Encyst

Encyst is a biological process in which a cell or organism forms a cyst, a dormant, protective envelope. Encystment is the act of entering this state or producing the cyst. The term is used for many groups, especially protozoa and some metazoans, and it serves to endure harsh conditions or to enable dispersal and transmission.

In protozoa, encystment is often triggered by environmental stress such as desiccation, nutrient limitation, or temperature change. The organism reduces metabolic activity and builds a cyst wall, yielding a thick, resistant structure. The wall comprises proteins and carbohydrates and can protect the cell from osmotic stress and chemical agents. Excystment, the exit from the cyst, occurs when favorable conditions are met, such as entry into a suitable host.

Two well-known human parasites that form cysts are Giardia lamblia and Entamoeba histolytica. Cysts are excreted with feces and can infect new hosts when ingested; in the intestine, cysts excyst to release trophozoites. Encystment also occurs in ciliates and some algae as a stress response, producing resting cysts that survive until conditions improve.

Cysts can be highly resistant to environmental stresses and some disinfection methods, making them important in water safety and disease transmission. Detection methods include microscopy, antigen tests, and molecular assays. Control focuses on preventing cyst formation and removing cysts from environments.