Canada and veterinary parasitology.

A World Association for the Advancement of Veterinary Parasitology tradition for its conference is to present some highlights of the country hosting the event, and with an emphasis on the history of, and research in, veterinary parasitology. A review of Canada's peoples, physiography, climate, natural resources, agriculture, animal populations, pioneers in veterinary parasitology, research accomplishments by other veterinary parasitologists, centres for research in veterinary parasitology, and major current research had been presented at a World Association for the Advancement of Veterinary Parasitology Conference in Canada in 1987, and was published. The present paper updates the information on the above topics for the 22 years since this conference was last held in Canada.

The persistence of benzimidazole-resistant cyathostomes on horse farms in Ontario over 10 years and the effectiveness of ivermectin and moxidectin against these resistant strains.

Three clinical trials with fecal egg count reduction tests and coproculture were conducted on 2 standardbred farms in Ontario. On Farm A, the treatment groups were mebendazole and ivermectin in trial 1, and fenbendazole and moxidectin in another. On Farm B, treatment groups were mebendazole and ivermectin. All horses treated with mebendazole or fenbendazole were subsequently treated with ivermectin or moxidectin. Strongyle eggs/g feces were estimated pre- and post-treatment using the Cornell-McMaster dilution and Cornell-Wisconsin centrifugal flotation techniques. After treatment, there was no change in the arithmetic mean eggs/g feces for horses given mebendazole, and a reduction of only 49.1% for those given fenbendazole. All horses receiving ivermectin or moxidectin had their egg counts reduced to 0. Only cyathostomes were found on culture. On both farms the benzimidazole resistant strains appeared to have persisted for at least 10 years. Development of and monitoring for anthelmintic resistance are briefly discussed.

Macrocyclic lactone-resistant Parascaris equorum on stud farms in Canada and effectiveness of fenbendazole and pyrantel pamoate.

The aims of studies in 2002 and 2003 on three farms with 76 foals naturally infected with Parascaris equorum were to (i) identify if the nematode was resistant to ivermectin and moxidectin, and (ii) confirm the effectiveness of fenbendazole and pyrantel pamoate for the parasite. Twelve clinical trials, each with a Fecal Egg Count Reduction Test, were conducted on two Thoroughbred and one Standardbred farms in southwestern Ontario, Canada. In each trial, Parascaris eggs/g feces were estimated for each foal pre- and post-treatment using the Cornell-Wisconsin double flotation and Cornell-McMaster dilution techniques. On each farm and for each trial, foals were randomized into treatment groups. Treatments were ivermectin, moxidectin, fenbendazole, pyrantel pamoate administered at the manufacturers' recommended dosages, and some foals were untreated. The overall efficacy for ivermectin was 33.5% (19 foals) and for moxidectin 47.2% (28 foals). Fenbendazole (16 foals) and pyrantel pamoate (21 foals) were highly effective for P. equorum each at 97.6%. For fenbendazole, 15 foals had 100% and for pyrantel pamoate 17 foals had >97% with 14 at 100%.

Clinical trials of efficacy of praziquantel horse paste 9% against tapeworms and its safety in horses.

The aim of this study with horses and a few ponies naturally infected with tapeworms was to confirm in clinical trials the efficacy and safety of a praziquantel horse paste 9%. The field trials were conducted in 1997 and 1998 in Canada, France, Germany and New Zealand. A secondary aim of the study in Canada was to determine if a 24h post-treatment fecal sample provides the best estimate of the prevalence of tapeworms in horses when using a fecal examination technique. Fecal samples were taken from each of 1062 animals at least three times pre-treatment (PRT). In Canada, fecal samples were examined using the Cornell-Wisconsin centrifugal flotation technique, and in France, Germany and New Zealand using a centrifugation/flotation technique. In each trial, the animals were randomized into two treatment groups: praziquantel horse paste 9% at 1mg/kg body weight (BW) and untreated. Fecal samples were taken from each animal nine times post-treatment and over a period of 5 weeks. In Canada, a fecal sample was taken also at 24h after treatment. Personnel examining the samples were "blinded" to treatment groups. On the day of treatment, each treated animal was examined for adverse reactions to the paste 10min after treatment and then hourly for 4h. Thereafter, each animal was examined once daily for 5 weeks. In Canada, Germany and New Zealand, the only tapeworm egg found was Anoplocephala perfoliata. In France, A. perfoliata was the most common species and a few animals had A. magna and Paranoplocephala mamillana. The prevalence of A. perfoliata among animals sampled in Canada, France, Germany and New Zealand was 51.8, 34.4, 13.1 and 26.2%, respectively. A total of 248 animals were treated with the praziquantel paste and all except one accepted it readily. There were 292 animals completing the study, 219 treated and 73 untreated. In Canada, Germany and New Zealand, the efficacy of the praziquantel horse paste 9% against A. perfoliata was 100%. In France, the efficacy against A. perfoliata, A. magna and P. mamillana was 90.9, 100 and 100%, respectively. The best estimate of prevalence for A. perfoliata in a herd was derived from fecal samples taken 24h after treatment. At 24h, 22 of 23 treated horses were positive, whereas on any day pre-treatment fewer horses were positive. Adverse reactions observed were mild to moderate colic and in only two treated horses.

Cyathostomes in horses in Canada resistant to pyrantel salts and effectively removed by moxidectin.

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 <80% reduction in egg/g feces. These mares were then given moxidectin and in all mares the eggs/g feces was reduced to zero. Only cyathostomes were found on culture and apparently there was side resistance among the pyrantel salts.

A modified critical test and its use in two dose titration trials to assess efficacy of praziquantel for Anoplocephala perfoliata in equids.

Aims of this study with 43 equids naturally infected with Anoplocephala perfoliata in two dose titration trials were to document (i) the usefulness of a critical test with a 48 h treatment to necropsy period, (ii) efficacy of an oral paste of 0.5-2.0 mg praziquantel/kg body weight, and (iii) when after treatment would fecal egg counts provide best estimates of the tapeworm's prevalence in a herd. All feces passed by an equid after treatment and collected in successive 12 h batches were examined for tapeworms. At necropsy, tapeworms were identified as attached to the mucosa or unattached. Tapeworms were examined with a stereoscope and identified as normal or abnormal. Fecal samples were taken for egg counts at treatment and at 6 h intervals thereafter. In 32 of 36 treated equids, efficacy was 100% and mean efficacies for 0.5, 1.0, 1.5 and 2.0 mg praziquantel/kg body weight were 85.5, 99.7, 100 and 100%, respectively. Two equids treated with 0.5 mg praziquantel/kg body weight had low efficacies (5.4 and 38.1%) and normal tapeworms were found attached in the ventral colon and in one equid also in the dorsal colon. In seven untreated equids, tapeworms were primarily in the cecum with 21.3% detached. "Major fragments" or worms without a scolex but otherwise nearly a complete worm were 20.5% of the number of intact worms; they were not included in the efficacy analysis but should be. If the two equids with low efficacy were eliminated and if the number of all tapeworms and major fragments are combined less than 0.5% were in feces within 12 h of treatment, about 20% were in the 12-24 h period, 42% in 24-36h, 24% in 36-48 h and 13.5% in the equids at necropsy. One horse passed all its tapeworms in 24 h. This 48 h test when compared with a 24 h one with no examination of feces was more efficient in use of trial animals and reduced underestimation and overestimation of efficacy. However, a protocol similar to the 48 h test but with a 24 or 36 h post-treatment period should be investigated. The mean egg count peaked 18-24 h after treatment and samples taken at that time would provide the best estimate of prevalence. The Cornell-Wisconsin centrifugal flotation technique had a specificity of 100% and at 18 and 24 h its sensitivity was 94%. A brief discussion on critical and controlled tests for assessing efficacy of an anthelmintic for A. perfoliata is presented.

A modified critical test for the efficacy of pyrantel pamoate for Anoplocephala perfoliata in equids.

Aims of this study with 13 equids naturally infected with Anoplocephala perfoliata were to document (i) a critical test with a period of 48 h from treatment to necropsy to assess the efficacy of an anthelmintic against the tapeworm, (ii) the efficacy of pyrantel pamoate oral paste at 13.2 mg pyrantel base/kg body weight, and (iii) the time after treatment when fecal egg counts would best estimate the tapeworm's prevalence in a herd. Feces passed in successive 12-h periods after treatment were examined for tapeworms. At necropsy, tapeworms in equids were identified as attached to the mucosa or unattached and, with a stereoscope, as normal or abnormal. At the time of treatment and at 6-h intervals thereafter, fecal samples were taken for egg counts. The efficacy of pyrantel pamoate was 96.6%; in 1 equid the efficacy was 75.3%, and in 8 it was 100%. "Major fragments" (worms without a scolex) accounted for 10% of the tapeworms recovered; they were not included in the efficacy analysis but should be. In 3 untreated equids necropsied, tapeworms were in the cecum, and 21.3% were detached. This protocol, when compared with a 24-h one without examination of feces, was more efficient in the treatment of trial animals and reduced underestimation and overestimation of an anthelmintic's efficacy. However, a protocol similar to this 48-h critical test but with a 24- or 36-h post-treatment period should be investigated. The mean egg count peaked 18 to 24 h after treatment and the samples taken at that time would provide the best estimate of prevelance of tapeworms in a herd. The Cornell-Wisconsin centrifugal flotation technique had a sensitivity and specificity of 100% at 18 h and 92% and 100%, respectively, at 24 h.