Anthelmintics for the control of nematode infections in the brushtail possum (Trichosurus vulpecula)

AIMS: To determine the efficacy of eprinomectin, doramectin and a combinati on of albendazole and levamisole in suppressing or eliminating nematode inf ections or faecal egg counts (FEC) in possums naturally or experimentally i nfected with Parastrongyloides trichosuri, Paraustrostrongylus trichosuri a nd Trichostrongylus colubriformis. METHODS: To establish an effective dose of eprinomectin, groups of naturall y infected possums were treated with 0, 0.5, 2.5, 5.0 or 7.5 mg/kg liveweig ht (LW) eprinomectin pour-on (n=6 possums/group) and changes in FEC and nem atode worm counts at necropsy determined, 18 days later. Efficacy of the 7. 5 mg/kg dose was re-examined in a second group of naturally infected possum s (n=12) by monitoring FEC weekly for 28 days post-treatment. Persistence o f the anthelmintic effect of doramectin injection was tested using nematode -free possums treated with 0, 0.2, 0.4, 0.6 or 0.8 mg/kg LW (n=3 possums/ g roup), which were experimentally infected 14 days later with T. colubriform is Paraustrostrongylus trichosuri and Parastrongyloides trichosuri infectiv e larvae. Response to treatment was assessed by FEC and nematode worm count s at necropsy, 42 days posttreatment. Efficacy of a 1.0 mg/kg dose of doram ectin was subsequently examined using naturally infected possums (n=11) by monitoring FEC weekly for 28 days post-treatment. To determine the efficacy of a levamisole-albendazole combination drench, possums with naturally acq uired nematode infections (n=6) were treated orally with 37.5 mg/kg LW leva misole plus 23.75 mg/kg LW abendazole on 2 occasions, 7 days apart, and res ponse to treatment was assessed by monitoring FEC for 57 days. RESULTS: Eprinomectin 7.5 mg/kg LW reduced Paraustrostrongylus trichosuri w orm counts by 98% (p<0.05). Dorameain 0.6 mg/kg LW reduced Parastrongyloide s trichosuri and Trichostrongylus spp worm counts by 99% (p<0.05) and 0.8 m g/kg LW reduced Paraustrostrongylus trichosuri by 100% (p<0.05), in possums challenged with larvae 14 days after treatment. Treating possums with a le vamisole-abendazole combination orally, twice, 7-days apart, reduced FEC by >99%. CONCLUSIONS: The doses of anthelmintics required to effectively control nem atodes in possums were higher than those recommended for animals for which they are currently registered. Possums tolerate the high dose rates of anth elmintics used in this study without apparent adverse effects.