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Parasitic helminths of equids are capable of causing ill-thrift, clinical disease, and death. Although young horses are the most susceptible to parasitic disease and are the most intensively treated cohort, deworming regimens are rarely evaluated within this age group. This study objectively evaluated the impact of deworming regimen on fecal egg counts (FECs), growth rates, and body-condition scores in young Thoroughbreds. Forty-eight Thoroughbred foals from three central Kentucky farms were randomly allocated to two treatment groups: an interval dose program receiving bi-monthly rotations of pyrantel pamoate and ivermectin and a daily deworming group receiving daily rations of pyrantel tartrate feed additive throughout the study, oxibendazole at two months of age, and moxidectin treatments at 9.5 and 16.5 months of age. Pre- and post-treatment eggs per gram of feces (EPGs) of Parascaris spp. and strongyle family parasites, gel/paste dewormer efficacies, and monthly weights and body condition scores were collected. Ascarid and strongyle FECs were not significantly different between groups but were significantly influenced by horse age with strongyle counts continually increasing and ascarid counts peaking at 4.5 months of age. Reduced strongyle efficacies of ivermectin and moxidectin were observed on two farms with consistently low pyrantel pamoate efficacies on all three farms. Ivermectin also exhibited reduced ascarid efficacy. Average daily gain did not differ significantly between groups and was only significantly influenced by age, mirroring average daily gain reference data for Kentucky Thoroughbreds born in 2013. Body condition scores also did not differ between groups, remaining in the optimal range (5-6) for the duration of the study. Management practices resulting in growth rates matching the reference data and in optimal body condition scores compensate for the negative impacts of parasitism even in cases of reduced drug efficacy. Performance parameters can provide useful information in cases of suboptimal parasite control.

The aims of this study were to determine the species of Parascaris present in foals in Sweden and to establish whether anthelmintic resistance to pyrantel and fenbendazole is present on Swedish stud farms. Ascarid eggs collected from different regions in Sweden were karyotyped and were all identified as Parascaris univalens, characterized by one chromosomal pair. Faecal egg count reduction tests were performed on a total of 142 foals on 9 farms between September 2016 and May 2017. Healthy foals with at least 150 eggs per gram faeces (EPG) were included in the study and treated with oral pastes of pyrantel embonate or fenbendazole according to manufacturer instructions. The efficacy of the drugs was calculated by a Bayesian model using the R package "eggCounts". In accordance with the American Association of Equine Practitioners, parasites were classified as resistant to pyrantel if the reduction in EPG was ≤ 85% and to fenbendazole if the observed efficacy was ≤ 90%. Four of eleven groups treated with pyrantel had an observed efficacy of ≤ 85%, and as many as 43% of the foals treated with pyrantel excreted eggs 10-16 days after treatment. In contrast, one of the six groups treated with fenbendazole had an observed efficacy of ≤ 90%, and only 6% of all foals were excreting eggs 10-16 days after treatment. Since resistance to ivermectin has earlier been shown to be widespread in Parascaris spp. in Sweden it is likely that multiresistant populations are present on Swedish stud farms. This is the first study showing the existence of pyrantel-resistant Parascaris spp. in Europe, and the first ever study where anthelmintic resistance has been shown in P. univalens.

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.

The main purpose of the research was to determine if three weekly samplings would produce consistent results for low strongyle egg shedders, generally associated with older horses. Strongyle egg counts per gram of feces (EPG) were done for 661 Thoroughbred mares on 14 farms in 2012-2013 once a week for three consecutive weeks. None of the mares had been treated with ivermectin or moxidectin for more than 90 days and with fenbendazole, oxibendazole, or pyrantel pamoate for more than 60 days. Strongyle EPG count data indicated that 38.3% of the mares were positive at first and second sampling, and 37.8%--at third sampling. There were 5.6-63.3% of horses positive per farm. Correlations between EPG count data in all three weeks are quite high (Rs = 0.84, p0.001). Level of horse infection was found to be dependent on horse age, type of farm and individual characters of horse. This study documented that strongyle egg counts (EPGs) from individual horses did not differ significantly between weeks. Thus, a single strongyle EPG count can be interpreted as indicative of the level of egg shedding for a given horse. These data support the current trend of not deworming all adult horses on a farm, so that high shedders can be identified and treated. This saves horse owners money and reduces development of potential drug resistance of parasites because of less frequent usage of antiparasitic compounds. Information from this study helps to conclude recommendations for parasite control in horses globally.

Anthelmintic resistance is an increasing challenge for the control of equine parasites. The fecal egg count reduction test (FECRT) is the practical gold standard method for evaluating reduction in anthelmintic efficacy, but the interpretation is complicated due to high levels of variability. A hierarchical statistical model was described for analysis of FECRT data from multiple farms to evaluate the role of biological factors in determining the strongyle efficacy of pyrantel pamoate in a study performed in Denmark. The model was then used to describe two notions of farm efficacy, namely conditional and marginal efficacy. The median of the lower prediction limits was used to describe a robust classification rule. The performance of the methodology was evaluated using Monte Carlo simulations. The field study was performed on 64 Danish horse farms of different breeds. Of 1644 horses, 614 had egg counts ≥200 eggs per gram (EPG) and were treated. Individual coprocultures were performed for identification of Strongylus vulgaris from all horses pre-treatment. Thirty-one farms (48.4%) were positive for S. vulgaris , but pyrantel efficacy was unaffected by the presence of this parasite in the statistical model. Further, there were no significant effects of age, gender, or interactions between these, while the pre-treatment egg count was negatively associated with the egg count reduction. The statistical model classified 81.3%, 10.9%, and 7.8% of farms as no signs of resistance (NR), suspect resistance (SR), and resistance (RE), respectively. In comparison, arithmetic calculations classified 68.8%, 17.2%, and 14.1% in the same categories. Using 10,000 simulated data sets, the methodology provided a classification of farms into different efficacy categories with a false discovery of reduced farm efficacy rate equaling 8.74%. In addition, model-classification was unaffected by presence of single outlier horses in a separate simulation study.

International audience; Drug resistance in equine gastro-intestinal parasitic nematodes has been reported throughout the world. While the focus is usually put on cyathostomins, observations of macrocylic lactone failure against Oxyuris equi have accumulated over the last decade. Here we report the failure of ivermectin in the control of O. equi in an experimental Welsh pony herd. In a first trial, 6 ponies previously drenched with moxidectin and showing patent O. equi infection were administered ivermectin and subsequently monitored for O. equi egg excretion over one month. This trial demonstrated a failure of ivermectin to control O. equi egg excretion as half of ponies demonstrated recurrent egg excretion in the peri-anal region during 21 days after treatment. One year later, six female Welsh ponies drenched with moxidectin demonstrated signs of itching and scratching in their peri-anal region with worms being found transiently in fecal materials three weeks later. Ponies were allocated to three treatment groups, i.e. ivermectin, pyrantel embonate and fenbendazole and monitored for egg excretion over five weeks. Fenbendazole and pyrantel embonate broke ivermectin suboptimal efficacy as soon as 8 and 14 days respectively after treatment, while egg excretion remained constant throughout the 41-day long trial in the ivermectin-treated ponies. This is the first report of ivermectin failure against O. equi in France. In the absence of critical efficacy test, it remains unclear whether true resistance is at stake or if these observations confound a constitutive suboptimal efficacy of ivermectin against O. equi.

Since 2002, selected populations of Parascaris equorum in several countries have been reported to survive treatment with macrocyclic lactone (M/L) anthelmintics. Clinical treatment failures are characterized by negligible fecal egg count reduction, but M/L resistance has been confirmed in ascarids by controlled efficacy testing. Resistance was selected by current parasite control practices for foals, which often include exclusive and excessively frequent use of M/L dewormers, thereby minimizing refugia within the host and in the environment. Chemical control of M/L-resistant isolates can be accomplished with pyrimidine and/or benzimidazole anthelmintics, but a few M/L-resistant populations have recently exhibited resistance to pyrantel pamoate as well. Some specimens of Oxyuris equi regularly survive treatment with macrocyclic lactones, but it is uncertain whether this constitutes resistance or merely confirms the incomplete oxyuricidal efficacy of virtually all broad spectrum equine anthelmintics. Variations in other biological parameters of Oxyuris and Parascaris, specifically atypical infection of older hosts and shorter prepatent periods, have been reported anecdotally. These changes may represent genetic modifications that have evolved in parallel with resistance as a result of anthelmintic selection pressure.

The expanding prevalence of Parascaris equorum populations that are resistant to macrocyclic lactone (ML) anthelmintics makes it desirable to identify dewormers which remain effective. The objective was to evaluate the efficacy of pyrantel pamoate in 14 suckling foals that had been infected orally with ∼600 larvated eggs of a P. equorum isolate selected for ML resistance (ML-R). Seventy days after inoculation, foals were weaned, housed individually, and fecal samples were examined frequently to detect the onset of patency. Between 73 and 80 days post-inoculation, all 14 foals developed P. equorum egg counts ≥150 eggs per gram (EPG). An initial cohort of eight foals was treated orally with ivermectin paste (200 μg/kg) 84–91 days post-inoculation. Egg counts were reduced by only 47% at 2 weeks after ivermectin treatment, confirming the ML-R status of the isolate. A second cohort of six foals was not treated with ivermectin. Within each cohort, eligible foals were allocated randomly to treated (pyrantel pamoate; n = 7) or untreated control (n = 7) groups. Treated foals were dosed orally on Day 0 with a paste formulation of pyrantel pamoate at 13.2 mg/kg. Mean ascarid egg counts of treated foals were reduced by 96.0% and 98.8% at 1 and 2 weeks post-treatment, respectively. On Day 14, foals were euthanatized and specimens of P. equorum were recovered from the gut contents, preserved in 10% formalin, and counted. Mean numbers of P. equorum adults recovered postmortem were significantly lower (P = 0.0031) in foals treated with pyrantel pamoate ( X ¯ = 1.7 ; range 0–16) compared to control foals ( X ¯ = 63.0 ; range 0–320). A paste formulation of pyrantel pamoate, at a dosage of 13.2 mg/kg, was 97.3% effective against a ML-R isolate of P. equorum.

Clinical trials using fecal egg count reduction tests and coproculture were conducted with yearlings and mares on a farm in 1997. Fecal samples were taken from each horse to estimate the number of strongyle eggs/g feces with Cornell-Wisconsin centrifugal flotation and Cornell-McMaster dilution techniques. Eleven of 15 yearlings, which had been on a daily feeding of grain with pyrantel tartrate for 66 d were found with strongyle eggs in feces. This was the first time the in-feed medication had been used on the farm. Nine yearlings were randomised into three groups; continuation of daily pyrantel tartrate or one treatment with pyrantel pamoate or moxidectin. Two of three yearlings given pyrantel tartrate or pamoate had no reduction in the eggs/g feces. These six yearlings were then given moxidectin and in all yearlings the eggs/g feces was reduced to zero. The 66 d of pyrantel tartrate use was an inadequate time for development of resistant cyathostomes and a hypothesis was the resistance was due to extensive use on the farm over many years of pyrantel pamoate at twice the label dose for control of tapeworms. That hypothesis was tested with 12 mares with strongyle eggs in the feces randomised into two treatment groups: pyrantel pamoate at label dose or moxidectin. Five of six mares given pyrantel had

The effect of two treatment programmes on egg shedding in dogs naturally infected with Toxocara canis, one based on a milbemycin oxime-praziquantel-lufenuron combination (SENTINEL) Spectrum; Group 1) and the other based on a febantel-pyrantel embonate-praziquantel combination (DRONTAL) Plus; Group 2), was compared in a study involving 104 suckling pups from three different kennels. The animals in Group 1 were treated at a minimum milbemycin oxime dose of 0.5 mg/kg bw starting at 2 weeks of age and subsequently every 4 weeks until reaching 26 weeks of age. The animals in Group 2 were treated every 2 weeks from week 2 until week 12 of age and then once at week 26 at a minimum febantel and pyrantel embonate dose of 15.0 and 14.4 mg/kg bw, respectively. Toxocara egg counts were determined fortnightly starting at 2 weeks of age and continuing until 26 weeks of age for every pup. Any adverse drug event was recorded during the trial. Both treatment programmes significantly reduced the zoonotic Toxocara egg shedding and were well tolerated by the pups. The pups in Group 1 showed lower average faecal egg counts and were found more frequently shedding no eggs than the pups in Group 2.

This study was conducted on a stud farm in Sweden to investigate the species composition of cyathostomins expelled in the faeces of horses after deworming using three different anthelmintic preparations. Twenty-seven horses excretingor = 200 strongyle eggs per gram faeces (EPG) were divided into three comparable groups and dewormed on day 0 with either of following compounds: 0.2 mg ivermectin per kg body weight (bw), 19 mg pyrantel pamoate per kg bw or 7.5 mg fenbendazole per kg bw. For each of the 3 days following anthelmintic treatment faeces was collected from individual horses and subsamples were fixed in formalin. Four days after the anthelmintic treatment all horses were re-treated with ivermectin and faeces was collected on day 5. Individual subsamples from each of the four sampling occasions were examined for cyathostomin nematodes. Sixty-three to 270 worms per horse were identified to the species level. The majority of the worms recovered were expelled during the first day from horses treated with ivermectin or pyrantel pamoate, and during the second day from horses treated with fenbendazole. Fifteen cyathostomin species were identified and the six most prevalent were Cylicocyclus nassatus, Cyathostomum catinatum, Cylicostephanus longibursatus, Cylicocyclus leptostomus, Cylicostephanus minutus and Cylicostephanus calicatus. These species composed 91% of the total burden of cyathostomins. The number of species found per horse ranged from 6 to 13, with an average of 9. No significant differences in species composition or distribution were found between the treatment groups. On day 5, i.e. 1 day after the last ivermectin treatment, 93% of the adult worms were recovered from horses in the fenbendazole group. This study showed that it was possible to identify cyathostomins expelled in faeces of dewormed horses, and that the most prevalent species corresponded to those found in autopsy surveys performed in other countries.

An eight-year-old, neutered, female Shetland Sheepdog presented with a 6-week history of small intestinal diarrhea. Regenerative anemia, hypoproteinemia, and an increased plasma C-reactive protein concentration were detected on blood examination. Fecal examination and abdominal radiography were unremarkable. Abdominal ultrasonography showed diffusely hyperechoic mucosa in the small intestine. Gastroduodenoscopy, performed under general anesthesia, revealed mucosal edema and increased granularity in the duodenum and jejunum. Histopathological examination of the endoscopically biopsied small intestinal mucosa revealed tapeworm infection. A single administration of a combined anthelmintic drug (5mg/kg praziquantel, 14.4 mg/kg pyrantel pamoate, and 15 mg/kg febantel) was successful for deworming, and the dog fully recovered. The parasites were removed from stored frozen duodenal mucosa and morphologically identified as Mesocestoides sp. immature adult worms. Mitochondrial (mt) 12S rDNA and mt cytochrome c oxide subunit 1 genes were amplified from the parasites. DNA sequence analysis showed that the genes shared 100% identity with those of reported M. vogae (syn. M. corti). This is the first reported case of protein-losing enteropathy caused by M. vogae in a dog.

Research on benzimidazole-resistant Population S small strongyles began in a Shetland pony herd in 1974 at the University of Kentucky and has continued for over 25 years. The present update, for the period 1992–1999, evaluated activity of pyrantel pamoate (PRT) in field tests in the pony herd. Additional critical tests with PRT and oxibendazole (OBZ) were done in foals born in the herd. Activity of PRT was initially excellent in field tests, based on epg/lpg count data, but declined rapidly during the second full year of pyrantel treatments. Critical test data for small strongyles indicated efficacies of PRT were about 60% at the beginning of the present observations and this intermediate level of removal continued throughout the seven-year period except for 1994 (75%). Unusual was the finding that field test epg/lpg data on small strongyles indicated much lower activity of PRT than found in worm count data in critical tests. The previously reported ineffective activity of OBZ on this population of small strongyles continued. Data are presented on prevalence and drug activity on several species of internal parasites besides small strongyles.

The egg output and humoral antibody response to scolex antigens of the equine tapeworm Anoplocephala perfoliata were monitored in naturally infected foals by an egg flotation/centrifugation method and an indirect enzyme-linked immunosorbent assay (ELISA). The study was performed on a stud farm in south-western Sweden between May 1994 and April 1995. Sequential blood and faecal samples were taken from 21 foals during their first summer on pasture and until tapeworm eggs were detected. Results were expressed separately for 10 and 11 foals born before and after the end of April 1994, respectively. Increased levels of antibodies were noticed from October and onwards in both groups whereas tapeworm eggs were detected in the faeces of all foals about 4 months later. The antibody response was similar in both groups but it was more pronounced in foals born before April 1994. All foals were treated in March 1995 with an oral paste formulation of pyrantel pamoate at a dose rate of 38 mg/kg bodyweight. Most animals responded to the anthelmintic treatment and one month later, tapeworm eggs were only detected in one out of the 18 foals examined one month after treatment. Thus, the treatment reduced the number of A. perfoliata egg positive horses by 94%. A concomitant decline in antibody levels was also observed. Western immunoblot analysis of sequential individual serum samples showed that at least 10 different scolex antigens in the molecular weight range 10-200 kDa were recognised. Banding intensities, especially of the 10 kDa, 45 kDa and 66 kDa proteins were different in the sequential sera taken during the course of infection.

Three fecal egg count reduction assays (FECR) and one critical trial were performed to determine the efficacy of pyrantel pamoate (PP) at 6.6 mg base kg−1 on a well managed stud farm in Louisiana where a loss of efficacy was suspected. Efficacy of PP based on FECR varied from 25% in mares to 83% in yearlings. Second treatments with PP 2 weeks following an initial treatment failed to reduce eggs per gram (EPG). A critical trial was performed to determine the cyathostome species resistant to PP. Three strongyle-naive ponies which acquired infections on the farm were used for this purpose. Following treatment with PP at the recommended dose, 11 species of cyathostomes remained in the intestine of the tracer ponies. Reduced efficacies (62%–88%) were noted for seven species. Resistance to oxibendazole (OBZ), which was > 90% effective on this farm in 1982, was also evaluated by FECR and found to exist. The results of one experiment indicate that dual resistance of parasites to PP and OBZ also exists.

Several compounds ( n = 13 single or combinations; most at therapeutic dosages) were evaluated between 1977 and 1992 in critical tests ( n = 91) against benzimidazole (BZ) resistant small strongyles (Population S) and several other species of internal parasites in Shetland ponies, mostly under 1 year old. The closed breeding herd, from which the test ponies were selected, had been treated every 8 weeks with cambendazole (CBZ) for 4 years (1974–1978) and oxibendazole (OBZ) for 14 years (1978–1992). Published field test data (1974–1992) on older ponies in the herd showed BZ resistance of small strongyles. Average efficacies in the present critical tests against small strongyles for OBZ ( n = 59 animals) were high in early years (95% or higher), but gradually declined to a low of 1% in 1991. Side-resistance of small strongyles was evident in critical tests ( n = 1–6/single drug or combination) for several other BZs and a pro-BZ; ivermectin and piperazine were highly active, but pyrantel pamoate exhibited weak activity. BZ resistance was evident for six small strongyle species ( Cyathostomum catinatum, Cyathostomum coronatum, Cylicocyclus nassatus, Cylicostephanus calicatus, Cylicostephanus goldi , and Cylicostephanus longibursatus ). Activity on bots, ascarids, large strongyles, and pinworms was essentially as expected, indicating no drug resistance.

The efficacy of six anthelmintics against natural infections of Baylisascaris procyonis in raccoons (n = 7 per drug) was determined in a series of critical tests. The drugs were given via moist cat food as a single dose or once daily for three consecutive days. Raccoons treated with pyrantel embonate (1 x 20 mg base kg-1 bodyweight (bwt.)), ivermectin (1 x 1 mg kg-1 bwt.), moxidectin (1 x 1 mg kg-1 bwt.), albendazole (3 x 50 mg kg-1 bwt.), fenbendazole (3 x 50 mg kg-1 bwt.) or flubendazole (3 x 22 mg kg-1 bwt.) expelled 1-198, 2-24, 2-14, 3-80, 2-70, or 2-35 B. procyonis stages, respectively, within the faeces. No roundworm was detected in any raccoon at post mortem examinations 7 days after the end of treatment. These results suggest that any of the six anthelmintics can be used at the dose rates tested in a deworming programme for captive raccoons.

Studies on a Thoroughbred breeding farm in Ohio were done to: (1) compare the effects of daily administration of pyrantel tartrate feed pellets with monthly administration of a pyrantel pamoate paste to yearling horses (21 January–3 September); (2) assess the effects of daily pyrantel tartrate given strategically in spring/summer to foaling mares (1 April–16 August) and given for a prolonged period to barren mares (21 January–3 September); (3) determine if strategic medication of foaling mares with daily pyrantel tartrate protected their foals until weaning. There were no differences in cyathostome egg counts, pasture larval counts, body condition scores, or body weights of yearlings treated with daily pyrantel tartrate or monthly pyrantel pamoate. Both treatments failed to maintain fecal egg counts of yearlings below 100 eggs per gram (epg), and mean counts exceeded 400 epg (pyrantel pamoate) and 700 epg (pyrantel tartrate) in August and September, resulting in a sharp, but moderate increase in pasture infectivity in October. By contrast, prolonged or strategic use of daily pyrantel tartrate in mature horses were each highly effective in reducing pasture contamination and infectivity with cyathostome eggs and larvae respectively. Strategic medication of foaling mares provided protection of their foals until weaning and first treatment of foals was delayed until after weaning when mean strongyle counts exceeded 100 epg. Treatment of weanlings with pyrantel pamoate had little effect on egg counts. A comparative anthelmintic study with ivermectin, oxibendazole, and pyrantel pamoate confirmed earlier studies showing reduced efficacy of anthelmintics in young horses.

This paper reports a survey conducted in France during 2011 to evaluate the efficacy of commonly used anthelmintics against horse cyathostomins. A total of 40 farms and 1089 horses were screened for the presence of cyathostomins. All farms but one were positive, with an overall animal infection rate of 53.7%, ranging from 9% to 83% on individual farms. On 445 horses from 30 of these farms, a faecal egg count reduction test (FECRT) was performed to evaluate the efficacy of oral formulations of fenbendazole (FBZ), pyrantel embonate (PYR), ivermectin (IVM) and moxidectin (MOX). Calculation of the mean FECR and 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. Resistance to FBZ was found on 17 of 18 farms investigated, with a mean reduction of 57% (95% CI: 38.5–71.2%). Suspected resistance for PYR was found on 6 of 30 farms, and confirmed on another 3 of 30 farms, with a mean reduction for PYR of 94.7% (95% CI: 88.9–98.5%). Reduced efficacy simultaneously of FBZ and PYR was found in 7 farms. Reduced efficacy of IVM was found in one animal on one farm and of MOX in one animal on another farm, and was combined with resistance against FBZ and/or PYR. These results indicate that single and multiple drug resistance and reduced efficacy in equine cyathostomins is present in France. Macrocylic lactones proved to be highly effective compounds against cyathostomins, with reduced efficacy for IVM and MOX in two farms only. These results extend present knowledge on the occurrence of drug resistant cyathostomins in Europe, and illustrate the necessity to use anthelmintics in appropriate worm control programmes.

A controlled laboratory study was conducted to evaluate the efficacy of four commercial products administered as a single treatment for the prevention of heartworm disease caused by Dirofilaria immitis in dogs. Forty-four commercially sourced Beagle dogs, 6-7 months of age, were received at the test site (Auburn University, Department of Pathobiology) on Study Day (SD) -72 to begin acclimation. On SD -30, each dog was inoculated subcutaneously with 100 infective, third-stage D. immitis larvae (MP3 strain, TRS Laboratories, Inc., Athens, GA). On SD -1, 40 dogs weighing 18.2-25.3 lbs were ranked by decreasing body weight and randomized to five groups of eight dogs each. On SD 0, the dogs assigned to Group 1 were treated orally with ivermectin/pyrantel pamoate chewable tablets, Group 2 dogs were treated orally with milbemycin oxime flavored tablets, Group 3 dogs were treated with selamectin topical solution, and Group 4 dogs were treated with imidacloprid/moxidectin topical solution. Group 5 dogs remained nontreated. Dosages for dogs in Groups 1-4 were based on the individual body weight of each dog and current labeled dose banding for each commercial product. All dogs were fasted overnight prior to treatment. Food was returned four hours after treatment. Animals were observed for abnormal clinical signs involving eyes, feces, respiration, behavioral attitude, locomotion/musculature, or skin conditions at prescribed intervals immediately after treatment and at twice daily intervals thereafter. On SD 90, whole blood was collected and tested for adult heartworm antigen. On SDs 119/120, the dogs were euthanized and subjected to necropsy examination for recovery of adult D. immitis and/or worm fragments. At necropsy, all 8 dogs in the nontreated group were infected with adult D. immitis (34-70 worms/dog, geometric mean (GM)=51.6 worms/dog). One or more adult D. immitis and/or worm fragments were recovered from 7 of 8 of the dogs each in Groups 1-3 (87.5% were heartworm positive). The respective GM worm burdens/dog for Groups 1-3 was 2.3, 2.4, and 2.3 which resulted in 95.6, 95.4 and 95.5% efficacy, respectively. No worms were recovered from any of the 8 dogs in Group 4 resulting in 100% efficacy.

The effectiveness of the combination of pyrantel pamoate (5 mg kg-1) and ivermectin (6 micrograms kg-1) against the canine hookworms Uncinaria stenocephala and Ancylostoma caninum was determined. This combination is intended for monthly use as a heartworm preventative and for treatment and control of canine hookworms. The formulation was found to be effective (99.6% reduction in worm burdens) against both species of hookworms in experimentally infected dogs. No adverse effects due to the drug combination were observed in any dog during the course of this study.

In recent years, numerous veterinary practitioners have reported anecdotal episodes in which anthelmintic treatment did not appear to deliver the expected efficacy against equine pinworms (Oxyuris equi). Anthelmintic resistance has not been demonstrated formally in equine pinworms, so a clinical study was designed to evaluate the efficacy of paste formulations of pyrantel pamoate or ivermectin against naturally acquired infections with O. equi. Twenty-one horses (>4 months to 15 years of age) with patent, naturally acquired pinworm infections were blocked by source of origin and allocated randomly to one of three treatment groups: horses (n=7) assigned to Group 1 were treated orally with pyrantel pamoate paste at a dosage of 13.2 mg/kg (2x label dosage), Group 2 horses (n=7) were untreated controls, and horses (n=7) assigned to Group 3 were treated orally with ivermectin paste at a dosage of 200 microg/kg. Fourteen days after treatment, horses were euthanatized, necropsied, and large intestinal contents were processed for recovery of adult pinworms. In addition, duplicate 1% aliquots of intestinal contents from the cecum, ventral colon, dorsal colon, and small colon were collected, preserved, and examined for recovery and enumeration of fourth-stage larval O. equi. Anthelmintic efficacy against pinworms was evaluated by comparing the post-treatment worm counts of Groups 1 and 3 to those of control animals. Mean numbers of O. equi adults recovered postmortem were significantly decreased by both pyrantel pamoate (P=0.0366) and ivermectin (P=0.0137) treatment, with respective efficacies of 91.2% and 96.0%. In addition, both products demonstrated >99% efficacy against fourth-stage O. equi larvae. The current study demonstrated acceptable adulticidal and larvicidal efficacy of both pyrantel pamoate and ivermectin paste formulations against O. equi and did not support the existence of macrocyclic lactone or pyrimidine resistance in the pinworm populations evaluated.

A study was carried out to assess the field efficacy of moxidectin (MOX) against Parascaris equorum in foals. A total of 70 foals from 2 Italian thoroughbred (Farms 1 and 2) stud farms and one trotter stud farm (Farm 3), aged 3-5 months and with faecal egg counts (FEC) for=300 eggs per gram (EPG) were included in the study. On each farm, foals were divided into 2 groups (of 10, 8 and 10 foals, respectively) and treated with either moxidectin (MOX, 400 mcg/kg b.w.) or ivermectin (IVM, 200 mcg/kg b.w.) on day 0 and examined for faecal count reduction (FECR) on day 14. Five, 4 and 5 foals, respectively, were kept as untreated controls. An individually based estimation of efficacy was assessed by a bootstrap simulation to evaluate the percent reduction of FECRs. Two thousand bootstrap resamples were constructed from individual FECRs and the parasite population was considered susceptible for FECsor=90% and 95% lower confidence limit (CL)90%, suspected resistant for FECRsor=90% and 95% LCL90% and resistant when FECR90% and 95% LCL90%. On day 14, foals with FECRs categorized as resistant or suspected resistant were treated with pyrantel pamoate (PYR, 13.2mg/kg b.w.) and examined for FECR on days 28 and 35. On day 14, MOX and IVM treatments were ineffective in all foals from both thoroughbred farms, while MOX ad IVM were effective (FECRs90%) in 7 and 5 trotter foals, respectively, and remained90% until day 35. PYR treatment given on day 14 to remaining 8 foals (3 MOX-treated and 5 IVM-treated) was fully efficacious at faecal examinations carried out on days 28 and 35.

Clinical field trials were conducted at five geographical locations in the USA (Oklahoma, Wisconsin, Tennessee, Virginia and Idaho) to evaluate the efficacy and safety of pyrantel pamoate paste (19.13%, w/w, pyrantel base) administered at the recommended dosage of 13.2 mg pyrantel base/kg (6.0 mg pyrantel base/lb) body weight (b.w.) against tapeworm infections of Anoplocephala spp. in naturally infected horses. Horses at each study site were allocated by restricted randomization based on the cestode status (positive or negative) of pre-treatment fecal egg counts to complete sets of four animals each or incomplete sets of fewer than four animals. Within sets comprising of two to four horses, one animal was randomly allocated to receive placebo vehicle paste and the remaining horse(s) received pyrantel pamoate paste administered orally at a minimum dosage of 13.2 mg pyrantel base/kg b.w. on Test Day (TD) 0. Single animal sets received pyrantel pamoate paste. Fecal samples of horses were collected and examined for equine tapeworm (Anoplocephala spp.) eggs a minimum of four times (once or thrice between TD -28 and -14, twice between TD -14 and -7, and once on TD 0) prior to treatment on TD 0. Fecal samples of horses that were positive for cestode infection pre-treatment were examined for cestode eggs on TD 7, 8, 9, 14, 15 and 16. Cestode-negative pre-treatment horses were not sampled again after treatment. A total of 241 horses (141 mares, 16 stallions and 84 geldings; 6 months-30 yrs of age; 173-646 kg; 13 recognized breeds and various crossbreds) were evaluated. The prevalence of Anoplocephala spp. determined by pre-treatment fecal examination ranged from 38.3% in Idaho to 68.1% in Tennessee with an overall prevalence of 52.3%. Ninety cestode-positive and 88 cestode-negative horses were treated with pyrantel pamoate paste, 36 cestode-positive and 27 cestode-negative horses were treated with placebo vehicle paste. Overall, 178 horses were treated with pyrantel pamoate paste, and 63 horses were treated with placebo paste. Of the 178 horses treated with pyrantel pamoate paste, no drug related, adverse clinical or neurological health events were observed. No doses of pyrantel pamoate paste were refused or lost during dosing. At each post-treatment time sampling interval, significantly fewer cestode eggs (P < 0.0115) were passed by cestode-positive horses treated with pyrantel pamoate paste compared to cestode-positive horses that received placebo paste. Efficacy of the pyrantel pamoate paste treatment ranged from 92 to 96% from TD 7 to TD 16 with an overall efficacy of 95%. The results of these trials demonstrated that pyrantel pamoate paste (19.13%, w/w, pyrantel base) administered orally at a dosage of 13.2 mg pyrantel base/kg b.w. is highly efficacious (95%) against Anoplocephala spp. and safe for use in horses with no adverse clinical or neurological health events observed under field use conditions.

The efficacy of fenbendazole granules against Toxocara canis in naturally infected greyhounds housed in contaminated environments was evaluated. Eight pens, each containing three to seven greyhounds, 3-12 months of age, were randomly allotted into two treatment groups. Greyhounds in Group 1 were treated with fenbendazole granules mixed in their feed at 50 mg/kg/day for 3 consecutive days once a month for 4 months. Greyhounds in Group 2 were treated with pyrantel pamoate suspension at 5.0 mg/kg per os once a month for 4 months. Quantitative fecal examinations were performed on days 0, 10 and then on the first day of each monthly treatment. Greyhounds administered fenbendazole had fecal egg count reductions (FECRs) of 95.8 and 99.8% at 10 and 31 days following initial treatment, respectively. Greyhounds administered pyrantel pamoate had FECRs of 85.8 and 88.3% at 10 and 31 days after the first treatment, respectively. T. canis fecal egg counts conducted from Day 31 through Day 128 were significant lower in those greyhounds administered fenbendazole as compared to greyhounds administered pyrantel pamoate. Fenbendazole produced FECRs in greyhounds from Day 31 through Day 128 by 96.8-99.8%. Pyrantel pamoate reduced fecal egg counts during the same time period 71.4-98.3%.

The effect of anthelmintic treatment of pigs on the embryonation and infectivity of Ascaris suum eggs isolated from expelled worms was investigated. Four groups of two naturally infected pigs were dosed with albendazole, pyrantel pamoate, ivermectin or piperazine dihydrochloride, respectively. Following worm expulsion, the eggs were removed from the uteri of female worms and embryonated in sulphuric acid. The infectivity of the embryonated eggs was tested through mouse inoculation. Egg development appeared normal in cultures from worms of the piperazine. pyrantel and ivermectin treated groups. In the albendazole cultures, egg development was largely arrested at the one-cell stage (81%). Where development occurred, irregular cell division was observed and only 7% of the eggs in the culture developed into fullgrown larvae. Following mouse inoculation with 2500 embryonated eggs, significantly lower lung larval counts on day 8 post inoculation (p.i.) were observed for mice in the piperazine and pyrantel treated groups (P < 0.01) compared to untreated controls. The larvae that developed in the eggs from ivermectin and albendazole treated groups appeared fully infective for mice. It was concluded that ovicidal activity of albendazole in vivo inhibits subsequent A. suum egg development in vitro; albendazole is, therefore, not suitable to obtain worms for egg embryonation to produce experimental inoculums. The anthelmintic treatment of pigs with ivermectin had only a limited effect on both embryonation and infectivity of A. suum eggs isolated from expelled worms.

Ten stables were included in a study to evaluate two in vitro methods for the detection of anthelmintic resistance in cyathostomes by comparing a faecal egg count reduction test (FECRT) to a larval development assay (LDA) and an egg hatch assay (EHA). The LDA was used in seven stables and EHA in the last three. On the basis of FECR values, resistance to benzimidazoles was detected in eight of the ten small strongyle populations. Resistance to pyrantel pamoate and ivermectin was not detected. The mean concentrations that inhibited hatching in 50% of the eggs (EC 50 ), using thiabendazole (TBZ) in an EHA, were 1.02 μM in resistant populations and 0.37 μM in susceptible or suspected resistant ones. In the LDA, TBZ concentrations preventing 50% development by first/second stage larvae to the third larval stage (LC 50 ) were 3.8 times lower than EC 50 values in resistant worm populations. Mean LC 50 for morantel, levamisol, ivermectin monosaccharide and avermectin-B2 in small strongyle population ssusceptible to pyrantel and ivermectin was 8.0 μM, 0.99 μM, 15.6 nM and 2.93 nM, respectively. Data on pyrantel and ivermectin resistant populations could not be obtained as no resistant populations were detected. This study concludes that in vitro tests may be useful as a supplement to FECRT for the detection of benzimidazole resistance in cyathostomes, even if reference populations to be used as controls in the assays were not available. It is suggested that EC 50 values for TBZ > 0.6 μ M in LDA and > 0.5 μ M in EHA strongly indicate benzimidazole resistance in equine small strongyles.

Pyrantel pamoate, formulated in a beef-based chewable tablet, was evaluated for efficacy in dogs against induced and natural infections of Toxocara canis, Toxascaris leonina, Ancylostoma caninum and Uncinaria stenocephala. Dose titration trials were conducted in Canada, the UK and Germany in dogs treated with pyrantel (as pamoate salt) at 0, 2.5, 5 or 10 mg kg-1 body weight. These studies showed that a dose rate of 2.5 mg kg-1, the efficacy of pyrantel against adult T. canis, T. leonina, U. stenocephala and A. caninum was 76.1, 85.6, 100 and 87.9%, respectively. Efficacy at 5 mg kg-1 against the same parasites was 94.2, 92.0, 93.5 and 93.8%, respectively, and at 10 mg kg-1 efficacy was 91.2, 97.6, 98.7 and 91.3%, respectively. No adverse effects due to treatment were seen in any of these trials.

The prevalence of benzimidazole-resistant small strongyles was determined in a survey, conducted on 14 thoroughbred studs, which compared the faecal egg counts of groups of horses before and after treatment with the recommended doses of cambendazole (20 mg kg −1 b.w.) or febantel (6 mg kg −1 b.w.). Benzimidazole-resistant cyathostomes were found on all farms examined. Pyrantel pamoate (19 mg kg −1 b.w.), oxibendazole (10 mg kg −1 b.w.) and ivermectin (0.2 mg kg −1 b.w.) reduced the strongyle egg counts on these studs by 97–100% at 2 weeks post-treatment. However, 6 weeks after dosing the reduction of the strongyle egg output had decreased to an average of 67.8% (8.7–97.1%) with pyrantel pamoate and 51.2% (0–95.8%) with oxibendazole, whereas ivermectin still suppressed the egg counts by 98.2% (95–100%).

A total of 59 equids (54 horses and five Shetland ponies) were treated with pyrantel pamoate once, at the dose rate of approximately 6.6 mg base kg-1, during the period November 1985-January 1988. The drug was administered as a paste formulation (51 equids) intraorally or as a suspension formulation by stomach tube (eight equids). The purpose of treatment was to evaluate the activity of pyrantel pamoate (at the therapeutic dose rate) for removal of the tapeworm, Anoplocephala perfoliata, by a modified (24-h) critical test. The presence or absence of tapeworms was not determined for the equids before treatment. Twenty-three (39%) of the 59 treated equids were found to be infected with A. perfoliata (from one to 180 specimens per infected equid) at necropsy. Removals varied from 67 to 100% (average 88%) for the 18 infected equids treated with the paste formulation. For the five infected equids treated with the suspension, removals were 58-100% (average 75%). The combined average removal of A. perfoliata for both formulations was 87%. Two abnormal (triradiate) specimens of A. perfoliata were recovered; one from each of two different equids.