Paul Louis Simond in India and the Discovery of Plague TRANSMISSION

Bombay plague epidemic, 1896-1897: interior of a plague hospital. Photograph attributed to Clifton & Co. Credit: Wellcome CollectionPublic Domain Mark

Paul-Louis Simond after studying in Bordeaux joined the Naval Medical Corps and was posted to French Guyana and the Far East. In 1895, he went to the Pasteur Institute in Paris where he followed Emile Roux’s teaching and worked in Elie Metchnikoff’s laboratory. During this time Simond studied coccidia in the intestinal flora of various animals. 

In March 1897, at Emile Roux’s request, Simond travelled to India (Bombay and Cutch-Mandvi in 1897; Jurrachee in 1898 [subsequently Karachi]) to replace Yersin in fieldwork. 

A large plague pandemic was making people suffer in Asia and Simond’s task, which he accepted with enthusiasm, was to help test the new Pasteur antiserum prepared from live cultures of Y. pestis. Beginner’s luck worked in his favour but not for long, later tests of serotherapy were disheartening despite which he continued furthering his research, looking for infected patients with the help of the-then French Consul in Bombay, Joseph Pilinski. 

During his research excursions, he observed that a large number of patients developed skin phlyctena that are small blisters that have plague bacilli and some fluid. These were early-stage patients. He then hypothesized that this phlyctena swells to become a neurotic buboe. The quest was to find the vector for the disease, the way it transmits and spreads, he thought that the initial lesion can be due to an insect bite. The concept of transmission was new to the fraternity, therefore it was treated with scepticism. 

Amongst sceptic academia, he found support for his thesis from his mentor and the man who first studied the malaria parasite in the blood, Charles-Louis Alphonse Laveran. His initial thoughts were that the cockroach could be a vector. However, it was counterintuitive to think of it as one because of its lack of mobility. Since rats were quite mobile and were prevalent everywhere, he thought that rat flea might have some clues and started studying it. It required temerity much more than it required courage to manipulate dead rats with bare hands and pick up their fleas in soaped water, but Simond was rewarded. Upon microscopic observation, he found that these fleas were full of bacilli. It was a moment of discovery. 

The Karachi Experiments

Paul-Louis Simond injecting plague vaccine June 4th 1898. Credit: Wikipedia

“Without delay, I proceeded to the experiment I had in mind since the time in Cutch-Mandvi when I had discovered Yersin’s bacillus in the digestive tract of fleas taken from plague-ridden rats. I prepared a device consisting of a large glass bottle whose bottom was covered with sand, which would absorb the urine of the rats. The lid consisted of wire mesh covered with fabric held tightly to the neck of the bottle with a drawstring. I was fortunate enough to catch a plague-infected rat in the home of a plague victim. In the rat’s fur, there were several fleas running around. I took advantage of the generosity of a cat I found stalking the hotel premises, borrowing some fleas from it. Once the sick rat was in the bottle, I deposited upon it the cat’s fleas from a test tube. I was thus quite sure the rat would be covered with parasites. After 24 hours the animal I was experimenting on rolled up into a little ball, with its hair standing on end; it seemed to be in agony. I then introduced into the bottle a small metal cage containing a perfectly healthy young Alexandria rat caught several weeks before and kept sequestered from any danger of infection. The cage was suspended with the inside of the bottle several centimetres above the layer of sand. The cage had three solid sides, but the other three sides were covered by a wire screen with a mesh size of about six millimetres. The rat inside the cage could not have any contact with the sick rat, the wall of the bottle or the sand. The next morning the sick rat had died without having moved from where it had been the day before. I left its body in the bottle for one more day. Then I carefully removed it, plunged it into alcohol and performed an autopsy. The blood and organs all contained an abundance of Yersin’s Bacillus. During the next four days, the other Alexandria rat remained imprisoned in its cage and continued to eat normally. About the fifth day, it seemed to have difficulty moving. By the evening of the sixth day, it was dead. An autopsy of this one (previously uninfected rat) revealed buboes both inguinal and axillary. The kidney and liver were swollen and congested. There were abundant plague bacilli in the organs and blood. That day, 2 June 1898, I felt an emotion that was inexpressible in the face of the thought that I had uncovered a secret that had tortured man since the appearance of plague in the world. The mechanism of the propagation of plague includes the transporting of the microbe by rat and man, its transmission from rat to rat, from human to human, from rat to human and from human to rat by parasites. Prophylactic measures, therefore, ought to be directed against each of these three factors: rats, humans and parasites. I subsequently repeated the same experiment with similar results” [Paul Louis Simond, Hotel Reynolds, Karachi, 1897] [A]

Pranav Sharma is a Science Historian and the Curator of the project on documenting the history of the Indo-French scientific partnership.


[A] Simond M, Godley ML, Mouriquand PDE. Paul-Louis Simond and His Discovery of Plague Transmission by Rat Fleas: A Centenary. Journal of the Royal Society of Medicine. 1998;91(2):101-104.