Trichinosis natural history, complications, and prognosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Danitza Lukac

Overview

If left untreated, infected patients develop manifestations within 1-2 days of infection. Infected patients with trichinosis may progress to develop periorbital edema, muscle pain, and fever. Complications of trichinosis affect the cardiovascular, neurological, ocular, respiratory, and digestive systems. Most people with trichinosis have no symptoms, the infection is usually self-limited. The prognosis of trichinosis is good with adequate treatment.

Natural History

• Trichinosis is usually self-limited, and the majority of individuals with trichinosis are asymptomatic.
• The symptoms vary depending on the phase, species of Trichinella, amount of encysted larvae ingested, age, gender, and host immunity.
• Patients infected by 10 or less larvae have either minor or no symptoms and no complications.

Enteral/Intestinal phase:

• From two to seven days after infection.
• The large burden of adult worms in the intestines promote symptoms such as nausea, heartburn, dyspepsia, and diarrhea.

Parenteral/muscle phase:

• The parental phase starts approximately seven days after infection.
• The severity of symptoms caused by larval migration from the intestines depends on the number of larvae produced.
• As the larvae migrate through tissue and vessels, the body's inflammatory response results in edema, muscle pain, fever, and weakness.
• A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis.
• If left untreated, the worms may cause enough damage to produce serious neurological deficits (such as ataxia or respiratory paralysis) from worms entering the central nervous system (CNS).
• The CNS is compromised by trichinosis in 10–24% of reported cases of cerebral venous sinus thrombosis, a very rare form of stroke (3-4 cases per million annual incidence in adults).
• Trichinosis can be fatal depending on the severity of the infection. Death can occur 4–6 weeks after the infection, and is usually caused by myocarditis, encephalitis, or pneumonia.

Trichinosis Classification Based on the Severity of Signs and Larval Density
Adapted from Clin Microbiol Rev. 2009 Jan; 22(1): 127–145.

Classification	Fever, Edema, and Myalgia	Recovery Time	Approx. number of larvae/g of muscle
Asymptomatic	None	N/A	<10
Abortive	1-2 days	N/A	10-100
Mild	+	3 weeks	10-100
Pronounced	++	6 weeks	10-100
Severe	+++	>6 months	>100

Complications

Common complications of trichinosis include:

Cardiovascular:

• Heart failure
• Heart rhythm problems (arrhythmias) from heart inflammation (myocarditis)
• Thromboembolic disease
  • Deep thrombophlebitis
  • Intraventricular thrombi
  • Pulmonary embolism
• Paroxysmal tachycardia
• Pericardial effusion

Neurological:

• Encephalomyelitis
• Neuromuscular disturbances:
  • Decreased muscular strength and tendon reflexes
  • Dysphagia
  • Trismus

Ocular:

• Edema and vascular lesions within the conjunctiva, uvea, retina, and, in some cases, the optic nerve
• Pain when moving the eyeballs
• Muscle paralysis
• Diplopia
• Disturbed accommodation

Respiratory:

• Dyspnea
• Pneumonia
• Obstructive bronchitis
• Löffler-type infiltrates or ventilature failures

Digestive:

• Hypoalbuminemia
• Acute intestinal necrosis
• Prolonged diarrhoea

Prognosis

• The prognosis of trichinosis is good with adequate treatment.
• Most people with trichinosis have no symptoms, the infection is usually self-limited.
• The mortality rate of trichinosis is approximately 0.2% worldwide.
• Prompt treatment with antiparasitic drugs can help prevent the progression of trichinosis by killing the adult worms and so preventing further release of larvae.
• Once the ''Trichinella'' larvae have become established in skeletal muscle cells, usually by 3 to 4 weeks post infection, treatment may not completely eliminate the infection and associated symptoms.
• If trichinosis treatment is not initiated within the first several days of infection, more prolonged or repeated courses of treatment may be necessary.