Trichinella Spiralis (Trichnellosis)


Article Author:
Prashanth Rawla


Article Editor:
Sandeep Sharma


Editors In Chief:
David Wood
Andrew Wilt
Hajira Basit


Managing Editors:
Avais Raja
Orawan Chaigasame
Khalid Alsayouri
Kyle Blair
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Abbey Smiley
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beenish Sohail
Hajira Basit
Phillip Hynes
Sandeep Sekhon


Updated:
6/26/2019 12:21:05 PM

Introduction

Trichinellosis also called trichinosis results from roundworms (nematodes) from the genus Trichinella. It is a parasitic infection. It is caused by consuming undercooked or raw meat (usually pork). Trichinella spiralis species is the common cause of human disease by eating raw or undercooked pork. Although, other mammals like wild carnivores and horses can be reservoirs of infection. It can cause symptoms varying from generalized fever, abdominal pain, diarrhea, nausea, vomiting’s, myalgia to more severe like myocarditis and encephalitis.

Etiology

Trichinella spiralis is a nematode (roundworm) parasite.[1] It possesses the capability of infecting a wide range of mammals including pigs, horses, reptiles, and birds but it causes disease only in humans. By eating improperly cooked or raw pork, horse, or other domestic animal meat and wild game meat like bear meat, humans acquire the infection. Some reports have mentioned an occasional acquisition of the disease by ingestion of reptile meat, including lizards and turtles.[2] There are no reports of human to human transmission.

Epidemiology

Trichinellosis occurs worldwide, and estimates are that about 10000 cases occur each year.[3] Cases usually tend to occur in clusters among groups of people who have consumed infected meat from a common animal.[4] There are nine species of Trichinella, and thus far reports exist of twelve genotypes trichinella.[5] The most common species of trichinella which can cause human disease is Trichinella spiralis, although other species of Trichinella implicated in human disease are: T. nativa, T. nelson, T. britovi, T. pseudospiralis, T. murelli, T. papuae.[5][6] Per the Centers for Disease Control and Prevention around 400 cases of trichinellosis were reported every year in the 1940s, but now the number of reported cases has dropped significantly and has been around 20 cases every year from 2008 to 2010.

Life cycle[3]:

  • The life cycle of trichinellosis divides into two stages: 1) domestic cycle and 2) sylvatic cycle
    • Domestic cycle: affects domestic animals, particularly swine, rodents, horses
    • Sylvatic cycle: affects wildlife like bear, wild boar, moose

Pathophysiology

Ingestion of undercooked or raw meat from domestic or sylvatic animal containing encysted larvae of Trichinella species can lead to Trichinellosis. T. spiralis results from the consumption of inadequately cooked or raw pork from domestic pigs.[7]

Enteric or gastrointestinal phase: After ingestion of infected meat by humans, the enzymes pepsin and hydrochloric acid act in the stomach and cause the release of the 1st stage of the larvae. These larvae invade the small intestine. Invasion can be asymptomatic or sometimes associated with abdominal pain, diarrhea, nausea, vomitings. Larvae then turn into adults and mate. Female trichinella worms produce larvae, which completes the gastrointestinal or enteric phase.

Systemic (parenteral) phase: Larvae enter the lymphatic circulation and then into the blood, reaching skeletal muscles, myocardium, and brain which are high in oxygen content. This phase leads to systemic symptoms like fevers, myositis, myalgias, periorbital edema and can even cause myocarditis and encephalitis.

History and Physical

Infection results from the consumption of raw or undercooked meat (especially pork). The incubation period is 1 to 6 weeks. In humans, the severity of infection severity of infection is related to the number of larvae ingested.[8]

Gastrointestinal symptoms are the first symptoms of trichinellosis. They usually occur in 2 to 7 days after consumption of raw or undercooked meat. Symptoms include abdominal pain, diarrhea, nausea, and vomiting.

Classic trichinellosis symptoms usually occur in 2 weeks after consumption of raw or undercooked meat and can last up to 8 weeks. Symptoms include fevers, chills, myalgias, periorbital or facial edema, weakness, and fatigue. Reports also exist of prolonged diarrhea.[9]. Other common symptoms are conjunctivitis and subconjunctival hemorrhages seen in about 50% of patients.[10] Splinter hemorrhages on nailbeds (subungual) and retinal hemorrhages can also occur.

Other less common manifestations include a headache, cough, rash, headache, dyspnea, and dysphagia. Hepatomegaly can also occur occasionally.[11] 

Severe complications include myocarditis, life-threatening arrhythmias, meningitis, encephalitis, respiratory myositis, secondary bacterial pneumonia, hematuria, and renal failure.[12][13][14][15]

Evaluation

Diagnosis is initially made usually based on clinical signs and symptoms. Diagnostic confirmation is by serology, or occasionally muscle biopsy may be needed.

A complete blood count can show leukocytosis and eosinophilia, which correlates with the number of worms causing infections.[3] Creatine kinase, lactate dehydrogenase, aldolase, and aminotransferases elevate due to the invasion of skeletal muscle by parasites causing muscle destruction.  Patients can also have hypokalemia, hypoalbuminemia, and increased serum IgE levels. All these tests are non-specific as can be seen in other parasitic disease and autoimmune diseases.[16]

Serological tests which are available are ELISA (enzyme-linked immunosorbent assay), indirect IF (immunofluorescence), and latex agglutination test. Serologic tests confirmation can be via western blot.[17] Sometimes serology is not reliable mainly during the early course of the disease(during the first 3 weeks or more). Infection with other organisms like nematodes or other helminths and autoimmune diseases can cause a false positive serologic reaction.

Definitive diagnosis method is a muscle biopsy.[10] Sensitivity is high if the biopsy is performed 4 weeks after infection. If performed early in the disease course it may be negative.

Treatment / Management

The clinical course of trichinellosis is self-limited in most cases, and it is uncomplicated.

Mild infections are treated symptomatically with antipyretics and anti-inflammatory agents.

Trichinella infection with systemic complications is treated with antiparasitic agents and corticosteroids.[18]

Albendazole 500mg twice daily given orally for 10 to 14 days (or) Mebendazole 200 to 400 mg thrice daily for 3 days, then 400 to 500 mg three times daily for 10 days.

Severe cases may require coadministration with prednisone at a dose of 30 to 60mg daily for a total of 10 to 14 days.

Albendazole and mebendazole are not considered safe in pregnant women and children less than or equal to 2 years of age. Specialist consultation is necessary in these cases and risk, and weighing the benefits vs. risks is necessary before administering the drug. The World Health Organization recommendations are that pregnant women can get antihelminthic medications (mebendazole, albendazole, pyrantel or levamisole) after their first trimester.[19]

Differential Diagnosis

  • Gastroenteritis - viral or bacterial
  • Polymyositis and dermatomyositis (autoimmune)
  • Periorbital cellulitis
  • Eosinophilia-myalgia syndrome

Eosinophilia can be present other helminthic infections like fasciola, schistosomiasis, toxocariasis, cysticercosis, visceral larva migrans, and sarcocystosis

Prognosis

Trichinellosis usually has a benign course and is self-limiting. Full recovery of patients within 2 months to 6 months of infection is the expectation. However, some cases might be severe, and even death is a possibility. Prognosis of the disease proportionately correlates with the parasitic burden.

Complications

  • Myocarditis
  • Pneumonitis
  • Secondary bacterial pneumonia
  • Nephritis
  • Chronic diarrhea
  • Neurotrichinellosis

Consultations

  • Infectious disease
  • Cardiology if complications like myocarditis or arrhythmias arise
  • Surgical consultation might be necessary for a muscle biopsy

Deterrence and Patient Education

Trichinellosis is caused by consuming raw or undercooked meat of infected animals. Patients should receive education about the risk of transmission when consuming undercooked or raw meat. There are no reports of human to human transmission. Cases can occur in clusters among groups of people from the same community or family who have consumed infected meat from a common animal. Patients should be educated to heat the meat for at least 77 degrees Celsius which kills Trichinella larvae. Patients should also receive counseling regarding proper food safety practices.

Pearls and Other Issues

Postexposure prophylaxis with mebendazole if given within 6 days of exposure may be effective.[20]

Enhancing Healthcare Team Outcomes

Treatment and prevention of trichinellosis require a multidisciplinary team effort. Collaboration and effective communication between the healthcare team is crucial to ensure excellent patient service. Infectious disease consultations should be sought when necessary to provide the best treatment options for the patient. Nurses should educate patients on risks of transmission when consuming undercooked or raw meat. Pharmacists, nurses, and physicians should be aware of the potential side effects of antihelminthic medications used in the treatment of trichinellosis and should explain the associated side effects to the patients.


  • Image 7382 Not availableImage 7382 Not available
    Image courtesy S Bhimji MD
Attributed To: Image courtesy S Bhimji MD

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Trichinella Spiralis (Trichnellosis) - Questions

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An elderly male took a trip to Alaska and feasted several times on a walrus. He now returns a week later with nausea, vomiting, urticaria, muscle pain, and a headache. If it is suspected that this patient has Trichinella spiralis, what pathognomic finding will be present on a physical exam?



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A 35-year-old male goes on a hunting trip with his friends. They kill a wild boar and eat it without properly cooking it. He also drinks water from the nearby river. Ten days later he has abdominal pain, nausea, diarrhea, and vomitings which resolves spontaneously after he took loperamide from his friend. Six weeks after the trip he starts having symptoms of fevers, muscle aches, swelling around his eyes which prompts him to visit the emergency department. On examination, he has a temperature of 100.4 F, blood pressure of 110/50, and respiratory rate of 15. A complete blood count is done which shows leukocytosis with a WBC count of 11,000 with eosinophils of 39%. On examination, he has axillary lymphadenopathy, and splinter hemorrhages are noted under his nails. What is the infectious form of the most likely causative agent?



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A patient presents with muscle aches, nausea, emesis, and diarrhea for the past week. He reports he recently ate some pork at a party before his symptoms. Physical exam shows periorbital edema. Which of the following would best aide in diagnosing this patient's condition?



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A 53-year-old male went on a hunting trip to mountains in the midwest area of the United States. They killed a pig in the forest and had it for supper. He also drank water from the nearby river. He had multiple mosquito bites during the trip. Five days later, he had abdominal pain, nausea, and diarrhea which resolved spontaneously. A month later, he started having fevers, muscle aches, swelling around his eyes which prompted him to visit the emergency department. On examination, he has a temperature of 100.2 F, blood pressure of 1100/50, respiratory rate of 16 along with axillary lymphadenopathy, splinter hemorrhages under his nails and subconjunctival hemorrhages. What is the most common abnormality seen on blood work in this patient?



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A 65-year-old male from the United States travels to Thailand for a 2-week vacation. He consumes an exotic turtle at the local restaurant while on vacation. After one week, he has diarrhea, abdominal pain, and he takes loperamide and ibuprofen, and his symptoms resolve. After he comes back from the vacation, a month later, the patient starts noticing increasing muscle aches. He also has fevers and chills. He presents to the emergency department for further evaluation. Vital signs were a temperature of 100.5 F, blood pressure of 110/50 mmHg, respiratory rate of 15 breaths per minute. Examination shows conjunctivitis, subconjunctival hemorrhages, subungual splinter hemorrhages, hepatomegaly. A complete blood count is done, which shows white blood cell count of 10,000 with 42% neutrophils, 30 % eosinophils, 20% lymphocytes, 7% monocytes, and 1 % basophils. His creatine kinase levels are elevated. Liver function tests are elevated. What is the organism which is the likely cause of his symptoms?



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A 65-year-old male eats undercooked pork at a local restaurant. He develops muscle aches, facial swelling a month later. He is diagnosed with Trichinellosis. What is the most likely complication that can occur with severe trichinellosis?



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Trichinella Spiralis (Trichnellosis) - References

References

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Taher EE,Méabed EMH,El Akkad DMH,Kamel NO,Sabry MA, Modified dot-ELISA for diagnosis of human trichinellosis. Experimental parasitology. 2017 Jun;     [PubMed]
Watt G,Saisorn S,Jongsakul K,Sakolvaree Y,Chaicumpa W, Blinded, placebo-controlled trial of antiparasitic drugs for trichinosis myositis. The Journal of infectious diseases. 2000 Jul;     [PubMed]
Gyorkos TW,Larocque R,Casapia M,Gotuzzo E, Lack of risk of adverse birth outcomes after deworming in pregnant women. The Pediatric infectious disease journal. 2006 Sep;     [PubMed]
Faber M,Schink S,Mayer-Scholl A,Ziesch C,Schönfelder R,Wichmann-Schauer H,Stark K,Nöckler K, Outbreak of trichinellosis due to wild boar meat and evaluation of the effectiveness of post exposure prophylaxis, Germany, 2013. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2015 Jun 15;     [PubMed]
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