Cyclospora cayetanensis is a microscopic intestinal protozoan parasite that has been known as a cyanobacterium-like, coccidia-like, and cyclospora-like body (CLB). It wasn't until 1993 that it was officially characterized as Cyclospora cayetanensis. Much is still unknown about C. cayetanensis, but it is a known cause of a gastrointestinal infection (cyclosporiasis), with increasing worldwide incidence, including cases in the United States and Canada.
The full host range of C. cayetanensis is currently unknown. At this time, humans are the only known host, with chimpanzees and other primates thought to be potential reservoirs. Infection with C. cayetanensis begins when ingested particles invade the epithelial cells of the small intestine. C. cayetanensis then replicates and continues to spread to nearby cells. This self-limiting and short-lived stage causes most of the symptoms associated with infection with this parasite.
During infection, some of the parasitic cells undergo a sexual reproductive stage, where survival structures called "oocysts" are produced. Oocysts pass out of the host's body in feces and spread infection. After about one to two weeks, shed oocysts become "activated" (infectious). If activated oocysts are consumed in contaminated food or water, the disease will spread to the new host. Due to this lag time in infectivity, direct person-to-person contamination is unlikely.
Environmental factors have an effect on the time required for shed oocysts to become capable of causing disease. The moderate temperatures of late spring and early summer, 68° to 70°F (20° to 21°C), especially when combined with periods of high rainfall, are ideal for oocysts to become infectious. Such conditions are also conducive to fruit and vegetable production, both domestically and abroad. If producers and workers in any country do not adhere to adequate sanitary practices or if crops are irrigated with untreated water, the risk of infestation with C. cayetanensis oocysts increases. Multiple domestic outbreaks of gastroenteritis have been linked to imported goods contaminated with Cyclospora.
Persons of all ages are at risk for infection. Young children under twelve years of age tend to exhibit symptoms more frequently due to their immature immune systems. The immuno-compromised and the elderly may exhibit more severe symptoms, while travelers touring in developing countries can be at higher risk of infection. The risk tends to vary with the season--moderate and rainy climates are the most conducive to infection spread.
Several types of fresh produce from various countries have been implicated as vehicles of transmission. For example, fresh raspberries, snow peas and mesclun lettuce imported from Guatemala have all been implicated in U.S. outbreaks. The U.S. Food and Drug Administration (FDA) and the CDC are working with Guatemalan officials to determine possible modes of contamination. The implication of three different vehicles of infection during 1997 highlights the need for prevention and control measures to ensure the safety of produce eaten raw and the need for improved understanding of Cyclospora's ability to cause disease.
Little information is available regarding animal hosts and environmental survival time. Oocysts, tend to be resistant to adverse conditions and have been known to survive for long periods of time if kept moist. Oocysts must be ingested for cyclosporiasis to develop; they are only shed in the fecal matter of an infected host. Thus, fecal contamination of food or water, or any substance someone may have oral contact with, is the only method of contamination.
Individuals should be aware the only way to prevent disease is to avoid oral contact with contaminated products; there is no vaccination for cyclosporiasis. Ingested food and water should be from treated and reliable sources. The best way to avoid exposure to Cyclospora is to avoid food from unsafe sources. Raw foods such as produce should be thoroughly washed with potable water before consumption; this will decrease but not eliminate the risk of Cyclospora ingestion. Travelers to areas with sub-standard waste treatment facilities should be advised to follow precautions as found in the CDC's "Yellow Book" or Health Information for International Travel.