Communicable Disease Control Health Article

IMPACT OF COMMUNICABLE DISEASES

The gathering of humans in settlements (and subsequently cities) resulted in the development of periodic epidemics of communicable diseases, often with devastating impact. In the fourteenth century, for example, bubonic plague (carried by rats and transmitted to humans by fleas) swept through Europe, killing approximately one-quarter of the population of the continent. Epidemics of "crowd" diseases such as measles and influenza resulted from person-to-person transmission, and inadequate water and sewage management led to epidemics of diseases such as cholera and typhoid. Milk-and food-borne diseases also were common. Until the end of the nineteenth century, communicable diseases were the leading cause of death throughout the world.

In the United States in 1900, tuberculosis was the leading cause of death, followed by pneumonia and diarrhea. Along with diphtheria (in tenth place), these conditions accounted for more than 30 percent of all deaths in the country. Major reductions in morbidity and mortality from communicable diseases have resulted from improvements in sanitation, housing, and nutrition as well as introduction and use of vaccines and specific therapies.

Improvements in sanitation have dramatically reduced the burden of water-and food-borne diseases. Improvements in housing have also played an important role in reducing transmission of tuberculosis, and improvements in nutrition have made persons with infectious diseases less likely to die from their infections. The introduction and use of vaccines have resulted in global eradication of smallpox, significant progress toward eradication of poliomyelitis, and a marked reduction in illness and death due to diseases such as diphtheria, whooping cough (pertussis), and measles. Specific therapies such as antibiotics and antiparasitic drugs have had a significant impact on deaths due to infectious diseases as well as having some impact on the occurrence of the diseases by shortening the period in which an infected person is infectious to others.

The most dramatic improvements have been seen in the United States and other developed nations (see Figure 1). Although significant progress has also been made in developing nations, the World Health Report 2000 reports that 14 million deaths (25 percent of all deaths in the world in 1999) resulted from infectious diseases or their complications. There is a marked disparity in the importance of infectious diseases in high-income countries compared to middle-and low-income countries. In high-income countries, infectious diseases accounted for only 6 percent of all deaths, whereas in middle-and low-income countries they accounted for 28 percent of all deaths.

Worldwide, lower respiratory infections (e.g., pneumonia) and diarrhea are the leading infectious causes of death; each of these conditions can be caused by a variety of microorganisms. AIDS

Figure 1

was the single leading infectious cause of death in 1998, with an estimated 2.2 million deaths, followed by tuberculosis, with nearly 1.5 million deaths, and malaria, with 1.1 million deaths. Nearly 900,000 children died as a result of measles in 1998, even though an effective vaccine against measles was introduced in 1963 and has had a major impact in developed nations. Half of the children who died from measles lived in sub-Saharan Africa.

Much of the continuing toll of communicable diseases could be reduced by more effective use of existing vaccines and other tools for control of infectious diseases. For example, more effective use of measles vaccine and administration of vitamin A could prevent most of the deaths from measles. More widespread use of oral rehydration therapy in diarrhea (to combat the dehydration that is one of the major causes of death) could dramatically reduce current mortality. More effective use of bed nets, anti-mosquito strategies, and appropriate treatment could dramatically reduce malaria deaths. However, new tools will be needed to bring about maximum control of some diseases. Because microorganisms are continually evolving, they may change enough so that prior experience (infection) with the infectious agent does not provide protection. For example, influenza viruses may undergo dramatic changes with the result that pandemics (worldwide epidemics) may occur. In 1918–1919, pandemic influenza killed millions of people worldwide, more than 500,000 in the United States alone (see Figure 1).