[A personal view of the history of the genus Yersinia].

The first recorded experience Australia had of the genus Yersinia was the arrival in 1889 of a French expedition led by Pasteur's nephew, Dr. Adrien Loir. At that time Australia was in the grips of an epidemic of rabbits, and Loir's purpose was to eradicate the rabbits by means of fowl plague (Pasteurella multocida). Sadly, bureaucratic and political obstacles prevailed, and Loir was never granted permission to release his biological control agent. Alexander Yersin had been tempted to join Loir's expedition, but elected in the end to travel to Hong Kong, where he discovered the plague bacillus. Had he gone to Australia, we might not now be speaking of the genus Yersinia... Historically, Yersinia pestis has affected not only world history but literature as well. In Shakespeare's Romeo and Juliet, the tragic denouement can be attributed directly to the consequences of the Great Plague. In times of plague, cities closed their gates to travellers, and houses their doors and windows. Thus Laurence's explanatory letter was prevented from reaching Romeo, who returned to take his life beside the drugged (but living) body of his beloved. Not only was the contemporary literature from which Shakespeare drew inspiration full of references to the plague, but he himself had experienced the social effects of the plague at first hand. The recent rejection of the name Y. pseudotuberculosis var. pestis in favour of Y. pestis is fitting, not simply on the grounds of preventing confusion - after all, Y. pseudotuberculosis can be an equally lethal pathogen. However, a review of the epidemiology for Y. pestis since the First Pandemic in the 6th Century AD lends support to Devignat's hypothesis that Y. pseudotuberculosis evolved from Y. pestis, rather than vice versa. This probably occurred in Europe shortly before the Second Pandemic, and the new mutant spread slowly through the European rodent population, immunising the carriers against plague. In other parts of the world which continued to be affected by plague, the rodent populations remained susceptible because they had not been immunised by exposure to Y. pseudotuberculosis. In some areas which have not been affected by plague, it is also possible that the native rodent populations have been immunised by Y. enterocolitica and its relatives. The plague, the first biological weapon, has killed more people than man's wars. It is our duty, as bacteriologists handling this pathogen, to refuse to allow our work to be used in modern warfare, to refuse to participate in any further warfare against humanity itself.