, fecal egg counts, body weights, body condition scores, and pasture larval counts were measured. The cumulative costs of both deworming regimens were calculated. Young horses treated three times at 90-day intervals with moxidectin gel had significantly lower monthly fecal egg counts than untreated controls from Days 30 through 300. Horses given ivermectin paste four times at 60-day intervals had significantly lower egg counts than controls 30 days after each treatment and 60 days after the third dose. Average daily gains of treated horses were significantly greater than controls from Days 120 through 360 (moxidectin) and from Days 210 through 360 (ivermectin). Quarterly moxidectin treatments reduced egg counts more effectively and cost less than ivermectin given bimonthly.     

Cyathostome fecal egg count trends in horses treated with moxidectin, ivermectin or fenbendazole

Commercial preparations of fenbendazole (Safe-Guard, Intervet), ivermectin (Eqvalan, Merial) or moxidectin (Quest, Fort Dodge) were administered once to horses scheduled for routine parasiticide treatment. In total, 93 horses from six cooperating farms were used in the study. Computer generated, random allocation of horses to treatment group was conducted at each farm. Fecal egg counts were determined for all horses on trial days 0, 56, 84 and 112, with corresponding calendar dates that were unique to each farm. Only strongyle egg counts from animals which were positive at day 0 were used for analysis of variance and comparisons. Counts for the three treatment groups were similar at day 0, moxidectin相似文献   

Faecal excretion profile of moxidectin and ivermectin after oral administration in horses

A study was undertaken to evaluate and compare faecal excretion of moxidectin and ivermectin in horses after oral administration of commercially available preparations. Ten clinically healthy adult horses, weighing 390-446 kg body weight (b.w.), were allocated to two experimental groups. Group I was treated with an oral gel formulation of moxidectin at the manufacturer's recommended therapeutic dose of 0.4 mg/kg b.w. Group II was treated with an oral paste formulation of ivermectin at the recommended dose of 0.2 mg/kg b.w. Faecal samples were collected at different times between 1 and 75 days post-treatment. After faecal drug extraction and derivatization, samples were analysed by High Performance Liquid Chromatography using fluorescence detection and computerized kinetic analysis.For both drugs the maximum concentration level was reached at 2.5 days post administration. The ivermectin treatment groups' faecal concentrations remained above the detectable level for 40 days (0.6 +/- 0.3 ng/g), whereas the moxidectin treatment group remained above the detectable level for 75 days (4.3 +/- 2.8 ng/g). Ivermectin presented a faster elimination rate than moxidectin, reaching 90% of the total drug excreted in faeces at four days post-treatment, whereas moxidectin reached similar levels at eight days post-treatment. No significant differences were observed for the values of maximum faecal concentration (C(max)) and time of C(max)(T(max)) between both groups of horses, demonstrating similar patterns of drug transference from plasma to the gastrointestinal tract. The values of the area under the faecal concentration time curve were slightly higher in the moxidectin treatment group (7104 +/- 2277 ng.day/g) but were not significantly different from those obtained in the ivermectin treatment group (5642 +/- 1122 ng.day/g). The results demonstrate that although a 100% higher dose level of moxidectin was used, attaining higher plasma concentration levels and more prolonged excretion and gut secretion than ivermectin, the concentration in faeces only represented 44.3+/- 18.0% of the total parental drug administered compared to 74.3 +/- 20.2% for ivermectin. This suggests a higher level of metabolization for moxidectin in the horse.     

Decreased ivermectin and moxidectin sensitivity in Haemonchus contortus selected with moxidectin over 14 generations.

Ivermectin resistance in the nematode Haemonchus contortus has been reported in many parts of the world and many ivermectin resistant isolates have been found to have reduced sensitivity to moxidectin. However, it is unclear whether parasites that are selected with moxidectin would demonstrate reduced sensitivity to ivermectin. In this study, the effects of moxidectin and ivermectin on an unselected strain and a strain of H. contortus derived from the unselected strain but selected over 14 generations with moxidectin, were compared in jirds. The recovery of adult worms and fourth stage (L4) larvae following treatment were compared between strains and anthelmintics. Moxidectin-selected H. contortus showed reduced sensitivity to ivermectin as well as to moxidectin. Doses of 0.1 mg/kg of moxidectin and 0.4 mg/kg of ivermectin were necessary to obtain an efficacy of 95% or above against the moxidectin-selected strain of H. contortus compared with 0.025 mg/kg for moxidectin and 0.1 mg/kg for ivermectin required for a similar efficacy in the unselected strain.     

Comparative plasma disposition kinetics of ivermectin, moxidectin and doramectin in cattle

The persistence of the broad-spectrum antiparasitic activity of endectocide compounds relies on their disposition kinetics and pattern of plasma/tissues exchange in the host. This study evaluates the comparative plasma disposition kinetics of ivermectin (IVM), moxidectin (MXD) and doramectin (DRM) in cattle treated with commercially available injectable formulations. Twelve (12) parasite-free male Hereford calves (180–210 kg) grazing on pasture were allocated into three groups of four animals each. Animals in each group received either IVM (Ivomec 1%, MSD AGVET, Rahway, NJ, USA), MXD (Cydectin 1%, American Cyanamid, Wayne, NJ, USA) or DRM (Dectomax 1%, Pfizer Inc., New York, NY, USA) by subcutaneous injection at a dose of 200 μg/kg. Jugular blood samples were collected from 1 h up to 80 days post-treatment, and plasma extracted, derivatized and analysed by high performance liquid chromatography (HPLC) using fluorescence detection. The parent molecules were detected in plasma between 1 h and either 70 (DRM) or 80 (IVM and MXD) days post-treatment. The absorption of MXD from the site of injection was significantly faster (absorption half-life (t_½ab) = 1.32 h) than those of IVM (t_½ab= 39.2 h) and DRM (t_½ab= 56.4 h). MXD peak plasma concentration (C_max) was reached significantly earlier (8.00 h) compared to those of IVM and DRM (4–6 days post-treatment). There were no differences on C_max values; the area under the concentration–time curve (AUC) was higher for IVM (459 ng.d/mL) and DRM (627 ng.d/mL) compared to that of MXD (217 ng.d/mL). The mean plasma residence time was longer for MXD (14.6 d) compared to IVM (7.35 d) and DRM (9.09 d). Unidentified metabolites were detected in plasma; they accounted for 5.75% (DRM), 8.50% (IVM) and 13.8% (MXD) of the total amount of their respective parent drugs recovered in plasma. The comparative plasma disposition kinetics of IVM, MXD and DRM in cattle, characterized over 80 days post-treatment under standardized experimental conditions, is reported for the first time.     

Plasma pharmacokinetics and faecal excretion of ivermectin, doramectin and moxidectin following oral administration in horses

The present study was carried out to investigate whether the pharmacokinetics of avermectins or a milbemycin could explain their known or predicted efficacy in the horse. The avermectins, ivermectin (IVM) and doramectin (DRM), and the milbemycin, moxidectin (MXD), were each administered orally to horses at 200 microg/kg bwt. Blood and faecal samples were collected at predetermined times over 80 days (197 days for MXD) and 30 days, respectively, and plasma pharmacokinetics and faecal excretion determined. Maximum plasma concentrations (Cmax) (IVM: 21.4 ng/ml; DRM: 21.3 ng/ml; MXD: 30.1 ng/ml) were obtained at (tmax) 7.9 h (IVM), 8 h (DRM) and 7.9 h (MXD). The area under the concentration time curve (AUC) of MXD (92.8 ng x day/ml) was significantly larger than that of IVM (46.1 ng x day/ml) but not of DRM (53.3 ng x day/ml) and mean residence time of MXD (17.5 days) was significantly longer than that of either avermectin, while that of DRM (3 days) was significantly longer than that of IVM (2:3 days). The highest (dry weight) faecal concentrations (IVM: 19.5 microg/g; DRM: 20.5 microg/g; MXD: 16.6 microg/g) were detected at 24 h for all molecules and each compound was detected (> or = 0.05 microg/g) in faeces between 8 h and 8 days following administration. The avermectins and milbemycin with longer residence times may have extended prophylactic activity in horses and may be more effective against emerging and maturing cyathostomes during therapy. This will be dependent upon the relative potency of the drugs and should be confirmed in efficacy studies.     

Comparison of the pharmacokinetics of moxidectin (Equest®) and ivermectin (Eqvalan®) in horses

A study was undertaken in order to evaluate and compare plasma disposition kinetic parameters of moxidectin and ivermectin after oral administration of their commercially available preparations in horses. Ten clinically healthy adult horses, weighing 390-446 kg body weight (b.w.), were allocated to two experimental groups of five horses. Group I was treated with an oral gel formulation of moxidectin (MXD) at the manufacturers recommended therapeutic dose of 0.4 mg/kg bw. Group II was treated with an oral paste formulation of ivermectin (IVM) at the manufacturers recommended dose of 0.2 mg/kg b.w. Blood samples were collected by jugular puncture at different times between 0.5 h and 75 days post-treatment. After plasma extraction and derivatization, samples were analysed by HPLC with fluorescence detection. Computerized kinetic analysis was carried out. The parent molecules were detected in plasma between 30 min and either 30 (IVM) or 75 (MXD) days post-treatment. Both drugs showed similar patterns of absorption and no significant difference was found for the time corresponding to peak plasma concentrations or for absorption half-life. Peak plasma concentrations (Cmax) of 70.3+/-10.7 ng/mL (mean +/- SD) were obtained for MXD and 44.0+/-23.1 ng/mL for IVM. Moreover, the values for area under concentration-time curve (AUC) were 363.6+/-66.0 ng x d/mL for the MXD treated group, and 132.7+/-47.3 ng x d/mL for the IVM treated group. The mean plasma residence times (MRT) were 18.4+/-4.4 and 4.8+/-0.6 days for MXD and IVM treated groups, respectively. The results showed a more prolonged residence of MXD in horses as demonstrated by a four-fold longer MRT than for IVM. The longer residence and the higher concentrations found for MXD in comparison to IVM could possibly explain a more prolonged anthelmintic effect. It is concluded that in horses the commercial preparation of MXD presents a pharmacokinetic profile which differs significantly from that found for a commercial preparation of IVM. To some extent these results likely reflect differences in formulation and doses.     

Reduced efficacy of ivermectin, abamectin and moxidectin against field isolates of Haemonchus contortus

OBJECTIVES: To investigate the reduced efficacy of ivermectin, abamectin and moxidectin against two field isolates of Haemonchus contortus. These isolates were identified on separate properties in the New England region of New South Wales. PROCEDURE: Reduced efficacy of macrocyclic lactone anthelmintics against two field isolates of H contortus was suspected. These isolates were obtained from sheep on separate farms and pen trials were performed to investigate the efficacy of macrocyclic lactones. The percentage efficacy was calculated for moxidectin, ivermectin and closantel against the isolate from one farm (VHR23) and for moxidectin, ivermectin and abamectin against the isolate from the second (VHR29). The persistent activity of moxidectin against both isolates was investigated. RESULTS: Ivermectin and closantel were found to have efficacies below 80% against established populations of VHR23. Moxidectin was effective against an established population of VHR23 but the persistent activity was reduced to 7 days. Moxidectin was also found to be effective against established populations of VHR29, however, ivermectin and abamectin were found to have efficacies below 80%. There was no evidence of persistent activity of moxidectin against VHR29. CONCLUSION: A reduction in efficacy of abamectin and/or ivermectin against field isolates of H. contortus was identified from two farms in the New England region of New South Wales. The persistent effect of moxidectin was reduced against both isolates.     

The difference in efficacy of ivermectin oral, moxidectin oral and moxidectin injectable formulations against an ivermectin-resistant strain of Trichostrongylus colubriformis in sheep

AIM: To evaluate the efficacy of ivermectin oral, moxidectin oral and moxidectin injectable formulations against an ivermectin-resistant strain of Trichostrongylus colubriformis in sheep. METHODS: Twenty-four mixed breed lambs were infected with 15,000 infective third-stage larvae of an ivermectin-resistant strain of T. colubriformis which had originally been isolated from a goat farm in Northland in 1997. Twenty-six days post infection, the lambs were divided into 3 treatment groups and a control group (n=6 lambs/group). Treatment consisted of either ivermectin oral formulation (0.2 mg/kg), moxidectin oral formulation (0.2 mg/kg), or moxidectin injectable formulation (0.2 mg/kg). Faecal egg counts (FECs) were determined at 0, 3, 5, 7 and 10 days after treatment. All animals were necropsied 12 days after treatment and worm counts were performed. Larval development assays were conducted 24 days post infection. A further 3 lambs were infected with 15,000 infective third-stage larvae of a fully susceptible strain of T. colubriformis for comparative purposes in the larval development assay. The efficacy of the moxidectin injectable formulation was also confirmed in these 3 lambs. RESULTS: The FEC reduction test at day 10 after treatment revealed 62%, 100% and 0% reductions in arithmetic-mean FECs for ivermectin oral, moxidectin oral and moxidectin injectable groups, respectively. The ivermectin oral, moxidectin oral and moxidectin injectable formulations achieved 62%, 98% and 4% reductions in arithmetic-mean worm burdens, respectively. Larval development assays showed resistance ratios for ivermectin of 4:1, avermectin B2 of 2.7:1, ivermectin aglycone of 37:1, moxidectin of 1.4:1, thiabendazole of 14.6:1 and levamisole of 1.8:1. CONCLUSIONS: The moxidectin oral formulation provided a high degree of control against ivermectin-resistant T. colubriformis whereas the moxidectin injectable formulation had very low efficacy. Ivermectin aglycone was the analogue of choice for diagnosis of ivermectin resistance in T. colubriformis in the larval development assay.     

Alternative antiparasitic treatment of horses with pyrantel pamoate suspension and ivermectin oral solution compared with horses treated only with ivermectin

A practical parasite control program was evaluated in a 2-year clinical trial using pyrantel pamoate suspension (PYR) and ivermectin oral solution (IVM) in a seasonal rotation program, in comparison with continued use of IVM given at 2-month intervals. At least 15 horses in each of 2 treatment groups were distributed over 8 locations. In the alternation program, IVM was given twice (October, December) during the botfly (Gasterophilus spp.) season and again in April to treat against the lighter botfly season and to kill existing Onchocerca microfilariae prior to heavy Culicoides swarming. Pyrantel was given in February, June and August to continue suppression of strongyle infections and to treat against potentially developing Anoplocephala infections. In the program of IVM continuous use, the drug was given on the same schedule as either treatment on the alternation program.The course of strongyle infections was monitored by fecal sample analyses (EPG) at semimonthly intervals and by larval cultures of treatment pairs prepared at each treatment interval (alternation program) or at 4-month intervals (continuous IVM program). The strongyle egg count numbers were reduced to zero by the first IVM treatment, increased only slightly by the next treatment at 2 months, and repeated the reduced pattern with each treatment for 2 years. The alternation program in the first year had typical responses to each drug: IVM reducing strongyle EPG counts to zero which increased slightly at 2 months, followed by the PYR treatment, which reduced the strongyle egg counts for 4 weeks with rebound at 6 and 8 weeks. At the end of the first year and into the second, the IVM treatments of October and December established a zero or low strongyle EPG pattern which continued through the spring with PYR and IVM treatments. The second summer PYR treatments then maintained far better cyathostome control than had been reported for this drug. There may be a complementary or enhancing effect by prior treatment with ivermectin within the rotation protocol. The practical therapeutic compatibility between these 2 antiparasitics became obvious. Anoplocephala eggs were found in feces of some horses treated with IVM only, but no Anoplocephala eggs were found in post-treatment feces of horses treated on the alternation program.Strongyle larval cultures prepared as treatment pairs indicated high efficacy by ivermectin throughout the 2 years whether used alone or as a rotational drug, with improved cyathostome control by pyrantel pamoate. The combined use of EPG determinations and concurrent larval cultures in anthelmintic evaluations provide a greater spectrum of reliable results than from parasite egg counts alone.     

Field efficacy of ivermectin, fenbendazole and pyrantel embonate paste anthelmintics in horses

Three anthelmintic pastes were compared in terms of their ability to suppress the output of parasite eggs in the faeces of 108 grazing horses at four sites in Britain; the horses were treated once with either ivermectin, fenbendazole or pyrantel. At each site, the horses grazed together throughout the trials which took place during the summers of 1985 and 1986. The median periods before parasite eggs reappeared in faeces were 70 days for ivermectin, 14 days for fenbendazole and 39 days for pyrantel embonate. Geometric mean faecal egg counts in the groups treated with ivermectin and pyrantel were significantly less (P less than 0.05) than in the fenbendazole group on days 21, 28, 35 and 42 after treatment. On days 49, 56, 63 and 70 the mean egg counts in the ivermectin group were significantly lower (P less than 0.05) than those in either of the other groups. The results indicated that in order to ensure minimal contamination of pastures, grazing horses treated with ivermectin paste would have required a second treatment approximately 10 weeks after the first, and to achieve similar control with fenbendazole or pyrantel embonate, a second treatment would have been required after approximately two weeks and six weeks, respectively.     

Alternative antiparasitic treatment of horses with pyrantel pamoate suspension and ivermectin oral solution compared with horses treated only with ivermectin oral solution

A practical parasite control program was evaluated in a 2-year clinical trial using pyrantel pamoate suspension (PYR) and ivermectin oral solution (IVM) in a seasonal rotation program, in comparison with continued use of IVM given at 2-month intervals. At least 15 horses in each of 2 treatment groups were distributed over 8 locations. In the alternation program, IVM was given twice (October, December) during the botfly (Gasterophilus spp.) season and again in April to treat against the lighter botfly season and to kill existing Onchocerca microfilariae prior to heavy Culicoides swarming. Pyrantel was given in February, June and August to continue suppression of strongyle infections and to treat against potentially developing Anoplocephala infections. In the program of IVM continuous use, the drug was given on the same schedule as either treatment on the alternation program.The course of strongyle infections was monitored by fecal sample analyses (EPG) at semimonthly intervals and by larval cultures of treatment pairs prepared at each treatment interval (alternation program) or at 4-month intervals (continuous IVM program). The strongyle egg count numbers were reduced to zero by the first IVM treatment, increased only slightly by the next treatment at 2 months, and repeated the reduced pattern with each treatment for 2 years. The alternation program in the first year had typical responses to each drug: IVM reducing strongyle EPG counts to zero which increased slightly at 2 months, followed by the PYR treatment, which reduced the strongyle egg counts for 4 weeks with rebound at 6 and 8 weeks. At the end of the first year and into the second, the IVM treatments of October and December established a zero or low strongyle EPG pattern which continued through the spring with PYR and IVM treatments. The second summer PYR treatments then maintained far better cyathostome control than had been reported for this drug. There may be a complementary or enhancing effect by prior treatment with ivermectin within the rotation protocol. The practical therapeutic compatibility between these 2 antiparasitics became obvious. Anoplocephala eggs were found in feces of some horses treated with IVM only, but no Anoplocephala eggs were found in post-treatment feces of horses treated on the alternation program.Strongyle larval cultures prepared as treatment pairs indicated high efficacy by ivermectin throughout the 2 years whether used alone or as a rotational drug, with improved cyathostome control by pyrantel pamoate. The combined use of EPG determinations and concurrent larval cultures in anthelmintic evaluations provide a greater spectrum of reliable results than from parasite egg counts alone.     

Comparative pharmacokinetic and pharmacodynamic response of single and double intraruminal doses of ivermectin and moxidectin in nematode-infected lambs

Abstract

AIMS: To compare the pharmacokinetics, distribution and efficacy (pharmacodynamic response) of intraruminal ivermectin (IVM) and moxidectin (MXD) administered at 0.2 and 0.4?mg/kg to naturally nematode-infected lambs, and to determine the ex vivo accumulation of these anthelmintics by Haemonchus contortus.

METHODS: Romney Marsh lambs, naturally infected with IVM-resistant H. contortus, were allocated to treatment groups based on faecal nematode egg counts. They received 0.2 or 0.4?mg/kg IVM or MXD (n=10 per group), or no treatment (Control; n=6), on Day 0. Samples from four animals from each treatment group, including abomasal parasites, were obtained on Day 1. Plasma samples were also collected from Day 0 to 14, and a faecal egg count reduction test (FECRT) and a controlled efficacy trial were carried out on Day 14. Concentrations of IVM and MXD in plasma, in abomasal and intestinal tissues and in H. contortus were evaluated by high-performance liquid chromatography. Additionally, the ex vivo drug accumulation of IVM and MXD by H. contortus was determined.

RESULTS: Peak plasma concentrations and the area under the concentration vs. time curve for both IVM and MXD were higher for 0.4 than 0.2?mg/kg treatments (p<0.05), but there were no differences for other parameters. Concentrations of IVM and MXD in the gastrointestinal target tissues and in H. contortus were higher compared to those measured in plasma. Concentrations of both drugs in H. contortus were correlated with those observed in the abomasal content (r=0.86; p<0.0001). The exposure of H. contortus to IVM and MXD was related to the administered dose. Mean FECRT and efficacy for removal of adult H. contortus was 0% for IVM at 0.2 and 0.4?mg/kg. For MXD, FECRT were >95% for both treatments, and efficacy against H. contortus was 85.1% and 98.1% for 0.2 and 0.4?mg/kg, respectively. The ex vivo accumulation of IVM and MXD in H. contortus was directly related to the drug concentration present in the environment and was influenced by the duration of exposure.

CONCLUSION: Administration of IVM and MXD at 0.4 compared with 0.2?mg/kg accounted for enhanced drug exposure in the target tissues, as well as higher drug concentrations within resistant nematodes. The current work is a further contribution to the evaluation of the relationship between drug efficacy and basic pharmacological issues in the presence of resistant parasite populations.     

Comparative plasma and milk dispositions,faecal excretion and efficacy of per os ivermectin and pour‐on eprinomectin in horses

The horse milk gains increasing interest as a food product for sensitive consumers, such as children with food allergies or elderly people. We investigated the plasma and milk disposition, faecal excretion and efficacy of per os ivermectin (IVM) and pour‐on eprinomectin (EPM) in horses. Ten mares were divided into two groups. The equine paste formulation of IVM and bovine pour‐on formulation of EPM were administered orally and topically at dosage of 0.2 and 0.5 mg/kg bodyweight. Blood, milk and faecal samples were analysed using high‐performance liquid chromatography. The plasma concentration and persistence of IVM were significantly greater and longer compared with those of EPM. Surprisingly, EPM displayed a much higher disposition rate into milk (AUC_milk/plasma: 0.48) than IVM (AUC_milk/plasma: 0.19). IVM exhibited significantly higher faecal excretion (AUC_faeces: 7148.54 ng·d/g) but shorter faecal persistence (MRT_faeces: 1.17 days) compared with EPM (AUC_faeces: 42.43 ng·d/g and MRT_faeces: 3.29 days). Faecal strongyle egg counts (EPG) were performed before and at weekly intervals after treatment. IVM reduced the EPG by 96–100% for up to 8 weeks, whereas the reduction in the EPM group varied from 78 to 99%. In conclusion, due to the relatively low excretion in milk, EPM and IVM may be used safely in lactating mares if their milk is used for human consumption. Nevertheless, much lower plasma and faecal availabilities of EPM could result in subtherapeutic concentrations, which may increase the risk of drug resistance in nematodes after pour‐on EPM administration compared with per os IVM.     

The efficacy and acceptability of ivermectin liquid compared to that of oral paste in horses

One hundred-twenty horses and ponies ranging in age from 142 days to 23 years were used to assess the efficacy and acceptability of ivermectin liquid for horses when given as an oral drench or by nasogastric intubation. Prior to treatment, animals in this study were found to have eggs in the feces of one or more of the following: strongyle type, Parascaris equorum, and Strongyloides westeri. While egg parasite per gram (EPG) numbers from 30 untreated controls remained consistently positive over a 14 day period, parasite EPG numbers from animals treated on Day 0 were reduced to 0 by day 14 as determined by a modified McMaster technique.     

Comparison of subcutaneous ivermectin and oral moxidectin for the treatment of notoedric acariasis in hamsters

Thirty hamsters diagnosed with a Notoedres infestation on the basis of their clinical signs and skin scrapings were allocated to three matched groups. The hamsters in group 1 received ivermectin at 400 microg/kg subcutaneously once a week for eight weeks, those in group 2 were treated with moxidectin at 400 microg/kg orally once a week, and those in group 3 were treated with moxidectin at the same dosage, but twice a week. The hamsters' skin lesions were scored weekly on the basis of the severity of crusting, erythema, scaling and excoriations at various sites. In all three groups the lesion scores were significantly lower after four and eight weeks, and there was no significant difference between the efficacy of the treatments. However, at the end of the treatment, skin scrapings were negative in only 60 to 70 per cent of the animals in each group.     

Prevalence of strongyles and efficacy of fenbendazole and ivermectin in working horses in El Sauce, Nicaragua

Horses, mules and donkeys are indispensable farming and working animals in many developing countries, and their health status is important to the farmers. Strongyle parasites are ubiquitous in grazing horses world-wide and are known to constitute a threat to equine health. This study determined the prevalence of strongyle infection, the efficacy of ivermectin and fenbendazole treatment, and strongyle re-infection rates of working horses during the dry months in Nicaragua. One hundred and five horses used by farmers for transport of people and goods were randomly allocated into three treatment groups, i.e., the IVM group treated with ivermectin, the FBZ group treated with fenbendazole and the control group treated with placebo. Determined by pre-treatment faecal egg counts (FECs), horses showed a high prevalence (94%) of strongyle parasites with high intensities of infection (mean FEC of 1117 eggs per gram (EPG) with an SD of 860 EPG, n=102). Body condition scores of all horses ranged from 1.5 to 3.5 with a mean of 2.4 (scales 1-5). Fourteen days after treatment faecal egg count reductions (FECRs) were 100% and 94% in the IVM and the FBZ groups, respectively. The egg reappearance period (ERP) defined as the time until the mean FEC reached 20% of the pre-treatment level, was estimated as 42 days for the FBZ group and 60 days for the IVM group. Individual faecal cultures were set up and the larval differentiation revealed a 36% prevalence of Strongylus vulgaris before treatment (n=45). In the FBZ group, 25% of the horses were S. vulgaris-positive 70 days post treatment compared to 11% in the IVM group. Our results indicate that strongyle infection intensities in Nicaragua are high and that S. vulgaris is endemic in the area. Furthermore, efficacies and ERPs of IVM and FBZ were within the expected range with no signs of anthelmintic resistance.