Cyclosporiasis

This is an uncommon cause of gastroenteritis. The pathogen is Cyclospora cayetanensis which is a coccidian protozoan parasite, about 8 to 10μm in diameter. At least 16 species of this genus have been identified in other animals, including primates, but this is the only species known to infect man. It was first described in Papua New Guinea in 1979.

Epidemiology

In the UK, between 44 and 66 cases are reported in England and Wales each year, most in people who have visited developing countries.^[1] These numbers may be an underestimate as not all laboratories are equipped to diagnose the disease. It is seen rather more often in the USA and in a number of developing countries where it is endemic. These include Bangladesh, Brazil, Chile, China, Cuba, Dominican Republic, Egypt, Guatemala, Haiti, India, Indonesia, Jordan, Mexico, Morocco, Nepal, Nigeria, Pakistan, Peru, Puerto Rico, Romania, Saudi Arabia, Tanzania, Thailand, Turkey, Venezuela, Vietnam and Zimbabwe.

Life cycle

It undergoes both sexual and asexual reproduction. Sporulated oocysts are ingested, often from fresh vegetables. It breaks out of the cyst, usually in the jejunum, and invades the intestinal epithelium. They reproduce asexually.

After several cycles they move to the sexual form. After invading epithelial cells, some form single macrogametes and others divide many times to form microgametes. When released, a microgamete fertilizes a macrogamete, which develops into a zygote. The zygote, in turn, develops into an oocyst with a resistant wall. The oocyst is passed out in the faeces.

Direct transmission from one human to another does not occur. They may survive in the environment for days or weeks. Contamination of food or drinking water leads to human ingestion and infection. Experimental challenge suggests that quite a large number of oocysts need to be ingested to produce clinical disease.^[2]

Presentation

There is usually a self-limiting diarrhoea of 7 to 9 weeks duration but treatment will curtail this. It may last months to a full year in the presence of HIV.

• In the non-immune the incubation period is 1 to 11 days with a mean of 7 days.
• There may be a prodromal flu-like illness but in about 30% of cases there is an abrupt onset of diarrhoea.
• Watery diarrhoea may be explosive with several stools per day. Sometimes the diarrhoea is much more frequent and in some patients it is absent.
• Anorexia and weight loss usually occur.
• Fatigue is often marked.
• Abdominal cramping pains with abdominal bloating.
• Oral flatulence and vomiting.
• There may be signs of dehydration.
• There is a low grade fever in a quarter of patients.

Differential diagnosis

This includes various forms of gastroenteritis eg bacterial and viral. Some examples are:

• Cryptosporidiosis
• Escherichia Coli Infections
• Food Poisoning
• Giardiasis

Investigations

Diagnosis can be based on identifying oocysts in the stool. Blood tests are not helpful although they may indicate the degree of dehydration. More recently polymerase chain reaction methods have been reported to increase the diagnosis rate.^[3]

• The standard requirement is for 3 stool specimens on alternate days. The number of oocysts in the specimens may vary considerably, but infected patients excrete them continuously.
• Standard laboratory procedures for ova and parasites fail to identify Cyclospora, and so the laboratory must be notified that Cyclospora is clinically suspected.
• Stool specimens may be submitted fresh but many laboratories request that specimens should be in a preservative.

Management

• Rehydration is usually required. This can usually be achieved by the oral route but intravenous rehydration may be necessary.
• A number of antibiotics are effective including ciprofloxacin, norfloxacin, metronidazole, tinidazole, quinacrine, and azithromycin but the usual choice, and possibly the most effective is cotrimoxazole.
• The course of antibiotic is usually 7 days in the immunologically competent and 10 days in the compromised. A week after finishing the course, samples must be repeated to confirm eradication.

Complications

Complications beyond dehydration seem to be isolated events that are reported as rare individual cases. They include Guillain-Barré syndrome, cholecystitis and reactive arthritis.

Prognosis

Immunologically competent patients usually make a full and uneventful recovery. In immunocompromised patients with HIV, the diarrhoea may persist for several months and after resolution, they require prophylactic cotrimoxazole 3 times a week to prevent reinfection.

Prevention

In endemic areas the following precautions are advised:

• Wash hands with soap and water before eating.
• Drink only purified water. Do not trust tap water.
• Purify water either by bringing to the boil or iodination or chlorination.
• Wash fresh fruits and vegetables with purified water and peel them after washing hands with soap and purified water. One study suggests that simply washing vegetables and fruit that cannot be peeled may not remove Cryptosporidium and Cyclospora completely.
• Raspberries and similar fruits eaten in developing countries and imported from developing countries are a particular risk for Cyclospora contamination because they cannot be decontaminated easily.^{[4, 5, 6]}