The number of wagon trains and pioneers had increased significantly since 1843. The settlers inadvertently brought with them diseases to which the Indians had no immunity. In the fall of 1847 measles carried west with an emigrant train swept through the Cayuse villages. In the cold and damp weather of November 1847 the epidemic reached its peak and half the tribe died, including most of the children. On November 29, 1847 the situation erupted into violence. A man from the east named Joe Lewis, hoping to create a situation in which he could ransack the Whitman Mission, spread the rumor among the local Cayuse that Marcus, who was attempting to treat them during the epidemic, was in fact deliberately poisoning them. On November 29, 1847, the Cayuse attacked Waiilatpu.