Helminths and Bacterial Microbiota: The Interactions of Two of Humans' "Old Friends".

Humans have coexisted with helminths and bacteria for the entire existence of our species. Nowadays, helminth infections affect more than 1.9 billion people worldwide, especially in underdeveloped regions that lack optimal sanitary conditions. In addition, commensal microorganisms inhabit several compartments of humans, including the gastrointestinal tract, constituting what we know as the microbiota. Helminths and bacterial microbiota can interact in various ways. In this review, the interactions between helminths and commensal bacteria are analyzed in both animal models and humans. In developing countries, the gut microbiota exhibits high diversity, which could be linked to the high burden of helminthiasis in these areas. In fact, several studies show that helminth infections are associated with an increased gut microbiota diversity and changes in its composition. Interestingly, these changes can modify the risk for some diseases, such as asthma, colitis, viral infections, and metabolic conditions. Besides, the microbiota is necessary for the establishment of some helminth infections and can also influence the evolution of these diseases. Specific bacterial taxa can contribute to the resistance or susceptibility to certain helminths. The mechanisms underlying helminth-microbiota interactions are not completely understood. More research is necessary to address this and other unmet needs, especially considering that available studies are heterogeneous and sometimes yield conflicting results.