PMID: 9184933Apr 1, 1997Paper

The death rate of Ostertagia circumcincta and Trichostrongylus colubriformis in lactating ewes: implications for anthelmintic resistance

International Journal for Parasitology
D M LeathwickI A Sutherland

Abstract

Lactating adult Romney ewes were infected, 4 weeks post-lambing, with benzimidazole (bz) resistant strains of Ostertagia circumcincta and Trichostrongylus colubriformis. Commencing 4 weeks after the initial infection the ewes were subjected to challenge 3 times weekly with 5000 L3 of bz-susceptible strains of both parasite species. At weekly intervals over the following 6 weeks, groups of ewes were drenched with a bz anthelmintic (oxfendazole) to remove bz-susceptible parasites and slaughtered to determine adult worm burdens of the bz-resistant parasites. The O. circumcincta infection declined exponentially with a mean daily death rate of 10.6% day-1 and no worms were recovered after 4 weeks or more of challenge. The T. colubriformis infection did not decline significantly over the 6 weeks of continuous challenge, indicating that the death rate could not be distinguished from zero. The upper 95% confidence limit for the death rate of T. colubriformis was 4.9%. The implications of these death rates on selection for drug resistance following ewe drenching during the post-partum period are discussed with selection pressure likely to be greater for T. colubriformis than for O. circumcincta.

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Citations

Apr 30, 1999·International Journal for Parasitology·D M LeathwickI A Sutherland
Jul 21, 2005·New Zealand Veterinary Journal·M HerveA R Sykes
Jul 21, 2005·New Zealand Veterinary Journal·D M Leathwick, A Vlassoff
Jan 18, 2014·Veterinary Parasitology·M K NielsenR M Kaplan
Aug 26, 2006·Veterinary Parasitology·J LearmountC Morgan
Sep 7, 2019·International Journal for Parasitology. Drugs and Drug Resistance·Dave M LeathwickMartin K Nielsen

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Anthelmintics (ASM)

Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. Discover the latest research on anthelmintics here.

Anthelmintics

Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. Discover the latest research on anthelmintics here.