David Bruce, bacteriologist and parasitologist, was the only son of David Bruce and his wife Jane Hamilton. He accompanied his parents to Scotland around 1860, returning to their country of origin. The family settled in Stirling, where he received his schooling. Even as a boy he had a keen interest in natural history, particularly in the habits of birds. After working in a business firm in Manchester for some time he matriculated at he University of Edinburgh in 1876. He intended to study zoology there, but qualified as Bachelor of Medicine (MB) and Master of Surgery (CM) in 1881. He then obtained employment as assistant to Dr H.S. Stone, a general practitioner at Reigate, near London. Here in 1883 he married Mary E. Steele, who became a talented artist and skilled medical technologist and assisted him in his research throughout his career. Having obtained a commission in the Army Medical Service he qualified first in his class at the Army Medical College at Netley, near Southampton, that same year. In 1884 he was posted to Malta as an army surgeon. Here he participated in the study of Malta fever, concentrating on its pathology and bacteriology. Within two years he had identified the causative organism, which was later named Brucella melitensis in his honour. Two papers on this work appeared in the journal Practitioner in 1887 and 1888. Another paper based on his stay in Malta dealt with "Surface animals collected in Maltese seas during 1886-1887" and was published in the Proceedings of the Liverpool Biological Society (1887).
During 1889 Bruce spent his leave in Berlin, where he and his wife studied in the laboratory of Dr Robert Koch*. He then became assistant professor of pathology at Netley, remaining until 1894 when he was posted to the British garrison in Pietermaritzburg, Natal Colony. The governor of Natal, Sir Walter Hely-Hutchinson (who had been governer of Malta during Bruce's stay on the island), arranged for his secondment to investigate nagana (later also known as tsetse fly disease) among cattle in Zululand. Captain Bruce and his wife spent from November 1894 to January 1895 at Ubombo, north-east of Lake St Lucia. During this period he found that nagana was caused by a blood parasite. In August 1895 he (now a major) and his wife again left for Ubombo, where they remained until the end of July 1897. In addition to his detailed description of the pathological anatomy of the disease, his experiments with dogs during this period proved that the tsetse fly acted as the carrier of the parasite, later named Trypanosoma brucei in his honour. Furthermore, he found that game animals showing no symptoms acted as a reservoir of the trypanosome. Thus he became the first to prove by experiment that a blood-sucking insect can convey a lethal protozoal parasite from infected to healthy mammals. This discovery was to prove of the utmost importance in the fight against human trypanosomiasis in Africa and has been described as "one of the most important pieces of research ever undertaken in the field of tropical medicine and parasitology" (Joubert et al, 1999, p. 67). His work was written up in three reports, issued in December 1895, May 1896, and 1903. For this, his most brilliant work, he was elected a Fellow of the Royal Society of London in 1899.
After his return to Pietermaritzburg the Colonial Veterinary Surgeon of Natal, H. Watkins-Pitchford* arranged for Bruce to be seconded to the Allerton Laboratory (opened during the first half of 1898), where they started an investigation into African horse sickness. They visited Dr Arnold Theiler* in Pretoria in January 1899, with the result that Bruce remained in contact with Theiler for the rest of his career. However, upon his return to Natal the British Army recalled him and when the Anglo-Boer War broke out in October that year he went on active duty. From November 1899 he commanded the military hospital at Ladysmith. He received the Queen's Medal (seven clasps), and was promoted to lieutenant-colonel in November 1900. Returning to England in 1901, he served on a committee of inquiry into casualties resulting from dysentery and typhoid in South Africa. His report on this work, Great Britain. Commission on dysentery and enteric fever in South Africa. Report of the commission on the nature, pathology, causation and prevention of dysentery and its relationship to enteric fever, was published in 1903. In 1902 he became a member of the Army Service Advisary Board, a position he held until 1911.
Early in 1903 the Royal Society of London requested his secondment to a commission to continue the investigation of sleeping sickness, recently introduced into Uganda. He left London accompanied by his wife and two assistants and within five months established by experiments that the disease was caused by a trypanosome, later named Trypanosoma gambiense, carried by tsetse flies. Leaving the rest of the commission to continue the work he returned to England in August 1903. A book by him, Sleeping sickness in Uganda, was published in 1904. The Royal Society next appointed him director of a commission formed to investigate the source of the organism causing Malta fever. His team, which included his wife, proved in 1905 that the source was goat's milk, and the finding led to the control of the disease by boiling or pasteurising the milk. He was honoured as a Companion of the Order of the Bath (CB) in 1905.
In 1905 Bruce became a member of the British Association for the Advancement of Science and president of its Section I (Physiology). That year he visited South Africa again to attend the joint meeting of the association with its South African counterpart. He delivered an evening lecture in Pietermaritzburg on "Sleeping sickness". In his presidential address to the Physiology Section he presented a comprehensive review of recent advances in knowledge of the causes and prevention of stock diseases in South Africa, with reference to the work of Theiler, Watkins-Pitchford, A. Edington*, D. Hutcheon*, and others. In 1908 he was knighted and in October that year returned to Uganda with his assistants on behalf of the Royal Society to continue the efforts to eliminate sleeping sickness there. In August 1909 Theiler joined him there for a short time. Bruce concluded from the research carried out under his direction that the parasites causing the disease are carried also in wild and domestic animals, thus spreading the disease beyond tsetse infested areas. With several co-authors he described the work in Sleeping sickness and other diseases of man and animals in Uganda during the years 1908-9-10, being Report No. 11 of the Sleeping Sickness Commission of the Royal Society. He returned to England in 1910 and was elected a Fellow of the Royal College of Physicians. The next year the Royal Society sent him to Nyassaland (now Malawi) for two years to study trypanosomes in wild and domestic animals there. He returned in 1913, having been promoted to surgeon-general of the Army Medical Services in recognition of his scientific work.
Bruce was a Fellow, and from 1917-1919 president, of the Royal Society of Tropical Medicine and Hygiene; president of the British Association in 1923; received honorary degrees from the universities of Dublin, Glasgow, and Toronto; and was awarded medals by the Royal Society of London in 1904 and 1922. During World War I (1914-1918) he was director of research and commander of the Royal Army Medical College, initiating important work on trench fever and tetanus. He was honoured as Knight Commander of the Order of the Bath (KCB) in 1918, and promoted to major-general upon his retirement in 1919. However, as chairman of the governing body of the Lister Institute and through other positions he kept in contact with medical research until just before his death. He was a pioneer medical researcher in the causation of disease and published many scientific papers. A forceful man with a strong physique, he was none the less somewhat reserved and self-contained.