Jean Danysz trained as a pathologist and worked mainly in France. His first published papers, in 1886 and 1888, dealt with new species and the evolution of Peridinium - protozoa belonging to the order Dinoflagellata. He also investigated artificial cultures for pathogenic microbes, and the action of tetanus toxin. By the middle eighteen-nineties he was a researcher at the Pasteur Institute in Paris.
In response to the spread of rinderpest to southern Africa in 1896 Danysz and his assistant, bacteriologist Jules Bordet*, made an offer to the government of the South African Republic (Transvaal) to come and work on a cure for this and other stock diseases. The offer was accepted and they arrived in Pretoria on 19 January 1897. An experimental station to study rinderpest had just been set up on the farm Waterval (near Onderstepoort), north of Pretoria. Here the two investigated the prevention and cure of the disease through inoculation with serum or defibrinated blood, in collaboration with the Government Veterinary Surgeon of the Transvaal, Arnold Theiler*. The main report on their work covered the period 15 February to 15 June 1897 and was published in the Government Gazette of 28 July as Rapport van de heeren Jean Danysz en Dr J. Bordet in zake hunne onderzoekingen op runderpest....
Earlier investigations of inoculation with serum had been conducted by Robert Koch* at Kimberley in January 1897 with limited success; and by Theiler and H. Watkins-Pitchford* in the western Transvaal, but the latter work was interrupted by Theiler's recall to Pretoria early in 1897. Danysz and Bordet used serum obtained from animals that had recovered from the disease and which had subsequently received several large doses of virulent rinderpest blood. The inoculated cattle were then put together with infected animals, from which they contracted a modified form of the disease under the protection of the serum. In this way the two investigators became the first to convert the passive immunity conferred by serum to active immunity.
One of their recommendations was that an Interterritorial Conference be held to discuss rinderpest. The conference took place in Pretoria from 2 to 13 August 1897 and provided an opportunity for a thorough exchange of ideas and results. Their method proved so successful that it was introduced throughout the country, replacing the bile inoculation method developed by Koch earlier in the year. By the end of the year the disease had been conquered. An English translation of their report was included in an article by Hutcheon (1898), while a report of the work, with Theiler as a third author, also appeared in the Veterinary Journal the same year.
Danysz was an uncongenial man, and more enterpreneur than scientist. He drove a hard bargain with the government to continue funding their research on other stock diseases, particularly horse sickness, again in collaboration with Theiler. A horse suffering from the disease was sent to them from Natal by David Bruce*. In compliance with a demand by Danysz their experimental station was moved from Waterval to a more suitable site at Belfast in October 1897. The amount of work done can be gauged from a comment by Watkins-Pitchford (1898) that their work produced bulky records, "the temperature charts alone when joined being over a mile in length". However, no breakthrough was made. Their contract expired after a year and Danysz left the country on 25 December 1897.
After his return to France Danysz made several more significant contributions to science. In 1900 he isolated Salmonella typhimurium, the causative agent of mouse typhoid and of food poisoning in humans. He became the first person to use the newly discovered radio-active element, radium, in the treatment of a malignant disease in 1903. This work eventually led to his thesis, Rescherches expÃ©rimentales sur les rays B de la famille de radium (Paris, 1913). At some time he described what came to be known as the Danysz phenomenon, namely that toxin added to antitoxin in an equal amount at once produces a non-toxic mixture, but when added at intervals results in a toxic mixture. Two of his books dealt with infectious diseases (1918) and non-infectious diseases (1920). An English translation, The evolution of disease, with a discussion of the immune reactions occurring in infectious and non-infectious diseases... was published in 1921.