The illness begins with a flu-like illness with myalgia, headache, leukopenia and thrombocytopenia; Some patients have signs and symptoms of meningitis either initially or after the flu-like illness; [CCDM]
Other symptoms seen in some cases are rash, arthritis, parotitis, orchitis, and myocarditis. Hemorrhagic cases have been reported among immunocompromised patients. The prognosis for full recovery is good even for severe cases, but convalescence with fatigue and vasomotor instability may be prolonged. [CCDM, p. 367] Occasionally, lymphadenopathy and a maculopapular rash accompany the initial fever. Orchitis, myocarditis, and arthritis are possible complications that usually resolve spontaneously within a few weeks. [PPID, p. 2035] After a flu-like illness in the first phase lasting 5 days to 3 weeks, patients improve. Some patients then relapse into fever, rash, headache, arthralgias, stiff neck, orchitis, parotitis, and hair loss. A minority of patients develop meningitis and usually recover without sequelae, but 1/3 of patients with encephalitis have persistent neurological symptoms. Encephalitis is a rare complication; it may be accompanied by paralysis, transverse myelitis, or acute Parkinson's syndrome. [Merck Manual, p. 1435-6] A large case series showed that 35% of patients were asymptomatic, 50% had a flu-like illness, and 15% had typical lymphocytic choriomeningitis. Sore throat and vomiting were common. Chest pain and pneumonitis occurred less frequently. [ID, p. 2136] Lab results in the early phase include leukopenia, thrombocytopenia, and elevation of liver enzymes. [Guerrant, p. 457]
Infected pet hamsters and laboratory animals have caused outbreaks. The natural reservoir is the common house mouse. The virus is transmitted to humans by the oral, respiratory, or percutaneous routes by food or dust contaminated with urine, saliva, or feces from infected animals. [CCDM, p. 368-9] Can be transmitted by an animal bite; [ID, p. 1424] Infection occurs after inhalation of virus in mouse urine, feces, or saliva. [Cecil, p. 1966] In the USA, Argentina, and Germany, there is 5-10% antibody prevalence. [Harrison ID, p. 1034]
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