I have lived in Thailand for several years and have used Goldenseal (Hydrastis canadensis) when I caught dengue fever. It works immediately and avoids the days of serious fever, vomiting, etc.
I used it on a friend who had dengue. She had been diagnosed with dengue at the hospital who sent her back home with nothing. She was really ill, fatigued, with a high fever. So I gave her some Goldenseal I had. I didn't know if it would work at all. The next day, when I called, she was working!
One day, I myself caught dengue. I nearly didn't have time to make it home and there I lay in my bed, the whole room swirling around me. I was getting chills, hot spells. Felt really sick. I took a capsule of goldenseal. Two hours later, the fever had gone, and I was ok. Extremely tired, but ok. I took another capsule. And it was completely gone.
Some naturopathic physicians have since confirmed that goldenseal cures dengue.