Dengue: the health risk that actually finds foreigners, per the MoPH

Dengue is the infectious risk most likely to put a healthy foreigner in a Thai hospital. The Department of Disease Control's own epidemiology: endemic nationwide, with epidemic years exceeding 100,000 cases and 100+ deaths; strongly seasonal, climbing from April and peaking June–August with the rains. It is spread by day-biting Aedes aegypti and Aedes albopictus mosquitoes — bed nets alone miss the point; the bites happen in daytime, often at home. Four serotypes circulate (DENV-1 to 4), and infection protects you long-term only against the serotype you caught, so you can get dengue more than once. In 2026 case numbers are running below the previous year, but DDC keeps active surveillance and its Dengue Zero programme targets zero deaths by 2030.

There is no antiviral; treatment is supportive. The single most important thing to know is written in the DDC's guidance: for the fever take paracetamol only — NSAIDs and aspirin (ibuprofen explicitly included) are absolutely forbidden because they trigger gastrointestinal bleeding and acute liver/kidney failure in dengue. Warning signs meaning go to hospital now: fever drops but you feel worse; abdominal pain or vomiting more than three times a day; dizziness, cold hands and feet, lethargy; little or no urine for 4–6 hours; any abnormal bleeding (nosebleeds, black stools, vomiting blood). Prevention that matters: repellent daily in the rainy season, and denying the mosquito breeding water — cover or empty standing water weekly. DDC hotline: 1422.