In other vector-borne diseases, flies and other insects transmit the infectious parasite. Sleeping sickness (African trypanosomiasis) for instance, is transmitted by the bite of the tsetse fly. Leishmaniasis is transmitted by the sandfly, again through a parasite-contaminated bite. This disease is a major problem in parts of Africa, Latin America, and the Middle East, where some 2 million cases occur each year (118). In its deadliest form, visceral leishmaniasis, fatality rates can reach 100 percent if untreated. In its more common form, the disease produces painful ulcers on the face, arms, and legs. WHO estimates that some 350 million people are at risk of contracting the leishmaniasis(119). As with other vector-borne diseases, its spread is accelerated by development projects such as road building or forest exploitation, which bring people into contact with the disease vector. Leishmaniasis is reappearing in some areas where it had once been controlled, in part because of the cessation of insecticide spraying to control malaria. A beneficial side effect of DDT, it turns out, was that it kept sandflies in check.
Chagas disease, also known as American trypanosomiasis, is unique to the Americas, where housing conditions pose the biggest risk factor. In this case the culprit, the parasite T. cruzi, is carried by both wild and domesticated animals. It is usually transmitted, however, by a blood-sucking bug that lives in thatched roofs. About one third of those infected develop a chronic form of the disease, which can lead to heart damage and death. WHO estimates that Chagas disease is the leading cause of cardiac death among young adults in parts of South America (120).
Airborne Diseases
Commonly known as ARI, acute respiratory infections kill more than 4 million people per year and are the leading cause of death among children under age 5 (121). This range of infections, which includes pneumonia in its most serious form, accounts for more than 8 percent of the global burden of disease (122). ARI’s reach is global: it is the most frequent disease worldwide and a common causes of visits to pediatricians in the industrialized countries, although essentially all deaths from ARI occur in the developing world.
The risk factors for ARI are numerous and difficult to sort out. Caused by different viruses or bacteria, ARI is closely associated with poverty. Overcrowding and unsanitary household conditions favor the transmission of the disease, which is spread by droplets from a cough or a sneeze or unwashed hands. Death most often strikes those children who are already weakened by low birth weight, other infections, and malnutrition (123).
Several other factors seem to exacerbate the disease. Exposure to tobacco smoke increases the risk of contracting these infections, and many studies implicate both indoor and outdoor air pollution. Indoor air pollution has been the focus of particular concern, specifically, the soot and smoke associated with the burning of biomass fuels such as wood, coal, or dung. Many people in the developing world, mostly in rural areas, rely on biomass fuels for heating or cooking. (See Changing Environments, Changing Health.) A cause-and-effect relationship between indoor air pollution and ARI has been difficult to prove, however, in part because people who use biomass fuels tend to be poor and exposed to multiple risks such as overcrowding, tobacco smoke, and malnutrition. Even so, the World Bank estimated in 1992 that switching to better fuels could halve the number of pneumonia deaths (124).
Other airborne diseases also thrive in conditions of poverty, exploiting enclosed spaces, crowding, and poor hygienic conditions. Tuberculosis (TB), to name just one, killed an estimated 3 million people in 1996, and nearly 7.5 million others developed the disease (125). TB is the single largest cause of adult death from infectious diseases. Roughly 95 percent of all TB sufferers are in the developing world, mostly in Southeast Asia, Western Pacific, and Africa – many in the slums of poor cities. In recent years, however, TB has resurfaced in developed countries, where it is concentrated among poor populations. (See Tuberculosis and Urban Inequality.)
Measles and diphtheria, also diseases of crowding and poverty, have been all but eliminated in the developed world since the advent of successful vaccines. In the developing world, however, measles still affects 42 million children per year who lack access to the vaccine; roughly 1 million of these children die (126). Since 1990, diphtheria has resurfaced in the former Soviet Union, triggered by social disruption and a drop in immunization rates (127).
Measles and diphtheria are just two of a cluster known as childhood (or vaccine-preventable) diseases. Other familiar diseases in this group are neonatal tetanus, poliomyelitis, and pertussis. This cluster, all linked with environmental conditions, accounts for nearly 15 percent of the total disease burden globally for children under age 5. Despite widespread immunization programs, these diseases nonetheless claimed the lives of 1,985,000 children in 1990 (128).
References and notes
118. World Health Organization (WHO)
, The World Health Report 1997: Conquering Suffering, Enriching Humanity (WHO, Geneva, 1997), p. 11.119. World Health Organization (WHO)
, The World Health Report 1997: Conquering Suffering, Enriching Humanity (WHO, Geneva, 1997), p. 11.120. World Health Organization (WHO)
, The World Health Report 1996: Fighting Disease, Fostering Development (WHO, Geneva, 1996), p. 53.121. World Health Organization (WHO)
, The World Health Report 1996: Fighting Disease, Fostering Development (WHO, Geneva, 1996), p. 25.122. Christopher J. L. Murray and Alan D. Lopez, eds., The Global Burden of Disease: Volume 1 (World Health Organization, Harvard School of Public Health
, and The World Bank, Geneva, 1996), p. 262.123. Sally K. Stansfield and Donald S. Shepard, “Acute Respiratory Infection,” in Disease Control Priorities in Developing Countries, Dean T. Jamison et al., eds. (Oxford University Press, Oxford, U.K., 1993), pp. 68- 70.
124. The World Bank
, World Development Report 1992: Development and the Environment (The World Bank, Washington, D.C., 1992).125. World Health Organization (WHO), The World Health Report 1997: Conquering Suffering, Enriching Humanity (WHO, Geneva, 1997), p. 15.
126. World Health Organization (WHO)
, The World Health Report 1996: Fighting Disease, Fostering Development (WHO, Geneva, 1996), p. 25.127. World Health Organization (WHO)
, The World Health Report 1996: Fighting Disease, Fostering Development (WHO, Geneva, 1996), p. 26.128. Christopher J. L. Murray and Alan D. Lopez, eds., The Global Burden of Disease: Volume 1 (World Health Organization, Harvard School of Public Health
, and The World Bank, Geneva, 1996), p. 465.
