What did Walter Reed prove caused yellow fever?

Walter Reed's research was pivotal in establishing that mosquitoes were the vector responsible for transmitting yellow fever. His groundbreaking work in the early 20th century involved carefully designed experiments, which included the observation that groups of volunteers who were exposed to the bites of infected mosquitoes developed yellow fever, while those who were kept safe from the mosquitoes did not. This demonstrated that the disease was not caused by water contamination, viruses, or parasites, but rather by the bites of mosquitoes, particularly the Aedes aegypti species.

Reed's findings significantly advanced the understanding of how yellow fever spreads and led to improved public health measures, including mosquito control efforts, which have been essential in preventing outbreaks. The recognition of mosquitoes as the carriers of the disease was a major step forward in epidemiology and in the fight against infectious diseases.