Parasites are organisms that live on or inside humans or animals. People can become infected with a parasite by eating contaminated food or drinking contaminated water.
While infections happen often — and parasites are especially tough to get rid of once they’re in your body — people usually refer to harmful bacterial pathogens like Listeria monocytogenes leading to outbreaks of Listeria, and grocery store recalls of staples like packaged salads and herbs, soft cheeses, ice cream and other frozen goods when they think of food-borne illnesses. Bacterial food contamination is the most prevalent cause of food-borne illness outbreaks across the world; however, parasites can do just as much damage.
To survive, parasites need a living host, and they can live inside humans’ digestive tracts for quite a while completely undetected. They can make you sick, too, and their role in the threat to human health is significant.
Contaminated water and soil can lead to infection
Most farm animals are treated to prevent parasitic infections, which makes transmission of parasites such as tapeworms and roundworms from meat products a rare 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 realises they’re sick with a parasitic infection, they usually have little to no idea how it happened!
Raw, undercooked foods are usually the culprits
Here are some of the most common food sources of parasites:
- undercooked pork
- raw fruits and vegetables
- raw or undercooked freshwater or marine fish
- raw or undercooked crustaceans or mollusks
- raw aquatic plants such as watercress
- unpasteurised cider and milk
- other undercooked or raw meats, such as beef
Parasites are more common than you think
Parasite-infested 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 one of the most commonly identified intestinal parasites in Australia, and it disproportionately affects children and rural Indigenous communities. 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 faecal-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 meats 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 unpasteurised cider and milk, and raw or undercooked shellfish.
Symptoms vary by parasite
If you have a parasitic infection, you may exhibit no symptoms, or mild ones, although sometimes, parasites can even cause death to the people they’ve infected. 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
- diarrhoea
- abdominal pain and bloating
- weight loss
- fatigue and general weakness
Parasites can be extremely difficult to get rid of once they’re in your body, so prevention is key.
Prevent parasites through safe food handling practices
Most instances of food-borne illness are caused by poor hygiene, ineffective cleaning and sanitising 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 an internal temperature of 75°C or higher, though different foods may have different temperature requirements. 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 your hands frequently and thoroughly! 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 Australia, the Food Standards Code requires anyone who works with food to be trained in food safety. Protect yourself and customers from food-borne illnesses with the Australian Institute of Food Safety’s (AIFS) comprehensive Food Safety Courses.
