In 1773 a mysterious disease appeared in the Baie Saint-Paul area which spread through neighbouring parishes and finally reached the Montréal region. It was marked by buccal ulcers, pain in the limbs and finally the destruction of the bones of the nose, the palate, the gums and the appearance of swellings on the head, the clavicles and the bones of the limbs.
Encore en 1953, 481 Canadiens moururent de poliomyélite et un nombre beaucoup plus grand en fut atteint, mais l'année suivante, grâce à I'administration étendue du vaccin Salk, le nombre de décès se limita à 157.