Physical evidence of direct antagonistic interactions between trematodes in the host gut: the kiss of death?

Abstract

Although within-host competition among parasites if often assumed to occur based on statistical patterns, actual physical evidence of direct antagonistic interactions between parasites, either intraspecific or interspecific, is very rare. Here, we report such evidence between and within two species of hemiurid trematodes infecting the deep-sea grenadier fish Coryphaenoides subserrulatus. We found pairs of worms attached together, with one worm using its ventral sucker against another worm, and sucking out a large protuberance on the victim. We also found single worms showing clear signs of past attacks. There was no evidence that these interactions were more common at high intensities of infection, where the conditions would be expected to be more conducive to competitive interactions. Our findings provide evidence that trematodes may cause some harm to co-occurring individuals, suggesting a direct form of interference competition among intestinal helminths.

Paracapillaria (Ophidiocapillaria) siamensis sp. nov. (Nematoda: Trichuroidea): a new nematode in Naja kaouthia from Thailand

“…P. siamensis sp. nov. and P. najae exhibit parasitism in different organs of the same host, potentially mitigating competition between the 2 species (Stancampiano et al ., 2010 ; Venter et al ., 2022 ; Presswell et al ., 2023 ). This phenomenon departs from the norm observed in other parasitic helminth groups, where co-infections occur regularly.…”