Over the last twenty years historians have uncovered and illuminated a new history of Amerindian peoples under European rule. Spanish defeat and subjugation of native populations, so an older historiography once held, were the history of these peoples in the sixteenth and seventeenth centuries. More recently, however, scholars have concentrated instead on the Indians' resilience and adaptability – their capacity, in the face of terrible odds, to maintain themselves and their societies.

The new historiography has begun to reveal the faces and voices of peoples long misunderstood. Still, little attention has been paid to another, very important element in the history of Amerindian populations – their biological adaptability and resilience. The social history of these peoples, in other words, will remain incomplete without further development of their pathogenic and immunological history. Disease, of course, existed in the Americas long before the sixteenth century. But, just as native societies resisted and eventually adapted to European conquest, so too did they adapt to Old World pathogens. Just as the responses of Indian communities to the economic and political demands of Spaniards varied over time, so did the immunological responses of indigenous populations change over generations. What began in the sixteenth century as contact and invasion soon would involve both Indians and Europeans in a new history of biological and social adaptation. And this story, as it developed in the northern sector of the viceroyalty of Peru – in Ecuador – is the subject of this book.