Climate variability and change in the United States: Potential impacts on vector- and rodent-borne diseases

Diseases such as plague, typhus, malaria, yellow fever, and dengue fever, t ransmitted between humans by blood-feeding arthropods, were once common in the United States. Many of these diseases are no longer present, mainly bec ause of changes in land use, agricultural methods, residential patterns, hu man behavior, and vector control. However, diseases that may be transmitted to humans from wild birds or mammals (zoonoses) continue to circulate in n ature in many parts of the country. Most vector-borne diseases exhibit a di stinct seasonal pattern, which clearly suggests that they are weather sensi tive. Rainfall, temperature, and other weather variables affect in many way s both the vectors and the pathogens they transmit. For example, high tempe ratures can increase or reduce survival rate, depending on the vector, its behavior, ecology, and many other factors. Thus, the probability of transmi ssion may or may not be increased by higher temperatures. The tremendous gr owth in international travel increases the risk of importation of vector-bo rne diseases, some of which can be transmitted locally under suitable circu mstances at the right time of the year. But demographic and sociologic fact ors also play a critical role in determining disease incidence, and it is u nlikely that these diseases will cause major epidemics in the United States if the public health infrastructure is maintained and improved.