CIESIN Thematic Guides

Programs for Surveillance, Treatment, and Control of Vector-borne Diseases

Surveillance, treatment, and control of vector-borne diseases should be part of a comprehensive public health policy that promotes cooperation among researchers, medical clinicians, and government staff at the local, regional, national, and international levels. Although local programs that use the best information and technology can be effective in curbing potential outbreaks, total eradication in regions where vector-borne diseases are endemic cannot be guaranteed over time. Climate change due to global warming may facilitate the spread of these diseases beyond the existing borders. In The Potential Health Effects of Climatic Change, the World Health Organization (WHO) (1990a) reports that changes in temperature and rainfall may make areas on the fringe of regions where these diseases are endemic more suitable for existing vectors and/or hosts. Potential mass human migration due to the effects of climate change may also transport pathogens, vectors, and/or intermediary hosts into new areas, possibly transforming their ecosystems and providing the necessary components to permit the reproduction and transmission of the disease to large, unexposed populations.

Only recently have researchers and policymakers considered modern technology as a means for collecting critical information about vector-borne diseases, developing effective control strategies, and setting appropriate priorities. In "Strategies for Surveillance, Prevention, and Control of Arbovirus Diseases in Western North America," Eldridge (1987) notes that the current strategies for the surveillance, prevention, and control of arthropod-borne virus diseases in North America are based primarily upon epidemiological studies conducted prior to World War II, and despite refinements predictions of disease outbreaks are still unreliable. Eldridge reviews the basic concepts and judges their current validity. He recommends better integration of modern information-management systems technology, recent developments of sampling theory, and vector-competency data to improve surveillance, prevention, and control methods.

Surveillance is critical to predict potential outbreaks of vector-borne diseases. In the unpublished article "Public Health Effects of Global Climate Change and Ozone Depletion," Patz, Burke, and Epstein suggest four types of surveillance to track vector-borne diseases: 1) recording human cases; 2) determining the distribution and infectivity of vectors; 3) monitoring a broad range of non-human vertebrate reservoir species; and 4) following the weather patterns to help predict vector distribution. In "A Biometeorological Model of an Encephalitis Vector," Raddatz (1986) demonstrates how monitoring climatic parameters provides sufficient information to forecast the population of the key vector for Western Equine Encephalitis in Winnipeg and to forewarn weeks ahead of imminent outbreaks. In the chapter "Infectious Diseases and Atmospheric Change" of the 1990 book Global Atmospheric Change and Public Health, Shope recommends that more studies, both in the field and the laboratory, examine the disease agent's ability to adapt to changing climatic conditions to allow prediction of which pathogens might migrate and their potential destinations. Information about the parameters limiting vectors are equally important. In "CLIMEX: Recent Developments in a Computer Program for Comparing Climates in Ecology," Maywald and Sutherest (1989) point out that readily available data on the survival conditions for specific vectors can enable early and appropriate responses by decision makers. In the 1993 Lancet article "Global Health Watch: Monitoring Impacts of Environmental Change" by Haines, Epstein, and McMichael, the contribution "Vector-borne Diseases" reiterates the importance of low-cost continuous-field monitoring of disease incidence and recommends the use of remote sensing to detect changes in terrestrial ecosystems, the habitats for animal hosts and vectors (Freier et al.). "Application of Remote Sensing to Vector Arthropod Surveillance and Control" by Washino and Wood (in press) summarizes the current status of malaria and disease-vector surveillance needs, presents a brief overview of remote sensing technology, and provides a historic review of the applications of remote sensing in vector surveillance and control.

Treatments exist for some vector-borne diseases that can reduce the severity of the disease and alleviate painful symptoms. In his 1993 technical note "Use of Geographic Information Systems in Control Programs for Onchocerciasis in Guatemala," in the Bulletin of PAHO, Richards suggests that to be more effective, programs dispensing the drug ivermectin for the treatment of onchocerciasis should use geographic information systems (GIS) to help classify communities within a region by disease risk and, accordingly, to set priorities for dispensing the drug in a timely and appropriate manner. Richards concludes that GIS has also permitted the rapid assessment of drug coverage, analysis of impact indicators, and periodic retreatment for communities participating in the Guatemalan ivermectin distribution campaign. Treatment of infected animal reservoirs and human populations may also help to control the spread of the disease by reducing the abundance of the pathogenic agent within a region. In "A General Model for the African trypanosomiasis," Rogers (1988b) suggests examining the exact role of the animal reservoir to determine the most effective target of treatment. He concludes that treating the animal population may, in fact, be more successful in reducing human infections than the sole treatment of humans. In the chapter "The World Bank Health Sector Priorities Review: Helminth Infections" of Disease Control Priorities in Developing Countries, Warren et al. (1993) provide an in-depth and comprehensive discussion of both treatment and control strategies.

Control measures can be targeted at several different aspects of the life cycle of vector-borne diseases. Vaccinations for animal and human populations are aimed at preventing the proliferation of the pathogen, and pesticides reduce or eliminate the vectors. Also, planning regulations may prohibit development projects that create suitable habitats for the vectors; immigraion policies and custom inspections attempt to limit pathogen and vector entrance; and drug treatment may help limit future transmissions. In the section "Vector-borne Diseases" of the Environmental Protection Agency's 1989 report to Congress, The Potential Effects of Global Climate Change on the United States, Smith and Tirpak comment that although vector-control programs and improved hygiene have made vector-borne diseases rare in the United States, their resurgence is possible given current restrictions on pesticide use, the presence of several potential vectors, the influx of visitors and immigrants from endemic areas, the lack of effective vaccines for most of the diseases, and the creation of suitable vector habitats due to global warming. These concerns are based on the 1989 paper by Longstreth and Wiseman "The Potential Impact of Climate Change on Patterns of Infectious Disease in the United States." As part of their study, the authors convened a workshop to address key issues related to this topic. The participants concluded that the greatest threat to controlling potential outbreaks from vector-borne diseases due to climate change was the decrease in funding and support of public health programs responsible for disease surveillance and vector abatement. They recommended the creation of multidisciplinary expert teams charged with developing effective programs to cope with anticipated changes in the incidence and distribution of vector-borne diseases.