Thesis (M.Sc.1981) from the Department of Zoology, University of Adelaide.

The parasitic nematodes Ancylostoma caninum and Oesophagostomum radiatum were collected and analyzed for intestinal inorganic granules. Three means of identification were utilized to determine the composition granules, including birefringence, x-ray diffraction and energy dispersive spectrometric (EDS) analysis. Initial x-ray diffraction results of the two worms showed a calcium sulfide presence within the worms. Closer examination of the granules within Ancylostoma caninum however, utilizing EDS analysis revealed their composition to be zinc sulfide. These results concur with those of Rogers (1940) and Clark (1956) who found zinc sulfide granules in several species of Strongylus. The ZnS granules seem to be a result of a detoxification function that binds excess zinc and sulfhydryl groups present from the ingestion and breakdown of dietary blood meals.

Actuellement, les infections des humains, des plantes et des animaux par les nématodes parasites ont un impact économique majeur. En l’absence de vaccin efficace, les anthelminthiques sont les principaux agents chimiothérapeutiques utilisés pour le traitement et la prophylaxie des infections à nématodes. Cependant, la résistance est apparue pour la plupart des anthelminthiques. Par conséquent il est urgent de comprendre la génétique des récepteurs ciblés par ces anthelminthiques et de trouver des cibles alternatives afin de développer de nouveaux anthelminthiques. Nous avons démontré les effets du nouvel anthelminthique cyclooctadepsipeptide, emodepside, sur le potentiel de membrane et les courants voltagedépendants chez le parasite du porc Ascaris suum. Enfin, nous avons cloné quatre gènes codant des sous-unités du récepteur de l'acétylcholine d'un autre parasite du porc, Oesophagostomum dentatum et caractérisé dans des ovocytes de Xenopus laevis quatre sous-types de récepteurs au lévamisole. / Parasitic nematode infections of humans, plants and animals are of major economic impact. Anthelmintics are the main chemotherapeutic agents used for treatment and prophylaxis of nematode infections because there is presently no effective vaccine on the market. However, resistance has been reported to the mainstay anthelmintics. There is therefore the urgent need to understand the genetics of the receptors targeted by these anthelmintics and to find alternative targets for developing new anthelmintics. We have demonstrated the effects of the new novelacting cyclooctadepsipeptide anthelmintic, emodepside, on the membrane potential and voltageactivated currents in the pig parasite Ascaris suum. Finally, we show the cloning of four acetylcholine receptor subunit genes from another pig parasite, Oesophagostomum dentatum and the expression and characterization of four levamisole receptor subtypes in Xenopus laevis oocytes.

Two studies were conducted to investigate anthelmintic resistance in goat parasites in New Zealand. In Study 1 parasites from goats on a farm with a long history of problems with anthelmintic efficacy were used to infect sheep for a controlled slaughter study. Nineteen lambs were acquired, effectively drenched and housed. Each was infected with a mixture of larvae comprising Haemonchus contortus, Teladorsagia circumcincta, Trichostrongylus colubriformis and Oesophagostomum venulosum. After 28 days lambs were restrictively randomised into 3 groups based on faecal egg counts. Group 1 was left untreated (n=6), Group 2 (n=6) was given a single dose of abamectin (0.2mg/kg) + levamisole HCL (8mg/kg) + oxfendazole (4.5mg/kg) (“Matrix Oral Drench for Sheep”®, Ancare, New Zealand) and Group 3 (n=7) was treated at twice the dose rate of Group 2. Fourteen days after treatment all animals were killed for total worm counts. The mean burdens of T. circumcincta in Group 1 was 337, in Group 2 was 68 (efficacy 80%) and in Group 3 was 10 (efficacy 97%). The mean burdens of T. colubriformis in Group 1 was 375, in Group 2 was 220 (efficacy 41%) and in Group 3 was 81 (efficacy 78%). Although the worm burdens in these lambs were low, all animals were infected with each of these two species except for T. circumcincta in Group 3 where only 3 lambs were infected. Efficacy against other species was 100%. These results clearly indicate that a single dose of a combination drench was ineffective against two species and even when a double dose was used the efficacy against T. colubriformis was only 78%. In Study 2 a survey of drench efficacy was conducted on 17 goat farms using the DrenchRite® larval development assay. Evidence of concurrent resistance to benzimidazoles, levamisole and ivermectin was detected in T. colubriformis and T. circumcincta on 11/17 and 3/14 respectively. Only 5 of 14 farms had previously undertaken some form of testing for drench resistance prior to this survey. Evidence from these two studies suggests that severe anthelmintic resistance is common on goat farms in New Zealand