encysts

Encystment is a biological process by which certain organisms convert into a cyst, a dormant, resistant form encased in a protective wall. This process is common among many protozoa and is an important part of their life cycles. The cyst form typically has reduced metabolic activity and heightened resistance to environmental stresses, enabling survival outside a host and transmission through the environment. Encystment is followed by excystment, in which the cyst wall breaks and the organism resumes active growth under favorable conditions.

Organisms: The best-known examples are protozoan pathogens such as Giardia lamblia, Entamoeba histolytica, and Cryptosporidium species. Cysts of these organisms can persist in water, soil, and food and are a major route of infection. Encystment also occurs in other protists that alternate between active trophozoite stages and cyst stages. In some multicellular parasites, cyst-like stages occur during development or transmission, though these are not identical to protozoan cysts.

Formation and structure: Encystment involves major changes in gene expression and metabolism, a withdrawal from active feeding, and the production of a multi-layered cyst wall. The wall is typically rich in proteins and polysaccharides and may contain chitin or cellulose, providing resistance to desiccation, chemical disinfection, and temperature extremes. The cysts are often released from the host into the environment, where they can survive for extended periods.

Ecological and health relevance: Cysts enable dispersal and survival under adverse conditions and contribute to disease transmission when cyst-containing material is ingested. Control measures focus on water safety, sanitation, and proper cooking or treatment of food to prevent cyst ingestion.