Cyclospora cayetanensis

Cyclospora cayetanensis is a parasite that causes disease in humans, and, perhaps, in other primates. It has been linked in the United States to fecally contaminated imported produce, and was virtually unknown before about 1990, but has been on the rise since. The health risk associated with the disease is usually confined to adult foreigners visiting regions where the species is endemic and acquiring the infection; consequently, C. cayetanensis is a cause of 'traveler's diarrhea'. This species was placed in the genus Cyclospora because of the spherical shape of its sporocysts. The species name refers to the Cayetano Heredia University in Lima, Peru, where early epidemiological and taxonomic work was done. The first published report of Cyclospora cayetanensis in humans appears to be by Ashford (1979), who found unidentified Isospora-like coccidia in the feces of three individuals in Papua, New Guinea. The photomicrographs in the paper reveal an organism morphologically identical to that seen now. Later, Narango et al. (1989) reported what may be the same organism from several Peruvians with chronic diarrhea and termed the organism Cryptosporidium muris–like. Other investigators thought the unsporulated oocysts appeared more similar to cyanobacteria, and the name 'cyanobacterium-like body' or CLB became prevalent in the literature (occasionally, authors also used the term 'coccidian-like body', or CLB). Eventually, Ortega et al. (1992) published an abstract reporting that they had sporulated and excysted the oocysts, resulting in placement of the parasite in the genus Cyclospora. They also created the name Cyclospora cayetanensis at this time. However, since no morphologic information was presented in the abstract, C. cayetanensis technically became a nomen nudum (a named species without a description). Although Ortega et al. (1993) later published additional details about this coccidian, a complete morphologic description was not published to validate the name until 1994. Thus, the correct name for this parasite is Cyclospora cayetanensis Ortega, Gilman, & Sterling, 1994, and the etymology of the nomen triviale is derived from Cayetano Heredia University in Lima, Peru. During this two-year period when C. cayetanensis was a nomen nudum, anyone wishing to publish a complete morphologic description and change the name would have been free to do so. Cyclospora cayetanensis is an apicomplexan, cyst-forming coccidian protozoan that causes a self-limiting diarrhea. In terms of morphology, It has spherical oocysts that are between 7.5 and 10 μm in diameter that also have a 50-nm-thick wall with an outer thread-like coat that has been called a wrinkle by some researchers. The oocyst formula is O.2.2 because one oocyst contains two sporocysts and each sporocyst contains two sporozoites. The only confirmed hosts for C. cayentanensis are humans. The protozoan lives out its lifecycle intracellularly within the host's epithelial cells and gastrointestinal tract. Infection is transmitted through the fecal-oral route, and begins when a person ingests oocysts in feces-contaminated food or water. Various chemicals in the host's gastrointestinal tract cause the oocysts to excyst and release sporozoites; generally, two are observed per oocyst. After these sporozoites invade the epithelial cells, they undergo merogony, a form of asexual reproduction that results in many daughter merozoites. These daughter cells may either infect new host cells and initiate yet another round of merogony or take on a sexual track via gametogony: Daughter merozoites become male macrogamonts—which form many microgametes—and female macrogamonts. After fertilization has occurred via male microgamete fusion with female macrogamont, the zygote matures into an oocyst and ruptures the host cell, from which point it is passed with the stool. The oocysts that are passed are not, however, immediately infectious. Sporulation can take from one to several weeks, meaning person-to-person transmission is not a likely problem. This differentiates C. cayentanensis from Cryptosporidium parvum—a closely related organism that causes a similar disease—since C. parvum oocysts are immediately infectious upon release from the host. C. cayentanensis causes gastroenteritis, with the extent of the illness varying based on age, condition of the host, and size of the infectious dose. Symptoms include 'watery diarrhea, loss of appetite, weight loss, abdominal bloating and cramping, increased flatulence, nausea, fatigue, and low-grade fever', though this can be augmented in more severe cases by vomiting, substantial weight loss, excessive diarrhea, and muscle aches. Typically, patients with a persistent watery diarrhea lasting over several days may be suspected of harboring the disease, especially if they have traveled to a region where the protozoan is endemic. The incubation period in the host is typically around a week, and illness can last six weeks before self-limiting. Unless treated, illness may relapse. The more severe forms of the disease can occur in immunocompromised patients, such as those with AIDS.Human cyclosporiasis is clinically similar to cryptosporidiosis, isosporiasis, giardiasis and microsporidiosis because of the similarclinical features. Flu like syndrome with myalgias and arthralgias may precede the onset of diarrhea. Fever is low grade and is unusual. There is presence of moderate to severe dehydration, compensatory tachycardia, systolic blood pressure (SBP<90 mmHg) and decreased skin turgor may occur. But mild infection produces few or no clinical symptoms. The immune system may determine the appearance of symptoms; that is, from symptomatic to asymptomatic stage depends on resistivity of the immune system. Persons living or traveling in poorly developed areas in the tropics and subtropics may be at an increased risk of acquiring C. cayetanensis, as they are identified as endemic areas. Additionally, in some regions infections tend to be more prevalent at certain times of the year, typically most frequently in late spring and summer. In addition, this time of year correlates with increased import of fruits and vegetables into the US from the more southern neighbors. Consuming food or water while visiting developing countries is a well-documented way of developing traveler's diarrhea. Travelers are often warned against such actions, but over 70 percent of certain produce items consumed in the United States is imported from developing countries, making 'traveler's diarrhea' possible without international travel.Since the oocysts are shed in the feces of infected persons and then have to mature in the environment 2–14 days before they can become infectious, it is unlikely for a person to get an infection directly from an infected person, such as a restaurant worker who did not wash their hands fully after using the toilet. Due to its small size, intracellular habitat, and inability to properly take up many histological stains, diagnosis of C. cayetanensis can be very difficult. Four methods have thus far been established for positive diagnosis of the protozoan: microscopic detection in stool samples of oocysts; recovering oocysts in intestinal fluid/small bowel biopsy specimens; demonstration of oocyst sporulation; and amplification by polymerase chain reaction (PCR) of C. cayetanensis DNA. Since detection is so hard, one negative result should not discount the possibility of C. cayetanensis: tests involving fresh stool samples over the next few days should also be considered.