It is not known where the outbreak began, but the epidemic was not limited to the colonies on the Eastern seaboard, nor to the areas ravaged by hostilities. The outbreak spread throughout the North American continent. In 1775 it was already raging through British-occupied Boston and among the Continental Army's invasion of Canada. During Washington's siege of Boston the disease broke out among both Continental and British camps. Many escaped slaves who had fled to the British lines in the South likewise contracted smallpox and died. In the South, it reached Texas, and from 1778 to 1779, New Orleans was especially hard hit due to its densely populated urban area. By 1779 the disease had spread to Mexico and would cause the deaths of tens of thousands. At its end the epidemic had crossed the Great Plains, reaching as far west as the Pacific coast, as far north as Alaska and as far south as Mexico, infecting virtually every part of the continent.