Cyclospora cayetanensis
Etiology/Bacteriology
Taxonomy
| Domain = Eukaryota | Phylum = Apicomplexa | Class = Coccidia | Order = Eucoccidiorida | Family = Eimeriidae | Genus = Cyclospora | species = C. cayetanensis
Description
Pathogenesis
Transmission
Cyclospora cayetanensis is spread via the fecal-oral route, meaning that the host must ingest something, food or water for example, that had been contaminated with feces that contain infectious oocysts; to be infectious the oocyst has to be sporulated. An unsporulated oocyst takes from days to weeks outside a host cell after being excreted in a fecal matter of an infected host to become a sporulated oocyst, now capable of infecting another host. 2 Imported fresh produce from tropical regions, such as raspberries, basil and lettuce have caused outbreaks of cyclosporiasis from contamination from feces. 3 Essentially, any food that has been contaminated with fecal matter containing infectious, sporulated oocysts have the potential to cause infection of Cyclospora cayetanensis . To date, there has been no documented transmission from human-to-human, likely due to the amount of time outside a host the oocyst has be to transform into a sporulated oocyst capable of infection. 5
Infectious dose, incubation, and colonization
The infectious dose of oocysts needed to infect the host is relatively unknown, but it is thought to be in the low numbers 3 The incubation period for Cyclospora cayetanensis infection is at average one week, but can range from even 1 day to around 10 days. 3 Cyclospora cayetanensis completes its life cycle in only one host, and can be broken into two phases-- exogenous and endogenous. The exogenous stage takes place outside the host, in the environment and is when an immature oocyst sporulates, becoming infectious for humans. During sporulation, the sporont divides into 2 sporocysts, each containing 2 sporozoites 5 This sporulation process requires some time, ranging from a few days to a couple of weeks, outside a host and exposed to the environment, which occurs only at appropriate oxygen concentrations, temperature, humidity, and other factors. 3 The endogenous stage takes place in the human host 10 After ingestion of a sporulated Cyclospora oocysts, which is its infectious state, the oocysts releasing the sporozoites into the small intestine due to some special stimuli, such as the anaerobic condition in the GI tract, or the presence of bile salts. These sporozoites invade small intestine epithelia, or enterocytes especially in the jejunum and reside intracellular in a parasitophorous vacuole 10. Now, they undergo asexual division followed by sexual division and eventually produce unsporulated oocysts, and as the enterocytes die, they are are shed in the stool. 5 In the environment, the oocyst sporulates, becoming infectious for humans and the life cycle process occurs again in another host that ingests the contaminated item 5
Epidemiology
Cyclosporiasis occurs in many countries all over the world, but is more prevalent in tropical and subtropical regions, where people living there have an increased risk of infection, as well as people traveling to those regions. 2 It is thought that infection is based on seasons, for example from epidemiological studies it seems that infection is higher in Peru from December to July or in the United States from May to July, however no consistent data has been able to prove that yet 3 In the United States, foodborne outbreaks of cyclosporiasis have involved imported fresh produce, for example in 1997, both contaminated raspberries and fresh basil resulted in 1,498 cases disease. 2 Epidemiologic data suggest that immunity may develop to C. cayetanensis in areas where cyclosporiasis is endemic and that the disease is more severe in naïve populations6
Virulence factors
Cyclospora cayetanensis infects the epithelial cells that line the small intestine using several mechanisms, however much is still not known about this parasites virulence factors and characteristics used to infected the host. Of course it is known that several requirements are needed for a parasite to cause disease in a host, and without these, the parasite would not be able to invade the host. These requirements include the ability for the organism’s infectious form, and in the case of Cyclospora , its oocyst, to survive in harsh environmental conditions. The oocyst has a thick bilayered wall, allowing the organism to be environmentally resistant and able to survive until ingestion of a host. 10 This characteristic help the oocyst to survive a chlorination process of water, leaving it still contaminated by the pathogen. Another helpful feature of the mature oocysts contributing to pathogenesis is its fibrillar coat, which is also seen in the noninfectious, unsporulated oocysts that are in the stool of infected hosts. 10 This fibrillar coat is thought to help the parasite adhere to the foods it is known to contaminate, like the basil leaf or raspberries. This fibrillar coat is thought to help the parasite adhere to the foods it is known to contaminate, like the basil leaf or raspberries. It has also been predicted that the symptom of watery diarrhea without blood or leukocytes present caused by Cyclospora cayetanensis infection may be due to an unidentified toxin causing said diarrhea. 10
Clinical features
Typical symptoms of Cyclospora cayetanensis infection include most commonly watery diarrhea, that can sometimes be described as explosive, along with abdominal cramping, loss of appetite, weight loss, nausea and vomiting, all associated with an early onset. 1 It can also include headaches, and a low fever, sometimes described as flu-like symptoms, however it is possible that the infected host do not even have symptoms. These symptoms, if not treated can last an average of 7 days, but can range anywhere from a few days to a month or longer, and even though the infection can resolve itself, if treated with specific drugs, the symptoms are resolved faster, compared to untreated patients 1 It is always possible for symptoms of infection to relapse, or come back 8 Infection in travelers are more severe in symptoms, while in Cyclospora endemic countries about 70% of children often have asymptomatic infections, while adults are occasionally infected. 5 Cyclospora cayetanensis infection is not considered a fatal disease, and there have been no reported deaths attributed to the actual parasite in the United States, however it is when the infection induces protracted diarrhea onto the host, which could possibly lead to severe dehydration if not taken care. 5 Infants are at greater risk for dehydration due to prolonged diarrhea as a symptom from infection. Diarrheal diseases attribute to over two million deaths in children each year, however it is not known how many of these could be due to Cyclospora infection 5
Diagnosis
The first step in diagnosis of Cyclospora cayetanensis infection should be when health care providers notice the symptom of prolonged diarrhea in the patient, and should also look at the other symptoms associated with the disease as well. If the patient has recently traveled to a tropical or sub-tropical area that is known for causing infection, the healthcare provider should ask the patient for a stool sample 3 However, because testing for Cyclospora is not usually done in most laboratories in the US when the stool is tested for parasites, identification for C. cayetanensis in the stool requires special lab tests not routinely done, therefore this microorganism can be difficult to diagnose, especially when it comes to laboratory tests. This is because even if an infected patient is symptomatic, there may not be enough oocysts in the stool to detect infection in lab examinations; therefore it is not uncommonly needed for the patient to provide multiple stool specimens ranging within several days. 2 Identification of this organism can be made through microscopic techniques, usually several different stains, such as Acid-fast stains, or using an epifluorescence microscope, in which the the Cyclospora oocyst appear a neon-blue color. 1 Due to the face that Cyclospora cayetanensis is unable to be culture in the laboratory and its small size, it is near impossible to detect and isolate the organism on the contaminated food since the amount of organisms on it are so low. 3
Treatment
The specific drug treatment for disease caused by Cyclospora cayetanensis is the combination of two antibiotics—trimethoprim and sulfamethoxazole (co-trimaxazole), which are also sold under the names of Bactrim, Cotrim, or Septra, and symptoms can diminish within the next several days. 8 Unfortunately, there have been no alternative drug treatment options that have been effective for patients that suffer from a sulfa allergy or do not respond to the combination antibiotic. 2 Of course anti-diarrheal medication can be given by a health care provider to reduce the diarrheal symptom, but this does not actually combat against the microorganism. Hydration and rest are also essential to patients with diarrhea, and in most healthy individuals the infection can be self-limiting, and most can recover in a few days, or possibly a month or longer. 2 If left untreated the protracted diarrhea can lead to severe dehydration, and in cases like these hospitalization may occur.
Prevention
Cyclospora cayetanensis oocysts, which are the cause of infection, are transmitted via the fecal-oral route, therefore the best prevention for infection of this microorganism is to simply avoid food or water that may have been contaminated with feces containing the infectious oocysts. 2 It is possible for Cyclospora to re-infect the same host more than once. Since most of the U.S cases of disease are caused from either imported contaminated food, or traveling to Cyclospora -endemic areas, it is important for travelers to be precautious about food and water consumption. Even if contaminated food or water is treated with chlorine and iodine, infectious Cyclospora oocyts are likely to remain, so drinking bottle water, and avoiding street venders are the safest ways to avoid infection. 2 Other good practices are to use proper hand washing techniques, and washing all food thoroughly.
