Spotlight on the recent outbreak of cyclosporiasis, a food- and water-borne parasitic disease

A balanced diet should contain fresh fruits and vegetables, whose long-term health benefits are indisputable. Simultaneously, it is crucial for continued good health to remember the importance of hygiene and safe handling of fruits and vegetables, as underscored by some recent findings of the Centers for Disease Control and Prevention (CDC) during an investigation into the suspected outbreak of a food-borne illness, called cyclosporiasis.

Cyclosporiasis is most common to tropical and subtropical regions; it has been found in Ghana, Guatemala, Egypt, Turkey, Nepal, Peru, and Haiti from water samples and human disease. Although it is not considered endemic to the continental United States, it is by no means unknown in this country; during 1990-95 three small outbreaks were reported in North America. Major outbreaks, confirmed by molecular methods, have been documented since c.1996, often associated with fresh produce – raspberries, lettuce, basil, and snow peas – mostly imported from countries endemic for the disease. Apart from multi-state outbreaks in 1996, 1997, and 2000, more than 1100 sporadic cases of confirmed cyclosporiasis occurred during 1997-2008, involving twelve US states. About a third of these cases were likely associated with international travel to endemic regions. In response, cyclosporiasis was made a nationally notifiable disease in January 1999; as of 2008, it is a reportable condition in 37 states, New York City (NYC), and the District of Columbia.

Earlier this year (June-August 2013), an unusually large number of cyclosporiasis reports were communicated to the CDC, involving more than 600 individuals from 25 states (with high numbers in Texas, Iowa, and Nebraska) and NYC. Epidemiologic and traceback investigations conducted jointly by the CDC, the Food and Drug Administration (FDA), and state and local public health officials revealed the possibility of two outbreaks; cases in Iowa and Nebraska were associated with restaurants, and involved a salad mix (iceberg and romaine lettuce, red cabbage, carrots) sourced from Taylor Farms de Mexico, whereas cases in Texas were associated with uncooked (but not cooked) cilantro sourced from Puebla, Mexico.

A total of 631 cases of cyclosporiasis were reported from 25 states and New York City: Texas (270), Iowa (140), Nebraska (87), Florida (33)¶, Wisconsin (18), Arkansas (16)†, Illinois (14)†, New York City (8)‡, Georgia (5), Missouri (5)†, Kansas (4)‡, New Jersey (4)†, Louisiana (3)‡, Massachusetts (3)†, Minnesota (3), Ohio (3), Virginia (4), Connecticut (2), New York (2)†, California (1)†, Michigan (1)†, New Hampshire (1), Pennsylvania (1), South Dakota (1), Tennessee (1), and Wyoming (1). † Includes one case that may have been acquired out of state. ‡ Includes two cases that may have been acquired out of state. ¶ May include one international travel-associated case. [Source: CDC]

Human cyclosporiasis is a disease caused by the single-celled apicomplexan protozoal parasite Cyclospora cayetanensis. Parasites of the genus Cyclospora have been found in nature in many members of the animal kingdom, including certain terrestrial arthropods (such as, centipedes), snakes, rodents, moles (a subterranean mammal), cattle (recently discovered in China), as well as in certain non-human primates (colobus monkeys, green monkeys, baboons and chimpanzees). Although there are about 18 different species of Cyclospora currently known, the four that infect non-human primates appear to be specific to these animals, and so far Cyclospora cayetanensis has been discovered only in humans. Attempts to create non-human animal models of C. cayetanensis infection have been unsuccessful, again suggesting host-specificity.

Four Cyclospora cayetanensis oocysts in fresh stool sample in 10% Formalin, variably stained with Acid-fast stain. Image courtesy: PHIL/CDC/DPDx – Melanie Moser.

Cyclospora transmission occurs via the fecal-oral route. In excreted fecal matter, Cyclospora exists in the form of oocysts (a thick-walled structure containing immature, dormant parasite spores), a product of sexual reproduction of the parasite. Interestingly, these are non-infectious, although highly resistant to common disinfectants used in food- and water-processing industries. However, within two weeks, the spores mature – making the oocysts infectious. Neither the natural environments of this process, nor the exact manner of transmission, are yet known, but contamination of water and/or food (such as raw produce) with oocyst-containing fecal matter likely contributes to the dissemination. Epidemiological studies indicate that higher risks of infection are associated with consumption of untreated water and/or food, lack of adequate sanitation, and the presence of animals in the household.

This parasite primarily targets the small intestines, and an infection often causes gastro-intestinal symptoms, such as watery diarrhea, abdominal cramping, anorexia (loss of appetite), flatulence (gas) and bloating, along with nausea, fatigue, weight-loss, sometimes accompanied by low-grade fever. In absence of proper treatment, some of these symptoms may continue for weeks on end, while some may be temporarily relieved, only to recur. The good news is that the infection is not generally life-threatening and people with healthy immune systems may not require treatment. However, in children and in the elderly, as well in individuals with compromised immunity (such as AIDS or cancer patients), untreated cyclosporiasis may cause severe, and occasionally fatal, illness.

The anti-protozoal antimicrobial Trimethoprim/sulfamethoxazole is currently the drug of choice for Cyclospora infection. Anti-diarrheal medication, taken under medical supervision, may help reduce diarrhea. However, for an effective preventative, the CDC strongly advises that general fruit and vegetable safety recommendations – covering washing, preparation, and storage – be followed by consumers.

[An abridged version of this post was published in The Conversation UK.]