THE DOCTOR'S WORLD BUENOS AIRES - When there is an extraordinary new outbreak of a well-known disease, it can provide new insights into how the disease is spread. A case in point is Chagas' disease, which exists only in the Americas, where it has infected an estimated 16 million people and causes about 50,000 deaths each year. This parasitic infection usually is transmitted through the bite of the kissing bug (also known as the reduviid bug and the triatomine bug). The insect lives in cracks and holes in poor housing, where it bites people, often on the face, while they...