Lyme disease--virtually unknown in the United States only a decade ago--has now been reported from almost every state; in the Northeast, it has become a major public health crisis. Under the name of borreliosis, the disease is also common in Europe. As Americans have become aware of the hazard they face from Lyme disease, they have become anxious to know how to avoid or control the disease. But the complex ecological interactions of Lyme disease make...