ABSTRACT
Impact on human health Fleas bite people and wild and domestic animals causing irritation, blood loss, and severe discomfort. They may serve as intermediate hosts for certain helminths (Figure 11.3). In addition, they are also important in disease transmission. Plague, a zoonotic disease caused by the bacterium Yersinia pestis, has been associated with humans since recorded history, causing devastating effects on human civilization. For example, in the 14th century approximately 25 million people died of plague in Europe.2 Even though treatable with antibiotics, to this day, there are still hundreds of cases occurring annually over much of the world (Figure 11.4). In the United Staters, from 1970 to 1994 a total of 334 cases of indigenous plague was reported; the peak years were 1983 and 1984, in which there were 40 and 31 cases, respectively.3 Sylvatic plague, sometimes also called campestral plague, is ever present in endemic areas, circulating among rock and ground squirrels, deer mice, voles, chipmunks, and others. Three clinical forms of plague are recognized: bubonic, septicemic, and pneumonic. The septicemic and pneumonic forms are usually secondary to the bubonic form, and
the bubonic form is the most common in the Americas. Pneumonic plague is the most dangerous because of its spread by aerosols (coughing).
