Relationship between sleep and parasitic infections. The sleep disorders that are caused by parasites include changes in sleep patterns, such as the amount of total sleep, and in the duration of each stage (wakefulness, sleep stages 1 and 2, slow wave sleep, and REM sleep). Other disorders comprise alterations in the sleep-wake transition at sleep onset and between sleep stages and electroencephalographic disorders. The disorders in parasitic infections, such as trypanosomiasis and trichinosis, have an immune component. The prostaglandins PGD2, PGE2, and PGF2a are induced by these infections; PGDs are somnogenic substances, explaining the effects of these parasites on sleep. The disorders in sleep due to parasites can modify certain behaviors to facilitate parasitic infection and completion of the life cycle.