QUESTION:
Why is there not a prevalence of malaria in the southern United States when we are bitten almost daily by the “little beasts?”
ANSWER:
Malaria once was relatively common in the southern United States. Transmission used to be possible due to the favorable climatic conditions for the development both of the mosquito as well as the malaria parasite. Huge advances in the control and treatment of malaria were made directly as a result of increased interest in the disease after the US occupation of Cuba and the building of the Panama Canal in the early years of the 20th century. This vastly reduced the number of cases of the disease, but the final, concerted effort to eradicate malaria came in the 1940s.
This was due to a federal public health program called the National Malaria Eradication Program (NMEP), and as a result of its actions, malaria transmission was halted throughout the United States by 1951. The program was launched in 1947, coordinated by the newly formed Communicable Disease Center (now the Center for Disease Control and Prevention, or CDC) and mostly involved reducing the number of mosquitoes in and around people’s homes. This was done through the wide-spread spraying of DDT—during the years of NMEP, it has been estimated that more than 6.5 million homes were sprayed with the insecticide. Alongside spraying, mosquito breeding habitats were also removed, through wetland drainage, and human monitoring and treatment efforts were stepped up. By 1949, malaria was no longer considered a disease of public health importance, and it was declared eradicated from the United States in 1951.
Having said that, the species of mosquito that transmit malaria still exist in the USA, and particularly in the southern states, which means that there is always a risk of small, localized outbreaks of the disease, particularly during hot and wet seasons.
Climate change may also increase the zones where malaria is at risk of being able to develop within the United States. For this reason, the CDC continually monitors the small number of cases reported each year in the USA (there were about 1500 cases in 2007—all but four of these cases, however, were the result of travelers to malarial areas outside of the USA bringing the disease back with them) to ensure that they are prepared and well-informed should an outbreak arise.