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Food Matters

Spud's Down to Earth Advice on...

CYCLOSPORA CAYETANENSIS

Cyclospora cayetanensis is a microscopic single-celled parasite that causes illness in humans by infecting the small intestine. The illness caused by Cyclospora infection is termed cyclosporiasis, with the first reported case being positively identified in 1979.

Life Cycle

When freshly passed in stools, the oocyst is not infective (thus, direct faecal-oral transmission cannot occur; this differentiates Cyclospora from another important coccidian parasite, Cryptosporidium). In the environment, sporulation occurs after days or weeks at temperatures between 22^oC to 32^oC, resulting in division of the sporont into two sporocysts, each containing two elongate sporozoites. Fresh produce and water can serve as vehicles for transmission and the sporulated oocysts are ingested (in contaminated food or water). The oocysts excyst in the gastrointestinal tract, freeing the sporozoites which invade the epithelial cells of the small intestine. Inside the cells they undergo asexual multiplication and sexual development to mature into oocysts, which will be shed in stools.

Incubation Period & Duration

Incubation Period
Approximately 7 days after infection. However, some people can be infected with Cyclospora and not show any symptoms. An infectious dose of between 10 and 100 oocysts ('eggs') has been suggested.

Duration
If not treated, the illness may last from a few days to a month or longer. Symptoms may seem to go away and then return one or more times (relapse).

Symptoms

watery, frequent and sometimes explosive diarrhoea; the diarrhoea may last for up to 6 weeks in some cases
loss of appetite
substantial loss of weight
bloating/increased gas
stomach cramps
nausea
vomiting
muscle aches
low-grade fever
fatigue

Cyclospora responds quickly to proper antibiotic treatment and is not considered life-threatening in otherwise healthy people.

Sources/Associated Foods

Investigations into outbreaks in the US indicated that fresh fruits and vegetables (e.g. raspberries, basil and lettuce) were sources of Cyclospora infection. As Cyclospora is not naturally found in or on fresh fruits and vegetables, or any other foods, it is thought that food contamination may occur during cultivation, harvest, packaging or transportation through contact with contaminated water or workers.

Spread

Cyclospora is spread by people ingesting something, for example water or food, that has been contaminated with human faeces containing viable, sporulated oocysts (an environmentally resistant cyst stage). Cyclospora needs time (days or weeks) after being passed in a bowel movement to become infectious. Therefore, it is unlikely that Cyclosporais passed directly from one person to another.

Control

From the farm to the retail store, extensive research and actions are being made to reduce the risks associated with Cyclospora contamination throughout the food production process.

The already low odds of becoming infected with Cyclospora can be reduced still further by simply washing fruits and vegetables well prior to consumption, although it should be noted that this will not guarantee 100% removal of any oocysts present.

Exclusion/Return to Work Parameters

Cases in risk groups 1- 4 not to return until 48 hours after first normal stool.

[Group 1 - food handlers; Group 2 - health care workers; Group 3 - children under 5 in nurseries etc.; Group 4 - older children and adults who may find it difficult to implement good standards of personal hygiene]

Additional Information

Data relating to the level of infection with Cyclospora must be treated with some caution due to probable under-reporting.
There are an average of 60 laboratory-confirmed cases of Cyclosporaspp. per year in England, Wales and N. Ireland. Just over 50% were of cases reported as being acquired abroad. Of these:

32% reported recent travel to the Indian sub-continent (mainly Nepal and India)
29% reported recent travel to south east Asia and the Far East (just over half to Indonesia).

The countries of acquisition of Cyclospora spp. are consistent with the regions of the world where the organism is endemic.
In North America the overall prevalence of Cyclospora appears to be far less than 1%. Outbreaks seem to occur most frequently in late spring and summer, and these warmer temperatures appear necessary to get oocysts to sporulate with any speed. In addition, this time of year correlates with increased imports of fruits and vegetables into the US from other countries.
There were 11 outbreaks of (probable) food borne cyclosporiasis, documented in North America in the 1990s, most of which seemed to have been transmitted by fresh produce, possibly sprayed with contaminated water.
Oocysts of Cyclospora cayetanensis are excreted in an unsporulated, non-infective form. These sporulate after about a week in the environment.
Cyclospora cayetanensis is morphologically similar to Cryptosporidium spp., but undergoes exogenous sporulation (i.e., it requires time outside the body to mature and become infectious) unlike Cryptosporidium spp. which are excreted from the human body in a fully infectious state.
Moderate numbers of unsporulated oocysts can be excreted in faeces for up to 60 days or more.

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Friday 10 September 2010