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The novel ectoparasiticide spinosad is a naturally occurring mixture of spinosyns A and D formed during a fermentation process. The spinosyns are tetracyclic macrolides with a unique ring system. Their mode of action differs from that of other commercially available insecticides. Laboratory and field trials were conducted to evaluate the use of spinosad in a chewable tablet at a dose range of 45 to 70 mg/kg for the treatment and control of flea infestations on dogs in Europe. Laboratory studies with artificially infested dogs confirmed persistent activity against Ctenocephalides felis of higher than 99 per cent at three weeks post-treatment with values of 96.5 to 97.8 per cent at four weeks. Two multicentric field trials with naturally infected client-owned animals in five European countries used selamectin as comparator. Monthly doses were given during the summer when many homes were heavily infested. Households with spinosad-treated dogs showed cumulative benefits with flea burdens reduced by about 97 per cent at 14 and 30 days and by 99.6 per cent at 60 and 90 days. Corresponding figures for selamectin were significantly lower (P<0.05) at all time points: between 88.5 and 91 per cent at 14 and 30 days, then 97.8 and 98.2 per cent at 60 and 90 days. Thus, the performance of spinosad compared favourably with that of the established reference product.

These guidelines are intended to assist the planning and conduct of laboratory and clinical studies to assess the efficacy of ectoparasiticides applied to dogs or cats for the purpose of treating, preventing and controlling flea and tick infestations. The term ectoparasiticide includes insecticidal and acaricidal compounds, as well as insect growth regulators. The range of biological activities accruing from animal treatment that are considered include: repellency and anti-feeding effects, knockdown, speed of kill, immediate and persistent lethal effects, and interference with egg fertility and subsequent development of off-host life cycle stages. Information is provided on the selection of animals, dose determination, dose confirmation and field studies, record keeping, interpretation of results and animal welfare. These guidelines are also intended to assist registration authorities involved in the approval and registration of new parasiticides, and to facilitate the worldwide adoption of harmonized procedures.

The control of Toxocara canis was investigated in naturally infected unweaned puppies. Anthelmintic treatments were administered to three litters of pups at 2, 4 and 6 weeks of age. When either a new combination anthelmintic containing febantel, pyrantel embonate and praziquantel or fenbendazole was used, the faecal egg output over the first 7 weeks of life was reduced by more than 80% and worm burdens by over 90%. In contrast, piperazine adipate had no appreciable effect on T. canis egg output, even though worm burdens were reduced by 86% by 7 weeks of age. In a further trial using three litters, the worm burden of pups treated with the combination anthelmintic was profiled before and after the 2 week dose and after the 4 week dose. Although worm numbers were substantially reduced by treatment, there was evidence of significant reinfection taking place throughout the control programme. It is concluded that more potent anthelmintics can provide longer term benefits by reducing the numbers of T. canis eggs shed into the environment, but that multiple dosing remains essential for this purpose.

Guidelines have been designed to assist in the planning, operation and interpretation of studies for the assessment of the efficacy of drugs against helminth parasites of dogs and cats. The advantages, disadvantages and application of critical and controlled tests are presented. Information is also provided on the selection of animals, housing, feeding, dose-titration, confirmatory and clinical trials, record keeping and necropsy procedures. These guidelines should assist both investigators and registration authorities involved in the evaluation of anthelmintics to employ comparable and standard procedures and will have the added benefit of minimising the numbers of animals needed for such tests.

In a series of controlled trials involving 59 naturally infected greyhounds, fenbendazole at a dose rate of 50 mg/kg/day for three consecutive days reduced the overall numbers of third and fourth stage Toxocara canis by 94.0 per cent and third stage, fourth stage and immature adult stages of Toxascaris leonina by 92.4 per cent. In contrast, piperazine at 100 mg/kg had little or no useful effect against the larval stages of T canis and T leonina and variable efficacy against immature adult T leonina. Fenbendazole was also 100 per cent effective against immature Trichuris vulpis. In a separate controlled experiment, puppies in three litters exposed to reinfection with T canis were treated with fenbendazole at two weeks old and again only after their mean faecal egg counts exceeded 200 epg. Between one and three doses were required to suppress the output of eggs during the puppies' first 12 weeks of life.

Field observations at breeding kennels in eastern England support the view that perinatal transmission is of minor importance in the epidemiology of Uncinaria stenocephala infections in greyhounds. Patent infections became established soon after weaned pups were put onto gas paddocks. Egg-counts rose to high levels, tending to peak in dogs 25-35 weeks old and to decline thereafter. This pattern was related to the age of the host and was not seasonal. The consequent deposition of large numbers of eggs onto the paddocks at irregular intervals distorted the seasonal fluctuations in herbage larval counts previously found to be a consistent feature of grass paddocks used for exercising adult racing greyhounds.

Conventional chemoprophylaxis of canine toxocariasis is based upon the treatment of young puppies. It is proposed that physiological considerations and the complexity of the host-parasite relationship in the case of Toxocara canis demand that anthelmintic evaluation should properly be conducted in such animals rather than in adolescent or adult dogs. A screening model using the critical trial technique in early weaned pups gave variable results even with compounds known to be of high efficacy in older dogs. Circumstantial evidence suggested that this inconsistency may be related to the rate of passage of ingesta through such young animals. More satisfactory results were obtained by pairing unweaned naturally infected puppies by weight and sex and treating one of each pair with the test compound. Natural in utero and transmammary infection was found to give fairly consistent worm-burdens within each litter and a good indication of efficacy could therefore be estimated by comparing post mortem worm-counts. On this basis, the apparent efficacies of pyrantel pamoate (5 mg kg-1) and piperazine (100 mg kg-1) were found to be 83.5 and 82.5%, respectively. This method was extended to evaluate a prophylactic programme in which anthelmintic therapy was given to pups when aged 10, 20 and 30 days. Intestinal T. canis populations were reduced, at 35 days of age, by between 94.2% and 98.0%. This programme increased overall weight gains between 10 and 30 days of age by 18% (P less than 0.05) although there was great variation between litters. The biggest response was observed in male pups between 20 and 30 days old.

The numbers of Uncinaria stenocephala larvae on the grass in a small paddock used continually for exercising greyhounds followed the seasonal pattern associated with gastro-intestinal nematodes of ruminants, pigs and horses in Britain. Contamination persisted throughout the winter months but near-zero values were recorded in the early summer, followed by a rapid rise in mid-July to a peak level in September.