Other organs, especially the testes, heart, and joints, may be involved. Orchitis usually is unilateral. Cardiac involvement is typical of viral myocarditis. The objective swelling, redness, and pain resolve within a few weeks. Variations in frequency occur locally and depend on rodent populations.
Illness is more common during the fall and winter months.
No racial differences exist in incidence of infection. No sexual predilection exists in incidence of infection. Young adults more commonly are infected, although illness may occur in any age group. Clinical manifestations range from a flulike illness to severe CNS involvement with encephalitis. The typical patient in phase 1 of LCM complains of fever and headache, often with lymphadenopathy and a maculopapular rash.