True cyst formation in Tritrichomonas foetus: a survival and drug-resistance strategy redefining protozoan biology

Abstract Tritrichomonas foetus, a protozoan parasite responsible for bovine and feline trichomonosis, has traditionally been considered to form only pseudocysts. Here, we reveal that T. foetus produces true cysts characterized by chitin like components-rich, fibrillar walls, cytoskeletal reorganization, and resistance to detergent treatment. Cystogenesis is induced by environmental stresses such as nutrient deprivation, alkaline pH mimicking the bovine preputial milieu, and exposure to metronidazole, a frontline antiparasitic drug. This encystation enhances parasite survival and suggests a novel drug-resistance mechanism. Transcriptomic profiling identifies key pathways involved in cyst wall biosynthesis and regulation, including Myb-like transcription factors and calcium/calmodulin-dependent kinases. Encysted parasites also undergo DNA replication without cytokinesis, suggesting a strategy for rapid multiplication through multiple fission upon excystation. Our findings fundamentally reshape the understanding of T. foetus biology, highlight a critical stage in its transmission cycle, and have significant implications for therapeutic and diagnostic strategies in veterinary parasitology.