Dr. Walter Reed was a military surgeon who proved in 1901 that yellow fever is caused by a virus transmitted by the bite of the Aedes aegypti mosquito. Following work to prevent the spread of typhoid and improve sanitary conditions during the Spanish-American Way, he was appointed to head a group studying yellow fever in Cuba. His commission disproved the belief that yellow fever was caused by bacteria and found that it was not spread by contact. That information led to the clearing of mosquito-breeding areas in the southeastern United States and in Latin America, and to the halting of the disease.