Walter Reed (1851 - 1902), American physician, specialized in the study of epidemic diseases. He discovered ways to prevent typhoid epidemics, proved that malaria was not caused by water, and studied yellow fever. He proved that yellow fever was not caused by Bacillus icteroides, which causes hog cholera. He showed that yellow fever was caused by a mosquito (Aedes aegypti) and identified the pathogen that causes the disease along with J. Caroll.