Are there any significant differences in the geography of Brazil that could also contribute to some of the difference in infection rates?

Very. In simple terms there's just a lot more of Brazil to deal with.

Brazil is a massive 8,514,215 km2 while Singapore is just a tiny 734 km2 island which is very highly urbanised and developed and doesn't have a significant rural population (hence the description of "city-state").

Its small enough that you can monitor mozzie levels at the individual building level, and locate and deal with breeding spots at that level too. That might also be practical in urban areas in Brazil, but for rural areas I suspect is not feasible?

> but for rural areas I suspect is not feasible?

Aedes aegypti is an urban mosquito. Degue is an urban disease. The big difference between Brazil and Singapore is sanitation: https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in...