What are the early symptoms of hantavirus?

Hantavirus illness begins with a flu-like prodromal phase that is easy to miss. The dominant complaints are abrupt fever to 38–40 °C, intense myalgia, and crushing fatigue out of proportion to the apparent infection. Headache and lightheadedness are common. Gastrointestinal symptoms — nausea, vomiting, diarrhea, abdominal pain — occur in a substantial minority and can mislead clinicians toward gastroenteritis. Critically, cough and shortness of breath are usually absent in this phase. In HPS, the prodromal phase lasts 3 to 5 days before progressing to a rapidly worsening cardiopulmonary phase; in HFRS, it transitions to a hypotensive and then renal phase. Anyone with these symptoms after possible rodent exposure should seek emergency evaluation — early ICU admission dramatically improves survival.