Difficult to diagnose | Parasites survive a long time in food and the environment and can cause severe sickness and death

TORONTO — Canadians do not usually get parasites.
However, the risk of picking them up and getting a mild to severe illness increases as people travel more and eat different foods.
“In Canada we are fairly fortunate, they are not known to occur here,” said Alvin Gajadhar, a parasitologist at the Canadian Food Inspection Agency.
“If they do occur there, they are sporadic or very limited.”
Parasites are different from bacteria and viruses because only a few of these tiny organisms can cause problems, he told a Canadian Meat Council food safety symposium held in Toronto Oct. 2-3.
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Two of these, toxoplasma and trichinella, are among the World Health Organization’s Top 10 serious parasites capable of harming people.
The United States reports that toxoplasmosis is the leading cause of death attributed to food-borne illness and estimated that as many as 60 million people are carrying it.
Few exhibit symptoms because their immune systems keep it in check.
Parasites are hard to diagnose, and conventional disinfections are often ineffective. As a result, they need to be controlled by other means in the food production chain.
They tend to survive a long time in food and the environment. As well, there is no good prevalence information in this country.
“The tests often lack sensitivity and specificity and there is a lack of surveillance data,” Gajadhar said.
Toxoplasma gondii is shed by cats and can be picked up by rodents, wildlife, birds or earthworms. It can also affect cattle, sheep, pigs and chickens.
“Once it is in the environment, it is very difficult to clean up,” he said.
Cats can shed millions of oocysts in a matter of days. However, the shedding only happens for a brief period of time.
It can survive in the sewers when cat litter is flushed down the toilet.
“These oocysts stick around for a long, long time, especially in a moist environment,” he said.
It can survive in a wide range of cold to warm temperatures, but research has shown an iodine based disinfectant is effective.
Children can pick it up playing in a sandbox where a cat defecated, and it can be particularly dangerous for pregnant women.
Infection in pregnant women can result in abortion or stillbirth or the child may develop encephalomyelitis, hydrocephalus or vision problems.
It has also been recognized as a leading cause of schizophrenia, depression, anxiety and suicidal tendencies.
Trichinella, the other serious infection, has been known for more than 150 years and was often picked up when eating undercooked pork. Testing meat started soon after.
No cases have been found in Canada for decades, but its risk should not be ignored.
“Just because we don’t have any trichinella cases in Canada does not mean it is not a risk,” Gajadhar said.
Pigs, bears, foxes, dogs, wild boars and rats can have forms of trichinella. Pigs are infected with the tiny nematode T. spirallis.
“Humans are highly susceptible to disease from trichinella infection,” he said.
It is a prolific producer of new-born larvae, which enter the bloodstream and then travel to the muscle cells for two to five years before they die.
The symptoms include muscle aches, inflammation, fever, diarrhea and food poisoning.
“Most physicians will not know this,” he said.
People may not recognize it because they think it is not in Canada.
Control measures for hog production include control of garbage feeding ,which is illegal in Canada, rodent control, controlled animal housing, good husbandry practices and producer education.
Meat packing plants can test for it and show it is not present. At the same time, testing may catch other parasites.
“Documenting that you don’t have it is important,” Gajadhar said.
It also important for slaughter plants to identify all animals and know where they came from.
Consumer education continues to be important. Proper cooking can kill it, and in some cases freezing meat works well.
- drinking water contaminated with toxoplasma gondii
- eating undercooked, contaminated meat, especially pork, lamb, and venison
- accidental ingestion after handling contaminated meat and not washing hands thoroughly
- using knives, utensils and cutting boards that have had contact with raw, contaminated meat
- mother-to-child (congenital) transmission
- accidentally swallowing the parasite through contact with cat feces that contain toxoplasma This might happen by:
- cleaning a cat’s litter box when the cat has shed toxoplasma in its feces
- touching or ingesting anything that has come into contact with cat feces that contain toxoplasma
- accidentally ingesting contaminated soil, such as by not washing hands after gardening or eating unwashed fruits or vegetables
