Cross-class selection for anthelmintic resistance in the hookworm Ancylostoma caninum

About This Grant

Summary Soil transmitted helminths (STH) are parasitic nematodes that infect over 1 billion people in developing countries. Of the 3 major STH, hookworms are the most virulent, causing anemia and stunting physical and cognitive development in heavily infected people. Currently, morbidity from hookworms and other STH is controlled by mass drug administration (MDA) using the anthelmintic drug albendazole (ABZ), a member of the benzimidazole (BZ) family of drugs. While relatively effective, rapid reinfection following treatment requires annual or biannual treatment in endemic areas. The rapidity with which anthelmintic resistance (AR) developed in parasitic nematodes of livestock suggests that increasing the selective pressure on human helminths by MDA will rapidly generate resistant worm populations as well. Detection of emerging AR will be critical to avoid losing the most effective anthelmintics for treatment of hookworm. Naturally resistant hookworm isolates are required to determine the genetic mechanism of resistance and for the development of molecular tools for detection of AR in natural populations. We identified a naturally occurring isolate (BCR) of the canine hookworm Ancylostoma caninum that is resistant to drugs from the 3 major anthelmintic classes: the BZs, the macrocyclic lactones (ML), and the tetrahydropyrimidines (THP). While testing a commercial dewormer for efficacy against the BCR strain, we found that treatment with a combination of the ML moxidectin (MOX) and the THP pyrantel pamoate (PYR) increased the frequency of the allele that confers BZ resistance to BCR without exposure to any BZ drug. This cross-drug class selection suggests linkage between one or both of the drug target mutations and the genetic mutation that confers BZ resistance, and therefore may provide insight into the underlying molecular mechanisms of IVM and PYR resistance, neither of which is currently known. Furthermore, confirmed linkage of resistance genes of one or both drugs to the known BZ resistance gene would provide a genetic marker to rapidly identify likely multi-anthelmintic drug resistant (MADR) populations of hookworm before they reach phenotypic resistance and treatment failure. Finally, knowledge of cross-class selection would permit rational deworming strategies that avoid generating multi-drug-resistant hookworm populations. In this project, we will confirm cross-selection and determine which drug is responsible, determine the resistance status of selected hookworms, and generate materials for future genomic studies to determine the underlying mechanism of cross-drug class selection.