The Impact of Tropical Diseases

Disease, like poverty, is not distributed uniformly among people and countries. In the developing world, the chance of dying is almost 30 times greater for an infant, at least 40 times greater for a child and more than a 1000 times greater for a pregnant woman compared to their counterparts living in an industrialized nation.

Infectious diseases account for approximately one half of all deaths in the tropical areas of the world. Nearly all of these deaths occur in children under the age of five. Those infectious diseases that are primarily found in the developing world or profoundly impact the health of people living in the tropics are frequently referred to as tropical diseases.

Disease distribution. Conditions that contribute to the risk for becoming infected with a tropical disease agent include biological factors related to population density, rural vs. urban living, nutritional status, climate and other environmental factors, as well as socioeconomic circumstances.

At one time, many of today's tropical diseases also occurred in temperate regions, since many of the same risk factors were found there. Today, however, industrial development and technological advances, including medical ones, have lessened the impact of these diseases in industrialized countries. For example, malaria and other mosquito-borne infections were once widespread in the United States.

Owing to improvements in land management and mosquito control, such diseases are no longer prominent in this country. Similarly, improvements in sanitation have reduced contact between man and infectious agents that are transmitted through contaminated food or water.

Global impact. These improvements have not yet been successfully transferred to large segments of the developing world. As summarized in the 1993 World Development Report of the World Bank, illness and death due to infection remain all too frequent occurrences in the tropics.

Every minute three children die of malaria alone, and seven people die of diarrheal diseases. The burden imposed by these diseases, however, extends beyond the sad story of young lives being lost. They impede the capacity of children to grow and learn, and of young adults to work and raise a family. They stifle efforts for individual, community and national advancement. They sap resources that would otherwise be utilized for improving the human condition.

It has been estimated 1 billion people in the world today lack access to adequate sanitation services and safe drinking water. Such poverty in the developing world has obvious global implications. It contributes to political instability and to the current worldwide debt crisis.

In addition, there are important ramifications for the world environment, as desperate populations explode in number and over utilize precious natural resources in an effort to obtain the most basic of human needs. In turn, all of these effects also influence worldwide emigration patterns. It is only with good, not bad, health that population overgrowth is consistently and voluntarily controlled.

  Impact on the United States. People living in poor and developing regions of the world are not alone in facing the ravages of infectious diseases. Infectious diseases continue to represent serious public health problems for people from industrialized countries like the U.S.

The outbreaks of plague in India and Ebola virus in Zaire in early 1995 galvanized the interest of the American public in the issue of emerging and re-emerging infections. Widespread media attention associated with these events, as well as increased incidence of other unexpected infectious disease problems in this country, have recently brought a new level of realization that developed countries are not immune to the health risks faced by rest of the world.

Historically, tropical diseases have impaired military operations. For example, malaria had a large impact on U.S. service personnel serving in southeast Asia; in some regions up to 60% of troops were reported to be infected.

Moreover, in the wake of recent Desert Storm operations, American military personnel who had served in the Persian Gulf were banned from donating blood so as to prevent infecting the U.S. blood supply with the parasitic disease leishmaniasis.

Citizens of industrialized countries may gain firsthand experience with tropical diseases, as increasing international travel makes them more liable to come into contact with the causative infectious organisms.

In 1993, almost 30 million Americans traveled to either Latin America, Africa, the Middle East or Asia. Air traffic allows an estimated one million people per day to cross international borders. Thus, it is becoming ever more common for business or vacation travelers from this country to venture into tropical areas, and conversely, ever easier for travelers from tropical areas to visit the U.S.

Malaria offers an example of the effects of this interchange. Malaria was widely prevalent in this country until well into the 20th century, when it was declared largely eradicated as a result of improved water management and access to effective drugs and insecticides. Thus, most Americans would likely consider it to be only an exotic "tropical" disease.

It may then be surprising that during recent years between 1,200 and 1,400 cases of malaria have been reported in the U.S. annually -- most acquired abroad. However, because vector mosquitoes capable of carrying malaria still inhabit the U.S., even a low level of infection has allowed limited local transmission of malaria in sites as diverse as California, Texas, Michigan, New York and New Jersey, where people who have never left this country have been diagnosed as having malaria.

Increasing international commerce also means that much of this country's food supply now is imported from tropical countries. The potential for transmission of food-borne pathogens was illustrated during the summer of 1996, with the unexpected outbreak of infections by the protozoan parasite Cyclospora cayatenensis carried by imported berries. More than 1,500 cases were reported from 14 states and Canada.

Health is a global concern. This increased awareness of the threat of infectious diseases cannot be taken as a rationale for isolationism. The international travel and trade inherent in our global economy is now an inescapable reality. Rather, with this realization that infectious diseases have not been conquered must come a renewed commitment to work together to discover new approaches to combat the common enemy.

There are many reasons why industrialized nations should be concerned about tropical diseases:

• the potential for emergence or re-emergence of these diseases in developed countries
• the effect of decreased child survival due to tropical diseases on future population overgrowth and quality of life worldwide
• the detrimental impact of tropical diseases on economic progress in developing countries, through the debilitation of young adults and the inhibition of physical and mental development in children
• the impact of inadequate living conditions in heightening the political divide between developing and industrialized nations
• the ultimate consequences of all these factors on the use of environmental resources in developing countries

Although the challenge of controlling tropical diseases is great, the needs and opportunities are enormous. If the risk of these diseases were reduced, investments in skills and education would be of greater value. From an economic point of view, improved health leads to increased and sustained productivity.

Consequent improvement of living conditions would lessen the gap between developing and industrialized nations, and improve our chances of working together toward successful solutions of mutual problems. Better health must be a global priority.

As stated by Dr. John Evans, chairman of the independent Commission on Health Research and Development, "with increased awareness of global interdependence in health, self-interest should reinforce humanitarian concerns in our efforts to mobilize the world's scientific talent to address the special health needs of the three quarters of the world's population who live in developing countries" (New England Journal of Medicine, volume 323, pages 913-915).

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