Infectious Diseases

Trichinosis: Causes, Symptoms & Prevention Explained

December 17, 2024

Trichinosis, also known as trichinellosis, is a parasitic infection caused by nematodes of the genus Trichinella. Humans contract the infection by consuming raw or undercooked meat contaminated with Trichinella larvae. Trichinella is an intestinal roundworm primarily seen in insufficiently cooked or raw food. Pork and its products are also the main sources of infection. This infection possesses the risk of being deadly, but commonly, it is a self-limiting disorder. Common complications include myocarditis, encephalitis, and respiratory failure.¹ Globally, an estimated 10,000 cases occur annually, with higher prevalence in regions where raw or undercooked meat consumption is common.² Sir Richard Owen and Sir James Paget first discovered trichinosis in 1835 while observing a mass of worms lining the diaphragm of a cadaver.³

Life Cycle and Transmission of Trichinella Species

There are several species of Trichinella. These include T. spiralis (Most Common), T.nativa, T. psuedospiralis, T. britovi, T.murelli, T.pupuae, T. zimbabwensis, and T. nelson. Encysted larvae and adult worms typically develop within a single vertebrate host. In the life cycle of Trichinella, an infected animal acts as both the definitive host (where adult worms reproduce) and the intermediate host (where larvae encyst). The life cycle requires a second host to propagate, as the encysted larvae must be consumed by another animal. The commonly studied T. spiralis life cycle involves pigs, rodents, and humans.⁴
Trichinellosis has a life cycle that consists of the following stages:

Domestic Stage:

The domestic cycle involves domestic animals such as pigs, rodents, and sometimes horses. Pigs often become infected by consuming infectious larvae in raw meat, such as from rats.

Sylvatic Stage:

The sylvatic cycle occurs in wildlife, affecting animals such as wild boars, bears, and moose. Wildlife can transmit the parasite when consumed by domestic animals or humans.⁵
T. spiralis typically infects domestic animals, while other Trichinella species are more common in wildlife. Poor management of domestic and wild animals facilitates the transfer of parasites from wildlife to domestic animals through urban wildlife, such as rats and mice. Infected animals include wild boars, bears, and foxes.⁶

Gastrointestinal Phase:

HHumans acquire infection by consuming raw or undercooked meat contaminated with encysted larvae. Once ingested, the larvae emerge from their nurse cells in the stomach and invade the intestinal mucosa. They molt four times and develop into adults within 30 hours. After five days of mating, predomination occurs, and females produce live offspring larvae. The size of newborn male larvae is 1.2 mm, and the female is 2.2 mm in length. The female worms can produce up to 1500 larvae in their life of six weeks.

Photomicrograph of an intestinal mucosa tissue specimen, revealing the presence of a Trichinella spiralis, which had burrowed itself into the columnar epithelial intestinal lining. Image Courtesy: Public Health Image Library (PHIL). Image ID: 14931.

Systemic Phase:

After being released, the larvae penetrate the intestinal barrier and enter the lymphatic vessels and bloodstream. They migrate to striated muscles, where they become encysted in active muscles such as the tongue, diaphragm, and intercostal muscles. Here, the larvae develop into the infective stage within nurse cells. The life cycle continues when the infected host is consumed by another animal.⁷⁸

Various lifecycle stages through which the intestinal nematode, Trichinella spiralis, passes as it matures from an egg to its adult form. Trichinellosis is acquired by ingesting meat containing cysts, or encysted larvae, of Trichinella spp. Organisms. After exposure to gastric acid and pepsin, the larvae are released from the cysts, invading the small bowel mucosa where they develop into adult worms. Image Courtesy: PHIL. Image ID: 5233

Causes of Trichinosis

Trichinella spiralis species is the most common cause of human disease. After getting trichinosis by eating infected meat, people cannot pass the parasite directly to another person. Infected meat comes from wild animals such as wolves, bears, wild boar, seals, cougars, and walruses. Domestic horses and pigs become infected when they feed on garbage containing infected meat scraps. You can not get trichinosis from beef, chicken, and other meats, as these animals do not eat meat. If beef or other kinds of meat were ground in a grinder previously used to grind the infected meat, it could also become a cause of the infection. You can also get trichinosis by eating improperly stored meats. Unclean kitchen utensils used to prepare meats also cause this infectious disease.⁹

Symptoms

The symptoms of trichinosis vary, and the severity of these symptoms depends on the number of larvae ingested through food. In some cases, symptoms are absent; in others, they last for even months.

Mild Symptoms:

In mild cases, trichinosis may present with non-specific flu-like symptoms, including:

Fatigue
Low-grade fever
Muscle aches

Gastrointestinal (Enteric) Phase:

Symptoms typically develop within 1–2 days after ingesting infected meat and include:

Diarrhea
Nausea
Fever
Vomiting
Abdominal pain and cramps
Heartburn and dyspepsia (less common)
Eosinophilia (elevated eosinophils in blood tests)¹⁰

Systemic Phase:

This phase occurs 1–2 weeks after ingestion as larvae migrate to tissues and muscles. Symptoms include:

Fever
Weakness and fatigue
Myalgia (muscle pain)
Periorbital swelling (swelling around the eyes)
Headache
Rashes
Itchy skin
Conjunctival redness (red eyes)
Edema (swelling in other body parts)¹¹

Clinical appearance of a patient’s eyes with periorbital swelling in case of trichinosis. Image Courtesy: PHIL. Image ID: 342.

Severe Symptoms:

In most severe cases, the symptoms can be:

Encephalitis
Meningitis
Myocarditis
Pneumonia
Ataxia¹²
Cerebral venous thrombosis¹³

Trichinosis can also be fatal, depending on the severity of the infection. Death can occur after four to six weeks of severe infection.¹⁴

Diagnosis

The diagnosis of trichinosis is primarily clinical and later supported by laboratory and molecular findings.

Clinical Evaluation:

Your clinician can diagnose the condition by doing a physical exam. The initial diagnosis began with a detailed history of symptoms such as myalgia, fever, eosinophilia, periorbital edema, and gastrointestinal symptoms. A more critical aspect of the diagnosis is determining the history and exposure to the parasite.

Laboratory Tests:

Laboratory tests that help in diagnosing trichinosis are blood and serological tests.

Blood Tests:

Blood tests include eosinophil count, leukocyte count, muscle enzymes, and antibody testing.

Eosinophil Count

An elevated eosinophil count is one of the main laboratory findings of trichinosis. They appear in between the second and fifth weeks of infection in almost every case. However, a massive decrease in eosinophil levels during an acute infectious stage predicts a severe outcome.

Elevated Levels of Muscle Enzymes in Blood

Myositis also appears between the second and fifth weeks of infection in 75 to 90% and can persist for up to four months. The elevated enzymes include aldolase, lactate dehydrogenase, and phosphokinase.

Leukocytosis

Polymorphonuclear leucocytosis is also a typical feature of trichinosis. It also appears early at the onset of the infection, between the second and fifth weeks of infection.

Immunodiagnosis

Anti-trichinella antibodies in the blood serum are also an important indication. An early increase in immunoglobulin E levels is observed in most of the cases.¹⁵

Serological Examination:

Serological testing is a cornerstone of diagnosis.

Anti-Trichinella Antibodies: The presence of specific antibodies in blood serum, such as immunoglobulin E (IgE) and IgG, is a significant indicator of infection. IgE levels rise early, while IgG is detected more reliably with techniques such as ELISA.
ELISA: Enzyme-linked immunosorbent assay (ELISA) is a widely used method to detect IgG antibodies in serum. However, it may yield false negatives during early stages, as antibodies take three to five weeks to develop. Serial testing may be required for confirmation.¹⁶

Muscle Biopsy:

Muscle biopsy helps identify the Trichinella larvae within muscle tissues. Findings of muscle biopsy also include inflammatory changes and encysted larvae. However, this process is most effective only after two weeks of infection when the larvae migrate into the muscle fibers.¹⁷

Photomicrograph of a muscle tissue sample, revealing the presence of a Trichinella spiralis larva from an individual with a case of trichinosis, of 2-weeks standing. Image Courtesy: PHIL. Image ID: 17933.

Imaging Techniques:

The imaging techniques usually used to diagnose trichinosis are X-rays, computed tomography, and electrocardiogram (ECG). X-rays show calcific densities in the muscles, and CT scans look for neurological dysfunction. ECG shows features of ischemia, myocarditis, pericarditis, etc.¹⁸

Molecular Techniques:

Advanced methods like polymerase chain reaction (PCR) are capable of detecting Trichinella DNA in muscle tissues. While not commonly used due to its complexity and cost, multiplex PCR offers a simpler and more economical approach for differentiating Trichinella species, making it useful in research and epidemiological studies.¹⁹

Treatment and Management

The available treatment methods are the following:

Anti-parasitic Medicines:

The most commonly used anthelmintics include mebendazole and albendazole. These are considered a cornerstone treatment of trichinosis as they target the larvae.

Mebendazole

The recommended dose of mebendazole is 200 mg to 400 mg thrice a day for three days. If required, another dose of 400 to 500 mg should be given thrice a Day for an additional ten days. It disrupts the mechanism of glucose uptake in parasites.

Albendazole

The recommended dose of this medicine is 400 mg twice a day for 10 to 14 days. It works by inhibiting the polymerization of tubulin, disrupting the parasite’s ability to absorb glucose and leading to its death. If administered early, albendazole can prevent muscular invasion of the larvae and prevent disease progression.²⁰

Prednisone

In most severe cases, doctors recommend coadministration of these anti-parasitic medicines with prednisone. The administered dose of prednisone is 30 mg to 60 mg daily for 10 to 14 days.²¹
However, albendazole and mebendazole are not safe for children below 2 years and pregnant women. So, practitioners consider alternative medicines.

Alternative Treatment:

The alternative option for children and pregnant women is Pyrantel. They administer it as a single dose of 10 to 20 mg/kg of the body weight. Primary chemotherapy for severe cases is prednisone, administered at a dose of 30 mg per day for 10 to 15 days. However, pyrantel does not affect muscle or newborn larvae. It only affects the intestinal larvae.²²

Supportive Care:

In addition to the anti-parasitic drugs, supportive care can help in managing the symptoms of the condition.
Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen can help in relieving muscle pain in patients. Corticosteroids such as prednisone can reduce inflammation in severe cases of infection and can also manage allergic reactions.²³
Healthcare providers should monitor patients for the potential side effects associated with the treatment. Most patients completely recover, while some experience complications.

Complications

In some cases, patients experience complications after treatment. These complications include:

Stillbirths
Vertical infection of the fetus
Menstrual irregularities
Weight loss
Hearing disorders
Nail and hair loss
Aphonia
Hoarseness
Muscle stiffness
Skin desquamation
Heart failure
Failure of the Central Nervous System (CNS)
Hypokalemia
Myocarditis
Encephalitis
Pneumonitis
Adrenal gland insufficiency
Obstruction of blood vessels

Some long-term complications that can persist up to 10 years post-treatment include:

Neuropathies
Conjunctivitis
Generalized myalgia²⁴

Prevention

Lack of education can be a potential source of trichinosis. Meats from horses, wild animals, exotic cuisines, and cultural practices can be a transmission factor. Education can decrease clinical cases. Healthcare providers should educate patients about the risk of transmission. People should know that only salting and smoking the meat is not enough to kill the trichinella cysts.²⁵
This infectious disease can be prevented by thoroughly cooking meats. Cooked meats should reach a minimum of 160 F internal temperature. This temperature can kill the larvae of Trichinella.
Properly clean the meat grinders and other kitchen utensils to prepare the meats.
After preparing the meat, wash your hands with soap.
If you want to freeze the meat, make sure that the meat is less than six inches in size.²⁶ Also, the freezing temperature for pork meat is -15 C. However, freezing can not kill the larvae of Trichinella in the meats of wild animals.
Prevention of trichinosis requires interprofessional teamwork.²⁷

Final Remarks

Trichinosis is a significant health problem in areas where people consume undercooked pork and wild game. This infectious disease presents a range of symptoms that vary according to the stage of infection. Most of the cases are mild and resolve simultaneously. Awareness of symptoms, timely diagnosis, and proper treatment are critical for preventing the severity of the infection. Promoting safe food practices and conducting educational initiatives can significantly decrease the incidence of this disease. By fostering a collaborative approach among healthcare providers, food safety communities, and regulators, we can enhance patient outcomes and reduce the global burden of trichinosis.

Refrences

1
Furhad S, Bokhari AA. Trichinosis. 2019.
2
Rawla P, Sharma S. Trichinella spiralis Infection. StatPearls [Internet]: StatPearls Publishing; 2023.
3
Furhad S, Bokhari AA. Trichinosis. 2019.
4
Bruschi F. Trichinella and trichinellosis: Elsevier; 2021.
5
yM Vaidya R, Zende J, Waghmare R, Moon S, Kale L. Trichinellosis/Trichinosis: Life Cycle, Transmission, Symptoms.
6
Rawla P, Sharma S. Trichinella spiralis Infection. StatPearls [Internet]: StatPearls Publishing; 2023.
7
Mousa ESI, Elgendy AM, Mohamed SM, SF H. An Overview about Trichinosis; Morphology, Pathogenesis, and Presentation.
8
yM Vaidya R, Zende J, Waghmare R, Moon S, Kale L. Trichinellosis/Trichinosis: Life Cycle, Transmission, Symptoms.
9
Chelsea Marie WAP, Jr. Trichinosis 2022 [Available from: https://www.msdmanuals.com/home/infections/parasitic-infections-nematodes-roundworms/trichinosis.
10
NOACK O. TRICHINOSIS
11
yM Vaidya R, Zende J, Waghmare R, Moon S, Kale L. Trichinellosis/Trichinosis: Life Cycle, Transmission, Symptoms.
12
yM Vaidya R, Zende J, Waghmare R, Moon S, Kale L. Trichinellosis/Trichinosis: Life Cycle, Transmission, Symptoms.
13
Evans RW, Pattern B. Trichinosis associated with superior sagittal sinus thrombosis. Annals of Neurology. 1982;11(2):216-7.
14
Gottstein B, Pozio E, Nöckler K. Epidemiology, diagnosis, treatment, and control of trichinellosis. Clinical microbiology reviews. 2009;22(1):127-45.
15
Mohamed SMAG, Taha AAR, Hamed EFA, Fawzy EM. Diagnostic Modalities of Trichinellosis. NeuroQuantology. 2022;20(16):2706.
16
Yayeh M, Yadesa G, Erara M, Fantahun S, Gebru A, Birhan M. Epidemiology, diagnosis and public health importance of Trichinellosis. Online Journal of Animal and Feed Research. 2020;10(3):131-9.
17
Mohamed SMAG, Taha AAR, Hamed EFA, Fawzy EM. Diagnostic Modalities of Trichinellosis. NeuroQuantology. 2022;20(16):2706.
18
Rawla P, Sharma S. Trichinella spiralis Infection. StatPearls [Internet]: StatPearls Publishing; 2023.
19
Yayeh M, Yadesa G, Erara M, Fantahun S, Gebru A, Birhan M. Epidemiology, diagnosis and public health importance of Trichinellosis. Online Journal of Animal and Feed Research. 2020;10(3):131-9.
20
Furhad S, Bokhari AA. Trichinosis. 2019.
21
Rawla P, Sharma S. Trichinella spiralis Infection. StatPearls [Internet]: StatPearls Publishing; 2023.
22
Furhad S, Bokhari AA. Trichinosis. 2019.
23
Chelsea Marie WAP, Jr, Trichinosis 2022 [Available from: https://www.msdmanuals.com/home/infections/parasitic-infections-nematodes-roundworms/trichinosis.
24
Furhad S, Bokhari AA. Trichinosis. 2019.
25
Furhad S, Bokhari AA. Trichinosis. 2019.
26
Chelsea Marie WAP, Jr, Trichinosis 2022 [Available from: https://www.msdmanuals.com/home/infections/parasitic-infections-nematodes-roundworms/trichinosis.
27
Rawla P, Sharma S. Trichinella spiralis Infection. StatPearls [Internet]: StatPearls Publishing; 2023.

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Life Cycle and Transmission of Trichinella Species

Domestic Stage:

Sylvatic Stage:

Gastrointestinal Phase:

Systemic Phase:

Causes of Trichinosis

Symptoms

Mild Symptoms:

Gastrointestinal (Enteric) Phase:

Systemic Phase:

Severe Symptoms:

Diagnosis

Clinical Evaluation:

Laboratory Tests:

Blood Tests:

Eosinophil Count

Elevated Levels of Muscle Enzymes in Blood

Leukocytosis

Immunodiagnosis

Serological Examination:

Muscle Biopsy:

Imaging Techniques:

Molecular Techniques:

Treatment and Management

Anti-parasitic Medicines:

Mebendazole

Albendazole

Prednisone

Alternative Treatment:

Supportive Care:

Complications

Prevention

Final Remarks

Refrences

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