What the future holds

What can we learn from historical and recent experience, and what does a social-ecological perspective reveal that can help with the challenges ahead in controlling diseases in an increasingly urbanized world? First, one-dimensional vector control measures and technological quick fixes will not work. The Aedes mosquito cannot be completely eliminated from any of today's cities in the tropics. Nor can effective vaccines be developed for every infectious disease that is a potential public health problem. Integrated multi-level disease prevention and control programs will be necessary (Gubler, 1989). However, if complacency prevails after these approaches achieve success, as it did when control programs against A. aegypti were disbanded and merged with other public health programs, prevention programs will again fail (Gubler, 1989, 1998a, 2005).

Moreover, a top-down approach and methods, based on a limited or inadequate understanding of mosquito ecology, evolution, and urban social ecology, will fail. This lesson can be learned from the flawed strategy of using ultra-low volume (ULV) insecticides to kill adult mosquitoes that replaced previous successful programs that targeted mosquito larvae in water containers (Gubler, 1989). ULV is a top-down reactive strategy, which relies heavily on prompt physician reporting of cases before widespread spraying is initiated. Space-spraying requires direct contact of pesticide with the adult mosquito. It does not penetrate inside houses or kill mosquito larvae in water containers, where the mosquitoes thrive. Within a few hours of spraying, A. aegypti is again feeding on and infecting humans.

Surveillance and public education should be constant and based on a bottom-up community participation and community ownership approach. Between outbreaks, it should be expected that the index of suspicion for primary care medical providers and public awareness will fall (Gubler, 1989). Public health professionals should stress the professional obligation to be aware of and report cases. Public education health messages should continue when there are no outbreaks, otherwise epidemics will proceed without public health attention until they are at near peak level. In the case of a mosquito-borne disease like dengue, at that point spraying is not likely to be effective. The consequence of this public health laxness in the Americas was that A. aegypti and dengue both reappeared and spread in the 1970s and 1980s in more frequent and longer epidemics (Gubler, 1989, 2005).

Prevention and control begin with recognizing the potential for a particular arthropod-borne disease in a given environment and understanding the specific conditions that promote its transmission and spread. For about a century it has been known that A. aegypti thrives in water containers, and public health prevention effectively targeted open-water reservoirs in population centers. That is still the case today, but the difference is that human population centers are an order of magnitude larger, resulting in more frequent and larger epidemics. Controlling breeding sites today requires the help of the community and the people who live in the homes where transmission occurs (Gubler, 1989). These interventions thus require public planning and education, as well as investment. Even financially-strapped local governments can do a better job through public education and outreach, while they work on and invest in more long-term expensive projects to improve water and sewage infrastructure.

Another lesson is to continue effective immunization programs, even when case incidence is low. African countries did not maintain their mass vaccination programs for yellow fever. There are many reasons for this, including financial constraints and civil instability, but keeping up and modernizing those programs might have prevented the resurgence of yellow fever.

Continuous, active public health surveillance with the assistance of modern laboratory virology must be the mainstay for effective tracking of dengue and other emerging arboviral diseases (Gubler, 1998). Active surveillance usually depends on mandatory reporting of suspected cases by diligent primary care health providers to public health agencies. Active surveillance also requires modern laboratory diagnostic methods, which may not be readily available in many developing countries. In these instances, a productive strategy is to develop ongoing partnerships with scientists and laboratories in developed nations. Fortunately, some of these features are beginning to be integrated within region-wide programs employing interdisciplinary approaches based on a largely social-ecological perspective, also called an "ecosystem approach" or "eco-bio-social approach," as in the case of a recent initiative aimed at controlling dengue in tropical developing countries (IDRC, 2006).

There is an immediate need for frontline medical professionals to be better educated in emerging diseases, and for modern laboratory-based epidemiological surveillance in endemic areas. This includes training primary care medical professionals to accurately diagnose patients that present with the symptoms of infectious diseases and promptly notify cases to public health departments. Tropical areas need up-to-date public health laboratories capable of accurately diagnosing disease. This includes the capability of doing genetic subtyping, which requires sophisticated training of laboratory personnel and is relatively costly. There also needs to be better sharing of surveillance information; this is a foundation stone for coordinating the prevention of epidemics across regions at-risk, and it helps link local government agencies to international NGOs. After being free of the disease since 1981, even Cuba, with its strong, centralized government health system, has experienced a re-emergence of dengue in the past 10 years. So while national attention to public health is essential, top-down planning and funding has limitations. Community partnerships with government agencies are not only a key part of the solution to overcoming short resources, they are also essential to sustaining disease control activities over the long term.

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