The truth is in the poo: Non-invasive method to detect endoparasitic infection

One of the greatest challenges for parasitologists is to determine whether an animal is infected by endoparasites, and how severe the infection is, without destructive sampling, i.e., killing and dissecting the host. Being able to detect naturally or experimentally infected individuals with minimal manipulation and high accuracy could improve experimental design and behavioural analyses, especially if infection impacts host behaviour. Here, we quantified extracellular DNA from two distantly related species of endoparasitic worm (both impact host behaviour and are found within the host body cavity) by collecting the frass of their insect host, a cave wētā (Orthoptera: Rhaphidophoridae) and an earwig (Dermaptera: Forficulidae), respectively. Collection was done at two time periods, to test if parasite growth correlated with relative DNA quantity in the frass. Using quantitative PCR with TaqMan assays to amplify short segments of parasite DNA, we were able to detect infection with 100% accuracy in cave wētā and 100% accuracy in earwigs that were subsequently identified as infected through post-study dissections. We also identified additional infections with DNA alone, since some worms were likely too small to detect during dissection. Finally, there was a positive, yet inconsistent trend in parasite DNA quantity detected in the frass of cave wētā between both sampling periods, but not for earwigs. This study demonstrates that a non-invasive method, imposing minimal stress upon the host, can be used to detect endoparasitic infection with greater accuracy than dissection alone, thus helping improve future studies on host-parasite interactions and insect behaviour.