Cichlid fishes are promising underutilised models to investigate helminth-microbiome interactions

Abstract

The "Old Friends Hypothesis" suggests that insufficient early exposure to symbionts may hinder immune development, contributing to increased immune-related diseases in the Global North. While the microbiome is often the focus, helminths, which may also offer health benefits, receive little attention. The infection and effect of helminths, in turn, are influenced and may be even determined by microorganisms. The mechanisms behind general parasite-microbiome interactions are poorly understood, despite their profound implications on the health of their hosts. Because these interactions are typically studied for single helminth species in laboratory animal models, the important aspect of helminth diversity remains overlooked in this context. A literature search for research on the relationship between host helminth diversity and microbial diversity, resulted in 27 publications; most focused on human or other mammalian hosts, and relied on natural exposure rather than experimental inoculation with helminths. Almost half of these studies did not empirically investigate health outcomes for the host. This understudied potential warrants consideration for additional candidate model systems. In view of the high burden of helminthiasis, and the high species diversity of helminths, we propose to seek these models in the Global South, where a considerable proportion of research on community diversity aspects of helminth-microbiome interactions took place. The low availability of genomic resources for parasitic worms in many regions of the Global South, however, calls for more integrative helminthological research efforts. Given the substantial similarities in immune systems, several fishes are models for human health and disease. More effort could be done to also establish this for cichlids, the representatives of which in the African Great Lakes would provide a well-delineated, closed natural system with relevance to human health in view of fish-borne zoonoses and other water-borne parasites. Moreover, a good baseline exists in terms of these cichlids' genomics, parasitology, and microbiology. We therefore call for the exploration of African Great Lake cichlids as model hosts to understand the interactions between microbial diversity, helminth diversity, and host health.