The Hidden Link Between Intestinal Helminthiasis, Gut Microbiome Alterations, and Colorectal Cancer Risk: A Systematic Review

Colorectal cancer (CRC) is an increasing health concern in low- and middle-income countries (LMICs), especially in Africa, driven by dietary shifts, urbanisation, infections, and limited treatment access. The gut microbiome plays a central role in CRC, while soil-transmitted helminths (STHs) exert complex effects that can promote or mitigate risk depending on species, infection intensity, and host context. This systematic review synthesised 17 human studies (2000–2026) examining helminth impacts on gut microbial diversity, revealing a dualistic pattern. Several studies reported that chronic or moderate helminth infections, such as Ascaris lumbricoides and Trichuris trichiura, were associated with increased bacterial richness and the expansion of beneficial taxa, including Paraprevotellaceae, Parabacteroides, Agathobacter, Ruminococcaceae, and Lactobacillus. These taxa are associated with the production of short-chain fatty acids (SCFAs), protection of the epithelial barrier, and regulation of the immune system, suggesting a potential buffering effect against inflammation-driven carcinogenesis. On the contrary, other studies demonstrated helminth-associated dysbiosis characterised by reduced diversity and enrichment of pro-inflammatory and oncogenic taxa. T. trichiura and Strongyloides stercoralis infections were associated with the expansion of Treponema succinifaciens, Streptococcus gallolyticus, Enterobacteriaceae, and Ruminococcus torques, which are linked to reduced gut microbiome diversity, pro-inflammatory states, and oncogenic processes. Furthermore, A. lumbricoides infections altered the host microbiome at the phylum level, with increased Proteobacteria and reduced Firmicutes and Bacteroidetes, alongside metabolome shifts in amino acid and lipid pathways that have been associated with tumourigenic processes. Collectively, the evidence shows that helminthiasis may either enrich potentially protective microbes or be associated with pro-tumourigenic dysbiosis, with outcomes shaped by species, infection intensity, and host context. Notably, none of the included studies directly assessed CRC, underscoring the fact that current evidence is indirect and mechanistic. Overall, helminths are associated with gut microbiome shifts in both potentially protective and potentially harmful directions. This systematic synthesis of human evidence provides an integrated understanding of how helminth-associated microbiome shifts may influence colorectal carcinogenesis and highlights the need for longitudinal mechanistic studies to clarify causality and inform biomarker discovery and prevention in endemic regions.