Variation in anthelmintic responses are driven by genetic differences among diverseC. eleganswild strains
Authors: Shaver Amanda O. , Wit Janneke , Dilks Clayton M. , Crombie Timothy A. , Li Hanchen , Aroian Raffi V. , Andersen Erik C. 
Published: November 2022

Treatment of parasitic nematode infections in humans and livestock relies on a small arsenal of anthelmintic drugs that have historically reduced parasite burdens. However, anthelmintic resistance (AR) is increasing, and little is known about the molecular and genetic causes of resistance for most drugs. The free-living roundwormCaenorhabditis eleganshas proven to be a tractable model to understand AR, where studies have led to the identification of molecular targets of all major anthelmintic drug classes. Here, we used genetically diverseC. elegansstrains to perform dose-response analyses across 26 anthelmintic drugs that represent the three major anthelmintic drug classes (benzimidazoles, macrocyclic lactones, and nicotinic acetylcholine receptor agonists) in addition to seven other anthelmintic classes. First, we found thatC. elegansstrains displayed significant variation in anthelmintic responses across drug classes. Dose-response trends within a drug class showed that theC. elegansstrains elicited similar responses within the benzimidazoles but variable responses in the macrocyclic lactones and nicotinic acetylcholine receptor agonists. Next, we compared the effective concentration estimates to induce a 10% maximal response (EC10) and slope estimates of each dose-response curve of each strain to the reference strain, N2, which enabled the identification of anthelmintics with population-wide differences to understand how genetics contribute to AR. Because genetically diverse strains displayed differential susceptibilities within and across anthelmintics, we show thatC. elegansis a useful model for screening potential nematicides. Third, we quantified the heritability of responses to each anthelmintic and observed a significant correlation between exposure closest to the EC10and the exposure that exhibited the most heritable responses. Heritable genetic variation can be explained by strain-specific anthelmintic responses within and across drug classes. These results suggest drugs to prioritize in genome-wide association studies, which will enable the identification of AR genes.

AUTHOR SUMMARY

Parasitic nematodes infect most animal species and significantly impact human and animal health. Control of parasitic nematodes in host species relies on a limited collection of anthelmintic drugs. However, anthelmintic resistance is widespread, which threatens our ability to control parasitic nematode populations. Here, we used the non-parasitic roundwormCaenorhabditis elegansas a model to study anthelmintic resistance across 26 anthelmintics that span ten drug classes. We leveraged the genetic diversity ofC. elegansto quantify anthelmintic responses across a range of doses, estimate dose-response curves, fit strain-specific model parameters, and calculate the contributions of genetics to these parameters. We found that genetic variation within a species plays a considerable role in anthelmintic responses within and across drug classes. Our results emphasize how the incorporation of genetically diverseC. elegansstrains is necessary to understand anthelmintic response variation found in natural populations. These results highlight drugs to prioritize in future mapping studies to identify genes involved in anthelmintic resistance.

GRAPHICAL ABSTRACT