Ross and the mosquito transmission of malaria

By the 1890s the parasite that causes malaria had been found, but no one could explain how it passed from one person to the next. Charles Laveran, Patrick Manson and several Italian malariologists suspected mosquitoes, although Manson at first thought people caught the disease by drinking water contaminated by them. In 1894 Manson, in practice in London and unable to travel to malarious regions, persuaded Ronald Ross, a 37-year-old army surgeon from India, to take up the question.

Ross went back to India and, guided by Manson in a long run of letters, dissected thousands of mosquitoes without success. He knew no entomology and sorted the insects by their look: grey, brindled and dapple-winged. On 20 August 1897, which he called "Mosquito day", he found pigmented bodies on the stomach wall of dapple-winged mosquitoes, now known to be anophelines, that had fed on a malaria patient.

He was then posted to Calcutta, where there was little human malaria, so he took up Manson's earlier suggestion of working with a malaria parasite of birds. Of 242 grey, culicine mosquitoes fed on infected birds, 178 developed the pigmented bodies. Ross followed the parasite from the mosquito's gut to its salivary glands, from which it entered a new host when the insect fed again, and he made the results public in 1898.

That same year Giovanni Battista Grassi and other Italian investigators showed that human malaria was carried by anopheline mosquitoes. Ross joined the Liverpool School of Tropical Medicine in 1899 and in Sierra Leone confirmed that anophelines transmit the human parasites. His partnership with Manson ended in acrimony.

In 1902 Ross received the Nobel Prize in Physiology or Medicine, and he was knighted in 1911.