Eating contaminated food is one of the most common ways to get intestinal worms, also known as helminths. There are many different types of worms that can infect humans, with the most common being roundworms, tapeworms, hookworms, whipworms and pinworms. While some worms may only cause mild symptoms, others can lead to malnutrition, anemia and more serious complications if left untreated. Understanding what foods are more likely to contain worm eggs or larvae can help you take precautions to avoid infection.
Undercooked Meat and Fish
Consuming undercooked or raw meat and fish is one of the leading causes of food-borne parasitic infections. The larvae and eggs of certain worm species can be killed by thorough cooking, but may survive in meat that is rare, medium-rare or lightly pickled, smoked or marinated. Types of worms that can be transmitted through undercooked meat and fish include:
- Trichinella spiralis – Causes trichinosis from eating undercooked pork or wild game infected with the larvae. Can lead to muscle pain, fever, diarrhea and weakness.
- Taenia solium – Pork tapeworm transmitted through undercooked pork. Can cause digestive issues and cysts in organs if larvae migrate.
- Diphyllobothrium latum – Fish tapeworm spread by eating undercooked or raw freshwater fish like salmon, trout and perch. Often asymptomatic but can cause vitamin B12 deficiency.
- Gnathostoma species – Found in undercooked fish, eel, frog and chicken. Causes stomach pain, nausea and skin rashes as larvae migrate through the body.
- Anisakis species – Parasitic roundworms transmitted through raw or undercooked saltwater fish like cod, salmon and herring. Can embed in the digestive tract, causing severe abdominal pain.
To kill any potential worm larvae or eggs, meat and fish should be cooked to an internal temperature of at least 145°F. Fish should appear opaque and flake easily with a fork when fully cooked. Use a food thermometer to verify temperature, and avoid any raw or rare meat, fish or shellfish.
Unpasteurized Dairy Products
Drinking raw, unpasteurized milk or eating certain soft cheeses made from it can expose you to worms through fecal contamination. Types of helminths that can be transmitted in this way include:
- Toxocara species – Roundworms that can cause vision loss and respiratory symptoms as larvae migrate through tissues.
- Echinococcus granulosus – Tapeworm that forms cysts in organs that can be fatal if they rupture.
- Fasciola hepatica – Spread through watercress and can cause liver abscesses and damage.
Make sure any dairy products you consume are pasteurized to kill potential worm eggs and larvae. Soft cheeses made from unpasteurized milk that could pose a risk include brie, camembert, blue cheeses, queso fresco and panela. Avoid unpasteurized milk and milk products when traveling in developing regions.
Contaminated Produce
Fresh fruits and vegetables can become contaminated with worm eggs, larvae or cysts through contact with infected feces from animals or humans. Examples include:
- Ascaris lumbricoides – One of the most common human intestinal roundworm infections transmitted through contaminated produce.
- Strongyloides stercoralis – Tiny roundworm that enters through unclean hands and contaminated soil clinging to raw vegetables and fruit.
- Taenia solium – Tapeworm eggs that can contaminate vegetables fertilized with human feces.
Thoroughly rinse, peel and/or cook produce to reduce risk. Grow fruits and vegetables at home using proper composting methods or certified fertilizers to avoid contamination. Wash hands after gardening or handling soil and before preparing food.
Undercooked Vegetables
Some vegetables can harbor worm larvae or eggs internally that may survive if not thoroughly cooked. At higher risk are vegetables that grow underground and may come in contact with feces through contaminated soil, such as:
- Carrots
- Potatoes
- Radishes
- Turnips
- Cabbage
- Broccoli
- Cauliflower
Wash vegetables carefully, peel when possible, and cook until soft to ensure any internal worm eggs or larvae are killed. Discard outer leaves of leafy greens and thoroughly wash produce even when peeling.
Contaminated Water
Drinking or washing foods with water contaminated with human or animal feces can spread worm cysts, eggs and larvae. Water can become contaminated through:
- Sewage runoff
- Improper disposal of human feces
- Infected livestock and pets
- Poor sanitation practices
At higher risk are raw foods washed in contaminated water, including salads and other produce eaten raw. Only drink clean, safe water from a sealed bottle, boiled or otherwise purified. When in doubt, peel produce or cook it thoroughly.
Improperly Handled Food
Foods prepared, handled or stored in an unsanitary environment can also transmit worms through cross-contamination. Risks include:
- Food prepared by infected handlers who do not wash hands properly after using the bathroom.
- Kitchen surfaces, cutting boards and utensils not cleaned thoroughly after handling raw meat, fish or contaminated produce.
- Prepared foods left sitting out for extended periods at room temperature.
Follow food safety basics like washing hands and surfaces often, separating raw and cooked foods, cooking foods thoroughly and refrigerating perishables promptly to avoid spreading worm eggs and larvae through food.
Foraging Plants, Berries and Mushrooms
Wild plants, berries and mushrooms foraged in areas contaminated by infected animal or human feces can also transmit worms. At higher risk are foraged foods that grow close to the ground and may not be thoroughly cooked. Only forage in known clean areas away from livestock, and cook foods thoroughly. Soaking in salt water for 30 minutes may help remove some worm larvae.
Imported Foods
Foods imported from regions with poor sanitation and agricultural practices may be more prone to worm contamination and infection. Higher risk imported foods include:
- Fresh produce
- Raw nuts and grains
- Unpasteurized cheeses
- Raw fish for sushi and sashimi
- Spices and herbs
When preparing imported higher-risk foods, take extra precautions like:
- Washing thoroughly
- Peeling when possible
- Cooking thoroughly
- Freezing fish to kill parasites
Pickled, Smoked or Dried Foods
Traditional preservation methods like pickling, smoking or drying may not always kill worm eggs and larvae. Contaminated foods may include:
- Pickled vegetables and fish
- Smoked meat and fish
- Dried fish
- Salted meats like ham or prosciutto
- Fermented foods
Cooking these foods thoroughly before eating can provide added protection against potential worm infection.
Wild Game
Hunting wild game in areas where worms are common exposes the meat to potential contamination. At higher risk is wild boar, which can harbor worms like:
- Trichinella
- Toxoplasma
- Taenia solium
Thoroughly cook all wild game to an internal temperature of 165°F. Freezing meat for an extended time at subzero temperatures may also kill some worms.
Foraged Wild Mushrooms
Wild mushrooms picked in contaminated areas may contain worm larvae that can survive cooking. Safest options include:
- Cultivating your own mushrooms from sterilized soil.
- Purchasing commercially grown mushrooms.
- Picking morels and other mushrooms only in known clean locations.
- Cooking wild mushrooms thoroughly.
Avoid foraging where animals graze, and wash mushrooms thoroughly before cooking. Peeling caps may reduce exposure to potential surface contamination.
Unsafe Food Handling When Camping or Backpacking
When camping or backpacking, eating raw foods and drinking unpurified water can increase risk of worm infections if precautions are not taken. Tips include:
- Cook meat, fish and eggs thoroughly.
- Wash hands and cooking surfaces often.
- Drink only purified water.
- Wash fruit and vegetables with purified water or peel when possible.
- Use proper waste and toilet hygiene to avoid contaminating water and soil.
Take care not to contaminate cooking areas with waste, and pack out all trash to avoid spreading eggs and larvae in the wilderness through poor disposal practices.
Commercially Raised Fish
While commercial aquaculture and raising fish in enclosed tanks reduces exposure to parasites, farmed fish can still contract worms in densely populated conditions. Fish at higher risk when eaten raw or undercooked include:
- Salmon
- Cod
- Tuna
Cooking farmed fish thoroughly, or freezing fish for at least 7 days at subzero temperatures before eating raw, can kill any potential worm larvae and eggs.
Street Foods and Buffets
Foods prepared and served outdoors by street vendors or left sitting for extended periods at buffets are at higher risk of worm contamination due to potential for:
- Use of contaminated water in preparation
- Unsanitary handling and storage
- Exposure to flies and other insects that can spread worm eggs
Opt for cooked foods over raw when eating street food or buffet meals, avoid anything that appears spoiled, and use caution when traveling in areas with poor food sanitation and hygiene. Washing hands before eating can also reduce risk of contamination from handling food.
Conclusion
While eating contaminated food is a common route of infection for intestinal worms, taking precautions when handling, preparing and consuming higher risk foods can greatly reduce your chances of getting worms from your diet. Cooking food thoroughly, drinking clean water and adhering to general food safety best practices are key preventive measures. Understanding which foods may be more prone to carrying worm eggs, larvae or cysts allows you to make informed choices and take proactive steps to avoid parasitic infections.