Cyclospora cayetanensis is a protozoan organism that is classified as a Coccidian parasite. Coccidian parasites are single-celled, obligate intracellular parasites, and spore-forming. The infection caused by Cyclospora is called Cyclosporiasis, and results in an intestinal illness, with the most common symptom being diarrhea. Cyclospora invades the small intestine, specifically the jejunum (Ortega and Sanchez, 2010). In the United States, it is estimated that there are 14,638 cases annually of Cyclosporiasis from food-borne contamination (Mead, 1999). The foods most commonly associated with Cyclospora contamination are raspberries, basil, snow peas, mesclun lettuce, and cilantro (CDC, 2018). An interesting, and important characteristic, is this a parasite of humans, and no infections have been described in other animals (Colley 1996). Humans are the only known host that the parasite is able to replicate in, which means that food and water contamination is directly, or indirectly, from infected humans shedding the parasite in their feces. The first documented cases of Cyclosporiasis were during the 1980s. Cyclospora was found to be an opportunist infection in AIDS patients. The parasite has probably been around for much longer than this, but the organism was not discovered until more recently in history.
Cyclospora is a parasite, which means that it relies on a host for replication. The infection begins when a human ingests food or water contaminated with a sporulated oocyst (an unsporulated oocyst will not cause an infection). The parasite invades the small intestine epithelium via excystation of the oocyst into sporozoites. Within the epithelial cells in the intestine, type 1 and type 2 Meronts produce asexually. Merozoites are produced, and some of these replicate via sexual reproduction (still in the epithelium), and these stages are called macrogametocytes and microgametocytes. The gametocytes reproduce to form a zygote. The zygote exits the host in the form of an unsporulated oocyst. Once the unsporulated oocyst is excreted, it takes 7 to 15 days to sporulate in order to be infectious (CDC, 2019; Ortega and Sanchez, 2010). The ideal temperatures for sporulation are 23-27°C. Direct fecal-oral transmission does not occur because the oocyst is not immediately infective. Symptoms of infection are watery diarrhea, nausea, flatulence, cramping, bloating, fatigue, and weight loss (CDC, 2018).
Cyclosporiasis is most commonly found in tropical and subtropical regions (CDC, 2018). In the United States outbreaks have been associated with imported fresh produce. Other infections in the United States have been from travelers to endemic areas of the world. In the United States, and other countries where there is not endemic infection, most people are susceptible to infection. In endemic countries, only the very young and old are susceptible (Ortega and Sanchez, 2010). No other animals have been found to be reservoirs of the parasite, and all attempts to infect other animals have been unsuccessful (Eberhard, 2000). Because there are no animal models for this disease, it has been more challenging to study the disease and the interesting life cycle. There are still many questions researchers are trying to answer about this parasite. Parasites are not as easy to study in a laboratory setting because they do not readily multiply like bacteria or fungi. Researchers must obtain spores from the environment, contaminated foods, or stool samples (there’s no way to create more cells in the laboratory setting due to the lifecycle!).
Cyclospora are infective as an oocyst. Oocysts (like bacterial spores) are able to protect themselves from their environment. Cyclospora are resistant to disinfectants used in water and food processing, as well as freezing and some hotter temperatures (Ortega and Sanchez, 2010). Rinsing and washing food is not likely to remove the parasite. The food most commonly implicated in Cyclospora infections is not normally cooked prior to consumption. Interestingly, the small hairs on raspberries actually allow for the parasite to stick to the berry easier! It is hypothesized that contamination of the fresh produce could be from agricultural water in some cases. The food is not always identified during an outbreak. The parasite may be present in such small numbers that a diagnostic test might not be able to identify the parasite. Recently, an outbreak that took place from May to August 2020 has been implicated to a bagged salad mix. There were 1,241 laboratory confirmed cases (CDC, 2020). Most cases in the United States are linked to contaminated imported foods produced in endemic regions. At a wedding in Pennsylvania in 1997, there was a Cyclospora outbreak. The raspberry filling in the cake was contaminated with the parasite (and the filling had been frozen prior to serving) (Ho, 2002). There was a waterborne case of infection that was caused by oral siphoning of a saltwater aquarium (Wurtz, 1993).
Early laboratory detection methods were limited to direct microscopy and staining methods. This is not a perfect method, since there is no way to increase the concentration of the parasite in the sample to “detectable levels”. It can be challenging to differentiate Cyclospora from other Coccidian parasites in a sample. There has been a new development in PCR testing for Cyclospora identification. This new method has an enhanced produce washing solution and a species-specific probe in the RT PCR reaction (Murphy, 2018). This new method will be very beneficial for laboratory identification of contaminated foods.
CDC – Parasites – Cyclosporiasis (Cyclospora Infection). (2020, March 12). Retrieved January 29, 2021, from https://www.cdc.gov/parasites/cyclosporiasis/index.html
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