Trichinosis (Trichinellosis) Clinical Presentation

Updated: May 01, 2018
  • Author: Darvin Scott Smith, MD, MSc, DTM&H, FIDSA; Chief Editor: John L Brusch, MD, FACP  more...
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The European Center for Disease Control has proposed definitions and algorithms for diagnosis of acute trichinosis 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.

Trichinosis 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:

  • Myocarditis [14]
  • Pneumonia [14]
  • Meningitis [15]
  • Encephalitis [15]

Long-term sequelae of the CNS include decreased mental power, numbness of hands and feet, decreased stress tolerance, loss of initiative, and depression.

Usually, full recovery occurs after cardiac or pulmonary involvement.

Prolonged weakness and myalgias may occur.

Adrenal gland insufficiency may occur.

Obstruction of blood vessels may occur.