Polio is a possibility. I honestly don't know though, I wouldn't have thought South-east Asia would have been so overrepresented compared to say, Sub-Saharan Africa? I'm just working on the assumption that polio isn't correlated, to my knowledge, with climate and has a readily available reasonably cheap vaccine (which should surely, within reason, be more accessible in relatively wealthy Indonesia?). My brain is telling me that Suharto did a big anti-polio drive in the mid-80s through, but I'm not a 100% sure. That's probably one of the better guesses so far because I honestly can't tell you anything about polio incidence in South-east Asia.
Some possible candidates with explanations
usually against: giardia (prevalent throughout Southeast Asia, but I know nothing of external distribution), dysentery (same thing as polio, I would expect Africa to be darker than it is), cholera (same thing as polio, albeit with Haiti as well), dengue (although that has a far more limited range than the map suggests; furthermore, Australia has dengue, New Zealand doesn't), leprosy (again it's been wiped out in Australia and New Zealand).
dwaxe said:
Might it be tropical diseases in general?
What's a tropical disease? You can catch malaria in some decidedly untropical places...