Public health officials are warning about an outbreak of Cyclospora infections in Canada, with several dozen cases under investigation. The illnesses began in May and have been reported mostly in Ontario, with a few cases in B.C., Alberta and Quebec. So far, the source of the outbreak has not been found.

Here's what to know about this bug.

What is cyclospora?

Cyclospora is a microscopic parasite that can cause a form of food poisoning called cyclosporiasis. People infected with the parasite can spread the bug when their feces contaminates food or water supplies.

The parasite is most common in tropical and subtropical countries where some Canadians have contracted it and become ill back home. There have also been small outbreaks of infection in Canada caused by contaminated imported produce.

Why have I never heard of it before?

Cyclospora only came to medical attention around 40 years ago, while the species, Cyclospora cayetanensis, was formally named in 1994.

The infection was once primarily a concern for Canadians who travelled to developing countries, but since the 1990s there have been several small outbreaks linked to contaminated imported lettuce, herbs and raspberries.

How serious is the illness?

Cyclospora is generally low risk. Some people do not get sick at all, while others feel the symptoms of a bad stomach bug. Most infected people experience:

  • watery diarrhea
  • loss of appetite and weight loss
  • stomach cramps and nausea
  • abdominal bloating and increased gas
  • fatigue

The illness can last from a few days to several weeks. People with a weakened immune system may be at higher risk for severe illness.

How do I know if I have cyclospora infection?

It takes at least two days for people infected with Cyclospora to begin developing symptoms after they have ingested it. Most notice symptoms beginning around a week after eating contaminated food.

If you suddenly develop watery diarrhea, you should contact your health care provider. If you suspect you have been infected with Cyclospora, a stool sample will be taken for testing.

How is a Cyclospora infection treated?

Cyclospora can be treated with a combination of two antibiotics, trimethoprim-sulfamethoxazole. Those infected are also advised to drink plenty of liquids to replace lost body fluids from diarrhea. Most people who have healthy immune systems will recover without further treatment.

If left untreated, the illness may last for a month or longer. Symptoms can sometimes go away and then return one or several times for weeks.

Is it contagious?

After the Cyclospora parasite leaves the body in feces, it needs several days outside the host to become infectious. For this reason, it is very unlikely one would contract the infection directly from an infected person, such as from a restaurant worker who doesn't wash his or her hands properly after using the toilet.

How can it be prevented?

Consumers can reduce their risk of infection by always washing their hands with soap before and after handling food.

All fruits and vegetables should be washed under running water before eating, cutting, or cooking. Firm fruits and vegetables, such as melons and cucumbers, should be cleaned with a produce brush.

Despite these precautions, it's not clear if all cyclospora can be completely eliminated from fresh food because the parasite is microscopically small. But thorough washing is thought to at least reduce the risk.

Sources:  Public Health Agency of Canada and the Centers for Disease Control