Introduction

The disease Trichinosis, also called trichinellosis, is caused by a parasitic roundworm within the genus Trichinella and has been a public health problem for more than 170 years.¹¹ The disease is transmitted to humans by eating raw or undercooked animal meat that contains the Trichinella larvae.¹ After the ingestion of the infected meat, digestion releases the larvae into the stomach, and they mature into adults in the intestine. The adult Trichinella then reproduce, and their larvae travel through the bloodstream till they reach the muscles, where they form cysts. These larvae then live inside the cyst for years until they are consumed along with their residing muscle by the predator of their host, and further repeating the cycle.¹¹

Animals do not show much visible symptoms when infected with Trichinella but humans can experience nausea, diarrhea, fatigue, fever and abdominal discomfort early in the Trichinosis disease progression.^{3, 11} Trichinosis progress to include symptoms such as headache, chills, cough, swelling of the face and eyes, joint, muscle pain, itchy skin, and digestive issues.³ In some instances, the ailment could become life-threatening, especially for elderly individuals, through the involvement of neurological, cardiac, and vascular complications. The occurrence of these complications varies from outbreak to outbreak, with some having neurological complications in <35% cases and 5-20% of cases having cardiac/vascular complications. Factors observed to affect the severity of infection depend on the number of larvae ingested, alcohol consumption during meals, overall health of the individual and which species of Trichinella is involved.⁶

Global burden of trichinosis

Trichinosis is a worldwide disease affecting both humans and animals. It can affect domestic animals such as pigs, horses and dogs as well as, wild meat-eating animals such as bears, wild boars, and walruses.³ Globally, there are about 10,000 recorded cases per year.³ This figure may be underestimating the real disease burden as many go undiagnosed or misattributed to other illnesses, since symptoms of the disease are non-specific and awareness is lacking. It is estimated that 11 million people worldwide might possibly be infected with Trichinella species.⁶ There are about 10,000 recorded cases in the world per year.3 The death rate with the disease is low at 0.2% but severe complications can be fatal, and the actual chance for death differs from outbreak to outbreak.⁶

Endemic regions and risk factors

Europe

Historically, trichinosis was once a major concern in Europe. In 1992, with the implementation of the European Union’s requirement to examine wild boar, domestic pigs and horse meat before processing them for human consumption, there has resulted in a sharp decline in the cases.¹ Currently, the main driver for contracting trichinellosis is travelling to endemic regions.¹

In Europe, countries that usually have a prevalence of trichinosis include the south-east Balkan countries such as Bulgaria, Romania and Serbia. Major sources of infections are from small private farms that are not subjected to parasite testing.¹ Furthermore, there are certain cultural practices that are linked to the disease. In Romania, for example, the region with the highest prevalence of human trichinosis is the Transylvania region, where a local ethnic group had the habit of eating raw meat.¹ Also, historical trends of cases in Romania show seasonal variations, with an increase in the month of June, which coincides with wild boar hunting seasons, while the peak diagnosis in January is linked to the Romanian winter tradition of pig slaughtering and the preparation of smoked raw sausages.¹⁰ The observed grouping of the many cases might be attributed to the tradition of “pig’s alms”, where people share a Thanksgiving meal offered to relatives, friends and neighbours who help in the slaughtering of the pigs.¹⁰

Other European countries that might not be currently endemic that have unique historical sources of the parasite include France, which eats raw horse meat, and the Slovak Republic consumes dog meat.

Asia

A major hot spot for trichinosis is the region of Asia. China in particular have one of the highest numbers of cases worldwide, and Southeast Asian countries such as Cambodia, Laos, Thailand, and Vietnam also experience frequent outbreaks.^4,7

Trichinosis is a major public health concern in China, with over 40 million individuals at risk of being infected.⁶ Historically, from 1964 to 2011, over 600 outbreaks were documented, and trichinosis became one of the top three parasitic diseases in the country from 2001 to 2004. Recently, outbreaks have often occurred in the Yunnan Province.⁴ Key contributing factors are pig breeding and dietary habits, which include consumption of wild animals, raw meat, and undercooked foods, including dumplings and scalded dog meat. Also, mandatory testing for meats other than pork is lacking, thus increasing the risk of infection.⁴

In Southeast Asia, trichinosis has been found in Cambodia, Laos, Thailand and Vietnam from 2001 to 2021.⁷ Cases in Thailand, Laos, and Vietnam mostly occur in the northern mountainous regions, in which indigenous communities practice free-roaming pig husbandry.7 In Lao, eating fermented pork has been linked to past outbreaks, and subclinical exposure might be common, as many people regularly consume raw meat.⁹

A unique pattern in Southeast Asia is that more males are affected than females compared to other regions, where the rates between the sexes are around the same.⁷ A reason for this might be the popular belief that eating raw wild pig meat transfers its strength to the men. Meanwhile, women tend to reject raw wild pig meat due to its strong taste.⁶ Another reason for the unbalanced sex ratios is that men tend to eat undercooked pork while they are hunting.⁷

Key contributors to the severity and high mortality rates in Cambodia include a high number of larvae consumed, late diagnosis in rural settings, preference for traditional medicine over modern treatment and limited healthcare infrastructure, allowing unregulated medical practices.⁷

North america

Trichinosis is rare in the United States, with only about 15 reported cases per year. The low number is due to strict food safety regulations, improved pig farming and public awareness.³ Eating wild game meat is currently the leading cause of cases.3 Between 2016 and 2022, 7 trichinosis outbreaks were reported, and most of these were caused by the consumption of black bear meat. The reasons for this might be hunting practice, as hunters might not be aware of the risks or may not cook the bear meat thoroughly. These bears host these parasites mainly due to ecological factors, as black bears frequently consume carrion or other infected animals, and the muscle of infected black bears contains more Trichinella larvae compared to other wild game species.⁸

South america

Trichinosis is endemic in Argentina and Chile, where infections are regularly reported in domestic pigs, wild animals, and humans.² It persists due to traditional food practices, small-scale farming, and unregulated meat distribution.

In Argentina, domestic pigs are the primary cause of human infections. Wild animals such as cougars, armadillos, peccaries, and wild boars serve as reservoirs and animals living near humans, such as dogs and rats, may contribute to the transmission. The rise of consumption of pork might be the driving force behind the increase in trichinosis infections.²

In Chile, rodents may also be a reservoir, as a study found that 4 out of 40 rodents tested positive for Trichinella larvae. Close contact between these rodents and small-scale farm pigs through poor farm hygiene may facilitate the transmission. In addition, there seems to be a lack of awareness among farmers, as only 12.5% surveyed farmers knew about Good Production Practices (GPP) and the importance of trichinosis detection.²

In Brazil, infection is absent in domestic species but is present in wild boars only in a few zones. Trichinosis is not endemic in Peru, but the country is known for the farming and eating of guinea pigs. Since guinea pigs are suitable hosts for many Trichinella species, and with the increasing annual consumption of guinea pig meat, there is a need for monitoring to prevent outbreaks.²

Factors contributing to endemicity

Trichinosis persists in certain regions due to a combination of food safety issues, cultural practices, and farming methods. A significant increase in the risk of consuming contaminated meat is brought by a lack of proper meat inspections and low awareness.¹

The consumption of raw or undercooked meat is the strongest cause for infection, and certain cultural food traditions present in endemic areas promote the practice. Certain cultures have dishes that involve raw or lightly cooked pork, wild boar, or wild game. Other preparations, such as fermenting or smoking of the meat, might not fully kill the Trichinella larvae.⁵

High-risk feeding practices contribute to Trichinella transmission for both domestic and wild animals. These feeding practices include intentionally feeding food scraps containing pig or wild animals' carcasses to livestock, allowing pigs to scavenge in garbage dumps, feeding wild animals with hunted animal remains and animal carcasses and feeding pig or other infected animal bodies to horses, dogs and crocodiles.¹¹ 

Prevention and control strategies

Effective prevention requires public awareness, emphasising the risks of consuming raw or semi-raw meat, and proper food safety measures, which include food handling, cooking practices and pig farming regulations.⁵ Best practices in handling raw meat is hand washing with warm water and soap before and after handling raw meat, and thoroughly cleaning the meat grinder, cutting boards, and other kitchen utensils after use.³

To kill the Trichinella larvae, the meat should be cooked to a core temperature of at least 71^oC or frozen at -15 oC (for less than 15cm thick pork).³ It is also important to note that cooking methods such as microwaving, curing, drying or smoking the meat do not reliably kill Trichinella.

Feeding raw meat scraps to pigs should be stopped, and certified feedstuff should be used.^5,12 In addition, a thorough meat inspection through microscopic examination to detect Trichinella cysts should be implemented. It is also essential to control rodents and dispose of dead animals properly and quickly to avoid scavenging.¹²

Summary

Trichinosis is a disease transmitted to humans through the consumption of raw or undercooked meat. Symptoms range from mild non-specific issues to severe neurological and cardiac complications. It is a worldwide problem involving both humans and animals and is endemic in several parts of Europe, Asia and South America. The reason for this is the lack of strict meat inspections, cultural food traditions on raw or undercooked meat and poor livestock feeding practices. In order to prevent the spread, it is important to educate the public about the risks, proper handling and preparation of food, and to further implement strict farming practices.