I had dengue fever as a baby. I've read that if you contract it again it is more severe. I was wondering if this is still the case after 25 years?

Likely. There are 4 serotypes of dengue. If you were to encounter the same serotype, you may be immune & not get it at all. However, it is true, having 1 form & getting another, does increase your risk for more severe disease such as dengue hemorrhagic fever: a potentially fatal form. It would be perhaps reasonable to antibody test before traveling to an epidemic region. Regardless, insect precautions!