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When people talk about food-borne illnesses, they’re usually referring to harmful bacteria such as Listeria monocytogenes causing outbreaks of Listeria, which has led to massive recalls of salad greens, fresh herbs, ice cream, soft cheeses, frozen produce and meat products and more.
Parasites, which are organisms that live on or inside humans or animals, are less often talked about than other biological hazards — even though parasitic infections can be as prevalent and dangerous as many of those bacterial illnesses you hear about in the media.
People get parasites by eating contaminated food or drinking contaminated water. Parasites require a living host to survive, and can live inside people’s digestive systems for a long time undetected. They can also make you very sick, and their role in the threat to human health should not be minimized.
How do parasites get into food?
Most farm animals are treated to prevent parasitic infections, which makes transmission of parasites such as tapeworms and roundworms from meat products a rarer occurrence.
Although preventive measures can help stop biological contamination, parasites can enter food at any point in the supply chain: from farming and production, to delivery, to packaging, to the grocery store shelves.
Food could be washed in contaminated water, for example, then carry parasites from the water through the supply chain. The soil food is grown in could be contaminated, or parasites could be transferred from person to person by Food Handlers who are infected and don’t know it. By the time someone realizes they’re sick with a parasitic infection, they usually have little to no idea how it happened!
What are the most common food sources of parasites?
Here’s a breakdown of some of the most common food sources of parasites:
- undercooked pork
- other undercooked or raw meats, such as beef
- raw fruits and vegetables
- raw or undercooked freshwater or marine fish
- raw or undercooked crustaceans or mollusks
- raw aquatic plants such as watercress
- unpasteurized cider and milk
What are some of the most common parasites?
These foods can lead to dozens of different infections and illnesses when not handled and prepared correctly. Some of the parasites that affect humans via food or water are:
- Giardia: This is the most commonly identified intestinal parasite in Canada. It can come from drinking untreated water.
- Cyclospora: This parasite is passed to humans through contaminated food or water. The eggs are shed in the stool of infected people.
- Pinworms: These can be passed on to customers by Food Handlers who haven’t adequately washed their hands after using the washroom. Roundworms, a type of pinworm, are also commonly transferred to humans by the fecal-to-oral route.
- Tapeworms: These usually affect humans who ingest undercooked beef, pork or fish containing the larvae that later grow into full tapeworms inside a person’s intestines.
- Taenia: This is a type of tapeworm, often referred to as “pork tapeworm” since it generally comes from raw or undercooked pork products.
- Trichinella: Like tapeworms, these are ingested in larval form when people eat raw or undercooked meats.
- Toxoplasma: This parasite can come from both undercooked contaminated meat as well as raw produce that has been infected and not adequately cleaned before consumption.
- Anisakis: This worm can be found in sushi or sashimi that was not prepared properly. Undercooked marine fish (e.g. cod, flounder, haddock, Pacific salmon) and squid are the usual culprits.
- Phocanema: Like anisakis, these parasites are also transmitted to humans through raw or undercooked marine fish.
- Clonorchis and Paragonimus: Sometimes called flukes, these parasites originate from freshwater fish and crustaceans that have not been cleaned or cooked adequately.
- Cryptosporidium: This parasite infects humans who consume unpasteurized cider and milk, and raw or undercooked shellfish.
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What are the symptoms of food-borne illness caused by a parasite?
If you have a parasitic infection, you may exhibit no symptoms or mild ones. Your symptoms will depend on the type of parasite that’s making you sick. Some of these symptoms include:
- nausea
- lack of appetite and weight loss
- diarrhea
- abdominal pain and bloating
- weight loss
- fatigue and general weakness
Sometimes, parasites can even cause death to the people they’ve infected.
Parasites can be extremely difficult to get rid of once they’re in your body, so prevention is key.
How can I prevent food-borne parasitic infections?
Most instances of food-borne illness are caused by poor hygiene, ineffective cleaning and sanitizing and inadequate time and temperature control.
As many parasites are transferred in unsanitary conditions along the supply chain, if you work in a food business, you need to ensure you only accept foods from reputable suppliers — especially high-risk or potentially hazardous foods such as raw fish and shellfish, fresh pork or beef. Check these foods thoroughly before accepting them. With fish, touch it and smell it. It should not have a strong fishy odour, and it should be firm and springy to the touch.
Most parasites can be killed with thorough cooking processes — as a general rule, food must be cooked to a temperature of 74°C / 165°F or above (82°C / 180°F or higher in Manitoba). Remember to follow the safe food cooking temperatures of potentially hazardous foods! When it comes to sushi or sashimi, strict time and temperature controls must be maintained to ensure safety.
And the most effective way to prevent parasites? Wash, wash, wash your hands! The importance of proper hand washing cannot be overstated. Ensure all Food Handlers wash their hands, especially after using the washroom, for at least 20 seconds in hot water using liquid soap.
Preventing every food-borne illness — not just parasitic infections — and keeping customers safe should be the top priority for anyone who works in the food service industry.
In most provinces and territories in Canada, food businesses are required by law to have a certain number of staff members who have completed a government-approved food handler course, such as the Canadian Institute of Food Safety (CIFS) Food Handler Certification Course. Our comprehensive course covers everything you need to know about food-borne illness, including how to prevent biological contamination from food-borne pathogens such as parasites. Contact CIFS to enroll!
Frequently Asked Questions
How does the risk of parasitic infection from food vary between different regions within Canada?
The risk of parasitic infection from food varies between different regions in Canada due to several factors, including local wildlife, environmental conditions and food handling practices.
Coastal regions might see different types of parasites in seafood compared to inland areas where freshwater fish might carry different risks. Climate and temperature can also affect parasite prevalence and survival, influencing their presence in food sources.
Are there specific seasonal trends in the prevalence of parasitic infections related to food sources?
Yes, there are specific seasonal trends in the prevalence of parasitic infections related to food sources. For example, certain parasites in seafood might be more prevalent during warmer months when water temperatures are higher, which encourages their growth and reproduction.
Similarly, parasitic risks in fruits and vegetables can vary with seasonal changes in agriculture, such as different harvesting and irrigation practices. These seasonal trends can affect the likelihood of encountering parasites in various foods at different times of the year.
What are the long-term health implications of untreated parasitic infections acquired from food?
Untreated parasitic infections acquired from food can lead to long-term health implications. Chronic symptoms may include digestive issues, malnutrition, and anemia, as parasites can interfere with nutrient absorption.
Some parasites also cause organ damage or systemic effects, depending on the type of parasite and the duration of the infection. In severe cases, neurological symptoms can occur if parasites invade the central nervous system. Regular medical check-ups and treatment are essential to prevent these long-term complications.
