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Emerging Infections: Microbial Threats to Health in the United States
scenarios in California and Florida will be repeated in other areas of the country. One recent report documented two cases of malaria in New Jersey in which neither individual had traveled outside of the state (Malaria Branch, Centers for Disease Control, unpublished report, 1991). States in the Southwest and along the Gulf of Mexico are at particular risk for malaria because of their proximity to the border with Mexico, where many of the illegal immigrants gain access to the United States.
The international transportation of goods has indirectly led to the emergence of a number of infectious diseases. Most often it is not the goods themselves that pose the problem. Rather, it is infected animals in the cargo hold of a plane or ship, or bilge water contaminated with potentially pathogenic microbes that can hitch a ride from one part of the world to another. As discussed later in this chapter, the current cholera epidemic in the Western Hemisphere appears to be the direct result of international shipping. Transportation also played a significant role in the emergence of plague in the United States in 1900 (see Chapter 1).
Viruses are a particular problem because of their wide distribution, the ecology of their vectors, and their potential to cause human disease. The current International Catalogue of Arboviruses (Karabatsos, 1985) lists more than 500 separate viruses, about a fifth of which are capable of causing human disease. In general, viral diseases are hard to diagnose because of their variety and the difficulties associated with working with them in the laboratory. Viruses are often maintained in nature through enzootic cycles of transmission. Human infection is not essential to their long-term survival; in fact, humans often represent a dead-end host. There are undoubtedly undetected viruses in rural areas of the United States and in remote corners of the world that could cause human disease. With continued movement of people into rural areas, environmental damage caused by development, and the transport of people and products between remote areas and more developed parts of the world, the stage has been set for the emergence of "new" viral diseases.
HANTAAN AND RELATED HANTAVIRUSES
The Hantaan virus and related hantaviruses are some of the most recently recognized causes of an emerging disease. This group of viruses causes hemorrhagic fever with renal syndrome (HFRS), which is known as epidemic hemorrhagic fever in China and Korean hemorrhagic fever in Korea. The prototype virus, Hantaan, was first isolated in 1976 (H. W. Lee et al., 1978) from the lungs of its natural reservoir host, the striped field