In the United States, where do the majority of malaria cases originate from?

The majority of malaria cases in the United States originate from travelers and immigrants returning from endemic countries. This phenomenon occurs because malaria is primarily prevalent in tropical and subtropical regions, where environmental conditions favor the breeding of the Anopheles mosquitoes that transmit the disease. When individuals travel to these areas and contract malaria, they can later introduce the disease into the U.S. population upon their return.

Local mosquitoes, while they can transmit malaria if they bite an infected person, do not play a significant role in the majority of cases because malaria has largely been eliminated in the U.S. since the mid-20th century. Consequently, the transmission cycle largely depends on international travel and immigration patterns rather than domestic factors. Understanding the source of these infections is crucial for developing appropriate surveillance and response strategies to prevent outbreaks in the United States.