What Foods Carry a Risk of Parasite Infection?

Foodborne parasitic infections are common, affecting at least 12 million people in the United States and more than 2 billion people worldwide. However, such infections often go undiagnosed due to poor awareness of these common microorganisms. 

Foodborne parasitic infections often stem from protozoa or intestinal worms getting inside the digestive tract via contaminated water, food, or exposure to feces. It’s vital to practice good hygiene, adopt food safety strategies, and know which foods to avoid with parasites. 

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Common Types of Parasites in Food

Parasites need a host to survive, grow, and spread. About 25% of the population worldwide has a parasite-related infection. The most common types of parasites found in foods are:

Protozoa

Protozoa are microscopic, one-celled organisms that can live in the intestines. Protozoa spread via contaminated water or food, insect bites, and person-to-person contact. Tens of thousands of types of protozoans exist, including:

• Ciliates: ciliates, including B. coli, contain short, hairlike structures that allow these parasites to gather food and move. 
• Amoeba: amoebas, including E. histolytica, use false feet used to move.
• Sporozoans: sporozoans, such as cryptosporidium and plasmodium, don’t move on their own but eat the digested food or body fluids of their host.
• Flagellates: flagellates, including giardia and toxoplasma, use whip-like structures to move and explore their surroundings.

Helminths

Helminths are parasitic worms that can live in the gastrointestinal (GI) tract, including the stomach and small and large intestines. Parasitic worms may be visible to the naked eye.

 Examples include:

• Tapeworms: flat, long worms that live in the intestines and feed off nutrients in their host’s food. The eggs they lay spread through infected water or foods like undercooked fish, beef, and pork.
• Flukes: flatworms that spread via aquatic animals (crabs, fish, snails, etc.), aquatic plants, and contaminated water. 
• Roundworms: parasites that live in the intestines and spread via foods (particularly pork), infected soil, and feces.  
• Pinworms: threadlike worms that spread through eggs in feces. 
• Ascaris: worms that resemble tiny earthworms and spread via contaminated soils and produce grown in these soils.
• Strongyloides: worms that spread through contaminated soils.
• Hookworms: worms with hooklike heads that attach to the intestines and spread through contaminated soil. 
• Whipworms: worms with a whiplike shape that spread via contaminated soil. 

How Are Parasites Transmitted Through Food?

Parasites spread by laying eggs, feces, and contaminated food or water. Risk factors for parasite transmission through foods include:

• Lack of proper hand washing before preparing or eating foods
• Not thoroughly cooking foods
• Lack of hand washing after using the bathroom
• Weakened immune system
• Infrequent showering or bathing
• Touching the hands to the mouth 
• Being in areas known to contain parasites

The risk of intestinal parasites increases in humid and warm climates, such as subtropical and tropical areas (Asia, Latin America, sub-Saharan Africa, and the Caribbean) and in rural areas in Appalachia and the Southeastern United States. 

Warm and humid climates, especially tropical and subtropical areas, including sub-Saharan Africa, Asia, Latin America, and the Caribbean (Strongyloides is more common in rural areas in the Southeastern U.S. and Appalachia

Reducing the risk of parasitic infections from food includes frequent hand washing, wearing gloves when preparing food, and thoroughly cooking foods — particularly meats.

Which Foods Carry a Risk of Parasitic Infection?

Foods that carry a higher risk of parasitic infection include:

Raw or Undercooked Meat

Not thoroughly cooking meats is a risk factor for parasitic infections through foods. Examples of specific parasites linked to raw or undercooked meat (beef, wild game, pork, or lamb) include:

• Trichinella
• Taenia
• Toxoplasma 
• Giardia

Thoroughly cooking meat can kill parasites and prevent an infection. 

Raw or Undercooked Fish and Seafood

Consuming raw or undercooked seafood is also a risk factor for foodborne illness and intestinal parasites. Examples of high-risk foods include sashimi, sushi, ceviche, and similar dishes. 

Common parasites in fish and seafood include:

• Anisakis
• Diphyllobothrium
• Eustrongylides
• Gnathostoma
• Clonorchis
• Opisthorchis
• Heterophyes
• Metagonimus
• Paragonimus
• Nanophyetus

Use caution when consuming undercooked fish and seafood, or simply cook these foods before eating them. 

Unwashed Fruits and Vegetables

Fruits and vegetables can carry parasites if exposed to contaminated soil or water and remain raw or unwashed. Cook fresh produce or thoroughly wash fresh fruits and vegetables.

Examples of the most common parasites on fruits and vegetables include:

• Giardia
• Cryptosporidium
• Cyclospora
• Entamoeba histolytica
• Ascaris lumbricoides
• Entamoeba coli 

Unpasteurized Dairy Products

Intestinal parasites that can affect dairy cattle include:

• Tapeworms
• Flukes
• Roundworms

Consuming unpasteurized milk, cheese, and other dairy foods can be risky. Always choose pasteurized products when consuming dairy foods. Check the food label to be sure. 

Other High-Risk Foods

Other high-risk foods are those potentially exposed to contaminated water or prepared in unsanitary conditions. Examples of such higher-risk foods include:

• Unpasteurized ciders
• Other unpasteurized juices
• Watercress
• Raw aquatic plants
• Raw eggs
• Chicken

Tips for reducing the risk of parasitic infections include purchasing pasteurized juices and milk and thoroughly washing fresh produce before consumption.  

Lab Testing for Parasitic Infections

Lab testing for parasitic infections allows providers to properly diagnose a patient's condition and determine the most effective treatment plan. 

Lab testing and other tests for parasites include:

Stool Tests

Stool tests can diagnose parasites, particularly helminths and protozoa, that live in the intestines. Some of these tests require three or more stool samples during the course of several days. They detect parasites or their eggs.

Top Stool Tests for Detecting Parasites:

• GI Effects® Comprehensive Profile - 3 day by Genova Diagnostics
• Comprehensive Stool Analysis + Parasitology - 3 Day by Doctor's Data
• Comprehensive Stool Analysis by Access Med Labs
• Comprehensive Stool Analysis by Mosaic Diagnostics (formerly Great Plains)

Blood Tests

Parasitic blood tests, such as serology are used to screen for antibodies in the blood. A blood smear showing parasites can be viewed under a microscope.

Top Blood Smear Test:

• Blood Parasite Smear by Access Med Labs

Colonoscopy or Enteroscopy

Colonoscopies and enteroscopies use long, flexible tubes with an attached camera to view the inside of the digestive tract and look for signs of intestinal parasites. 

Imaging Procedures

X-rays, an MRI, a CT scan, or other imaging procedures can detect intestinal damage caused by parasites. 

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When is Lab Testing Necessary?

Situations that warrant lab testing include patients with persistent symptoms, those with weakened immune systems, and individuals with high-risk exposures. Examples of symptoms of parasitic infections include:

• Bloating
• Gas
• Abdominal pain
• Diarrhea
• Vomiting
• Nausea
• Anal itching
• Blood or mucus in the stool
• Fever
• Weight loss
• Foul-smelling or greasy, floating stools
• Electrolyte imbalance
• Dehydration

Obtaining an extensive medical history is vital to guide diagnostic testing, including which labs are the most appropriate and what the results mean. 

How to Understand Lab Results

Proper interpretation of parasite lab testing results is crucial to determine if a patient has (or doesn’t have) parasites or eggs in their body.

• Negative result: there are no eggs or parasites present or there aren’t enough to show up in the test. 
• Positive result: confirms the presence of parasites or their eggs. The result shows the type and number of parasites (or eggs) present in the body. 

Treatment recommendations and follow-up testing are important to eliminate intestinal parasites that cause bothersome symptoms or complications. 

The Benefits of Early Detection

Early lab testing can lead to prompt treatment and a lower risk of parasite-linked medical complications, such as dehydration, malnutrition, pancreatitis, dysentery, iron-deficiency anemia, gallbladder inflammation, appendicitis, and organ damage. 

Lab testing in public health and food safety settings is important to prevent the spread of parasites and communicable diseases. 

How to Prevent Parasitic Infections from Food

There are several ways to reduce the risk of parasitic infections from food.

Always Use Safe Food Handling Practices

Safe food handling practices lessen the chance of intestinal parasites and other foodborne illnesses. Cook foods, particularly meats, chicken, fish, and seafood, to safe temperatures of:

• Ground poultry: 165 °F
• Leftovers: 165 °F
• Casseroles: 165 °F
• Poultry: 165 °F
• Eggs: 160 °F
• Ground meats: 160 °F
• Pork, beef, lamb, veal, chops, and roasts: 145 °F
• Ham: 145 °F
• Fish: 145 °F
• Shellfish: 145 °F

Use a meat thermometer to measure the internal temperature of the center of meat, poultry, fish, or seafood. Thoroughly wash all produce and choose pasteurized milk, milk products, and juices. 

Food safety recommendations, particularly in commercial food service settings, include frequent handwashing, wearing gloves, and sanitizing dishes after each use. Commercial kitchen areas should be kept clean.

Ensure Consumer Awareness and Education

Educating the public about the risk of foodborne parasites, including symptoms to watch for, ways to cook food properly, and when to get tested for intestinal parasites, is important. Many people do not realize they have intestinal parasites, and practitioners might not know to test for them, without increased awareness. 

Take Public Health Measures

Public health measures include following food safety and sanitation regulations and scheduling routine inspections to reduce foodborne parasites. Collaboration between healthcare professionals and public health agencies is crucial for preventing and prompt identification of foodborne contamination. 

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Key Takeaways

The following food safety tips reduce the risk of a parasitic infection:

• Foods to avoid with parasites include raw or undercooked meats, poultry, fish, seafood, and eggs. 
• Don’t eat unwashed fruits and vegetables.
• Avoid unpasteurized milk and juices.
• Cook all meats to the recommended internal temperatures to kill any parasites. 
• Follow safe food handling practices.

Consider lab testing for early detection of intestinal parasites and seek medical advice at the first sign of a parasitic infection.