J Parasitol. 2013 Feb;99(1):168-9.

Efficacy of ivermectin versus dual infections of Haemonchus contortus and Heligmosomoides polygyrus in the mouse.

Ostlind DA, Mickle WG, Smith S, Ewanciw DV, Cifelli S.

Merck Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065, USA.



This report describes a novel assay for the detection of gastrointestinal anthelmintics using mice infected with Haemonchus contortus and adapted to the 1 animal per group protocol.   Mice infected with both H. contortus and Heligmosomoides polygyrus were fed ivermectin-medicated diets for 6 days.  A dietary level of 0.09375 ppm was 98.1% effective against the 0 to 6-day-old abomasal stomach worm of sheep, whereas a level of  0.75 ppm reduced the 3 to 9-day-old Hpolygyrus worm burden by 94.0%.  H. contortus was approximately 8-fold more sensitive to ivermectin than H. polygyrus in this model.  The sensitivity of this assay rivals that of the gerbil-Trichostrongylus colubriformis model.

PMID: 23145469



The first operational in vivo assay to use the 1-animal/ group screening concept was introduced at the Merck Institute for Therapeutic Research in 1968.  The concept was used for more than 25 yrs at the Merck Research Laboratories.    The 1-animal/group screening protocol was used to discover the fasciolicide, clorsulon in 1969 (Ostlind et al., 1977), the avermectins in 1975 (Stapley and Woodruff, 1982), paraherquamide (Ostlind et al., 1990), the systemic ectoparasiticide nodulisporic acid in 1992 (Ostlind et al., 2001) as well as the development of the anthelmintic eprinomectin (Shoop et al., 1996), thus validating the concept.  All of the major anthelmintics commercially available up to 1996 (DA Ostlind retired) that were tested demonstrated their expected activity against  Haemonchus contortus, thus validating the concept.    It also fascilitated the in vivo testing of natural products (Campbell, 1992).

The results described herein led to the development of an assay (unpublished data) whereby the  anthelmintic and systemic ectoparasiticide activity could be simultaneously ascertained in a single rodent and was in operation for more than 10 yrs.



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