application of a variety of environmental management tools and approaches,6 coupled with improvements in general hygiene, enabled much of the world to experience decades of respite from major vector-borne diseases in the first half of the 20th century. This success proved fleeting, however, and vector control programs waned due to a combination of factors including the development of pesticide resistance or—sometimes doomed by their own success—the loss of financial support when vector-borne diseases were no longer perceived as an important public health threat.
Today, vector-borne diseases are once again a worldwide concern and a significant cause of human morbidity and mortality, as Figure SA-1 illustrates (WHO, 2004c). Table SA-1 lists the disease burden (calculated in disability-adjusted life years, or DALYs) associated with each of several major human vector-borne diseases (WHO, 2004b).
Malaria accounts for the most deaths by far of any human vector-borne disease. The causative agents, Plasmodium spp., currently infect approximately 300 million people and cause between 1 and 3 million deaths per year, mainly in sub-Saharan Africa (Breman, 2001). As described by keynote speaker Duane Gubler, of the University of Hawaii, malaria provides a particularly dramatic example of vector-borne disease reemergence (Gubler, 1998). As stated by Scott and Morrison (see Chapter 2), when done properly, vector control is a well-documented and effective strategy for prevention of mosquito-borne disease. Familiar examples of successful mosquito vector interventions include: the worldwide reduction of malaria in temperate regions and parts of Asia during the 1950s and 1960s (Curtis, 2000; Rugemalila et al., 2006); yellow fever during construction of the Panama Canal; yellow fever throughout most of the Americas during the 1950s and 1960s (Soper, 1967); dengue in Cuba and Singapore (Ooi et al., 2006); and more recently, dengue in parts of Vietnam (Kay and Nam, 2005). Following the drastic depopulation of its vector, the anopheline mosquito, in the first half of the 20th century, malaria began its resurgence in Asia in the late 1960s. In Sri Lanka, where only 17 cases of malaria were reported in 1963, an epidemic of more than 440,000 cases erupted 5 years later after preventive vector control strategies were replaced with case-finding and drug treatment. Similarly, by the mid-1970s, millions of new post-control cases had occurred in India. In Africa, a recent upsurge in infection, punctuated by several major epidemics, has erupted in endemic areas (Nchinda, 1998).
Explosive epidemics have also marked the resurgence of plague, dengue, and yellow fever, a situation that Gubler characterized as particularly worrisome.
Some of these approaches include improvements in drainage and sanitation systems; filling standing water areas (pits/ponds/lagoons/irrigation ditches, etc.) that can be breeding sites for vector larvae; and the use of treated mosquito nets and covering of domestic water tanks and other potable water sources. The effective application of these environmental control measures greatly reduces the reliance on pesticides for vector control (Center for Science and Environment, 1999).