tive pulmonary TB patients can exceed 50 percent (Dye et al., 1999; Mukadi et al., 2001).

Malaria

Malaria, caused by plasmodia parasites, is responsible for 300–500 million clinical cases and 1.5–2 million deaths each year (Bloland, 2001). Malaria is the most prevalent vector-borne disease and is endemic in 92 countries (Martens and Hall, 2000). It disproportionately affects rural populations living in housing without screens and doors, children under 5 years of age, and pregnant women. Africa accounted for nearly 90 percent of new cases reported worldwide in 1998; of these, 40 percent occurred in children under 5 years of age (WHO, 1999b).

Nearly all people who live in endemic areas are repeatedly exposed to mosquitoes that carry the infective agent, and those who survive malaria develop partial immunity. Endemic areas are subject to irregular rapid increases in incidence as the warm seasons arrive, rainfall and humidity increase, and populations migrate (IOM, 1991; WHO, 1999b). In areas where the infection rate is low and people are rarely exposed to the disease, however, the population is generally much more susceptible to the devastation of epidemic malaria—and the number of malaria epidemics is growing worldwide. Between 1994 and 1996, malaria epidemics in 14 countries of sub-Saharan Africa caused a high number of deaths, many in areas previously free of the disease (Nchinda, 1998). Drug resistance has been implicated as a contributing factor in the spread of malaria to new areas and the reemergence of the disease in areas where it had previously been eliminated, leading to increased morbidity and mortality (Bloland, 2001).

In 1999, the Centers for Disease Control and Prevention (CDC) received 1,227 reports of malaria cases with onset of symptoms in 1998 among persons in the United States and its territories; 98 percent of these cases were classified as imported, primarily from Africa (60 percent), Asia (20 percent), and the Americas (19.1 percent) (Holtz et al., 2001). Western European countries are reporting similar statistics for imported malaria (Fayer, 2000). Between 1990 and 1996, malaria increased as much as 100-fold in certain southern regions of the former Soviet Union; more recently, it has begun to emerge even as far north as Moscow (Fayer, 2000). Only a few isolated cases or small outbreaks have occurred in the United States, in areas where individuals with imported disease have provided a reservoir of infection for local-vector mosquitoes that have subsequently transmitted the infection to persons from that locality (Olliaro et al., 1996). However, increasing global travel, immigration, and the presence of competent anopheline vectors throughout the continental United States all contribute to the growing threat of malaria transmission even in nontropical North



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