Trichinosis, also known as trichinellosis, is a parasitic infection caused by roundworms from the Trichinella genus. Trichinella can infect wild animals and livestock and can spread to humans through the consumption of raw or undercooked meat. When infected with trichinosis, most people exhibit little to no symptoms. However, complications may occur in some people, particularly if the quantity of Trichinella in the body is high. Mild symptoms include nausea, diarrhoea, muscle and abdominal pain, headaches, fever, and swelling around the eyes; more severe symptoms include inflammation of the heart, brain and lungs, leading to respiratory difficulties, heart problems, seizures, and even death.¹ 

Due to the risk of transmission through meat, regulations on food safety have been implemented to prevent trichinosis outbreaks. Pork was historically the main mode of Trichinella transmission. However, successes in food safety regulations have eliminated domestic pigs as a reservoir for Trichinella, leaving wild game as the current main source of trichinosis outbreaks.² To understand the impact of trichinosis on food industry regulations, this article will explore the transmission of trichinosis, resulting food industry regulations, and the effectiveness of these regulations. 

What is trichinosis?

Trichinosis is a parasitic infection caused by roundworms from the Trichinella genus.

Trichinosis is a parasitic infection caused by roundworms from the Trichinella genus. There are several species of Trichinella, including:^2,3 

• T. spiralis- found in carnivores and omnivores worldwide, and is the most common agent of trichinosis
• T. pseudospiralis- found in mammals and birds worldwide
• T. nativa- found in Arctic and subarctic regions
• T. murelli- found in North America
• T. nelsoni- found in eastern and southern Africa
• T. britovi- found in Europe and western Asia
• T. papuae- found in Papua New Guinea and Thailand

Life cycle

Image: Trichinosis infection pathway. Diagram created using BioRender( free version.

Trichinosis is a zoonotic disease, meaning it can be spread from animals to humans. This typically occurs when a person eats raw or undercooked meat infected with Trichinella cysts – small sacs containing Trichinella larvae. The cysts are broken down by stomach acid, releasing Trichinella larvae to migrate and burrow into the small intestine lining. The larvae develop into adults and mate with each other. After one week, the now-adult Trichinella produce larvae, which burrow through the small intestine into the bloodstream. The larvae are carried throughout the body via the bloodstream. They burrow into muscle tissues and form cysts around themselves, where they can survive for months or even years.¹

Symptoms and prognosis

Trichinosis infection can be divided into two stages: enteral (through the gastrointestinal tract) and parenteral (outside of the gastrointestinal tract). The enteral phase lasts for approximately one week, from the release of Trichinella larvae from their cysts to the production of new larvae by the now-grown Trichinella. During this period, patients may experience nausea, diarrhoea and abdominal cramps. 

The parenteral phase begins around one week after infection. Trichinella larvae spread through the bloodstream to burrow into muscles around the body. This may lead to muscle pain, weakness, fever, headaches and swelling around the face and eyes. Some patients may also experience pink eyes and increased sensitivity to light. Without treatment, most symptoms disappear around three months after infection, as the Trichinella larvae form cysts around themselves and become inactive. However, some symptoms, such as muscle pain, weakness and diarrhoea, may persist for months to years after the initial infection. 

The severity of trichinosis depends on the quantity of Trichinella in the patient’s body. Patients infected with a small amount of Trichinella may experience mild symptoms. They are often able to recover without medical intervention. Patients infected with a large amount of Trichinella may experience severe pain and swelling, reducing their range of movement and interfering with daily activities, including eating and speaking. Complications may occur in patients with severe trichinosis. They may experience inflammation of the heart, brain and lungs, which may lead to respiratory difficulties, heart problems, and seizures. Rarely, such complications may result in death.^1,3

Mode of transmission

Trichinella larvae survive as cysts in the muscles of infected animals, allowing trichinosis to spread through the consumption of the contaminated meat. In the wild, carnivores, omnivores and scavengers may become infected after eating meat from infected animals. In domestic animals, pigs may become infected with Trichinella, along with horses in rare cases.² In humans, trichinosis may originate from various types of meat, including pork, horse, wild boar, bear, wild cat, fox, dog, wolf, seal and walrus meat. Eating meat prepared with equipment previously used on contaminated meat, such as butcher knives and meat grinders, may also lead to trichinosis. 

Pigs were historically the most common source of Trichinella transmission to humans, due to the now-banned practice of feeding pigs with raw meat scraps and animal carcasses. Exposure to infected rodents and wildlife may also cause Trichinella infection in pigs.⁴ However, stringent standards for pig-rearing facilities and individual testing of pig carcasses have significantly reduced the risk of Trichinella infection through pork.

Food safety regulations

As a foodborne disease, trichinosis can be prevented through the careful regulation and treatment of pork. Regulations may differ across countries. In the European Union and the United Kingdom, pig-rearing facilities are separated into controlled and non-controlled housing. Pigs in controlled housing are typically raised indoors. They are physically separated from wildlife and rodents, reducing the risk of exposure to infected animals. They are fed from certified sources, which are transported to the pig farm in a closed container to prevent infestation by rodents and wildlife. Dead animals are promptly transported off-site to minimise disease transmission. Traceability is also emphasised: pigs brought in from outside the pig farm must be raised under controlled housing conditions, with clear records of the pigs’ origins and movements. This minimises the exposure of healthy pigs to infected pigs. If a Trichinella outbreak does occur, keeping clear records of livestock movements also helps in tracking down the source of the outbreak and the potentially infected pigs.

In contrast, pigs in non-controlled housing are raised outdoors, including free-range pigs and those raised in backyards in rural areas. Due to potential close contact with infected rodents and wildlife, as well as difficulties in regulating their food sources, pigs from non-controlled housing are required to undergo individual carcass testing after slaughter. 

Individual carcass testing involves extracting muscle tissue samples from each pig carcass to test for Trichinella larvae. This enables the detection of infected pork, preventing it from being consumed by humans. Pigs reared in non-controlled housing are legally required to undergo testing, while pigs from controlled housing are considered low risk of Trichinella infection, so are exempted from testing. 

Farms with controlled housing are regularly audited to ensure they maintain standards and low infection rates. This provides economic incentive, as failure to maintain the above standards results in the facilities being relabeled as non-controlled housing. Farmers would be required to test their livestock, which is a time-consuming and costly process^4,5,6

Effectiveness

The effectiveness of food safety regulations is clear in the elimination of pork as a significant source of trichinosis in humans. In 2022, the European Union/European Economic Area had an extremely low incidence rate of 0.01 cases of trichinosis per 100,000 individuals, with sixteen cases due to the consumption of wild boar meat compared to only three cases due to domestic pork. All reported instances of Trichinella detected through individual carcass testing originated from pigs raised in non-controlled housing, while no trichinosis was detected in pigs raised in controlled housing.⁷ 

However, individual carcass testing produces a significant financial burden on farmers and governments that subsidise the tests, with a price tag of around US$570 million in Europe alone.² This has led experts to suggest expanding testing exemptions, removing the testing requirement for all domestic pigs in regions where trichinosis has not been consistently detected.⁶ While food safety regulations are effective in preventing trichinosis incidence from pork, reducing the impact of trichinosis on society, trichinosis testing of pigs places another burden on society. 

Summary

Trichinosis is a parasitic infection caused by roundworms from the Trichinella genus. There are seven confirmed species of Trichinella known to infect humans, with T. spiralis being the most common. Trichinosis spreads when a person eats raw or undercooked meat contaminated with Trichinella cysts, which are digested by stomach acid, releasing Trichinella larvae into the body. In domestic animals, trichinosis is typically spread to humans through pork. Fortunately, this has become less of a concern due to regulations in the food industry, which reduce the risk of Trichinella infection in pigs through environmental regulation. Pigs at higher risk of trichinosis are tested for Trichinella larvae before their meat can be sold. However, testing for Trichinosis infection in pigs is a time-consuming and costly procedure. It can be concluded that food safety regulations are mostly effective in reducing the impact of trichinosis on society.