Most "tropical" diseases have tropical reservoirs, but are fundamentally socio-economic. Malaria has mainly a human reservoir and is therefore almost completely socioeconomic. Malaria was once endemic in N. America up to the Arctic. The reason we have no more malaria is wealth. DDT is hardly a cure-all, people give it way too much credit. It is good for general mosquito control, but the secret to eliminating malaria and many other transmittable diseases is a high quality disease monitoring system (from high quality health care), isolation of victims, elimination of specific populations of mosquitoes (lots of DDT alternatives for that) and other first world factors.
The third world pimps like to blame the "tropical" diseases for their predicament. But the problem is socialism, authoritarianism, etc.
Smallpox has no known non-human reservoir, and over 99% of the human population has been vacc'ed against it -- yet it keeps coming back. Malaria would be a good one to eliminate worldwide, but an effectice vaccine for it is pretty new.