To determine the efficacy of
eprinomectin,
doramectin and a combination of
albendazole and
levamisole in suppressing or eliminating
nematode infections or faecal egg counts (FEC) in possums naturally or experimentally infected with Parastrongyloides trichosuri, Paraustrostrongylus trichosuri and Trichostrongylus colubriformis.
METHODS: To establish an effective dose of
eprinomectin, groups of naturally infected possums were treated with 0, 0.5, 2.5, 5.0 or 7.5 mg/kg liveweight (LW)
eprinomectin pour-on (n=6 possums/group) and changes in FEC and nematode 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 possums (n=12) by monitoring FEC weekly for 28 days post-treatment. Persistence of 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/ group), which were experimentally infected 14 days later with T. colubriformis, Paraustrostrongylus trichosuri and Parastrongyloides trichosuri infective larvae. Response to treatment was assessed by FEC and nematode worm counts at necropsy, 42 days posttreatment. Efficacy of a 1.0 mg/kg dose of
doramectin 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 acquired
nematode infections (n=6) were treated orally with 37.5 mg/kg LW
levamisole plus 23.75 mg/kg LW
albendazole on 2 occasions, 7 days apart, and response to treatment was assessed by monitoring FEC for 57 days.
RESULTS:
Eprinomectin 7.5 mg/kg LW reduced Paraustrostrongylus trichosuri worm counts by 98 % (p<0.05).
Doramectin 0.6 mg/kg LW reduced Parastrongyloides trichosuri and Trichostrongylus spp worm counts by 99% (p<0.05) and 0.8 mg/kg LW reduced Paraustrostrongylus trichosuri by 100% (p<0.05), in possums challenged with larvae 14 days
after treatment. Treating possums with a
levamisole-
albendazole combination orally, twice, 7-days apart, reduced FEC by 99%.
CONCLUSIONS: The doses of
anthelmintics required to effectively control nematodes in possums were higher than those recommended for animals for which they are currently registered. Possums tolerate the high dose rates of
anthelmintics used in this study without apparent adverse effects.