The incubation period usually is one to three weeks, but may range from three to 42 days. Almost all casepatients have a fever and muscle aches. Many have a cough, chills, headache, and gastrointestinal symptoms such as nausea, vomiting, or diarrhea. After three to four days of nonspecific symptoms, the disease worsens rapidly. Patients develop difficulty breathing, a rapid heart rate, and decreased blood pressure.
Fluid enters the lungs, causing acute respiratory distress syndrome.
White blood cell and platelet counts are abnormal. Treatment consists of providing supplemental oxygen and ventilator support. Even with intensive care, mortality is high. Experimental treatment protocols are being tested. Rodent Reservoir Deer mice had the highest prevalence of the Sin Nombre strain of hantavirus antibody of all rodents tested in the southwestern United States, although other rodent species have antibody indicating exposure to the virus.