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Trichinosis Clinical Presentation

  • Author: Darvin Scott Smith, MD, MSc, DTM&H; Chief Editor: Burke A Cunha, MD  more...
Updated: Nov 16, 2015


The European Center for Disease Control has proposed definitions and algorithms for diagnosis of acute trichinellosis in humans.[13] They focus on clinical, laboratory, and epidemiological criteria, along with a series of symptoms. The criteria can also be used to differentiate very unlikely, suspected, probable, highly probable, and confirmed cases (see Staging). Knowledge of the incubation period can help pinpoint the source of the infection, both in individual cases and in outbreaks.

Trichinellosis may progress from an enteric (ie, intestinal) phase to a parenteral (ie, invasive) phase to a period of convalescence.

Intestinal phase

The intestinal phase usually causes symptoms in the first week of illness.

Diarrhea is the most common symptom.

Constipation, anorexia, and diffuse weakness may occur.

Occasionally, severe enteritis due to a massive inoculum of Trichinella species occurs.

Symptoms typically last 2-7 days but may persist for weeks.

With certain Trichinella species and in certain population groups and geographic regions, the disease may not progress beyond the intestinal stage.

Nausea is reported in 15% of patients, vomiting in 3%, and diarrhea in 16%.

Dyspnea may occur with exertion.

Abdominal discomfort and cramps may occur.

Invasive phase

The invasive phase corresponds to the migration of the larvae from the intestine to the circulatory system and eventually to the striated muscles. This phase is associated with a higher rate of symptoms than the intestinal stage.

The duration varies from weeks to months.

Severe myalgia develops in 89% of patients.

The central nervous system (CNS) is involved in 10%-24% of patients, with a mortality rate of 50%. Approximately 52% of patients present with headaches. Other symptoms include deafness, ocular disturbances, weakness, and monoparesis.

Cardiac system involvement occurs during the third week of infection, with a mortality rate of 0.1%, often during the fourth to eighth week of infection. Death may result from congestive heart failure and/or arrhythmias.

Pulmonary system involvement occurs in 33% of patients, with symptoms lasting up to 5 days. Patients present with dyspnea, a cough, and hoarseness.

Convalescent phase

The convalescent phase, which corresponds to encystment and repair, may be present for months to years after infection.

The encystment of larvae can lead to cachexia, edema, and extreme dehydration.

Symptoms usually decrease around the second month, except in the case of T pseudospiralis infection, which may cause symptoms for several months.



Intestinal phase

Abdominal distention may be present.

Macular or petechial rashes affect 20% of patients.

Diarrhea may occur.

Invasive phase

After 2 weeks, 91% of patients have a fever that peaks around the fourth week. This degree of fever is unique among helminthic infections. Temperatures can reach 104°F (40°C).

Weakness and/or myositis occur in 82% of patients. Muscles become stiff, hard, and edematous. Muscles with increased blood flow (eg, extraocular muscles, masseters, larynx, tongue, neck muscles, diaphragm, intercostals, limb flexors, lumbar muscles) are most frequently involved. Involvement of the diaphragm may result in dyspnea.

Periorbital edema is reported in 77% of patients.

Rash (macular or petechial) is reported in 15%-65% of patients.

Ocular findings include subconjunctival hemorrhages in 9% of patients, conjunctivitis in 55%, and incidences of chemosis and retinal hemorrhage.

The CNS is involved in 10%-24% of patients. Of these, 53%-96% exhibit meningoencephalitis, 40%-73% exhibit focal paralysis and/or paresis, 39%-71% exhibit delirium, 20% exhibit decreased or absent deep-tendon reflexes, 17% exhibit meningitis, and 2% exhibit evidence of psychosis.

Signs of cardiac system involvement include hypertension, increased venous pressure, and, in 18% of patients, peripheral edema.

Subungual splinter hemorrhages occur in 8% of patients.

Convalescent phase

Edema is present in 18% of patients.

Patients are easily fatigued.

Weakness may occur.

Weight loss may occur.

Myalgia may occur.

Ocular signs with chronic headaches may be present.



Trichinella species develop in a single host and are then spread from that host to the next without an arthropod intermediate. The intensity and frequency of exposure to infected meat determine the severity of the disease.

Infections are related to cultural differences in food cooking and storing methods, specifically the inadequate cooking or freezing of meat.



Apart from heavily infested cases of trichinosis, complications are rare. In severe cases, Trichinella larvae may migrate to the host organism's vital organs. Once the larvae reach the host's vital organs, they can cause dangerous, and even fatal, complications, including the following:

Contributor Information and Disclosures

Darvin Scott Smith, MD, MSc, DTM&H Adjunct Associate Clinical Professor, Department of Microbiology and Immunology, Stanford University School of Medicine; Chief of Infectious Diseases and Geographic Medicine, Department of Internal Medicine, Kaiser Redwood City Hospital

Darvin Scott Smith, MD, MSc, DTM&H is a member of the following medical societies: American Medical Association, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, International Society of Travel Medicine

Disclosure: Nothing to disclose.


Lauren E Wedekind Stanford University

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

John L Brusch, MD, FACP Assistant Professor of Medicine, Harvard Medical School; Consulting Staff, Department of Medicine and Infectious Disease Service, Cambridge Health Alliance

John L Brusch, MD, FACP is a member of the following medical societies: American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital

Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

Pranatharthi Haran Chandrasekar, MBBS, MD Professor, Chief of Infectious Disease, Program Director of Infectious Disease Fellowship, Department of Internal Medicine, Wayne State University School of Medicine

Pranatharthi Haran Chandrasekar, MBBS, MD is a member of the following medical societies: American College of Physicians, American Society for Microbiology, International Immunocompromised Host Society, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Stephanie A Nevins Research Assistant, Department of Genetics, Snyder Lab, Stanford University School of Medicine

Disclosure: Nothing to disclose.


Clinton Murray, MD Program Director, Infectious Disease Fellowship, San Antonio Uniformed Services Health Education Consortium

Clinton Murray, MD is a member of the following medical societies: American College of Physicians-American Society of Internal Medicine, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Association of Military Surgeons of the US, and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

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Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella. After exposure to gastric acid and pepsin, the larvae are released from the cysts and invade the small bowel mucosa, where they develop into adult worms (females, 2.2 mm in length; males, 1.2 mm; 4-week life span in the small bowel). After 1 week, the females release larvae that migrate to the striated muscles, where they encyst. Trichinella pseudospiralis, however, does not encyst. Encystment is completed in 4-5 weeks, and the encysted larvae may remain viable for several years. Ingestion of the encysted larvae perpetuates the cycle. Rats and rodents are primarily responsible for maintaining the endemicity of this infection. Carnivorous/omnivorous animals, such as pigs or bears, feed on infected rodents or meat from other animals. Different animal hosts are implicated in the life cycle of the different species of Trichinella. Humans are accidentally infected when eating improperly processed meat of these carnivorous animals (or eating food contaminated with such meat). Life cycle image and information courtesy of DPDx.
Cumulative number* of patients with trichinellosis, by sex and age group, in the United States 2002-2007. (*N = 52 years. Age was unknown for one patient, and sex was unknown for another patient.) Courtesy of the US Centers for Disease Control and Prevention (
Encysted larvae of Trichinella species in muscle tissue, stained with hematoxylin and eosin (H&E). The image was captured at 400X magnification. Courtesy of the US Centers for Disease Control and Prevention (
Trichinella larvae, in pressed bear meat, partially digested with pepsin. Courtesy of the US Centers for Disease Control and Prevention ((
Larvae of Trichinella from bear meat. Courtesy of the US Centers for Disease Control and Prevention (
Table 1. Biologic and Zoogeographic Features of Trichinella Species
Species Distribution Major Hosts Reported from Humans
T spiralis Cosmopolitan Domestic pigs, wild mammals Yes
T britovi Eurasia/Africa Wild mammals Yes
T murrelli North America Wild mammals Yes
T nativa Arctic/subarctic, Palaearctic Bears, foxes Yes
T nelsoni Equatorial Africa Hyenas, felids Yes
T pseudospiralis * Cosmopolitan Wild mammals, birds Yes
T papuae * Papua New Guinea, Thailand Pigs, crocodiles Yes
T zimbabwensis * East and South Africa Crocodiles, lizards, lions No
* Nonencapsulating types      
Table 2. Number of Trichinellosis Cases and Outbreak Cases, by Reporting State -- United States, 2002--2007 [4]
State 2002 2003 2004 2005 2006 2007 Total Outbreak cases
Alaska 7 0 0 3 0 0 10 8
California 0 2 1 2 4 1 10 2
Florida 0 0 0 1 1 0 2 0
Illinois 1 0 0 0 0 0 1 0
Maryland 0 0 0 0 1 0 1 0
Massachusetts 0 0 0 1 0 0 1 0
Michigan 0 0 0 3 0 0 3 0
Minnesota 0 0 0 0 3 0 3 2
New Hampshire 0 1 0 0 0 0 1 0
New Jersey 0 0 0 0 2 1 3 0
New York 0 1 0 0 0 3 4 2
North Dakota 0 0 2 0 0 0 2 0
Ohio 0 0 0 1 0 0 1 0
Pennsylvania 1 0 1 3 0 0 5 0
Rhode Island 0 0 1 1 0 0 2 0
Tennessee 0 2 0 0 1 0 3 2
Vermont 1 0 0 0 0 0 1 0
Washington 0 0 0 0 1 0 1 0
Total 10 6 5 15 13 5 54 16
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