After Malaria Is Controlled, What's Next?†

Because words mean everything, the vocabulary of the goal of a coordinated impact on a disease is important. Let us review the working definitions of three words: eradication, elimination, and control. Eradication represents permanently breaking the link of transmission of an agent, such that it no longer exists in circulation anywhere in the world and is not a threat to reemerge by natural means. Eradication is the highest goal and currently even theoretically possible for only those infectious diseases for which humans are the reservoir. Falling short of a stated goal of eradication has a history of engendering the people’s loss of confidence in public health, and thus, eradication should be undertaken only with a plan that is likely to succeed. Eradication has been accomplished only for smallpox in humans and rinderpest in ruminant animals. Current programs to eradicate dracunculiasis and polio have excellent chances of success. Measles is also a feasible and worthy target of eradication. In contrast, elimination represents the establishment of a geographic area free of a formerly endemic disease. Elimination has been achieved for some infectious diseases in regions as large as continents, but there is always the threat of reintroduction. Control can be defined as a reduction in the incidence of a disease to a defined target level. Although control sounds like a less impressive goal, it is not easy to accomplish and indeed, is a very significant achievement. Control of malaria would be such an achievement. Where do we stand today in regard to falciparum malaria? Its incidence has been reduced significantly by rapid diagnosis and treatment, insecticide-impregnated bednets, and vector control. Although a highly effective vaccine has yet to be developed, significant progress in vaccine research has been made. Even implementation of a vaccine that is only 30% effective would have a major impact on control and result in many lives saved. I do not know what the ultimate outcome of the efforts to control and eliminate malaria will be. If malaria were to be eradicated, a large portion of our society’s membership would have to find other scientific problems to address. A century ago, there was a medical specialty called syphilology. Reading medical records from my hospital from that long ago era revealed what a major public health problem tertiary syphilis was. The discovery of penicillin led to effective treatment of primary and secondary syphilis, the near disappearance of the late effects of syphilis, and in fact, the disappearance of the field of syphilology. It can happen. We would celebrate the removal of malaria from the field of tropical medicine. If this eradication occurs, what would we tackle next? The major strength of the American Society of Tropical Medicine and Hygiene relates to infectious diseases that afflict populations that are poor and reside in regions with limited resources. Our members are leaders in the scientific and clinical studies of vector-borne viruses, bacteria, protozoa, and helminths and their diseases, enteric infections, and other tropical infectious diseases. These fields need more scientific and clinical investigative effort today and have room for more persons’ contributions if funds were available for their support. To foreshadow my ultimate conclusion, we all need to develop collaborations that are interdisciplinary, share opportunities and resources, and maximize the breadth and impact of our strategies and efforts. Indeed, we really know less about the causes of suffering and death in the tropics than many believe. Even vital statistics of birth and death are unrecorded in many areas of the world, much less the accurate causes of disease and death. Some diagnoses, such as malaria, dengue fever, and typhoid fever, are often ascribed to patients’ illnesses without laboratory confirmation. Under the shadow of the umbrella of these diagnoses, other diseases are lurking. I have found significant incidences of spotted fever and typhus group rickettsioses and ehrlichiosis among series of diagnostic samples of patients suspected to have malaria, typhoid, and dengue in tropical geographic locations, where these rickettsial and ehrlichial diseases were previously not even considered by physicians to exist. Control of malaria or dengue would reveal the presence and magnitude of other currently hidden diseases and stimulate studies to identify the etiologic agents. In southeastern Asia, intensive studies of undifferentiated febrile diseases have documented that the incidences of scrub typhus and rickettsioses, including murine typhus, leptospirosis, and Japanese encephalitis, are as high as the incidence of dengue and in some studies, greater than the incidence of typhoid fever. In these studies, a specific diagnosis was not established in more than one-half of the subjects enrolled, despite the tremendous efforts. Thus, not only would greater knowledge of the true diagnosis improve the outcome for patients with more accurately diagnosed treatable life-threatening diseases, such as scrub typhus, but also, the large pool of cases without a diagnosis established at all would serve as a likely source for discovery of novel emerging infectious diseases. Just before I graduated from medical school, the war on infectious diseases was declared to be over and indeed, won. In 1992, more than two decades later, a period during which scores of newly discovered disease agents were identified, the concept of emerging infections was promulgated by a very prominent publication from the Institute of Medicine. Our *Address correspondence to David H. Walker, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 775550609. E-mail: [email protected] †Presidential address given at the 62nd Annual Meeting of the American Society of Tropical Medicine and Hygiene, November 16, 2013, Washington, DC.