This month marks the 100th anniversary of the discovery by Sir Ronald Ross that mosquitoes transmit malaria. The popular view had been that malaria was caused by bad air (mal aria) or contaminated water. In 1887, however, Charles Laveran had shown that patients with malaria carried a protozoan parasite in their blood, and doctors began speculating that mosquitoes spread the parasite. Ross, an English physician working in India, set out to test that hypothesis.
Ross collected and identified various kinds of mosquitoes, dissected their guts, and in August 1897 found his quarry in an Anopheles mosquito that had just fed on a malaria patient. The mosquito yielded a cyst containing sporozoites, the same parasite that Lavaran had seen in the blood of his patients.
The mosquito-malaria connection suggested strategies for cutting malaria transmission: kill mosquitoes, and prevent them from biting or breeding. When diligently followed, as they were on the Malay peninsula and during the construction of the Panama Canal, those measures succeeded in controlling the disease. Ross received the 1902 Nobel Prize in physiology or medicine for his work.
[Source: Roy Porter, Ed., The Biographical Dictionary of Scientists, Second Edition. Oxford University Press. 1994.]