Mean Faecal Egg Count Reduction Research Articles

Patterns of Equine Small Strongyle Species Infection after Ivermectin Intervention in Thailand: Egg Reappearance Period and Nemabiome Metabarcoding Approach.

The indiscriminate use of anthelmintics to control parasitic nematodes in horses has led to the emergence of anthelmintic resistance worldwide. However, there are no data available on using ivermectin for treating strongyle infections within domesticated horses in Thailand. Therefore, this study aimed to use the fecal egg count reduction (FECR) test to determine the strongylid egg reappearance period (ERP). Additionally, the nemabiome metabarcoding approach is incorporated to study patterns of strongyle species infection following ivermectin treatment. The study results indicate that, although ivermectin effectively eliminated adult strongyle parasites within two weeks post-treatment, the ERP was shortened to 6 weeks post-treatment with a mean FECR of 70.4% (95% CI 46.1-84.0). This potentially indicates a recent change in drug performance. In addition, nemabiome metabarcoding revealed that strongyle species have different levels of susceptibility in response to anthelmintic drugs. The reduction in ERP was associated with the early reappearance of specific species, dominated by Cylicostephanus longibursatus and Cylicocyclus nassatus, indicating the lower susceptibility of these species. In contrast, Poteriostomum imparidentatum, Triodontophorus nipponicus, and Triodontophorus serratus were not found post-treatment, indicating the high level of susceptibility of these species. This information is vital for comprehending the factors contributing to the emergence of resistance and for devising strategies to manage and control strongyle infections in horses.

Anthelmintic Resistance Status in Gastrointestinal Nematodes of Seven Different Breeds of Sheep in intensive management

The severe use of anthelmintics to control gastrointestinal nematodes has become an essential issue in many countries, especially related to resistance issues. A study was carried out to determine the anthelmintic resistance status of intestinal nematodes of sheep, which were kept intensively in Bogor District, Indonesia. A total of 220 sheep of 7 breeds that routinely received Benzimidazole anthelmintics group to control gastrointestinal nematode were designated for this study. The animals were divided into 7 groups based on the breed and treated with Albendazole at the required dose. The Fecal Egg Count Reduction Test (FECRT) method was used to evaluate the anthelmintic’s effectiveness. The mean fecal egg count reduction was recorded at seven and fourteen days of treatment. The result indicated that 7 breeds of sheep were resistant to the anthelmintic used. Garut Local and Barbados Cross breeds showed relatively high resistance to Albendazole, with the mean fecal egg count at fourteen days of treatment being 60.24% and 67.97%, respectively. Haemonchus spp. larvae were the nematode larvae of strongyles species that grew the most in each breed of sheep from the fecal samples on day 0 (before treatment), day 7, and day 14 after treatment.

Equine strongylids: Ivermectin efficacy and fecal egg shedding patterns.

Equine cyathostomins are ubiquitous in grazing horses around the world and a main target in parasite control programs. Anthelmintic resistance has been reported with increasing frequency in these parasites over the past decades, and recent findings of fulminant resistance to the macrocyclic lactone class have raised severe concerns. This study aimed to evaluate ivermectin efficacy in cohorts of yearlings and mares present on four different farms in Central Kentucky. Strongylid egg counts were determined with an automated egg counting system, and the percent fecal egg count reduction (FECR) was calculated using a hierarchical Bayesian analysis. Novel principles were used for classification of groups to either no signs of anthelmintic resistance, evidence of resistance, or inconclusive. Furthermore, an epidemiological analysis was conducted evaluating the possible influence of pregnancy status, time of foaling, and year of arrival on mare strongylid egg shedding levels. A total of 102 yearlings and 247 mares were enrolled in the study. Evidence of ivermectin resistance was documented in one group of yearlings with a mean FECR of 91.2% and a 95% credible interval of 84.0-95.8. The results from one mare group and one additional yearling group were deemed inconclusive, whereas the remaining five groups displayed no evidence of ivermectin resistance. Strongylid shedding in the mares was not positively associated with any of the evaluated factors. This study is the first to demonstrate ivermectin resistance in US bred horses, and the findings emphasize the need for routine monitoring of anthelmintic efficacy on horse farms.

PSXV-21 Assessment of the presence of anthelmintic resistance in Maryland beef cattle herds

Abstract Reduced anthelmintic efficacy in beef cattle has recently been documented at the national level. The objective of this study was to determine if anthelmintic resistance is present in Maryland beef cattle herds. For this study, the fecal egg count reduction (FECR) test was used to assess anthelmintic efficacy of composite samples. Between July and October 2020, anthelmintic efficacy was assessed for 17 groups of cattle across 14 individual farms in Maryland. Each test group consisted of 24 ± 6 calves or yearlings (< 16 months of age). Previous anthelmintic treatment history was used to assign each group to one of four commercially available anthelmintics: moxidectin (injectable), moxidectin (pour-on), doramectin, or fenbendazole. Prior to treatment, cattle were weighed to ensure appropriate dose according to the product label. Fecal samples were collected from all cattle within each group before and after (17 ± 5 d) treatment. Pre- and post-treatment samples were composited for each group on an equal-weight basis (10g per animal) and the number of eggs within the sample was determined using the 3-chambered McMaster technique. The mean FECR across all four anthelmintics was 60 ± 19% (mean ± 95% confidence interval), indicating that the anthelmintics tested in this study were largely ineffective. The FECR for the moxidectin injectable, moxidectin pour-on, doramectin, and fenbendazole treatments were 71 ± 38%, 47 ± 46%, 35 ± 88%, and 96 ± 18% (mean ± 95% confidence interval), respectively. Although these data indicate no statistically significant differences for efficacy among the four products tested, they do suggest that efficacy is highly variable across different anthelmintics and farms. Results also indicate that anthelmintic resistance exists on many cattle farms in Maryland. This study provides evidence that supports the need for more judicious anthelmintic use and alternative gastrointestinal parasite control measures in Maryland beef cattle herds.

26 Copper oxide wire particles to complement control of gastrointestinal nematodes with levamisole and/or albendazole in lambs

Abstract Due to high prevalence of anthelmintic resistance (AR), complementary approaches to anthelmintic use to control gastrointestinal nematodes (GIN) in sheep are necessary. Copper oxide wire particles (COWP) are effective against Haemonchus contortus but not other GIN, and FAMACHA aids to minimize further development of AR. The objective was to determine the efficacy of COWP alone or in combination with levamisole, albendazole, or a 3-way combination to control GIN known to have AR to these anthelmintics. Naturally infected Katahdin lambs were selectively dewormed based on FAMACHA© and/or packed cell volume (PCV). If FAMACHA© scores were 3, 4, or 5, lambs received 1 g COWP alone (n = 120), COWP and levamisole (n = 47) or albendazole (n = 6), or a 3-way combination (n = 10), respectively. Untreated lambs were included (CON; n = 31). Feces and blood were collected on days 0 (day of deworming) and 14 for determination of fecal egg counts (FEC) and FEC reduction (FECRED) and PCV. Data were analyzed using repeated measures in a mixed model. The mean FECRED was greater for the combination of levamisole and COWP than COWP alone (P < 0.001). In a mixed GIN population, COWP in combination with levamisole increased the efficacy of FECRED of H. contortus and other GIN genera present, offering greater GIN management in the presence of resistance to these anthelmintics.

Anthelmintic Efficacy of Strongyle Nematodes to Ivermectin and Fenbendazole on Working Donkeys (Equus asinus) in and around Hosaena Town, Southern Ethiopia.

Background Gastrointestinal helminth parasite infection is a major influencing factor against profitability of working equines all over the world. Objectives A study was conducted from October 2016 to May 2017 in and around Hosaena to determine the efficacy of benzimidazole (BZ) and avermectin (AVM) chemical groups against strongyle nematodes in working donkeys. Methods A total of 230 donkeys from Hosaena, Soro, Anlemo, and Gombora were randomly allocated into 5 groups of 46 donkeys in each group. All groups, except group 1 (control), were treated with ivermectin 1%, ivertong 10%, fenbendazole, and Fenacure 750 mg, respectively. Fecal samples were collected perrectally before treatment (day 0) and after treatment (day 14), and an egg per gram (EPG) value of >200 was used as a cutoff for inclusion to assess the efficacy of anthelmintics. Results Accordingly, the study revealed that AVM was effective against strongyle nematodes of donkeys with the mean fecal egg count reduction (FECR) of 100% in three study areas and 97.2% in one study area, respectively, whereas BZ resistance was suspected in the areas where the drug was tested, with the mean FECR of less than 94% in the three study areas. The study also revealed that 73% of the donkeys were affected with a severe degree of strongyle infection as determined by EPG, while 10.4% of donkeys were affected with a mild degree of Parascaris equorum infection. Conclusions The findings of the present study are expected to serve as baseline data for future investigations and control actions to design realistic control programs to minimize factors that favor emergence of anthelmintic resistance and improve the overall health of the donkeys. Thus, further detailed studies are needed to determine the factors that reduce anthelmintic efficacy and increase anthelmintic resistance in donkeys.

Combination deworming for the control of double-resistant cyathostomin parasites – short and long term consequences

Equine cyathostomin are pervasive gastrointestinal parasites with wide-spread resistance to the benzimidazole and tetrahydropyrimidine drug classes worldwide. Combination deworming has been proposed as a more sustainable parasite control strategy. Simulation studies have found combination deworming to be effective in controlling drug resistant ovine trichostrongylid parasites. One equine study demonstrated an additive effect of a combination of oxibendazole and pyrantel pamoate against cyathostomins. However, this is the only equine study evaluating combination therapy, and the effects of repeated combination treatments administered over time remain unknown. The purpose of this study was to observe the efficacy of repeated oxibendazole/pyrantel pamoate combination therapy administered over one year against a cyathostomin population with resistance to benzimidazole and pyrantel products. Fecal egg counts were determined for the entire herd (N = 21) at the day of anthelmintic treatment and at two-week intervals for eight weeks post treatment. Starting efficacies of oxibendazole (OBZ, 10 mg/kg) and pyrantel pamoate (PYR, 6.6 mg base/kg) were 66.7% and 63.3%, respectively. Hereafter, the herd was treated four times with an oxibendazole/pyrantel pamoate combination, eight weeks apart, followed by repeating the single active treatments before concluding the study. While the first combination treatment exhibited an additive effect of the two active ingredients, this efficacy was not sustained over the course of the study. Mean fecal egg count reduction (FECR) was significantly greater for the first combination treatment (76.6%) than the second (42.6%, p = 0.0454), third (41.6%, p = 0.0318), and fourth (40.7%, p = 0.0372) combination treatments. The final single active mean FECRs were 42.3% for oxibendazole, and 42.7% for pyrantel pamoate. These efficacies were not significantly different from the initial single active efficacies (OBZ, p = 0.4421; PYR, p = 0.8361). These results suggest that combination therapy against double resistant equine cyathostomin populations is not sustainable, when using actives with markedly decreased starting efficacies.

Multi-drug resistant Haemonchus contortus in a sheep flock in Antioquia, Colombia.

A sheep farm experiencing high lamb mortality and poor body conditions of ewes due to haemonchosis was tested for the presence of anthelmintic-resistant nematodes in August 2014. A fecal egg count reduction test was performed in Colombia on this farm and a DrenchRite® Larval development Assay (LDA) was shipped to the University of Georgia in the United States for resistance testing. The fecal egg count reduction test (FECRT) was conducted on 70 out of 500 animals allocated into five groups of 14 animals each: untreated control, albendazole (ABZ; 3.5mg/kg sc), ivermectin (IVM; 0.2mg/kg sc), moxidectin (MOX; 0.2mg/kg sc) and levamisole (LEV; 5mg/kg sc) plus triclabendazol/ivermectin (TBZ; 10mg/kg and IVM; 0.2mg/kg po). Individual fecal egg counts (FEC) using the modified McMaster technique and pooled larval cultures were performed 10days after anthelmintic treatment. Following 10days the initial results from the ABZ and IVM groups, 24 animals were treated twice with trichlorfon (TCF; 50mg/kg po) on days 0 and 6, and then checked for FEC on day 10. Mean differences in FEC before and after treatment were negligible (3 to 8% change) for the control, ABZ, LEV-TBZ and IVM groups. The MOX treatment resulted a mean FEC reduction of 76.7%, which was not-significant by t-test (p=0.08). The TCF treatment showed a mean FEC reduction of 42.3%, which was also not-significant (p=0.1). The DrenchRite® LDA was used to evaluate the resistance status to benzimidazole, levamisole, ivermectin and moxidectin on this farm. Coprocultures indicated that the predominant worm species was Haemonchus contortus (Colombia 94-100%) (UGA 77% H. contortus and 23% Trichostrongylus colubriformis). Resistance was evaluated for both H. contortus and T. colubriformis. The LDA results indicated high resistance to all 4 anthelmintics for both parasite species. The current study, together with similar surveys in 4 other Antioquian goat and sheep farms, confirms the presence of multi-drug resistant H. contortus to all three classes of anthelmintics in this region of Colombia.

Fecal egg count reduction test evaluating macrocyclic lactones using cattle treated 118 days earlier with saline, albendazole in combination with doramectin, or an extended-release formulation of eprinomectin

A fecal egg count reduction (FECR) test was conducted on stocker cattle treated 118 days earlier with saline injection (S); 0.09 mg/lb (200 mcg/kg) BW doramectin injection concomitantly with 4.54 mg/lb (10 mg/kg) BW albendazole oral suspension (DA); or 0.45 mg/lb (1 mg/kg) BW eprinomectin extended-release injection (ERE), and then continuously grazed by treatment group in groups of 4 until the start of the current study. In total, there were 8 S, 12 DA, and 12 ERE grazing groups (pastures of origin). Three animals from each pasture were randomly allocated for injection with ivermectin, doramectin or moxidectin, all at the rate of 0.09 mg/lb (200 mcg/kg) BW. Fecal samples were obtained at days -1 and 15, with treatments on day 0. Additionally, coprocultures were conducted on individual fecal samples collected on days -1 and 15.
 On day -1 of the FECR test, the arithmetic mean strongyle eggs per gram of feces counts (EPG) across all pastures of origin were 412, 570, and 321 for the ivermectin, doramectin, and moxidectin-treated cattle, respectively. Day 15 egg counts in the same order were 177, 335, and 28. Using the above arithmetic means and by standard equation, the overall mean FECR percentages were 57.0, 41.2, and 91.2 for ivermectin, doramectin, and moxidectin, respectively. Lowest FECR test percentages were seen for animals from the ERE pastures. Coproculture larvae populations harvested on both days -1 and 15 were primarily Haemonchus placei and Cooperia punctata, regardless of animal's pasture of origin or FECR test treatment.

Efficacy of Commercially Available Anthelmintics in Controlling Gastrointestinal Nematodes in Goats Managed Under Natural Conditions in the South Western Highlands of Uganda

Goat production is of great importance especially to the rural farmers in Uganda, serving a number of socio-economic functions. Among the limitations of goat production in Uganda are Gastro Intestinal Nematodes (GINs). These are usually controlled using commercial Anthelmintic compounds. Due to continual improper usage of these drugs by the farmers, evolution of resistant strains has resulted thus affecting their effectiveness in controlling the GINs. The aim of this study was to determine the efficacy of four commercially available anthelmintics used for controlling Gastro Intestinal Nematodes (GINs) in goats on natural pastures in the south western highlands of Uganda. A mini survey was conducted prior to the current study to get information about the most commonly used anthelmintics in the study area. Initially, 240 goats were enrolled into the study and, 210 were used in the final analysis. The goats were randomly allocated to 5 different treatment groups at district level namely; untreated controls (CTRL), Albendazole 10% (ABZ), Ivermectin (IVE), Levamisole (LEV) and Closantel (CL). Faecal and blood samples were collected from each animal at 0, 14, 28 and 42 days post-treatment respectively and analysed for faecal egg counts (FEC) using the modified McMaster method. The percentage reduction, FECR % was calculated from the arithmetic mean and difference in FEC between breeds, district and age were assessed by univariate analysis of variance in SPSS. Results at day zero indicated that age and district had significant effect on FEC (P-value= 0.001 and 0.035respectively) while breed had no significant effect (P-value=0.465). At 14 days post-treatment, district, breed and treatment had significant effects on FEC (P-value=0.00, 0.02 and 0.05 respectively) while age was not (P=0.931). Albendazole and Levamizol were the most used drugs in the study area while Closantel and Ivermectin were the least used. Drug efficacy varied between districts, with the highest mean Fecal Egg Count Reduction (FECR) achieved with Closantel (FECR%=100%), while the lowest mean FECR observed with Albendazole (FECR%=49%) in Rukungiri and Kisoro districts respectively. Ivermectin was effective in all the four districts (FECRT% > 95%). Our study confirmed presence of Anthelmintic resistance (AR) by GIN in goats in the south western highlands of Uganda. Closantel is highly effective against GINs, but albendazole is not due to its wide spread usage. Further research is necessary to find and validate alternative strategies for the control of GINs in goats.

Comparison of a single dose of moxidectin and a five-day course of fenbendazole to reduce and suppress cyathostomin fecal egg counts in a herd of embryo transfer-recipient mares.

To compare larvicidal regimens of fenbendazole and moxidectin for reduction and suppression of cyathostomin fecal egg counts (FEC) in a transient herd of embryo transfer-recipient mares. Randomized, complete block, clinical trial. 120 mares from 21 states, residing on 1 farm. An initial fecal sample was collected from each mare; mares with an FEC ≥ 200 eggs/g were assigned to treatment groups. Eighty-two horses received fenbendazole (10.0 mg/kg [4.5 mg/lb], PO, q 24 h for 5 days) or moxidectin (0.4 mg/kg [0.18 mg/lb], PO, once); FEC data were analyzed 14, 45, and 90 days after treatment. Mean FEC reduction was 99.9% for moxidectin-treated mares and 41.9% for fenbendazole-treated mares 14 days after treatment. By 45 days, mean FEC of fenbendazole-treated mares exceeded pretreatment counts; however, FECs of moxidectin-treated mares remained suppressed below pretreatment values for the duration of the 90-day study. Fecal egg counts were significantly different between groups at 14, 45, and 90 days after treatment. Failure of the 5-day regimen of fenbendazole to adequately reduce or suppress FEC suggested inadequate adulticidal and larvicidal effects. In contrast, a single dose of moxidectin effectively reduced and suppressed FEC for an extended period. Given the diverse geographic origins of study mares, these results are likely representative of cyathostomin-infected mares in much of the United States, confirming previous findings indicating that fenbendazole resistance in cyathostomins is widespread and that moxidectin remains an effective treatment for control of these important parasites.

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

SummaryAnthelmintics 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.

Hookworm Infection among School Age Children in Kintampo North Municipality, Ghana: Nutritional Risk Factors and Response to Albendazole Treatment

Children (n = 812) 6-11 years of age attending 16 schools in the Kintampo North Municipality of Ghana were screened for participation in a study on hookworm infection, nutrition, and response to albendazole. The prevalence of Necator americanus hookworm infection (n = 286) was 39.1%, and significant predictors of infection included age, malaria parasitemia, lack of health care, school area, levels of antibodies against hookworm, and low consumption of animal foods. The cure rate after a single dose (400 mg) albendazole was 43%, and the mean fecal egg count reduction rate was 87.3%. Data for an in vitro egg hatch assay showed a trend toward reduced albendazole susceptibility in post-treatment hookworm isolates (P = 0.06). In summary, hookworm infection is prevalent among school age children in the Kintampo North Municipality and animal food intake inversely correlates with infection status. Modest cure rates and fecal egg count reduction rates reinforce the need for further investigation of potential benzimidazole resistance in Ghana.

A survey of farm management practices and their associations with anthelmintic resistance in sheep flocks in Ontario, Canada

To describe parasite control and farm management practices commonly used by Ontario sheep farmers, and to determine whether any of these practices were associated with the level of anthelmintic resistance (AR) to ivermectin, fenbendazole or levamisole, we conducted fecal egg count reduction (FECR) tests in Ontario sheep flocks, and administered a questionnaire pertaining to farm practices that were considered putative risk factors for AR. In the previous 5 years, most of the producers had used ivermectin and fenbendazole drenches (95% and 68%, respectively), while only 11% had used levamisole drench. Producers treated their animals a mean of 2.6 times per year. Routine treatment was practiced by 82% of the producers; most ewes were treated either at lambing (55%) and/or at the beginning of winter housing (48%). The majority of the producers (82%) also used targeted or targeted selective treatment; however, it was often in addition to, rather than in lieu of, routine treatment. Twenty-five producers (66%) brought in new animals in the previous year. Many producers (45%) did not calibrate the drench gun before use. The mean FECR percentages following treatment with ivermectin, fenbendazole, and levamisole were 23.7%, 28.6% and 99.1%, respectively. Although univariable analyses identified several marginally significant risk factors (0.10>p>0.05), none were significant in the final model for ivermectin FECR percentage. In contrast, use of benzimidazoles in the previous 5 years was associated (p=0.01) with increased resistance (lower mean FECR percentage) to fenbendazole. Levamisole resistance could not be modeled due to the very low levels of resistance on the farms surveyed. This study: (1) provided a picture of management practices employed by Ontario sheep producers who were experiencing AR to one or more anthelmintic drugs on their farms; and (2) allowed us to identify areas for further AR risk factor research.

Anthelmintic efficacy against cyathostomins in horses in Southern England

Cyathostomins are considered to be the most important group of helminths to affect equids due to their high prevalence, potential pathogenicity and ability to develop anthelmintic resistance. Their control relies almost exclusively on frequent anthelmintic use. Currently, fenbendazole (FBZ), pyrantel embonate (PYR), ivermectin (IVM) and moxidectin (MOX) are licensed for use in horses in the UK. With no new anthelmintics likely to be licensed in the near future, it is essential that investigations into the efficacy of current anthelmintics in different locations are performed to help inform control programmes. Here, efficacy of FBZ, PYR, IVM and MOX in horse populations in the South of England was investigated. Horses with a strongyle faecal egg count (FEC) of ≥50eggs per gram (EPG) were enrolled onto a faecal egg count reduction test (FECRT) study. Efficacy was determined by calculating the percentage reduction in FEC between the group mean at Day 0 and 14 days post-treatment. Efficacy was indicated when a group arithmetic faecal egg count reduction (FECR) of ≥90% was recorded for FBZ and PYR, and ≥95% for IVM and MOX. Between March and December 2012, 404 FECRT were performed on 12 yards examining 101, 110, 93 and 100 equids for FBZ, PYR, IVM, and MOX, respectively. FBZ resistance was identified on all yards (mean FECR range 0–65.8%). On 10 of 12 yards, PYR efficacy was >90% (91.0–99.4%) and on two yards, PYR resistance was suspected (86.8–87.2%). IVM (96.4–100%) and MOX (99.9–100%) were >95% efficacious on all yards. As the prevalence of FBZ resistance was 100%, the future use of this anthelmintic for the control of strongyles should be questioned. PYR should be used strategically to reduce reliance on the macrocyclic lactone class products. Over-dispersion of FEC between horses was observed (average k=0.21) with 80% of the strongyle eggs counted measured in 15% of horses tested, strongly supporting the application of targeted helminth control programmes in this host species.

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

SummaryThis 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.

Shortened strongyle-type egg reappearance periods in naturally infected horses treated with moxidectin and failure of a larvicidal dose of fenbendazole to reduce fecal egg counts

Deworming horses with anthelmintics that have activity against encysted small strongyle larvae (L 3 and L 4) is a common practice in parasite control programs. The two drugs currently available for this use are moxidectin (MOX) administered in a single dose of 0.4 mg/kg and fenbendazole (FBZ) given at the larvicidal dose (10 mg/kg for 5 days). Here, we report the efficacy of MOX and the larvicidal dose of FBZ for reducing counts of strongyle-type eggs per gram of feces in naturally infected horses. Fecal egg counts (FECs) of 15 yearlings were observed following deworming. On day 0, 6 of the 15 yearlings were administered a larvicidal dose of FBZ; 14 days later, all 15 yearlings received MOX at a single dose of 0.4 mg/kg. Feces were collected on day 0 for pre-treatment egg counts. Feces were collected at weekly intervals thereafter during FEC observation periods. FECs of FBZ-treated horses were compared at day 0 and 14 days post-treatment. The difference in means pre- and post-treatment with FBZ was not statistically significant ( p = 0.65). On days 0 and 42 of the MOX treatment observation period the mean FEC of the yearlings that had not received the FBZ treatment did not differ significantly from that of the FBZ-treated yearlings. MOX was effective in reducing fecal egg counts to 0 EPG for 21 days. At day 35 all but 2 of the yearlings had some eggs present (range = 4–361 EPG) and at day 42 all but 1 yearling had eggs present (range = 3–432 EPG). At day 42 the group mean FEC reduction had fallen from 100% to 67%. Results of this study do not support the use of the larvicidal dose of FBZ for small strongyle control. Larger field studies will be needed to investigate whether egg reappearance periods are shortening for MOX-treated horses.

Moxidectin-resistant nematodes in cattle in Brazil

The frequent use of anthelmintics in cattle has contributed to the emergence of gastrointestinal nematode populations resistant to the drugs available in the market. This study aimed to evaluate moxidectin efficacy in a property with suspected presence of Oesophagostomum spp. resistant to such anthelmintic. The accuracy of fecal egg count reduction test (FECRT) was also assessed through comparison with the data obtained in the controlled efficacy test (worm burden determination after necropsy). Twenty worm free steers were placed together with cattle of the farm with suspected moxidectin resistance. They became naturally infected with the parasite species present in the farm, and when fecal egg counts (FEC) were higher than 200 eggs/g, the animals were randomly distributed into two groups. One group ( n = 10) was treated with moxidectin (0.2 mg/kg; Cydectin ®, Fort Dodge) and the other was the control group ( n = 10). Fecal samples from each steer were collected on the treatment day and three, seven, 10 and 14 days later for FEC and fecal cultures. At 14 days after treatment, all animals were sacrificed and the gastrointestinal nematodes were recovered, identified and counted. Mean FEC reduction in the treated group (compared with control group) was of 88, 85, 88 and 92% at days three, seven, 10 and 14 after treatment, respectively. In fecal cultures, third stage larvae of Cooperia spp. and Oesophagostomum spp. were predominant. As regards the controlled efficacy test, moxidectin had 100% efficacy against the genera Haemonchus spp. and Trichostrongylus spp., and efficacy of 65.2% for Cooperia spp. ( Cooperia punctata and Cooperia pectinata), 44.8% for Oesophagostomum radiatum, and 81.4% for Trichuris spp. Most of the Cooperia spp. females obtained from the control animals showed eggs inside the uterus (98.5%); conversely, only 48.2% of the females from the treated group had eggs ( P < 0.001). Considering the suppression in egg output following moxidectin treatment, FECRT has to be employed with caution to avoid under estimation of the anthelmintic resistance. From necropsy results, it can be concluded that C. punctata, C. pectinata, O. radiatum and Trichuris spp. showed resistance to moxidectin.

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

The present study was carried out in the northwestern region of São 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.

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.