After about three weeks of infection, larval encystment in muscles begins. Patients experience myalgias, muscle edema and weakness, fever, and eosinophilia. Headache, cough, dyspnea, dysphagia, and macular or urticarial skin lesions develop less commonly. Although larvae encyst only in striated muscle, inflammatory lesions may develop in the heart, lungs, and central nervous system. Fatalities usually result from myocarditis.
Symptoms generally abate slowly after the third week of infection.
Infections with T. pseudospiralis may be associated with years of myositis. Serologic tests are positive in most patients with acute infection, but diagnostic antibody titers may not be detectable until the third week of infection. Definitive diagnosis requires demonstration of larvae in muscle. A portion of the biopsied muscle should be submitted for histopathological examination. In addition, another portion should be compressed between glass slides and examined microscopically for larvae.