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Summary Article: Ross, Ronald (1857-1932)
from The Hutchinson Dictionary of Scientific Biography

Place: United States of America

Subject: biography, biology

British physician who proved that malaria is transmitted to human beings by the bite of the Anopheles mosquito. He also devoted much of his time to public health programmes concerned with the prevention of the disease. For his significant contribution to the battle against malaria, which has plagued people for centuries, he received the 1902 Nobel Prize for Physiology or Medicine.

Ross was born in Almora, India, on 13 May 1857, the son of a British army officer serving there. He was educated in the UK and received his medical training at St Bartholomew's Hospital, London, graduating in 1879. He was unenthusiastic about medicine, his interests at that time being in the arts and mathematics. When he joined the Indian Medical Service in 1881, however, he gradually became absorbed with medical problems. During his first leave in England, 1888-89, he obtained a diploma in public health and took a course in bacteriology. On retiring from the Indian Medical Service in 1899, he returned to the UK and lectured at the new School for Tropical Medicine in Liverpool, later holding the chair in tropical medicine there. He was knighted in 1911 and a year later moved to London, where he established a consulting practice at King's College Hospital. During World War I he was consultant on malaria to the War Office and when the Ross Institute of Tropical Diseases was opened in his honour, in 1926, he became its first director. He died in London on 16 September 1932.

While on leave in England in 1894, Ross became acquainted with the Scottish physician Patrick Manson, who demonstrated that the blood of malarial patients contained pigmented bodies and parasites. (The discovery that malaria was caused by a protozoan in the bloodstream had been made by Charles Laveran in Algeria in 1883.) Manson's suggestion was that malaria was spread by mosquitoes and Ross returned to India determined to investigate this hypothesis and to identify the mosquito responsible. The shortage in India of literature on the subject delayed the identification of species of mosquitoes and parasites, and Ross was also cut off from the work of others. He missed, for example, Albert King's suggestion that malaria might be transmitted via mosquito bites.

Ross refused to believe the popular idea that malaria was caused by bad air (mal aria) or contaminated water, and he continued to collect mosquitoes, identifying the various species and dissecting their internal organs. In the stomachs of some insects he found ‘motile filaments’, which, although Ross was unaware of it, were gametes. He thought that the filaments might develop to further stages, and dissected a few mosquitoes that had fed on malarial patients. In August 1897 he discovered a cyst containing the parasites that had been found by Laveran in the blood of malarial patients, in an Anopheles mosquito. These sporozoites of the malarial parasite remain in the human blood for only an hour after a bite, before invading liver cells, and their subsequent developmental stages are distinct from those in the mosquito. The biting mosquito may suck up various stages of the parasite with the blood, but all are digested except those that produce gametes. After fertilization the zygote bores through the stomach wall of the mosquito and forms an external cyst. Sporozoites are formed in the cyst, which migrate to the mosquito's salivary glands, ready for injection into a victim. Later, using caged birds with bird malaria, Ross was able to show that the ‘motile filaments’ do develop to further stages. The life history of the parasite inside a mosquito was thus revealed and the mode of transmission to the victim was identified as taking place through a mosquito bite.

© RM, 2018. All rights reserved.

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