By Kent, Mary M; Yin, Sandra; Fontaine, Olivier; Boschi-Pinto, Cynthia
The 20th century was a triumph for human health and longevity. An Indian born in 1900 had a life expectancy of 22 years; an American baby born that year could expect to live about 49 years. By century’s end life expectancy had soared to unprecedented levels even in many poor countries. In 2005, average life expectancy at birth in the United States was 78 years; in India it was 62 years.1
The falling death toll from infectious diseases-primarily among infants and young children-led to these spectacular improvements in human life expectancy. For most of human history, communicable diseases such as malaria, smallpox, and tuberculosis (TB) were leading causes of death. TB was the second-highest cause of death in the United States in 1900, and malaria was a major problem in southeastern U.S. states. These diseases were effectively controlled in the United States and declined throughout much of the world in the 20th century. One major disease-smallpox-was virtually wiped out; another-polio-may be close to eradication.2
Improvements in sanitation and the development of vaccines and antibiotics accelerated the decline of infectious and parasitic diseases (IPDs) in the 20th century.
But, with a few exceptions, communicable diseases have not been vanquished. The microbes that cause these diseases continue to evolve, sometimes requiring new drugs and methods to combat them. New pathogens emerge, or make the jump from infecting animals to infecting humans. The most recent global estimates show that communicable diseases cause about one-third of all deaths (see Figure 1). Pneumonia and other lower respiratory diseases are the largest group, followed by HIV/AIDS, diarrheal diseases, TB, and malaria.
Communicable diseases impose vastly different health burdens on the wealthy and poor. They are the primary reason why a baby born in Somalia today is 30 times more likely to the in infancy than a baby born in France.3 Most of these diseases-including measles, HIV, TB, and malaria-are preventable and treatable using proven and often surprisingly low-cost health interventions. But control of communicable diseases will require additional financial investments, fundamental improvements in health delivery, and longer-term political commitments.4 International and national organizations such as the U.S. Agency for International Development (USAID), the World Health Organization (WHO), the World Bank, and UNICEF-aided by private funders such as the Bill & Melinda Gates Foundation-have spearheaded major efforts to attack infectious diseases.
Figure 1
Global Deaths by Leading Cause, 2002
Large-scale vaccination campaigns, for example, save millions of lives from measles and whooping cough each year. Other diseases- such as malaria-have proved more difficult to control. Although greatly diminished worldwide, malaria has resurged in many countries and continues to be a leading cause of childhood deaths in Africa and a drag on health in several other regions. Likewise, TB, which lost its hold on Europe and the United States by the mid-20th century, continues to devastate the health of millions in developing countries-especially where HIV/AIDS is prevalent. TB is re-emerging in many Eastern European countries where HIV is rapidly increasing.
Some of the miracle drugs that suppressed major diseases have lost their magic as viruses and parasites develop resistance to them. The mosquitoes that transmit malaria, dengue fever, and other diseases have become immune to some common insecticides. The parasites carried by mosquitoes have developed a resistance to drugs formerly used to treat them. Medical researchers are in a race to develop new weapons against diseasecarrying pests, viruses, and parasites before the current arsenal is obsolete.
In the late-20th century, the world was also hit with a new pandemic-HIV-that infects more than 40 million people today and causes at least 3 million deaths annually. HIV undermines the immune system-causing AIDS and making it harder for HIV-infected individuals to fight other diseases. It has increased death and disability from other IPDs, especially TB.
Other infectious diseases have emerged that have proved especially lethal-including Ebola and hantaviruses. While outbreaks tend to be highly localized, some bioterrorism professionals fear these viruses could be used as weapons.5 Influenza experts warn that we are likely to experience a worldwide influenza pandemic with the potential of causing millions of deaths, as did the Spanish Flu pandemic in the early 20th century. No one can predict when this might occur, or how deadly the next flu pandemic will be. The public health community is currently focused on the H5N1 avian flu, which is spreading around the world. H5N1 has not been transmitted person- to-person so far, but it could evolve into a major human health threat.6
Aspects of life in the 21st century-frequent travel, population migration, international trade, even climate change-all favor the spread and persistence of infectious and parasitic disease (IPDs). Dengue fever probably arrived in Latin America in recent decades as larvae in tire shipments from Asia, and cholera may have been carried in the holding tanks of freighters.7 Both are now major health concerns in parts of Latin America. If average temperatures continue to rise throughout the world, the range of disease- carrying mosquitoes will expand, exposing more people to malaria and dengue, among other diseases.8
This Population Bulletin explores the major health threats from infectious and parasitic diseases, with a special focus on malaria, diarrheal diseases, and TB. It examines recent trends and obstacles to prevention and treatment. It will also look at the potential threats from new pandemics and what the international health community and national governments are doing about them.
Demographic Dimension
For much of human history, populations grew slowly, if at all, because high birth rates were matched by high death rates from infectious diseases and other hazards. Major epidemics, such as the black plague that killed off one-third of Europe’s population in the 13th century, and smallpox, which decimated the indigenous population of the Americas in 16th and 17th centuries, were extreme examples.9 But tuberculosis, measles, pneumonia, and diarrheal diseases (including cholera and typhus) were constant threats. Living conditions improved in Europe after the 18th century because of a confluence of economic, political, and social developments, and a long stretch of moderate weather that made food more plentiful. But basic knowledge of what caused infectious disease was minimal. It wasn’t until the late 19th century that medical researchers accepted the idea that invisible microorganisms transmitted dis ease through water, pests, food, or close personal contact.10 On average, mortality remained quite high until the late 19th and early 20th centuries. After that time, several factors greatly reduced the mortality from IPDs, and ushered in an epidemiological transition to lower mortality:
* People learned the importance of better hygiene; especially washing hands and safely handling food, as knowledge of the “germ theory” of disease spread;
* Antibiotics and vaccines effective against IPDs became available; and
* Governments invested in clean water and sanitation systems.
Figure 2
Increase in Life Expectancy in Four World Regions, 1950-2005
These developments occurred at different times in different countries-better hygiene and sanitation practices helped IPDs fall markedly in developed countries even before antibiotics and vaccines were widely available, for example.11
Death rates declined, but birth rates remained high in many countries, creating an unprecedented surplus of births over deaths and causing growth rates to surge. Birth rates began to decline as families realized that more of their babies would survive to adulthood, especially as families moved away from farming and other livelihoods in which having many children might be an advantage. As birth rates declined, population growth rates subsided in many countries throughout the world, especially in Europe and North America.
But infant and child mortality from infectious diseases is still too high in many developing countries and among disadvantaged groups in nearly every country. This is the primary reason for the life expectancy gap between low mortality Western Europe and highermortality sub-Saharan Africa and South-Central Asia (see Figure 2). Progress against IPDs in many lowincome countries has lagged or stagnated because of a lack of resources, political instability, and corruption, among other barriers. HIV/AIDS epidemics have blocked progress in many sub-Saharan African countries.
The demographic toll of infectious diseases is reflected in the age and sex structure of high mortality countries. Except for AIDS and TB, the young are disproportionately affected by IPDs. Although children under age 15 account for one-quarter of all deaths in low- and middleincome countries, they account for one-half of the deaths from infectious and parasitic diseases, including lower respiratory infections (see Figure 3). More than 7 m\illion children under age 15 die each year from IPDs, at least 85 percent die before their fifth birthday.
As IPDs are controlled, infant and child mortality rates could fall quickly, as they did in many countries in the 1950s and 1960s. This welcome improvement in child survival could produce other demographic effects: a bulge in the number of children in high- mortality countries and a spike in population size. The magnitude and length of any surge in population growth will depend on whether couples in those countries want to limit their childbearing and whether they have easy access to family planning services. We are not likely to see a repeat of the rapid global population growth of the 1960s and 1970s, in part because the remaining high mortality countries make up less than 10 percent of world population. Sustained and rapid growth is also unlikely because fertility in most countries is lower than it was in the 1960s and because family planning is more acceptable and available.
Figure 3
Percent of all Deaths and Deaths From Infectious Diseases by Age in Low- and Middle-Income Countries, 2001
Geographic Disparities
The geographic disparities in the toll from infectious and parasitic diseases are most evident for children. In more developed regions, IPDs cause just 5 percent of deaths of children under age 5 (see Figure 4, page 6). This contrasts sharply with the percentages in lower-and middle-income countries. More than three-fourths of child deaths in Africa were attributed to infectious diseases around 2001, more than one-half in Southeast Asia, and just over one-third in Eastern Europe and in Latin America and the Caribbean.
Sub-Saharan Africa is the region plagued by the worst death and disability from IPDs, led by HIV/AIDS. Because of HIV, average life expectancy in southern Africa declined from 62 to 48 between the early 1990s and the early 2000s, reversing hard-won gains in life expectancy in the previous three decades.12 HIV/AIDS is the largest single cause of illnesses and deaths in the region, accounting for 19 percent of deaths in 2001. Five other IPDs accounted for another 34 percent of deaths: malaria, lower respiratory diseases, diarrheal diseases, measles, and TB.13
Sub-Saharan Africa also suffers the most death and disability from communicable tropical diseases such as onchocerciasis (river blindness), trypanosomiasis (sleeping sickness), and helminth infections.14
South Asia-including Bangladesh and India-is the other major world region where poverty is widespread and where infectious diseases are a major health problem (see Table 1). The tropical and semitropical climates, poverty, and lack of adequate infrastructure and health care have hindered the fight against preventable infectious diseases in this region.
The leading IPDs in South Asia are lower respiratory diseases and diarrheal diseases, which especially target children. Other IPDs in the top 10 causes of death are TB and HIV/AIDS, which especially affect working-age adults. The HIV/AIDS epidemic has been another setback for disease control. Although HIV prevalence has remained far below the levels in southern Africa, it is a growing problem.
Figure 4
Percent of Child Deaths From Infectious Diseases in Selected Regions, 2000-2003
Table 1
Top 10 Causes of Death in Low- and Middle-Income Countries, Selected Regions, 2001
Countries in Latin America and the Caribbean have made more progress in controlling infectious diseases. IPDs caused less than 15 percent of all deaths, and 38 percent of deaths of children under age 5 in the region around 2001. The incidence of measles deaths, for example, has fallen markedly throughout the region, and, except for Haiti, HIV has not exceed 1 percent in most countries in the region.15
Some parasitic diseases, such as schistosomiasis, are endemic in parts of Latin America, and dengue fever and its more serious complication, dengue hemorrhagic fever, actually increased in urban areas during the 1990s.
Differences by Age
Pneumonia, diarrheal diseases, and malaria are the major causes of death for children under age 15-with the vast majority succumbing before age 5. Children who survive until their fifth birthdays have already fought off a number of childhood infections and have a good chance of living until age 15. The 5-to-l4 age group in high- mortality countries tend to be a healthier group-they developed resistance to many IPDs and they are not yet subject to most of the health problems that harm adults, including complications of pregnancy and childbirth, TB, HIV, and such noncommunicable diseases such as cancer and cardiovascular diseases.
HIV/AIDS, TB, and lower respiratory infections (especially pneumonia) are the top three infectious diseases that strike those ages 15 to 59. People age 60 or older are most likely to die of a noncommunicable disease, including heart disease, cancer, and stroke, but older people also succumb to infectious diseases. Pneumonia is a major cause of death to the elderly in all countries. Older people often have several health problems that make them less able to recover from respiratory infections. People whose immune systems are compromised by TB and malaria and other parasitic infections are especially vulnerable. In low- and middleincome countries, lower respiratory diseases, TB, and HIV are the top three causes for people age 60 or older.
Childhood Diseases
A relatively small number of infectious diseases are responsible for 62 percent of deaths to children under age 5 in low- and middle- income countries.16 Children rarely the from these causes in more developed countries because of widespread vaccination, greater access to health care, and better hygiene and sanitation. Less developed countries have made great strides in combating IPDs, and infant mortality rates have declined in most regions. But the gap between rich and poor countries remains substantial.
In 1974, WHO launched the Expanded Programme of Immunization (EPI), with the aim of vaccinating all children against six major childhood killers: whooping cough (pertussis), diphtheria, tetanus, polio, measles, and childhood tuberculosis. Three doses of the vaccines for pertussis, diphtheria, and tetanus are required during the child’s first year of life for full protection-meaning three separate visits with health-care workers. The polio vaccine also requires additional doses. By 2004, at least three-fourths of children in less developed countries were protected by at least one of the EPI vaccines, and coverage was above 90 percent in some regions. Yet maintaining these high coverage rates for each new generation of children is an ongoing challenge in resource- constrained countries.
Vaccination rates are still quite low in many countries. Fewer than one-half of the children in the Dominican Republic, Haiti, and Jordan were protected from all six EPI target diseases, as were fewer than onefifth of children in Chad, Ethiopia, and Nigeria.17 Within countries, children living in rural areas are often much less likely to have received all their vaccinations. In Jordan, just 7 percent of children in rural areas were vaccinated in 2002, compared with 34 percent of urban children. In Vietnam, the rural rate was 62, compared with 87 in urban areas (see Figure 5). In Bangladesh, in contrast, the gap between urban and rural is smaller and the overall percentage fully vaccinated is much higher, demonstrating that low-income and largely rural countries can achieve high vaccination rates.
Infant and child mortality is greater in rural areas of most countries. In Bolivia, 81 infants died per 1,000 births in rural areas around 2003, for example, compared with 57 deaths per 1,000 births in urban areas.18
But the WHO immunization programs have saved millions of lives and have nearly eliminated polio. Around 2001, measles was still claiming at least 676,000 lives per year, but vaccine coverage had averted more than 1 million deaths (see Table 2, page 8). The pertussis vaccine averted more than another 1 million deaths, according to estimates.
EPI has been expanded and additional vaccines are being developed and administered. In particular, many less developed countries are vaccinating children against hepatitis B, yellow fever, and a deadly strain of influenza (Haemophilus influenzae type b, or Hib). A vaccine to protect children against the rotavirus-which causes severe diarrhea-may soon be available in less developed countries, with the potential of saving thousands of lives each year. Vaccines against meningitis and pneumococcal disease may also become available, further cutting the disease burden from IPDs.19
Figure 5
Percent of Children Fully Vaccinated, by Residence, Selected Countries, 2002-2005
Table 2
Vaccine-Preventable Childhood Diseases, 2001
Disability and III Health
While the IPDs cause excess and often preventable deaths, their total effect on global health is much greater. Infectious diseases affect physical and mental growth in childhood, which can cause life- long disabilities that impair a person’s ability to support themselves and their families. Pneumonia, which is responsible for about one-fifth of deaths of children under age 5, can permanently damage lungs. Measles can lead to blindness, polio to crippling, and hepatitis to liver cancer, for example. Malaria in pregnant women can cause low birth-weight babies, which can lead to a host of developmental problems. Malaria and other parasitic diseases often produce severe anemia, which can render their victims unable to work. Skin diseases can disfigure or disable victims, affecting their ability to function normally in society.20
Many people suffer from more than one IPD, which may be exacerbated by other health problems-especially malnutrition. WHO estimates that malnutrition is the underlying cause of more than one- half of the deaths among children under age 5.
Helminth infections caused by parasitic worms are exa\mples of IPDs that rarely cause death directly but undermine health in ways that can affect all aspects of an individual’s life. Some helminth infections are transmitted by close contact with soil or water containing the parasites, which links them to poor living conditions. They tend to thrive in warm climates in tropical and subtropical areas. The persistence of some helminths, such as schistosomiasis, has been attributed to building of dams and other construction projects that alter the flow of waterways in ways that promote the growth of the snail that is integral to the parasites life cycle. As such, an increase in schistosomiasis can be an unintended consequence of economic development.
Helminth infections can thwart educational advancement and hinder economic development. The severe anemia triggered by helminth infections in children can stunt physical growth, undermine physical fitness, and cause behavior-related problems. These infections can also cause chronic urinary and kidney problems in adults. Disability, pain, and undernutrition hinder individuals’ ability to contribute to society and the economy. Such infestations can be prevented by using clean water, handwashing, and disposing of human wastes adequately. Routine deworming programs in schools have proved highly effective against some of the most common parasitic infections.21
The total health burden of a disease can be estimated by combining the estimated years of life lost prematurely by people who died of the disease, and the number of years of disability caused by the disease. Malaria, for example, caused an estimated 2 million deaths in 2002, but was responsible for the loss of 46 million disability-adjusted life years, or DALYs (see Table 3). The DALYs lost because of schistosomiasis in 2002 were more than 100 times the number of deaths from the disease. Each DALY represents one lost year of health.
Table 3
Deaths and DALYs Caused by Selected Communicable Diseases, 2002
Conclusion
Reducing the health burden from communicable diseases is a top priority for the international community. Two of eight millennium development goals (MDGs) embraced by all members of the United Nations in 2000 deal specifically with infectious diseases:
* Reduce the child mortality rate to two-thirds the 1990 level by 2015. Because IPDs causes at least one-half of deaths to children under age 5, this cannot be achieved without drastic reduction in communicable diseases.
* Combat HIV, malaria, and TB, among other diseases. This MDG not only calls for halting the spread of these diseases, but for reducing their incidence in the population by 2015.
Because health affects and is affected by so many aspects of life, the fight against communicable diseases is advanced by efforts to meet all the MDGs, including eradicating poverty and hunger, achieving universal primary education, promoting gender equality, improving maternal health, and ensuring environmental sustainability.
The means for preventing or controlling the major infectious diseases already exist-and are affordable even in poor countries. The most cost-effective health interventions have been documented by the monumental Disease Control Priorities Project and released in 2006.22 If these measures are implemented around the world-for example fully vaccinating children, providing insecticide-treated bednets to combat malaria, and improving basic health services for children-the health burden from infectious diseases could be drastically reduced. And, new vaccines and drugs offer hope in the fight against the most pernicious communicable diseases.
The control of IPDs is an ongoing endeavor. We can eliminate unnecessary death and disability, but we will always face the threat of new and evolving microbes. As American historian William McNeill has stated:
“Ingenuity, knowledge, and organization alter but cannot cancel humanity’s vulnerability to invasion by parasitic forms of life. Infectious disease which antedated the emergence of humankind will last as long as humanity itself… “23
References
1 Carl Haub, 2005 World Population Data Sheet of the Population Reference Bureau (Washington, DC: Population Reference Bureau, 2005); United Nations (UN), Population of India: Country Monograph Series, no. 10 (New York: UN, 1982): 137; and Elizabeth Arias, “United States Life Tables, 2003,” National Vital Statistics Reports 54, no. 14 (2006): table 11.
2 S. Jay Olshansky et al., “Infectious Diseases-New and Ancient Threats to World Health,” Population Bulletin 52, no. 2 (1997).
3 Haub, 2005 World Population Data Sheet.
4 Dean T. Jamison et al., ed., Priorities in Health (New York: Oxford University Press, 2006).
5 U.S. Centers for Disease Control and Prevention, Emergency Preparedness: Bioterrorism, accessed online at www.bt.cdc.gov, on April 24, 2006.
6 World Health Organization (WHO), Epidemic and Pandemic Alert and Response: Pandemic Preparedness, accessed online at www.who.int, on May 1, 2006; and Lone Simonsen et al., “Pandemic Influenza and Mortality,” in The Threat of Pandemic Influenza, ed. Stacey Knobler et al. (Washington, DC: The National Academies Press, 2005): 89- 114.
7 Olshansky et al., “Infectious Diseases”; and WHO, Media Centre: Dengue and Dengue Haemorrhagic Fever, accessed online at www.who.int, on April 28, 2006.
8 Anthony J. McMichael, Planetary Overload (Cambridge, UK: Cambridge University Press, 1993): 132-69.
9 William H. McNeill, Plagues and Peoples (New York: Anchor Press, 1989): 209-15; and Jorge A. Brea, “Population Dynamics in Latin America,” Population Bulletin 58, no. 1 (2003).
10 Ian R. H. Rockett, “Population and Health: An Introduction to Epidemiology,” 2d ed., Population Bulletin 54, no. 4 (1999): 7-8.
11 Olshansky et al., “Infectious Diseases.”
12 UN, World Population Prospects: The 2004 Revision (New York: UN, 2005): xxii; and Peter R. Lamptey, Jami L. Johnson, and Marya Kahn, “The Global Challenge of HIV and AIDS,” Population Bulletin 61, no. 1 (2006).
13 Colin D. Mathers, Alan D. Lopez, and Christopher J. L. Murray, “The Burden of Disease and Mortality by Condition: Data, Methods, and Results for 2001,” in Global Burden of Disease and Risk Factors, ed. Alan D. Lopez et al. (New York: Oxford University Press, 2006): table 3.10.
14 See the following chapters from Dean T. Jamison et al., eds., Disease Control Priorities in Developing Countries, 2d ed. (New York: Oxford University Press, 2006): Jan H.F. Remme et al., “Tropical Diseases Targeted for Elimination: Chagas Disease, Lymphatic Filariasis, Onchocerciasis, and Leprosy”; Pierre Cattand et al., “Tropical Diseases Lacking Adequate Control Measures: Dengue, Leishmainiasis.and African Tryponosomiasis”; and Peter J. Hoetz et al., “Helminth Infections: Soil-Transmitted Helminth Infectious and Schistosomiasis”: 433-483; and Donald G. McNeil Jr., “Dose of Tenacity Wears Down a Horrific Disease,” The New York Times, March 26, 2006.
15 Lamptey, Johnson, and Kahn, “HIV and AIDS.”
16 Mathers, Lopez, and Murray, “The Burden of Disease and Mortality”: table 3.1.
17 ORC Macro, Stat Compiler, accessed online at www.measuredhs.org, on April 12, 2006.
18 ORC Macro, Stat Compiler, accessed online at www.measuredhs.org, on May 15, 2006.
19 UNICEF, The State of the World’s Children 2006 (New York: UNICEF, 2005): table 3; GAVI, GAVI Fact Sheets, accessed online at www.vaccinealliance.org, on April 12, 2006; Logan Brenzel et al., “Vaccine-Preventable Diseases,” in Disease Control Priorities in Developing Countries, 2d ed., ed. Dean T. Jamison et al. (New York: Oxford University Press, 2006): 397.
20 Disease Control Priorities Project, In Brief. Factsheet, Infectious Diseases, accessed online at www.dcp2.org, on April 25, 2006.
21 Disease Control Priorities Project, In Brief. Factsheet, Infectious Diseases.
22 The publications and related information for the Disease Control Priorities Project are available at www.dcp2.org.
23 McNeill, Plagues and People: 295.
SPECIAL SECTION: Diarrheal Diseases
by Olivier Fontaine and Cynthia Boschi-Pinto
Two decades ago diarrhea was responsible for around 5 million deaths of children under age 5 each year. Now diarrheal diseases account for less than 2 million child deaths a year, thanks to major public health efforts to prevent and treat dehydration, the main cause of death from diarrheal disease.
Diarrhea causes severe loss of water and electrolytes (sodium, chloride, potassium, and bicarbonate). Children can become dehydrated when these losses are not replaced adequately. The early stages of dehydration present no signs or symptoms. As dehydration increases, children may exhibit thirst, restless or irritable behavior, sunken eyes, and less elastic or supple skin.1 In infants, the soft boneless areas in the skull may be sunken.
These symptoms become more pronounced in a child (or adult) suffering severe dehydration, and the child may go into shock, which may be characterized by diminished consciousness, lack of urine output, cool moist extremities, a rapid and feeble pulse, and low or undetectable blood pressure. If the child is not rehydrated promptly, death quickly ensues. Dehydration from diarrhea can be prevented by providing the child more fluids than usual, and/or increased frequency of breastfeeding, during acute episodes.
Decreased food intake, decreased nutrient absorption, and increased nutrient requirements during diarrhea episodes often combine to cause weight loss and failure to grow: The child’s nutritional status declines and any preexisting malnutrition is made worse. In turn, malnutrition contributes to even more severe and frequent diarrhea. One can prevent the nutritional consequences of diarrhea by ensuring that children continue to feed during diarrhea and increasing food intake afterward.2
Increasing the intake of fluids a child would normally drink, supplemented by oral rehydration salts (ORS) to treat dehydration together with continued feeding to prev\ent malnutrition have proven to be powerful interventions for the prevention of childhood deaths from diarrhea.
In many countries, the decline in diarrhea mortality observed over the years is linked to the increased use of oral rehydration therapy (ORT), defined as “increased administration of fluids plus continued feeding,” the public health intervention recommended by WHO and UNICEF.3 However, diarrheal diseases remain a leading cause of preventable death, especially among children under age 5 in developing countries.
The Scope of the Problem
Of the 10.6 million child deaths a year globally, 1.9 million, or 18 percent, are related to diarrheal diseases. Almost all (98 percent) of the 1.9 million diarrheal deaths occur in low- and middle-income countries. Forty percent of all diarrheal deaths are in Africa and 32 percent in South and Southeast Asia. Moreover, country-specific estimates have revealed that just 15 countries (eight in sub-Saharan Africa and four in South and Southeast Asia) account for about 70 percent (1.3 million) of all diarrheal deaths worldwide. In the developing world, mortality rates are about twice as high in infants than in children ages 1 to 4.4
While the estimated number of deaths due to diarrhea have declined markedly over the last two decades, the incidence of diarrhea has declined very little. Between the 1980s and 2000, there were between two and three episodes of diarrhea per child under 5 per year. Since 1990, some studies show a slight increase in diarrhea incidence rates.5 Morbidity rates have been consistently greatest among infants ages 6 to 11 months.6
Of the 1.9 million deaths due to diarrhea, 61 percent are associated with undernutrition.7 Diarrhea and malnutrition reinforce one another in a potentially deadly spiral: Frequent and prolonged episodes of diarrhea can lead to malnutrition, and malnutrition can facilitate the evolution of diarrhea towards death. Children living in poor households are more likely to be exposed to health risks, less resistant to disease, and less likely to receive appropriate care from a health provider.8 In addition, the main risk factors for developing diarrheal disease-poor access to water and sanitation, improper hygiene and feces disposal practices at home, poor housing, and crowding-are intrinsically linked to poverty. In the African region, where the proportion of diarrhea deaths is highest, approximately one-half of the population has no access to safe water and two-thirds lack access to hygienic sanitation.9 Disparities within countries also illustrate income inequalities: Diarrhea prevalence in some countries is almost twice as high among the poorest 20 percent of the population as it is among the richest 20 percent (see figure).
The long-term consequences of diarrheal diseases remain poorly understood. However, repeated diarrheal episodes can affect a person’s overall intellectual capacity and concentration.10 In addition, early childhood malnutrition-a common consequence of repeated episodes of diarrhea-reduces physical fitness and work productivity in adults.11
Successful Preventive Interventions
Strategies to control and treat diarrheal diseases have remained relatively unchanged since the 1980s. Seven effective interventions continue to be high priorities:
* Breastfeeding;
* Improvement in weaning practices;
* Rotavirus immunization;
* Cholera immunization;
* Measles immunization;
* Improvement of water supply and sanitation facilities; and
* Promotion of personal and domestic hygiene.
Promoting Exclusive Breastfeeding
Breastfed children under age 6 months are six times less likely to die of diarrhea than infants who are not breastfed.12 In 1984, researchers estimated that exclusive breastfeeding could reduce diarrheal deaths by 24 percent to 27 percent in the first six months of life.13 Based on this evidence, exclusive breastfeeding for the first six months of life has been promoted as an important weapon against diarrhea. Breastfeeding is encouraged-and early bottlefeeding discouraged-through hospital policies and actions; counseling and education by peers or health workers, mass media campaigns, community education, and mothers’ support groups; and implementation of the International Code of Marketing of Breastmilk Substitutes. This code is designed to ensure adequate information about the importance of breastfeeding young infants and appropriate marketing and distribution of breast milk substitutes. Increases in exclusive breastfeeding as a result of education and promotion have been associated with a significant reduction in the risk of diarrhea.14
Complementary Feeding
Complementary feeding, in which an infant transitions from exclusive breastfeeding to normal family foods, typically occurs between 6 months and 18 to 24 months of age. It is a very vulnerable period for infants’ health. All infants should start receiving foods in addition to breast milk after 6 months of age. The complementary foods should be at least as nutritious as breast milk, they should provide enough calories for a developing child, and they should be appealing enough for the child to eat. To minimize the risk of contamination with pathogens, all food should be prepared and served under hygienic conditions.
Improved complementary feeding practices to prevent or treat malnutrition could save as many as 800,000 lives per year. 15 While the increased incidence of diarrhea associated with the introduction of foods in addition to breast milk feeding has been recognized for a long time, two key risk factors have not received sufficient attention: feeding with contaminated foods, and failing to provide appropriate nutrients during and after a diarrheal episode.16 Several interventions have been proposed to reduce microbial contamination of common foods, including education, improved household storage of foods, reduced pathogen multiplication in food (such as food fermentation), and the use of probiotics, nonpathogenic organisms (Lactobacillus GG) that colonize the gut and create an environment that resists infection by pathogens.17 However, the effectiveness of these techniques has not been adequately evaluated.
While mothers and other caregivers are told to introduce infants to the foods eaten by the whole family, it is practically impossible to meet all of an infant’s essential micronutrient requirements with unfortified foods, especially in places where meat, fish, and dairy products are limited.18 While vitamin A supplementation may not significantly reduce the incidence of diarrhea and other common childhood illness, it may reduce the incidence of severe diarrhea and mortality due to gastroenteritis.19 Adding zinc to the diet can also reduce the incidence of diarrhea.20
Diarrhea Prevalence in Under-5 Children by Socioeconomic Status in Selected Countries, 2002
Advances in Management
Two recent advances in managing diarrheal diseasenewly formulated oral rehydration salts (ORS) containing lower concentrations of glucose and salts, and zinc supplementation-can drastically reduce the number of child deaths. These new advances, used in addition to prevention and treatment of dehydration with appropriate fluids, breastfeeding, continued feeding and selective use of antibiotics, will reduce the incidence, duration, and severity of diarrheal episodes.
New Oral Rehydration Salts (ORS) solution
To improve acceptance of ORS solution by mothers and health workers, researchers developed an ORS solution that could not only prevent or treat dehydration from all types of diarrhea, but provide other important clinical benefits. Reducing the solution’s salt and glucose content reduced stool output, vomiting, and especially, the need for intravenous fluids. Rehydration salts with lower salt and glucose content could substantially reduce childhood deaths from diarrhea (except for cholera), especially in areas where intravenous fluids or the skills to administer them are not available.21 Based on this finding, WHO and UNICEF launched the new ORS solution in May 2002 and included it in the WHO model list of essential medicines in March 2003. Since January 2004, the new ORS formulation is the only one procured by UNICEF.
Zinc Supplementation
When a zinc supplement is given during an episode of acute diarrhea, it reduces the episodes duration and severity.22 In addition, zinc supplements given for 10 to 14 days lower the incidence of diarrhea in the following two to three months.23 Using zinc to manage diarrhea could save 300,000 children each year.24 Accordingly, WHO and UNICEF have issued new recommendations for the clinical management of diarrhea. Along with increased fluids (ORS solution or home-made fluids) and continued feeding, all children with acute diarrhea should be given zinc supplements for 10 to 14 days.25
There is now good evidence that the promotion of oral rehydration therapy with other key preventive and curative interventions have played a large role in the welcome reduction in childhood deaths caused by diarrhea.26 To reach the United Nations Millennium Development Goal (MDG) of reducing the 1990 mortality rate among children under 5 by two-thirds by 2015, the challenge for the next decade will be to increase or ensure universal coverage of these interventions in developing countries.
To meet this challenge, health worker capacity must be maintained to ensure that all mothers and caretakers are taught:
* To prevent dehydration through early administration of increased amounts of appropriate fluids available in the home (and ORS solution, if on hand);
* To continue feeding (or increase breastfeeding) during the episode and increase all feeding after the episode;
* To recognize the signs of dehydration and the need for medical care; and
* To provide children with 20 milligrams per day of zinc for 10 to 14 days.
Over the long term, the most promising improvements in child health will come from integrating health care \through initiatives such as the Integrated Management of Childhood Illness (IMCI), which promotes the accurate identification of childhood illnesses, ensures appropriate combined treatment of all major illnesses, strengthens the counseling of caretakers, and speeds up the referral of severely ill children. However, in lowresource settings, immediate action may be still be necessary to quickly reduce the high disease burden of diarrhea.
References
1 Skin turgor is visible when a fold of skin that is pinched and then released holds a tent-like shape for a few seconds instead of flattening out immediately.
2 To help prevent dehydration, home fluids, which are normally made at home and do not require special ingredients, should always be available. Depending on the local culture, such fluids might include soup, rice water, or yoghurt drinks.
3 Sofia Villa et al., “Seasonal Diarrhoeal Mortality Among Mexican Children,” Bulletin of the World Health Organization 77, no. 5 (1999): 37580; Peter Miller and Norbert Hirschhorn, “The Effect of a National Control of Diarrhoeal Diseases Program on Mortality: The case of Egypt,” Social Science at Medicine 40, no. 10 (1995): S1- S30; Cesar G. Victora et al., “Falling Diarrhoea Mortality in Northeastern Brazil: Did ORT Play a Role?” Health Policy and Planning 11, no. 2 (1996): 132-41; Cesar G. Victora et al., “Reducing Deaths from Diarrhoea Through Oral Rehydration Therapy,” Bulletin of the World Health Organization 78, no. 10 (2000): 1246- 55; and Jane C. Baltazar, Dinah P. Nadera, and Cesar G. Victora, “Evaluation of the National Control of Diarrhoeal Disease Programme in the Philippines, 1980-93,” Bulletin of the World Health Organization 80, no. 8 (2002): 637-43.
4 Jennifer Bryce et al., “WHO Child Health Epidemiology Reference Group. WHO Estimates of the Causes of Death in Children,” Lancet 365, no. 9465 (2005): 1147-52; World Health Organization (WHO), World Health Report 2005: Make Every Mother and Child Count (Geneva: WHO, 2005); and Margaret Kosek, Caryn Bern, and Richard L. Guerrant, “The Global Burden of Diarrhoeal Disease, as Estimated From Studies Published Between 1992 and 2000,” Bulletin of the World Health Organization 81, no. 3 (2003): 197-204.
5 Claudio Lanata, comment at WHO rotavirus meeting in Geneva, Nov. 30 to Dec. 1, 2005.
6 Kosek, Bern, and Guerrant, “The Global Burden of Diarrhoeal Disease”: 197-204; John D. Snyder and Michael H. Merson, “The Magnitude of the Global Problem of Acute Diarrhoeal Disease: A Review of Active Surveillance Data,” Bulletin of the World Health Organization 60, no. 4 (1982): 605-13; and Caryn Bern et al., “The Magnitude of the Global Problem of Diarrhoeal Disease: A Ten-Year Update,” Bulletin of the World Health Organization 70, no. 6 (1992): 705-14.
7 Laura E. Caulficld et al., “Undernutrition as an Underlying Cause of Child Deaths Associated With Diarrhea, Pneumonia, Malaria, and Measles,” American Journal of Clinical Nutrition 80, no. 1 (2004): 193-98.
8 Cesar G. Victora et al. “Applying an Equity Lens to Child Health and Mortality: More of the Same is Not Enough,” Lancet 362, no. 9379 (2003): 233-41.
9 WHO/UNICEF/WSSCC, Global Water Supply and Sanitation Assessment 2000 (Geneva: WHO, 2000).
10 Mark D. Niehaus et al., “Diarrhea is Associated With Diminished Cognitive Function 4 to 7 years Later in Children in a Northeast Brazil Shantytown,” American Journal of Tropical Medicine and Hygiene 66, no. 5 (2002): 590-93.
11 John Dobbing, “Early Nutrition and Later Achievement,” Proceedings of ‘the Nutrition Society 49, no. 2 (1990): 103-18.
12 WHO Collaborative Study Team, “Effect of Breastfeeding on Infant and Child Mortality Due to Infectious Diseases in Less Developed Countries: A Pooled Analysis,” Lancet355, no. 9202 (2000): 1104.
13 Richard G. Feachem and Marjorie A. Koblinsky, “Interventions for the Control of Diarrhoeal Diseases Among Young Children: Promotion of Breastfeeding,” Bulletin of the World Health Organization 62, no. 2 (1984): 271-91.
14 Marcia F. Westphal et al., “Breastfeeding Training for Health Professionals and Resultant Institutional Changes,” Bulletin of the World Health Organization 73, no. 4 (1995): 461-68; J. Sikorski et al., “Support for Breastfeeding Mothers,” Cochrane Database of Systematic Reviews 1 (2002): CDOOl 141; F. Barras et al., “The Impact of Lactation Centers on Breastfeeding Patterns, Morbidity, and Growth: A Birth Cohort Study,” Acta Paediatrica 84, no. 11 (1995): 1221-26; Rukhsana Haider et al., “Breastfeeding Counselling in a Diarrhoeal Hospital,” Bulletin of the World Health Organization 74, no. 2 (1996): 173-79; and Nita Bhandari et al., “Infant Feeding Study Group: Effect of CommunityBased Promotion of Exclusive Breastfeeding on Diarrhoeal Illness and Growth: A Cluster Randomised Controlled Trial,” Lancet 361, no. 9367 (2003): 1418-23.
15 Gareth Jones et al., “How Many Child Deadis Can We Prevent This Year?” Lancet 362, no. 9377 (2003): 65-71.
16 MGM Rowland, “The Weanling’s Dilemma-Are We Making Progress?” Acta Paediatrica Scandinavica 323 (1986 suppl): 33-42; Sujit K. Mondai et al., “Occurrence of Diarrhoeal Diseases in Relation to Infant Feeding Practices in a Rural Community in West Bengal, India,” Acta Paediatrica 85, no. 10 (1996): 1159-62; Kare Molbak et al., “Risk Factors for Diarrhoeal Disease Incidence in Early Childhood: A Community Cohort Study From Guinea-Bissau,” American Journal of Epidemiology 146, no. 3 (1997): 273-82; and Salma Badruddin et al., “Dietary Risk Factors Associated With Acute and Persistent Diarrhoea in Karachi, Pakistan,” American Journal of Clinical Nutrition 54, no. 4 (1991): 745-49.
17 Katharine S. Guptill et al., “Evaluation of a Face-to-Face Weaning Food Intervention in Kwara State, Nigeria: Knowledge, Trial, and Adoption of a Home-Prepared Weaning Food,” Social Science & Medicine 36, no. 5 (1993): 665-72; Ruth M. English et al., “Effect of Nutrition Improvement Project on Morbidity From Infectious Diseases in Preschool Children in Vietnam: Comparison With Control Commune,” British Medical Journal 315, no. 7116 (1997): 1122-25; Joel E. Kimmons et al., “The Effects of Fermentation and/or Vacuum Flask Storage on the Presence of Coliforms in Complementary Foods Prepared for Ghanaian Children,” International Journal of Food Sciences & Nutrition 50, no. 3 (1999): 195-201; and SJ. Alien et al., “Probiotics for Treating Infectious Diarrhea,” Cochrane Database Systematic Reviews 2 (2004): CD003048.
18 Georgia S. Guldan et al., “Culturally Appropriate Nutrition Education Improves Infant Feeding and Growth in Rural Sichuan, China,” Journal of Nutrition 130, no. 5 (2000): 1204-11; K. Dewey and K. Brown, “Update on Technical Issues Concerning Complementary Feeding of Young Children in Developing Countries and Implications for Intervention Programmes,” food and Nutrition Bulletin 23 (2003): 5-28; K. Brown, K. Dewey, and L. Alien, Complementary Feeding of Young Children in Developing Countries: A Review of Current Scientific Knowledge (Geneva: WHO, 1998); and Pan American Health Organization (PAHO), Building Principles for Complementary Feeding of the Breastfed Child (Washington, DC: PAHO, WHO, 2003).
19 G.H. Beaton et al., “Effectiveness of Vitamin A Supplementation in the Control of Young Child Mortality in Developing Countries,” Nutrition Policy Discussion Paper no. 13 (Geneva: 1993); Usha Ramakrishnan and Reynaldo Martorell, “The Role of Vitamin A in Reducing Child Mortality and Morbidity and Improving Growth,” Salud Publica de Mexico 40, no. 2 (1998): 189-98; Mauricio L. Barreto et al., “Effect of Vitamin A Supplementation on Diarrhoea and Acute Lower Respiratory-Tract Infections in Young Children in Brazil,” Lancet 344, no. 8917 (1994): 228-31; and David A. Ross et al., “Child Morbidity and Mortality Following Vitamin A Supplementation in Ghana: Time Since Dosing, Number of Doses, and Time of Year,” American Journal of Public Health 85, no. 9 (1995): 1246-51.
20 Z.A. Bhutta et al., “Prevention of Diarrhoea and Pneumonia by Zinc Supplementation in Children in Developing Countries: Pooled Analysis of Randomized Controlled Trials,” Journal of Pediatrics 135, no. 6 (1999): 689-97.
21 Christopher Duggan et al., “Scientific Rationale for a Change in the Composition of Oral Rehydration Solution,” Journal of the American Medical Association 291, no. 21 (2004): 2628-31.
22 Robert E. Black, “Zinc Deficiency, Infectious Disease and Mortality in the Developing World,” Journal of Nutrition 133, Suppl. 1, no. 5S (2003): 1485S-89S; and Mary E. Penny et al., “Randomized Controlled Trial of the Effect of Daily Supplementation With Zinc or Multiple Micronutrients on the Morbidity, Growth, and Micronutrient Status of Young Peruvian Children,” American Journal of Clinical Nutrition 79, no. 3 (2004): 457-65.
23 Bhutta et al., “Prevention of Diarrhoea and Pneumonia by Zinc Supplementation.”
24 Jones et al., “How Many Child Deaths Can We Prevent This Year?”
25 WHO and UNICEF, WHO-UNICEFJoint Statement on the Clinical Management of Diarrhoea (Geneva and New York, 2004).
26 Victora et al., “Reducing Deaths”: 1246-55.
SPECIAL SECTION: Malaria
by Sandra Yin
In 1955, malariologist Paul Russell wrote in the preface to Man’s Mastery of Malaria that one could be confident that “malaria is well on its way towards oblivion.”1
His prediction was too optimistic. While large-scale insecticide spraying and the widespread use of the miracle drug chloroquine freed millions of people from the grip of malaria in the decades after World War II, this relief was halted in many areas. The emergence of drug resistance, widespread resistance to available insecticides, and deterioration of national control programs suggest we are losing the battle. Malaria is reappearing in areas of the world formerly deemed disease-free.2
Each year, malaria kills up to 3 million people. It threatens close to one-half the world’s population, and more than 1 million children die e\ach year of complications related to malaria. Almost 5 billion clinical episodes resembling malaria occur each year, with more than 90 percent of the burden occurring in Africa.3
Malaria can be debilitating for people who live with the disease. It is characterized by extreme exhaustion and associated with high fever, sweating, shaking chills, and anemia.4 Through chronic malaria-induced anemia and time lost or wasted in the classroom due to illness, malaria can have long-term effects on a child’s cognitive development.
Malaria also causes and perpetuates poverty. Couples may have more children than they otherwise would because diey fear losing a child to the disease. People living with the disease are less productive and earn less household income. Regions with endemic malaria have substantially lower economic growth rates than neighboring regions where malaria has been controlled. Fear of malaria has blocked foreign investment, tourism, and trade.
Who Is Most at Risk?
Malaria is an infection caused by a parasite of the genus Plasmodium. Of the four species of Plasmodium that infect humans, P. falciparum causes most of the severe disease and deaths attributable to malaria. It is most prevalent in sub-Saharan Africa and in certain parts of South Asia, Southeast Asia, and the Western Pacific.
The mosquito vector plays a crucial role in the malaria parasite’s life cycle. The disease is transmitted when female Anopheles mosquitoes that carry the malaria parasite bite humans.5
Climate and ecology determine the distribution of the mosquitoes that carry the malaria parasites, and in turn the prevalence and severity of the disease. Malaria is endemic only in tropical and subtropical zones-in parts of Asia, Africa, Central and South America, Oceania, and some Caribbean islands (see figure).
Adults living in regions where malaria is endemic develop immunity, but pregnancy reduces a woman’s immunity, raising her risk of death or severe anemia. Malaria infection in a pregnant woman may also result in spontaneous abortion, neonatal death, and low birthweight babies.
Malaria accounts for 1 in 5 childhood deaths in Africa. About three-fourths of all deaths due to malaria infections occur in African children younger than 5 who are infected with P. falciparum.
Patterns of malaria transmission and disease vary markedly among regions and within individual countries due to variations among malaria parasites and mosquito vectors, ecological conditions that affect malaria transmission, and quality of housing. Malaria disproportionately affects the poorest of the poor within those countries: 58 percent of the cases occur in the poorest 20 percent of the world population.6
The increase in human population worldwide over the past century has influenced the percentage of the human population exposed to malaria risk. Despite human activities that reduced by half the land area supporting malaria, demographic changes resulted in a 2 billion increase in the total population exposed to risk of malaria because of continued population growth in malaria-endemic areas.7 The population at risk in Africa grew from 60 million to 650 million. Southeast and South Asia, which is dominated by India, saw even more dramatic growth, from 200 million to 1.5 billion people at risk.
Malaria’s Comeback
In the 1950s and 1960s, DDT spraying, elimination of mosquito breeding sites, and the use of antimalarial drugs freed more than 500 million people from the threat of malaria.8 But the use of DDT to control malaria became highly controversial, and many countries banned or reduced its use beginning in the 1970s. Evidence of DDTs harmful effects on wildlife, including thinning eggshells in birds and reproductive or endocrine deformities in reptiles, raised fears that long-term use would harm human health and destroy some animal species. Much of the developed world banned most uses of DDT by 1972. Many international donors were reluctant to fund DDT-spraying programs in developing countries.9 The abandonment of DDT was followed by a resurgence of malaria in some areas.
Countries at Risk of Malaria Transimssion, 2001
During the 1980s and 1990s, malaria increased in Africa for several reasons, including increased resistance to chloroquine, the most commonly used antimalarial drug; the deterioration of primary health services in many areas; and the emerging resistance of mosquitoes to insecticides. New breeding grounds for mosquitoes were created by dams and irrigation projects. During the past decade, malaria also resurged or intensified in South and Southeast Asia after eradication efforts were interrupted. It has reemerged in several Central Asian republics and in other former Soviet republics due in part to weakened public health infrastructure.10
Prevention
Long before the 19th century, when researchers discovered that mosquitoes spread malaria, people developed ways to avoid mosquito bites. In the 5th century B.C.E., Egyptians who lived in marshy lowlands slept under fishing nets steeped in fish oil to repel mosquitoes.11
Centuries later, during World War II, American forces in the South Pacific dipped bed nets and hammocks in DDT. After DDT use was discouraged or banned, bed nets were treated with biodegradable insecticides called pyrethroids.
Pyrethroid-treated nets paired with antimalarial drugs halved mortality in children younger than 5 in the Gambia. The nets are credited with saving many lives in Kenya, Ghana, and Burkina Faso.
ITNs have some drawbacks. At $2 to $6 each, nets are too expensive for many of the people who need them most. Nets usually have to be redipped every six to 12 months to remain effective. Some newly developed nets, however, promise longer-lasting protection. The nets are impregnated with an insecticide that lasts four to five years.
Indoor residual spraying can be a highly effective method for malaria vector control. It reduces human and mosquito contact by repelling some mosquitoes before they enter a dwelling and killing others that alight on treated walls after a blood meal. Such spraying can achieve a rapid reduction in transmission during epidemics and other emergency situations, provided it is well-timed and has wide coverage.
Public health officials in malarious countries see the reintroduction of DDT as integral to malaria controlparticularly as they confront a growing resistance to other, more costly pesticides and hardier, more drugresistant parasites. Health officials say the current use indoor spraying of DDT for disease vector control releases only tiny amounts of DDT, compared with more destructive wide-area crop spraying of the 1950s.12
WHO currently recommends indoor residual spraying of DDT for malaria vector control. In some parts of the world, this long- lasting toxin offers the best hope for reining in malaria.
The dwindling availability of low-risk and cost-effective insecticides poses an ongoing challenge to malaria control. In areas of intense malaria transmission, use of insecticidetreated nets is more sustainable.
In areas of high and stable transmission of falciparum malaria, intermittent preventive treatment (IPT) is recommended for pregnant women. It usually consists of two curative doses of antimalarial treatment given during prenatal care visits. IPT can significantly reduced the incidence of severe maternal anemia and low birthweight births.13
Treatment
The most effective drug treatments vary depending on a host of factors including the type of malaria parasite involved and how stable the transmission of malaria is. All malarious countries and territories have national malarial treatment policies. Ideally, health workers monitor the effectiveness of drugs closely and change treatments when parasite resistance to chloroquine and other drugs emerges. In many malaria-endemic areas, ongoing obstacles to speedy diagnosis and effective drug treatment persist. Among them: unreliable microscopy, widespread distribution and use of substandard and counterfeit drugs.
Drug Resistance
Antimalarial drug resistance presents one of the biggest challenges in malaria control.
While the former “miracle drug,” chloroquine, is losing effectiveness against ever more robust forms of the malaria parasite, it remains a top-selling antimalarial drug in Africa. The next most affordable drug in Africa, sulfadoxine-pyrimethamine, is also coming up against ever more hardy and resistant strains of P. falciparum.
In response to widespread resistance of P. falciparum to monotherapy, or single drug therapies, with conventional antimalarial drugs such as chloroquine, WHO now recommends combination therapies as the treatment policy for falciparum malaria. Malaria experts believe combinations of drugs will work, especially if they include a form of artemisia annua, a medicinal herb once used as a fever remedy in ancient China. Artemisinins fight malaria parasites more quickly than any other treatment and also block malaria’s spread from humans to mosquitoes. If used alone, the artemisinins will cure falciparum malaria in seven days. In combination with certain synthetic drugs, artemisinin-based combination therapies (ACT) produce high cure rates in three days. They can also retard the development of resistance to the partner drug. But artemisinins cost 10 to 20 times more than weaker malaria drugs, including chloroquine. And the global supply of ACTs is tight.
Since 2001, WHO has recommended that artemisinin be used only in combination with other antimalarials to prevent the malaria parasite from developing artemisinin resistance. In January 2006, the head of WHOs malaria section warned that using artemisinin alone could leave the world with no effective weapon against malaria. “We can’t afford to lose artemisinin,” said Arata Kochi, head of WHOs Roll Back Malaria department. “If we do, it will be at least 10 years before a drug that good is discovered.”14
Kochi, a physician who earlier headed WHO\’s TB program against tuberculosis, said he was trying to prevent a repeat of what happened to TB-the emergence of strains that are resistant to all drugs. By mid-May 2006, 13 drug companies agreed to comply with WHOs recommendation to phase out single-drug artemisinin medicines and focus on producing ACTs.15
In an ideal world, countries where malaria is endemic could institute policies that include insecticidetreated nets, indoor residual spraying, and IPT. But the cost of mounting such a campaign could be too high. In resource-poor areas, insecticide-treated nets would be the most cost-effective preventive measure.
While malaria has attracted both funding and the attention of international organizations, it remains a major global problem that exacts a heavy toll on the health and economic life of the world’s poorest communities. Before the battle against malaria is over, more research is needed to improve existing interventions and develop new weapons to fight malaria.
In 1958, WHO, the Pan American Sanitary Bureau, and other international organizations aided governments in a fight against malaria. The goal was to wipe malaria off the face of the earth in 10 years. Today’s goals are more limited. There’s no talk of eradicating malaria. The Millennium Development Goal accepted by 190 countries in 2000 calls for a halt the spread of malaria and progress in reversing its incidence by 2015.
References
1 Simon Hay et al., “The Global Distribution and Population at Risk of Malaria: Past, Present, and Future,” The Lancet Infectious Diseases 4, no. 6 (June 2004): 327.
2 Clive Shiff, “Integrated Approach to Malaria Control,” Clinical Microbiology Reviews 15, no. 2 (April 2002): 278-93.
3 Joel G. Breman et al., “Conquering Malaria,” in Disease Control Priorities in Developing Countries, 2d ed., ed. Dean T. Jamison et al. (New York: Oxford University Press, 2006): 413-32.
4 WHO, Malaria, accessed online at www.who.int, on May 2, 2006.
5 Roll Back Malaria, WHO, and UNICEF, World Malaria Report 2005 (Geneva: WHO and UNICEF, 2005): 11.
6 Joel G. Breman, Martin S. Alilio, and Anne Mills, “Conquering the Intolerable Burden of Malaria: What’s New, What’s Needed: A Summary,” The American Journal of ‘Tropical Medicine and Hygiene 71, no. 2suppl. (2004): 1-15.
7 Hay et al., “The Global Distribution and Population at Risk of Malaria: Past, Present, and Future”: 327-35.
8 Claire P Dunavan, “Tackling Malaria,” Scientific American (December 2005): 78.
9 Donald R. Roberts et al., “DDT, Global Strategies, and a Malaria Control Crisis in South America,” Emerging Infectious Diseases 3, no. 3 (July-September 1997): 300.
10 Roll Back Malaria, WHO, and UNICEF, World Malaria Report 2005: xii.
11 Dunavan, “Tackling Malaria”: 80.
12 Donald Roberts et al., “DDT, Global Strategies.”
13 Breman et al., “Conquering Malaria”: 420.
14 Donald G. McNeil Jr., “Drug Makers Get a Warning From the U.N. Malaria Chief,” The New York Times, Jan. 20, 2006.
15 WHO, Who Announces Pharmaceutical Companies Agree to Stop Marketing Single-Drug Artemisinin Malaria Pills, accessed online at www.who.int, on May 25, 2006.
SPECIAL SECTION: Tuberculosis
by Sandra Yin
Humans have had a long relationship with TB: Evidence of TB has been found in ancient mummies in Egypt and Peru. As late as 1900, TB was the second most common cause of death in the United States. Although TB is no longer a major killer in most developed countries, it remains the worlds deadliest curable infectious disease. One- third of the world population is currently infected with the bacillus that causes TB. People infected with latent TB have a 10 percent to 20 percent risk of developing active TB, which, untreated, can lead to debilitating illness and death. Although drugs to cure TB have been around since the 1940s, approximately 2 million people died from TB in 2004; another 3.9 million new cases of the most infectious form of TB appeared that year.1
Developing countries bear the brunt of the TB epidemic. An estimated 95 percent of TB cases and 98 perent of TB deaths occur in the developing world. Just five countries-Bangladesh, China, India, Indonesia, and Pakistan-account for nearly half die new cases each year.2
The incidence of TB worldwide is growing by roughly 1 percent a year, driven primarily by the HIV epidemic. Accordingly, TB is spreading fastest in areas hardest hit by HIV/AIDS-sub-Saharan Africa and Eastern Europe. Between 1990 and 2004, TB incidence in Africa more than doubled, from 153 cases to 356 cases per 100,000 people. In the former Soviet bloc countries of Eastern Europe, TB incidence per capita rose through the 1990s, but has eased since 2001. Incidence rates may still be increasing in some Central Asian republics such as Tajikistan and Uzbekistan.3
What Makes TB So Deadly?
The bacteria that cause TB usually attack the lungs, but can spread to other parts of the body. Symptoms may include fever, cough, night sweats, weight loss, fatigue, and coughing up blood.
Most people infected with TB bacilli will not become sick. The immune system may wall off the TB bacilli in a thick waxy coat that allows them to lie dormant inside the body for decades. People with latent TB infection do not feel sick, do not have any symptoms, and cannot spread the disease. But, between 5 percent and 10 percent will develop TB in the future.4
TB spreads through the air, like the common cold. Only people who are sick with TB in their lungs or throat are infectious. People who have TB in other parts of their body are not infectious. When infectious people cough, sneeze, spit, or j
