Alexandre Yersin
Swiss-French bacteriologist who discovered the plague bacillus.
Alexandre Émile John Yersin (22 September 1863 – 1 March 1943) was a Swiss-French doctor and bacteriologist known for his early contributions to microbiology and immunology. Alongside Émile Roux, he helped identify the toxins behind diphtheria and tetanus in 1890. In 1894, with Kitasato Shibasaburō, he also found the bacterium that causes bubonic plague, later named *Yersinia pestis* in his honor. Yersin was the first to show that the same germ appeared in both rodents and humans, pointing to how the disease might spread.
Yersin was born in 1863 in Aubonne, Switzerland, the youngest of three boys. His father, also named Alexandre, worked as a gunpowder superintendent and taught natural sciences, but died of a cerebral hemorrhage shortly before Alexandre’s birth. His mother, Fanny-Isaline-Emilie Moschell, raised the children alone in Morges, where she ran a school for girls. Yersin began studying medicine in Lausanne in 1883, then moved to Marburg and later to the Hôtel-Dieu in Paris from 1884 to 1886.
In 1886, Émile Roux invited Yersin into Louis Pasteur’s lab at the École Normale Supérieure, where he helped develop an anti-rabies serum. He earned his doctorate in 1888 with a thesis on experimental tuberculosis and spent two months with Robert Koch in Germany. To practice medicine in France, he became a French citizen in 1888. The next year, he joined the new Pasteur Institute as Roux’s collaborator, and together they discovered that *Corynebacterium diphtheriae* releases a soluble toxin responsible for diphtheria’s effects.
From 1890 to 1894, Yersin worked as a ship’s doctor for the Messageries Maritimes company, sailing routes between Saigon, Manila, and Haiphong. He took part in one of Auguste Pavie’s missions and led three expeditions across French Indochina—covering what is now Vietnam, Laos, and Cambodia. He never returned to Europe. On 5 June 1894, the French government sent him to Hong Kong, where a plague outbreak had already killed about 100,000 people. Within fifteen days, he isolated the plague bacillus. In 1895, back at the Pasteur Institute in Paris, he worked with Roux, Albert Calmette, and Amédée Borrel to create the first anti-plague serum. That same year, he returned to Indochina and set up a small lab in Nha Trang to produce the serum; this became a Pasteur Institute branch in 1905. Trials of the serum in Canton, Amoy, and Bombay in 1896 and 1897 gave disappointing results.
Yersin decided to stay in French Indochina and founded the Pasteur Institute in Nha Trang in 1895. There, he studied cattle breeding to produce anti-plague serum. He also turned to agriculture, pioneering the cultivation of rubber trees (*Hevea brasiliensis*). In 1897, he got a government concession for an agricultural station at Suoi Dau, and in 1915 he opened another at Hon Ba, where he acclimatized the quinine tree (*Cinchona ledgeriana*) imported from the Andes. This tree became the first effective treatment for malaria, and Yersin’s trees allowed Indochina to meet its quinine needs during World War II. He also introduced cacao and coffee to the region. Yersin helped create the Medical School of Hanoi and, on 8 January 1902, was appointed its first headmaster by Governor-General Paul Doumer. In 1934, he was named honorary director of the Pasteur Institute and a member of its board. In Vietnam, he is fondly remembered as Ông Năm (Mr. Five), a nickname from his rank as a colonel in the French army, marked by five horizontal lines on his insignia.
Roux and Yersin studied filtrates of *Corynebacterium diphtheriae* using a porcelain filter developed by Charles Chamberland. This filter removed the bacteria themselves, leaving only soluble components. When injected into guinea pigs, these filtrates killed the animals, showing that a toxin produced by the diphtheria bacterium caused the disease. They also found the same toxin in urine from children who died of diphtheria. In August 1891, Roux presented their view at the seventh International Congress of Hygiene and Demography in London, arguing that microbes act through chemical poisons specific to each disease, and that an infectious disease is essentially a poisoning by the microbe’s toxin. This diphtheria toxin was the first bacterial toxin ever discovered. In their experiments, Roux and his team observed that the substance could be produced in horses and then extracted in large amounts.
- born
- 22 September 1863
- died
- 1 March 1943
- field
- Microbiology, immunology
- nationality
- Swiss-French
- known_for
- Co-discoverer of diphtheria and tetanus toxins; discoverer of Yersinia pestis
Verified Timeline
Lore & Background
Yersin was born in 1863 in Aubonne, Switzerland, the youngest of three sons. His father, also named Alexandre, died of a cerebral hemorrhage shortly before Alexandre's birth. His mother, Fanny-Isaline-Emilie Moschell, raised their three children alone and settled in Morges, where she opened a school for girls. From 1883 to 1884 he studied medicine at Lausanne, then continued 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' and spent two months with Robert Koch in Germany. He obtained French nationality in 1888 and joined the Pasteur Institute in 1889 as Roux's collaborator, together discovering that Corynebacterium diphtheriae secreted a soluble toxin responsible for diphtheria. From 1890 to 1894, Yersin became a ship's doctor for the Messageries Maritimes shipping company on the Saigon-Manila line and then the Saigon-Haiphong line. He participated in one of the Auguste Pavie missions and led three expeditions across French Indochina. On 5 June 1894, he was sent by the French government to Hong Kong, where a plague outbreak had already caused 100,000 deaths. Just 15 days later, he isolated the plague bacillus, Yersinia pestis. He obtained specimens after bribing English sailors responsible for disposing of plague victims' bodies. In 1895 he returned to the Pasteur Institute in Paris and with Émile Roux, Albert Calmette and Amédée Borrel prepared the first anti-plague serum. He then returned to Indochina, installing a small laboratory at Nha Trang to manufacture the serum (which became a branch of the Pasteur Institute in 1905). Yersin tried the serum in Canton and Amoy in 1896, and in Bombay in 1897, with disappointing results. He founded the Institut Pasteur in Nha Trang in 1895, studied cattle breeding, and pioneered rubber tree cultivation (Hevea brasiliensis). He obtained a concession for an agricultural station at Suoi Dau in 1897, and opened a station at Hon Ba in 1915 where he acclimatized the quinine tree (Cinchona ledgeriana), enabling Indochina to meet its quinine needs during World War II. He also introduced cacao and coffee to Indochina. On 8 January 1902, Yersin was accredited as the first Headmaster of Hanoi Medical University. In 1934 he was nominated honorary director of the Pasteur Institute and a member of its Board of Administration. In Vietnam, he was affectionately called Ông Năm (Mr Nam/Five), a nickname due to his rank as a Colonel in the French army, with five horizontal lines in his army insignia.
Reader's Guide
Alexandre Yersin's significance lies in his dual role as a foundational figure in microbiology and a practical contributor to public health in Southeast Asia. His co-discovery of the diphtheria toxin with Émile Roux established the concept of bacterial exotoxins. Roux and Yersin studied filtrates of Corynebacterium diphtheriae through a porcelain filter, excluding the bacteria themselves. When injected into guinea pigs, the filtrates resulted in death, allowing them to claim a toxin was created by the bacterium. They also found the same toxin in urine from children sick with diphtheria shortly before their deaths. The diphtheria toxin was the first bacterial toxin discovered. His isolation of the plague bacillus in Hong Kong on 23 June 1894, though disputed with Kitasato Shibasaburō (who had discovered it on 14 June), led to the naming of Yersinia pestis. Yersin correctly described his bacillus as Gram-negative, while Kitasato insisted his was Gram-positive. Yersin also demonstrated for the first time that the same bacillus was present in rodents as well as in humans, underlining possible means of transmission. This was communicated to the French Academy of Sciences in a classic paper titled 'La peste bubonique à Hong-Kong'. Beyond the laboratory, he applied his knowledge in French Indochina, founding the Nha Trang Pasteur Institute, introducing rubber and quinine cultivation, and serving as the first headmaster of Hanoi Medical University. His legacy endures in Vietnam, where he is affectionately remembered as Ông Năm. The article notes that his anti-plague serum trials in Canton, Amoy, and Bombay yielded disappointing results, reflecting the challenges of early serum therapy.
Did You Know?
- Yersin's father died of a cerebral hemorrhage shortly before Alexandre's birth.
- Yersin obtained specimens of plague victims in Hong Kong by bribing English sailors responsible for disposing of bodies.
- Yersin correctly described the plague bacillus as Gram-negative, while Kitasato insisted his organism was Gram-positive.
- Yersin acclimatized the quinine tree (Cinchona ledgeriana) at Hon Ba in 1915, enabling Indochina to meet its quinine needs during World War II.
- In Vietnam, Yersin was affectionately called Ông Năm (Mr Nam/Five) due to his rank as a Colonel in the French army, with five horizontal lines in his insignia.
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