CYCLOSPORIASIS: Biology, Pathogenesis, Detection, Control, Treatment & Prevention

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Cyclosporiasis is a persistent diarrheal parasitic disease that is acquired through the consumption of food and water contaminated with feaces of man and other animals containing the oocysts of the parasite, Cyclospora cayetanensis. The disease predominantly occurs in persons who are immunocompromised due to HIV infection, chemotherapy (tumor treatment) or organ transplant. Cyclosporiasis is an AIDS-associated disease that is manly characterized by profuse stooling and long-lasting diarrheal sickness in immunocompromised patients. A global water-borne and food-borne disease, cyclosporiasis is a widespread protozoal infection that causes severe gastroenteritis in human populations. The disease occurs with varying rates of infectivity in all age groups including adults and children, but its occurrence is common amongst AIDS patients.

Cyclosporiasis is caused by the protozoan Cyclospora cayetanensis. C. cayetanensis is found in the phylum Apicomplexa, class Coccidia, and genus Cyclospora. C. cayetanensis is among the human intestinal coccidia that causes diarrheal disease in man. Other human intestinal coccidia include: Cryptosporidium parvum and Isospora belli. All human intestinal coccidia are notorious in causing prolonged diarrheal disease in persons infected with HIV. Generally, C. cayetanensis and other human intestinal coccidia are opportunistic protozoal pathogens in immunocompromised individuals.

Type and morphology of Cyclospora cayetanensis

C. cayetanensis is an intracellular intestinal parasite. Morphologically, C. cayetanensis exist in only one form, the oocyst which is spherical in shape. C. cayetanensis oocysts measures about 8-10µm in diameter and its oocysts produce two sporocysts that usually have two sporozoites each. Oocysts of C. cayetanensis are usually shed unsporulated in feaces. Sporulation of oocysts occurs outside the body of the hosts few days after shedding to become infectious.    

Vector, reservoir and habitat of Cyclospora cayetanensis

C. cayetanensis and the other human intestinal coccidia species have no insect vector. Humans, domestic animals, birds and fowls are the primary definitive hosts (reservoirs) of C. cayetanensis. The human intestines including the intestines of other mammals and animals that the parasite is known to parasitize are the habitat of C. cayetanensis. Oocysts of C. cayetanensis can also survive in water bodies and food (which they contaminate) when passed out of the body via feaces.  

Clinical signs and symptoms of cyclosporiasis

Cyclosporiasis may be symptomatic or asymptomatic in individuals infected by the causative agent of the disease. The clinical presentation of cyclosporiasis may include: appetite loss, abdominal pain, flatulence, mild or even prolonged diarrhea, fever, malaise and weight loss. However, many parasitic infections involving any of the human intestinal coccidia are normally asymptomatic in nature, but infected immunocompromised patients suffer from a persistent diarrheal disease and weight loss before becoming well again after therapy.

Pathogenesis of Cyclospora cayetanensis infection

Human infection with C. cayetanensis begins following the ingestion of oocysts of the parasite from water and food contaminated with feacal matter from man and other animals including birds and fowl (Figure 1). Oocysts of C. cayetanensis encyst in the small intestine to form sporozoites which invade the intestinal mucosa to cause a range of inflammatory reactions that eventually culminate to diarrhea or watery stooling. Cyclosporiasis is usually a self-limiting infection, and infected patients start recuperating some few weeks after infection. However, chronic cyclosporiasis may persist in individuals who are immunocompromised by cancer treatment or HIV infection, and even in people who live in poor sanitary conditions and who are malnourished as well. Oocysts of C. cayetanensis are finally excreted by infected humans via feaces from where they go on to contaminate food and water from which the infection can be acquired by man. 

Figure 1. Life cycle of Cyclospora. CDC

Laboratory diagnosis of Cyclospora cayetanensis infection

Cyclosporiasis is mainly diagnosed in the laboratory by detecting oocysts of C. cayetanensis (Figure 2.) in fresh stool samples of infected patients through direct wet mount under light microscopy and stool concentration techniques (formol-ether oocysts concentration method). Oocysts of C. cayetanensis can also be detected in stained smears of stool samples using the modified carbol-fuchsin and Ziehl-Neelsen technique or safranin stain (Figure 3.). 

Figure 2. Oocysts of C. cayetanensis (arrow) in an unstained wet mount of stool specimen. CDC
Figure 3. Safranin-stained oocysts of C. cayetanensis (arrow). CDC

Treatment of Cyclospora cayetanensis infection

Sulphamethoxazole-trimethoprim (co-trimoxazole) is the most preferred drug of choice for treating cyclosporiasis. Trimethoprim and ciprofloxacin can also be used singly to treat the infection. Pyrimethamine in addition to ciprofloxacin may be used for treating immunocompromised patients who are allergic to sulphonamide drugs. Improvement in the nutrition of infected patients especially children can also support the healing process of the disease.

Control and prevention of Cyclospora cayetanensis infection

Cyclosporiasis is a sporadic parasitic disease that is widespread. Since the disease is contacted via feacally contaminated food and water, and it is thus a food-borne and water-borne infection; improvements in sanitary, water, food and environmental conditions will help in containing the disease in places where it is endemic. Foods especially vegetables and fruits eaten raw should be properly washed before consumption. Human feaces should not be directly used for agricultural purposes, and public water should be properly disinfected and treated before distribution to the suburban areas. 


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