Overview

The most common source of infection by Trichinella is from eating raw or undercooked meat from infected game animals or pigs grown in conditions that favour the presence of rodent populations. Pigs produced in outdoor farming methods are clearly at risk of contracting Trichinella spp infections. 

In this article, we will review the safe meat handling practices used to reduce the risk of contracting Trichinosis from meat.

Is trichinosis a disease?

Trichinosis, a common zoonotic illness strongly linked to dietary and cultural behaviours, is caused by the worm Trichinella spp. Meat that has been undercooked and contains infected encysted larvae can infect humans.²

The first cases of trichomoniasis were identified in 1962 in individuals who had eaten pig flesh.¹

Rodents and pigs are important in the disease's transmission.

It is frequently stated that human sickness can develop from consuming a meal of diseased meat that has as few as one larva per gram of tissue.⁷

Signs and symptoms

People who contract trichinosis can be asymptomatic, or if the infection is mild, they may have nausea and diarrhea.

In severely infected individuals, frequent complaints or signs include headache, vertigo, tinnitus, deafness, aphasia, convulsions, and abnormalities related to peripheral reflexes, among others.⁴

How to prevent trichinosis?

You can prevent trichinosis infection by taking the following steps:

• avoid the consumption of contaminated meat
• destruction of the parasite by heating, freezing, curing, and drying
• following pig feeding guidelines
• control of mice and rats on farms 

Educating the public about this illness and how to prevent it is also important in reducing the number of infections caused by consuming raw or undercooked meat.

Treatment of choice

You can read more about the treatment options for trichinosis here.

The condition is treated with antiparasitic drugs or anthelmintics (drugs to treat parasitic worm infections). 

Thiabendazole, albendazole and mebendazole are usually administered as a first-line treatment to prevent the development of the larvae into the adult form. Levamisole and mantel may be used only against adult Trichinella.

Safe meat handling practices

Pork prepared according to the guidelines established by the Food Standards Agency (FSA) in the UK (cooking, curing, including smoking and freezing) and labelled to the effect that such food may be consumed without further processing can be considered safe and can be eaten.³

Management of animals on the farm

Animals must be raised using controlled management techniques, such as controlled housing systems, to prevent exposure to Trichinella infection sources. These are discussed below. Routine audits can be performed to confirm the status of pigs in regulated management, low-risk herds, or compartments.⁶

Requirements for producing pigs with a low risk of trichinella

• Controlled housing: physical barriers in swine housing keep pigs separate from wildlife, notably birds
• Feed and feed storage: feed ingredients are kept in sealed silos or containers that keep rodents and other wildlife out
• Rodent control: a document provided by the production facility's employer should show no signs of an active rat infestation
• Hygiene control: ensuring that new animals are introduced exclusively from facilities with comparable hygiene standards
• Farm hygiene: dead animals are removed from pig housing areas and disposed of off-site, or they are held in animal-proof containers before being removed from the grounds

Control of trichinella in pork by testing

Pigs raised in controlled housing do not need to be tested for Trichinella. Pigs not raised in controlled housing environments must be tested before they can enter the food chain. In the UK, the methods for testing are set out in the retained EU law, Regulation 2015/1375. 

Improved testing procedures have been developed to allow meat producers to test for Trichinella on-site. The previous approach of compressing small bits of pig muscle between two glass slides and inspecting under a microscope was extremely time-consuming.

The single most significant innovation in the direct detection of Trichinella spp. in pig muscle was the creation of the pooled sample (magnetic stirring) digestion method (Zimmermann, 1967). This test combines the capacity to evaluate several samples with digestion in acidified pepsin.⁷

What type of meat is consumable?

Raw meat remains fresh and safe if stored for less than 2 days between 0 °C and 5 °C, or for three months at 18 °C ¹³

Pre-cooked raw meat is safer and tastes better.

Packed and labelled products are to be consumed as per the label, as this informs consumers about ingredients and allergens.

Practices to be followed regarding raw meat

The USDA (2005) states that there are three safe methods for thawing raw meat: in a refrigerator, in cold water in a leak-proof container, or a microwave if cooking is to be done right away. Since it is dangerous to leave meat above 5 °C, it should never be thawed on the counter or in hot water.

• Prevent cross-contamination from cutting boards and hands if not washed properly
• Ensure sufficient cooking, particularly when a larger portion is stir-fried
• The use of thermometers should be encouraged
• Throw away any leftover meat that has been at room temperature for more than two hours or refrigerated for more than four days
• Training food handlers on operating behaviours
• Promoting hygiene and safety practices among street food vendors in townships is crucial for ensuring the well‐being and health of the community ⁹ 
• Meat should be refrigerated within 2 hours after purchase and kept separately to prevent juices from dripping onto other foods¹³

Recontamination

Recontamination can occur at any point along the slaughter, fabrication, or subsequent processing line; therefore, meat facilities must use a variety of technologies and policies aimed at eradicating pathogens.¹²

 To reduce the risk of recontamination, there are four simple steps to follow: clean, separate, cook and chill. These will be discussed in turn below.

Clean

• Before and after handling the meat, wash your hands well with warm water and soap for at least 20 seconds
• After preparing each food item, thoroughly clean your cutting boards, dishes, utensils, and surfaces with hot, soapy water
• Consider using paper towels to wipe kitchen surfaces
• When opening canned products, remember to clean the lids first

Separate

• Keep raw meat apart from other foods in your refrigerator, grocery bags, and shopping cart
• Use a different chopping board for raw meat and other items, and another one for fresh produce

Cook

Texture and colour are not always dependable markers of safety. To eliminate any dangerous microorganisms, these items must be cooked to a safe minimum internal temperature. When reheating, always boil gravy, soups, and sauces.

Safe minimum internal temperatures

The safe minimum internal temperatures for pork are listed below:

• Pork: 63°C (chops, roasts, steaks) 
• Ground Meat: 71°C
• Ham, uncooked: 63 °C 
• Ham, fully cooked: 74°C

Raw pork

At the grocery store, choose pork right before you check out. When possible, place raw pig items in throwaway plastic bags to prevent leaks that can contaminate produce or cooked, ready-to-eat foods. Bring the pork home right away and store it in the refrigerator, chilled to at least 5 °C. Use it within the use-by date, or if purchased from the butcher, keep for up to 2 days. Pork can also be frozen on any day before the use-by dateUse within three months to maintain the quality.¹⁵ 

Ready-prepared Pork

Use cooked pork within 2 hours (or 1 hour if the ambient temperature is higher than 32 °C or store it in shallow, covered containers in the refrigerator at 5 °C or lower.

Eat cold or reheated to 74 °C (hot and steaming) within 3–4 days. Prepared pig meals can be safely frozen. Use within three months to maintain the quality.

Safe thawing

Pork can be safely thawed in three different ways: in the microwave, in cold water (in an airtight or leak-proof bag), or in the refrigerator. The best course of action is to thaw slowly and safely in the refrigerator. By following this method, raw pig can be safely thawed in the fridge for three to five days before cooking.

Frozen pork can be safely cooked in the oven, on the stove or a grill without first defrosting; however, the cooking time may be a little longer. Slow cookers should not be used to cook pork from frozen.

Marinating

Marinate pork for up to five days in a sealed jar in the refrigerator. Before brushing the cooked pork with the marinade, bring it to a boil. Throw away any marinade that hasn't been cooked.

Irradiation

The Food and Drug Administration and FSIS have approved the use of low doses of radiation to reduce trichinella in pigs. Even though treated pork is not sterile, it still needs to be handled carefully. Trichinella might be alive, but it couldn't reproduce. For easy identification at the store, packages containing irradiated pork must be labelled with the irradiation logo and the words "Treated with Irradiation" or "Treated by Irradiation."

Partial Cooking

Pork can be safely microwaved or partially precooked before being moved to a hot grill to continue cooking.

Safe Cooking

For safety, the USDA recommends cooking ground pork patties and ground pork mixes like meat loaf to 71 °C.

Cook all organs and variety meats (including heart, kidney, liver, tongue, and chitterlings) to 71 °C.

Cook raw pork steaks, chops, and roasts to a minimum internal temperature of 63 °C. Always use a meat thermometer.

Can Pork be pink when cooked safely?

Even after the meat has reached a safe internal temperature, cooked muscle meat may still be pink. Even though it can still be pink in the middle, fresh pork should be fine if it has reached 63 °C throughout.

Microwave cooking is not entirely efficient in eliminating larvae in large chunks of meat, such as a complete fresh gammon, because there are unavoidable 'cold spots' in the pattern of the microwave beam.

Microwave Directions

• Pork slices of varying sizes should be arranged in a dish or on a rack with the thicker portions on the exterior and the thinner portions in the middle when cooking in a microwave on medium-high or medium power
• Put a roast in a covered saucepan or an oven cooking bag
• For recommended cooking times, consult the microwave oven's manufacturer's instructions
• Use a food thermometer to test 

Chilling/Freezing the meat - is it effective?

The effectiveness of freezing to kill Trichinella larvae varies based on freezing temperature, storage time, Trichinella species, and host animal. However, freezing at -18°C or -21°C for one week efficiently kills Trichinella spiralis and Trichinella britovi in contaminated meat.⁵ Use the following guidance when freezing pork:

• Refrigerate or freeze meat within two hours of cooking or purchasing¹¹
• If the outside temperature surpasses 32 °C, refrigerate within an hour 
• Never defrost food at normal temperature, such as on a countertop
• To ensure the larvae's demise, all pork products should be fully frozen before cooking
• Cooking meat at 58 °C for 10 minutes will also kill larvae 
• Freezing muscle tissue from game animals (e.g., black bear, raccoon, or opossum) is not effective because it is thought that the antifreeze protein molecule common to most wild animals also protects worms in their muscle tissue from ice crystal formation and even preserves the worms in carcasses⁴

Summary

Outbreaks are still associated with immigrants or ethnic groups who enjoy raw or undercooked pork or its components, while wild animals may also serve as carriers. Better prevention and control of trichinosis necessitate health education to discourage the consumption of diseased and undercooked meat. Community-level prevention relies on good animal husbandry and excludes raw meat from all farm animals' diets, particularly pigs. Pork should be regarded as safe for human consumption in both domestic and international markets when controlled management is implemented following the previously mentioned criteria.