Alexandre Émile John Yersin (22 September 1863 – 1 March 1943) was a Swiss-French physician and bacteriologist. He is remembered for his work as a pioneer in microbiology and immunology. Yersin is the co-discoverer of both the Diphtheria and Tetanus toxins (1890 with Émile Roux) and of the bacillus responsible for the bubonic plague (1894, with Kitasato Shibasaburō). The bacteria was later named in his honour: Yersinia pestis. Yersin also demonstrated for the first time that the same bacillus was present in the rodent as well as in the human disease, thus underlining the possible means of transmission.
Yersin was born in 1863 in Aubonne, in the canton of Vaud, Switzerland, the youngest of three sons. His father, also named Alexandre (1825-1863), was the gunpowder superintendent for French-speaking Switzerland, based in La Vaux, in the Aubonne valley, and also a professor of natural sciences at the colleges of Aubonne and Morges and was passionate about studying insects. He died of a cerebral hemorrhage shortly before Alexandre's birth. Yersin's mother, Fanny-Isaline-Emilie Moschell raised their three children (Émilie, Franck, and Alexandre) alone and settled in Morges, at 11 rue de Lausanne, where she opened a school for girls.
From 1883 to 1884 he studied medicine at Lausanne, but then continued his studies at Marburg, and the Hôtel-Dieu de Paris (1884–1886).
In 1886, Yersin entered Louis Pasteur's research laboratory at the École Normale Supérieure, by invitation of Émile Roux, and participated in the development of the anti-rabies serum. In 1888, he received his doctorate with a dissertation titled Étude sur le Développement du Tubercule Expérimental (Study on the Development of Experimental Tubercule) and spent two months with Robert Koch in Germany.
In order to practice medicine in France, Yersin applied for and obtained French nationality in 1888. He then joined the recently created Pasteur Institute in 1889 as Roux's collaborator and together they discovered that Corynebacterium diphtheriae secreted a soluble toxin that was responsible for the effects of diphtheria.
From 1890 to 1894, Yersin became a ship's doctor for the Messageries Maritimes shipping company on the Saigon-Manila line and then on the Saigon-Haiphong line. He participated in one of the Auguste Pavie missions. He led three expeditions across the French Indochina (current Vietnam, Laos and Cambodia) in Southeast Asia. He never returned to Europe.
On 5 June 1894, he was sent, by request of the French government, on a mission to Hong Kong where an outbreak of plague had already caused 100,000 deaths from the plague. Just 15 days later, he isolated the plague bacillus, Yersinia pestis.
In 1895 he returned to the Institute Pasteur in Paris and with Émile Roux, Albert Calmette and Amédée Borrel, prepared the first anti-plague serum. In the same year, he returned to Indochina, where he installed a small laboratory at Nha Trang to manufacture the serum (in 1905 this laboratory became a branch of the Pasteur Institute).
Yersin tried the serum received from Paris in Canton and Amoy, in 1896, and in Bombay, India, in 1897, with disappointing results.
Having decided to stay in French Indochina, Yersin founded the Institut Pasteur in Nha Trang in 1895. While there he studied cattle breeding (to produce anti-plague serum).
Yersin tried his hand at agriculture and was a pioneer in the cultivation of rubber trees (Hevea brasiliensis) For this purpose, he obtained in 1897 a concession from the government to establish an agricultural station at Suoi Dau. He opened a new station at Hon Ba in 1915, where he acclimatized the quinine tree (Cinchona ledgeriana), which was imported from the Andes in South America, and which produced the first known effective remedy for preventing and treating malaria. Yersin's trees enabled Indochina to meet its quinine needs during the Second World War. He also successfully introduced cacao and coffee to Indochina. He participated actively in the creation of the Medical School of Hanoi On 8 January 1902, Yersin was accredited to be the first Headmaster of Hanoi Medical University by the Governor-General of French Indochina, future president of France Paul Doumer.
In 1934 he was nominated honorary director of Pasteur Institute and a member of its Board of Administration.
Alexandre Yersin is well remembered in Vietnam, where he was affectionately called Ông Năm (Mr Nam/Five). This nickname due to his rank as a Colonel in the French army, with five horizontal lines in his army insignia.
Roux and Yersin studied filtrates of the Corynebacterium diphtherie bacterium obtained through the porcelain filter set up by Charles Chamberland (1851–1908), one of the closest collaborators of Pasteur. This filtration method excluded the bacteria themselves from the soluble components in the filtrate that are made by the bacteria. Once injected in guinea pigs, the filtrates resulted in the death of the animals. These analyses allowed them to claim that a toxin was created by the bacterium known to cause diphtheria. Furthermore, they also found the same toxin in urine collected from children sick with diphtheria shortly before their deaths. In August 1891, Roux had the opportunity to present his view during the seventh International Congress of Hygiene and Demography in London. "It is natural to conclude that microbes act through their chemical products, true poisons specific to each of them, and which determine the symptoms of the disease in man and in animals. The infectious disease is therefore a poisoning: the source of the poison is the microbe settled in the tissues; it elaborates his toxin there at the expense of the living being that it is going to kill".
The diphtheria toxin was the first bacterial toxin discovered. During their experiments, Emile Roux and his associates observed that this substance could be produced in horses and then extracted in large quantities without causing trauma. They decided to inoculate dozens of children at risk of diphtheria with the serum. Twice as many of the inoculated children survived as had been expected.
Antisera would be made from the diphtheria toxin by Emil von Behring (1854–1917) and Shibasaburo Kitasato (1853–1931), creating the first effective treatment for the disease.
Discovery of the Plague Bacteria
The first case discovered in Hong Kong was by Scottish doctor James Alfred Lowson, acting superintendent of the Government Civil Hospital, on 8 May 1894. The patient, named "A. Hung", was a ward boy, presumably working in the Government Civil Hospital. "A. Hung" died 5 days later. On 10 May 1894, the city was declared an infected port.