Review Article

Anthelmintic resistance: markers for resistance, or susceptibility?

R. N. BEECHa1 c1, P. SKUCEa2, D. J. BARTLEYa2, R. J. MARTINa3, R. K. PRICHARDa1 and J. S. GILLEARDa4

a1 Institute of Parasitology, Macdonald College, McGill University, Ste Anne de Bellevue, QC, H9X 3V9 Canada

a2 Parasitology Division, Moredun Research Institute, Penicuik, Midlothian, EH26 0PZ, UK

a3 Department of Biomedical Sciences, Iowa State University, Ames, IA 50011, USA

a4 Department Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, T2N 4N1, Canada


The Consortium for Anthelmintic Resistance and Susceptibility (CARS) brings together researchers worldwide, with a focus of advancing knowledge of resistance and providing information on detection methods and treatment strategies. Advances in this field suggest mechanisms and features of resistance that are shared among different classes of anthelmintic. Benzimidazole resistance is characterized by specific amino acid substitutions in beta-tubulin. If present, these substitutions increase in frequency upon drug treatment and lead to treatment failure. In the laboratory, sequence substitutions in ion-channels can contribute to macrocyclic lactone resistance, but there is little evidence that they are significant in the field. Changes in gene expression are associated with resistance to several different classes of anthelmintic. Increased P-glycoprotein expression may prevent drug access to its site of action. Decreased expression of ion-channel subunits and the loss of specific receptors may remove the drug target. Tools for the identification and genetic analysis of parasitic nematodes and a new online database will help to coordinate research efforts in this area. Resistance may result from a loss of sensitivity as well as the appearance of resistance. A focus on the presence of anthelmintic susceptibility may be as important as the detection of resistance.

(Received July 07 2010)

(Revised July 13 2010)

(Accepted July 13 2010)

(Online publication September 09 2010)


c1 Corresponding author: Institute of Parasitology, Macdonald College, McGill University, Ste Anne de Bellevue, QC, H9X 3V9 Canada. Tel: + 514 398 7535. Fax: + 514 398 7857. E-mail: