Host-parasite-microbiome interactions in gastrointestinal trematodes and cestodes of small ruminants: current advances and future perspectives.

Gastrointestinal helminth infections remain a major problem for sheep and goat farming worldwide. In the past, research mainly focused on the shape, classification, spread, health effects, and genetic makeup of the parasites. With the advent of new next-generation sequencing technologies, we now better understand the gut ecosystem and the important roles of host-parasite-microbiome interactions in animal health. The digestive tract of sheep and goats contains microbes that aid digestion, nutrient utilization, immune function, and the maintenance of homeostasis. New research shows that helminths can change these microbial communities by affecting the immune system, damaging tissues, and competing for nutrients. At the same time, the existing microbes can affect how parasites settle, survive, and cause disease. Unlike studies on other parasites, research on the microbiomes of rumen flukes (Paramphistomum, Cotylophoron, and Calicophoron) and cestodes (Moniezia, Avitellina, and Stilesia) remains very limited, despite these parasites inhabiting environments rich in microbes, such as the rumen and small intestine. This review brings together what is currently known about the diversity, distribution, preferred habitats, and interactions among hosts, parasites, and microbiomes of gastrointestinal trematodes and cestodes in small ruminants. It focuses on metagenomic methods, the microbiota linked to these parasites, and new possibilities for microbiome research. The review also highlights important gaps in our knowledge and emphasizes the need for combined morphological, molecular, and next-generation sequencing studies, especially in areas such as Kashmir, where these parasites are common. Learning more about the microbes associated with these helminths could offer new insights into parasite biology and help develop better ways to diagnose, monitor, and control infections, supporting more sustainable small-ruminant farming.