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Introduction

Infectious diseases present a major threat not only to world health, but also to its prosperity and security. Jonathan Mann, previous director of the Harvard AIDS Institute, noted that

Moreover, the distribution and spread of infectious diseases raise questions of justice and equity for they attack particular populations and places disproportionately, especially those living in poverty in the developing world. Poverty increases risk and incidence of infectious disease, which perpetuates the cycle of underdevelopment. "People cannot contribute to the economic progress of their families and communities when they are rendered helpless or die from infectious diseases" (WHO, 2000a:9). Such localized vulnerability does not mean that other populations and places of the world are immune - more than ever before, infectious diseases transcend national and regional boundaries.

The World Health Organization (WHO) (1997) identifies two sets of hazards that lead to vulnerability. Traditional hazards are associated with a lack of development - they are related to poverty; lack of access to safe drinking water; inadequate basic sanitation in the household and community; indoor air pollution from cooking and using biomass fuel; and inadequate solid waste disposal. Modern hazards are associated with unsustainable development practices and include water pollution from populated areas, industry, and intensive agriculture; urban air pollution from vehicular traffic, coal power stations, and industry; climate change; stratospheric ozone pollution (depletion); and transboundary pollution. Traditional and modern hazards join and conspire to ensure the conditions for the development and diffusion of infectious diseases, especially in the developing world.

Clearly then, globalization trends combined with environmental change have profound effects upon the health and therefore the security of human populations (see Box 1). This article traces the human security threats posed by infectious diseases. After describing infectious diseases and how they spread, it provides recent examples and incidence statistics of disease outbreaks. These incidences exemplify the changing pattern of disease outbreaks in recent years, as well as their devastating impacts. Since environmental factors, particularly the availability and quality of water and its consequences for health are perhaps the most significant causes of vulnerability, we discuss these ramifications before closing with policy recommendations for ameliorating and controlling infectious diseases.

What are infectious diseases and how do they spread?

An infectious or communicable disease is an illness caused by a specific infectious agent or its toxic products. It arises through the direct or indirect transmission of that agent or its products from an infected person, animal, or reservoir to a susceptible host. Direct transmission is the immediate transfer through touching, kissing, biting, or sexual intercourse or by droplets spread during sneezing, coughing, spitting, singing, or talking. Susceptible tissue may also be directly exposed to agents in the soil, decaying vegetable matter, or through animal bites. Transplacental transmission - transmission from mother to fetus through the placenta - is another form of direct transmission. There are three forms of indirect transmission - vehicle-borne, vector-borne, and airborne. Contaminated objects such as soiled bedding or dressings, or poorly cleaned utensils, as well as water, food, milk, blood, and serum can lead to vehicle-borne infections. Vector-borne infections usually involve insects either mechanically, usually through the feet or the gastrointestinal tract, or biologically, usually involving a bite and an incubation period before infection. Finally, microbial aerosols may enter the respiratory tract indirectly - most airborne transmission is however, direct. Virtually everything humans do then potentially exposes them to infectious agents. The world is indeed a dangerous place!

The potential for micro-organisms to cause disease outbreaks is dependent on exposure of humans to environmental risks, the overall health of the individual, and the ability of the pathogen to affect humans. There is an intrinsic relationship between pathogen, host, and environment (physical, biological, social, cultural, and economical). A weak immune system, such as those of individuals suffering from AIDS or young children, enhances and provides the factors necessary for these pathogens to thrive, cause an infection, tissue damage, or in extreme cases, death. Disease outbreaks caused by pathogens within water are exposed to humans via the mouth through contaminated food or drink, unsanitized water, or from food grown in poor soils.

Box 1. The Environment and Health • Environmental quality is an important direct and indirect determinant of human health. Deteriorating environmental conditions are a major contributory factor to poor health and poor quality of life and hinder sustainable development. • Major challenges to sustainable development are posed by mismanagement of natural resources, excessive waste production, and associated environmental conditions that affect health. • Impoverished populations living in rural and peri-urban areas are at greatest risk from degraded environmental conditions. The cumulative effects of inadequate and hazardous shelter, overcrowding, lack of water supply and sanitation, unsafe food, air and water pollution, and high accident rates, impact heavily on the health of these vulnerable groups. • Poor environmental quality is directly responsible for around 25% of all preventable ill health in the world today, with diarrhoeal diseases and acute respiratory infections (ARI), such as pneumonia heading the list. Other diseases such as malaria, schistosomiasis, other vector-borne diseases, chronic respiratory diseases, and childhood infections are also strongly influenced by adverse environmental conditions, as are injuries. • In today's world, it is children's health that is most damaged by poor environmental quality. As much as two-thirds of all preventable ill health due to environmental conditions occurs among children. • Lack of basic sanitation, poor water supply, and poor food safety contribute greatly to diarrhoeal disease mortality and morbidity. Curative measures have brought the number of deaths from diarrhoeal diseases down, but action that deals with the root causes of these diseases continues to be lacking. • Air pollution figures prominently as a contributor to a number of diseases (ARI, chronic respiratory diseases, cardiovascular disease, and cancer) and to a lowering of the quality of life in general. • The occurrence of the major vector-borne diseases is closely related to naturally existing environmental conditions. In addition, the incidence, severity, and distribution of vector-borne diseases are affected substantially by human activities such as water and agricultural developments and by urbanization. • Hazardous chemicals and various forms of hazardous waste, including healthcare wastes, are increasing health and environment concerns. The lack of detailed quantitative information on the production and disposal of such waste, and the lack of information on the resulting health risks, severely hamper efforts to control this problem. • Global environmental change has great implications for health, particularly that of the poor. Marginalized population groups are again at greatest risk, as their ability to adapt is limited due to lack of resources. • There are some promising signs - not yet in terms of environmental improvement, but rather in the national development of policies and infrastructure to address the problems described here. However, the lack of financial and human resources is a major deterrent to progress. • The health sector has an essential advocacy role to play in highlighting the links between health, environment, and sustainable development when future policies are developed and actions planned. A much stronger partnership between the health sector and other sectors is required for successful reduction of health threats arising from poor environmental conditions. Renewal of the WHO Health-for-All Policy for the 21st Century, which is currently in progress, provides guidance for the way ahead. Source: WHO, 1997

The main infectious diseases:
The world's greatest health threats and killers

As the WHO (1999) points out, 6 diseases cause about 90% of infectious disease deaths (see Figures 1 and 2). The big killers are pneumonia, tuberculosis, diarrheal diseases, malaria, measles, and more recently HIV/AIDS. Pneumonia affects children in particular, although childhood deaths from pneumonia are rare in industrialized nations. Children with low birth weight and those weakened by malnutrition and other diseases are most susceptible. In their massive study of the global burden of disease, Murray and Lopez (1996) calculate that malnutrition is responsible for 11.7% of all deaths worldwide and 15.9% of disability-adjusted life years (see Table 1 for the relative contribution of selected risk factors). Localized vulnerabilities are obvious in malnutrition related deaths, which contribute to 31.9% of total deaths in sub-Saharan Africa (32.7% of disability-adjusted life years). However, pneumonia is also present in the developed world, where malnutrition related vulnerability is less of a factor. For example, influenza (a virus that causes pneumonia) causes 10,000-40,000 deaths in the U.S. alone every year. Since it is directly transmitted through air, health experts view influenza as a "pandemic in waiting" (for the right conditions). A modern-day influenza pandemic could devastate the world as it did in 1918-1919, but with far more deaths than the nearly 20 million deaths worldwide, as the movement of people and goods is significantly more rapid today.

Figure 1. Leading Infectious Killers               All Ages, 1998 estimate Back

Figure 2. Most deaths amoung young people in                developing countries are caused by just                a few illnesses Deaths: Ages 0-44 in South-East Asia and Africa Back

Table 1. Factors in infectious disease emergence

Factor	Examples of specific factors	Examples of diseases
Ecological changes (including those due to economic development and land use)	Agriculture; dams, changes in water ecosystems; deforestation/ reforestation; flood/drought; famine; climate changes	Schistosomiasis (dams); Rift Valley fever (dams, irrigation); Argentine hemorrhagic fever (agriculture); Hantaan (Korean hemorrhagic fever) (agriculture); hantavirus pulmonary syndrome, Southwestern US, 1993 (weather anomalies)
Human demographics behavior;	Societal events: Population growth and migration (movement from rural areas to cities); war or civil conflict; urban decay; sexual behavior; intravenous drug use; use of high-density facilities	Introduction of HIV; spread of dengue; spread of HIV and other sexually transmitted diseases
International travel and commerce	Worldwide movement of goods and people; air travel	"Airport" malaria; dissemination of mosquito vectors; rat-borne hantaviruses; introduction of cholera into South America; dissemination of 0139 V. cholerae
Technology and industry	Globalization of food supplies; changes in food processing and packaging; organ or tissue transplantation; drugs causing immunosuppression; widespread use of antibiotics	Hemolytic uremic syndrome (E. coli contamination of hamburger meat), bovine spongiform transfusion-associated hepatitis (hepatitis B, C), opportunistic infections in immuno-suppressed Creutzfeldt-Jakob disease from contaminated batches of human growth hormone (medical technology)
Microbial adaptation and change	Microbial evolution, response to selection in environment	Antibiotic-resistant bacteria, "antigenic drift" in influenza virus
Breakdown in public health measures	Curtailment or reduction in prevention programs; inadequate sanitation and vector control measures	Resurgence of tuberculosis in the United States; cholera in refugee camps in Africa; resurgence of diphtheria in the former Soviet Union
		Source: Morse, 1995

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Tuberculosis (TB) kills 2 million people each year. The WHO (2000b) estimates that between 2000 and 2020, nearly one billion people will be newly infected, 200 million people will get sick, and 35 million will die from TB, unless there are changes in controls. The threat of TB has been enhanced by its association with HIV/AIDS and the emergence of multi-drug resistant TB. In fact, one-third of the world's population is currently infected with the TB bacillus; Southeast Asia bears the biggest burden. Also worrying are outbreaks in places that have seen years of decline in TB rates, such as Eastern Europe. Furthermore, global trade and travel, migration, and forced migrations of displaced people and refugees into camps help spread the disease. In the US, nearly 40% of TB cases are among people from TB endemic countries and 30% of homeless people in San Francisco are infected (compared with 7% in the total US population).

Yearly, diarrheal diseases claim the lives of nearly two million children under the age of five. The burden is particularly high in areas with poor sanitation, unsafe drinking water, and where inadequate hygiene practices are common. Such diarrheal diseases as dysentery and cholera are epidemic in some countries and regions. For example, cholera is endemic in the deltas of the Ganges and Meghna Rivers in Bangladesh, the deltas of the Irrawaddy and Salween Rivers in Myanmar, and in the coastal areas of Indonesia and Africa.

Malaria is the world's most significant tropical parasitic disease, killing over one million people a year. It is a public health problem in over 90 countries, where 40% of the world's population resides (WHO, 1998a). Yet, more than 90% of all malaria cases are in sub-Saharan Africa. It kills a child every 30 seconds. "In absolute numbers, malaria kills 3,000 children per day under five years of age. It is a death toll that far exceeds the [child] mortality rate from AIDS" (WHO, 1998a). The majority of malaria related deaths occur in children living in remote rural areas with inadequate access to clean water supplies and health services. "More than any other disease, malaria hits the poor" (WHO, 1998a). The economic cost of malaria in sub-Saharan Africa alone has been calculated at US$2 billion (1997 estimate). Its reach, however, is spreading. Malaria is specific to the ecosystem that breeds it. As climate and weather patterns change, as new dams, canals and irrigation channels are dug, and as people migrate, different reservoirs for mosquitoes to breed are created. The many emerging varieties of reservoirs make control difficult in that techniques must be adapted. As with all infectious disease killers, global forces result in the development and spread of malaria with specific local impacts.

Measles is often associated with diarrheal diseases, as well as pneumonia and malnutrition. It remains a major childhood killer in developing countries. About one million children die from measles each year. It is a highly contagious vaccine-preventable disease and probably the best known and most deadly of all childhood rash/fever illnesses. Recent outbreaks, such as in Korea from March 2000 to January 2001 where nearly 40,000 people contracted measles, exemplify the need for expanding awareness and availability of immunization programs. They also illustrate increased mobility patterns that accompany globalization trends for the outbreak was nation-wide.

Currently, over 36.1 million people are living with HIV/AIDS worldwide with sub-Saharan Africa being the worst affected (70% of those infected). In 2000, 3 million people died from AIDS related causes. Life expectancy gains across Africa have been reversed. In Botswana, for example, life expectancy at birth has fallen from 70 to about 50 years. Other parts of the world experiencing rapid change - economic, political, and cultural - are also being seriously affected by HIV/AIDS. For example, rises in intravenous drug use in Eastern Europe and Central Asia are associated with significant increases in those living with these infections (UNAIDS, 2000).

Several other infectious diseases (than the major 6 killers noted above) also cause much disability and illness. For example, lymphatic filariasis is second only to mental illness as the world's leading cause of long-term disability. It results from a mosquito-borne disease involving infection with parasitic worms causing enlargement of limbs and damage to internal organs. It affects about 120 million people, but 1 in 6 of the world's population is at risk. Schistosomiasis, a debilitating disease spread by water snails in stagnant water, affects 200 million people, causing chronic urinary tract disease. It can be spread to new areas through dam and irrigation projects. River blindness affects over 85 million people in Africa, Latin America, and the Middle East. It is a parasitic disease transmitted by blackflies (WHO, 1999). Finally, dengue and dengue hemorrhagic fever are mosquito-borne infections. The WHO (1998b) estimates that over two-fifths of the world's population is at risk from these diseases. There have been explosive outbreaks, for example, in Brazil in 1998. Dengue is now a greater threat because of rapid rises in urban populations, especially where household water storage is common and where solid waste disposal services are inadequate. All these examples - and there are many more - point to the exacerbation and convergence of traditional with modern hazards to create the conditions for the spread of infectious diseases.

Localized outbreaks of global infectious diseases

As noted previously, particular places are vulnerable to certain types of infectious diseases. Local vulnerability to infectious diseases has global causes and implications. Factors such as globalization trends and environmental change are altering traditional locations of outbreaks and their severity. The recently reported outbreaks of West Nile (WN) virus, which is a type of Japanese encephalitis, exemplify these changes and how local vulnerability to infectious diseases has global implications. Mosquito-borne WN virus fever is endemic in Africa, the Middle East, and southwest Asia. This viral infection was unknown in Europe until 1996 when more than 500 cases were observed in the Bucharest region of Romania. The outbreak caused high rates of neurological disorder and death. It was not detected in the western hemisphere until 1999 when 56 cases of WN encephalitis were confirmed in New York City. Of these 56 cases, 7 died. Another particularly virulent outbreak occurred in Volgograd City in Russia when about 480 suspected WN virus cases were found (Platonov et al., 2001). Among these, there were 84 cases of acute aseptic meningoencephalitis, 40 of which were fatal. Most of the cases, in all three places, were among the elderly. Similar environmental conditions were evident in each of these areas as they are located near large bodies of water and on bird migration pathways. Furthermore, all had unusually dry summers in the year of the outbreak. There may be a complex relationship between climate change, mosquitoes, birds, and human activities, such as trade and travel, which led to industrialized and newly industrialized countries in atypical locations being affected by this apparently tropical disease.

The cholera outbreak between 1991 and 1996 in Mexico of over 43,500 cases presents another example of localized vulnerability. The cholera incidence was almost two and a half times higher in coastal states than in the interior. Furthermore, the poorest sector of the population had a six times greater incidence than the least poor and the least urbanized had a four times greater incidence than the most urban group. Those at greatest risk were the poor living in rural areas of the Gulf of Mexico and Caribbean-bordering states (Borroto and Martinez-Piedra, 2000). Cholera, however, is endemic in many populations living in coastal areas and seems to recur seasonally, affecting children and those without well-developed immune responses, in particular. Local environmental conditions, especially contaminated water sources cause most sudden large outbreaks. Cholera survives in estuarine environments and is often associated with algae blooms (plankton), which are influenced by the temperature of the water; thus, climate change may have significant impacts on incidence rates.

A final example of a global disease with significant local impact is HIV/AIDS. Sibanda (2000) charts the dramatic increase in the number of people living with HIV and those dying of AIDS-related diseases in Zimbabwe since the early 1990s. He writes of a nation in pain and of an epidemic out of control. It is estimated that one in four adults are living with HIV, although there are within-country variations. Blood samples taken from pregnant women at maternity clinics show between one-fifth and one-half of all pregnant women tested positive for HIV. Most transmission occurs through unprotected heterosexual intercourse or from an infected mother to a fetus. It is argued that the AIDS epidemic has turned back the clock on development. The underlying factors that drive the pandemic include: gender inequality, poverty, lack of education/illiteracy, traditional cultures, denial, complacency and policy failure in the early years of the disease, and increased mobility. Sibanda (2000) discusses these factors within the cultural context of sex and reproduction, which emphasizes masculinity and the importance of bearing children; traditional contexts and cultures that mitigate against the use of condoms and medical treatments; and economic conditions that often result in separation from partners, which may encourage participation in the commercial sex industry. The economic structural adjustment policies of the 1990s have reinforced these conditions by driving many people further into poverty.

Environmental change and infectious diseases

The environmental factors that most affect health are linked to underlying pressures on the environment such as population growth, inequitable resource distribution, consumption patterns, technological advances, and economic development (WHO, 1997). Climate change, stratospheric ozone depletion, transboundary air and water pollution, acid precipitation, biodiversity loss, desertification, and deforestation have major implications for health. For example, climate change patterns, particularly those related to global warming are shifting territorial locations and reaches of plant and animal species. Insect vectored infectious diseases, such as those that are mosquito driven are extending their range and moving to higher elevations. Algae blooms, the habitat for the microbe that causes cholera, are increasing in quantity and spreading geographically due to warmer sea temperatures. Desertification, depletion of fertile soil, groundwater, and natural fish stocks are weakening the productivity of food-producing ecosystems, thereby posing greater food security threats, which results in greater incidences of malnutrition. Malnutrition weakens the immune system significantly, making it vulnerable to infectious disease. Air, water, and food are the principal exposure routes of environmental health hazards, but inadequate solid waste and sewage disposal combined with insecure living and working conditions, in many locations around the world, also increase vulnerability to disease. Infectious diseases such as diarrheal diseases, schistosomiasis, and hepatitis are endemic in such areas.

In different ways and to different degrees each of the infectious diseases discussed above owe their presence to one environmental factor or another. However, many of the infectious diseases highlighted are linked to water sources and local conditions, especially the quantity and quality of water available.

Water and infectious diseases

For many years, water quality has been regarded as the prime indicator of health and well-being, as it plays a crucial role in determining the cause and transmission of disease. Approximately 10 million people die each year from water-related diseases or inadequate sanitation. Global environmental change affects pathogens (e.g., viruses, bacteria, protozoa, fungi), vectors, and hosts by influencing their survival, abundance, and dispersal. Waterborne disease outbreaks can be localized (particular city or village), national, or international in shape. Increased temperatures, flooding, and run-off are some examples that enhance the transmission route of microorganisms to humans.

Water is a significant route for disease transmission - typhoid fever, cholera, dysentery, enteritis (bacteria), infectious hepatitis (viruses), amoebic dysentery, giardiasis (protozoa), and schistosomiasis (worms) are all transmitted via water. As mentioned earlier, disease outbreaks and their associated transmission routes that are linked to water can be categorized in the following manner: waterborne (infections spread through water supplies); water-washed (infections spread through lack of water for personal hygiene); water-based (infections spread though an aquatic invertebrate host); and water-vectored (infections spread by insects that depend on water).

Waterborne diseases

Cryptosporidiosis is prevalent both in the developed and developing world where it can be found in untreated surface waters, as well as places such as swimming and wading pools. It is a zoonosis, in that infection is associated with fecal-oral contamination through exposure to farm animals and other wild animals, such as beavers. With increased precipitation and higher temperatures, as seen in patterns in North America, oocysts from these organisms found in fecal matter may be washed into drinking water supplies, thus exposing the populations to risk through ingestion of contaminated water. These oocysts are particularly of concern as they are resistant to chlorine treatment in regular municipal water treatment facilities and are small and difficult to filter. The largest known recorded waterborne outbreak of cryptosporidiosis in US history occurred in Milwaukee, Wisconsin in 1993 where approximately 400,000 individuals were infected.

Cholera, which was discussed previously, is caused by the microorganism Vibrio cholerae. Transmission occurs by bathing in or drinking contaminated water or ingesting contaminated food. Movements of tidal waters towards land as well as river flows bring the bacterium in contact with humans. Cholera outbreaks occur seasonally and are associated with monsoon seasons, warm temperatures, heavy rainfall, and increased plankton populations. New major outbreaks of cholera are continuing to occur, especially in the wake of climate changes. During 1998, there was a dramatic increase in the number of cholera cases worldwide compared to 1997, with the total number of cases almost doubling. Figure 3 shows the relationship between increased sea-surface temperatures and cholera incidence in Bangladesh. Figure 4 provides information about the incidence and fatality rates of cholera over the past 5 decades.

Figure 3. Relationship between sea-surface temperature                and cholera, case data in Bangladesh from                January to December 1994. Source: Colwell and Patz, 1997 Back

Figure 4. Cholera, reported number of cases and case                fatality rates, per continent Source: WHO, 2000b Back

Water-washed diseases

Diseases in this category, such as shigella, salmonella, E. coli, and pseudomonas, are transmitted primarily through inadequate supplies of water for basic hygiene practices; thus, exposing individuals to risk through the fecal-oral route. Most often in many developing countries, the only source of water available to populations for drinking, bathing, washing clothes, and for animal care is contaminated with pathogens, from raw sewage, and human and animal feces. The survival rates of the pathogenic organisms that cause water-washed diseases are enhanced in warm moist environments, and where situations such as increased flooding facilitate the transportation of the organism, the risk of diarrheal outbreaks increases. However, lack of water, through environmental change, also plays an important role in the transmission of pathogenic microorganisms to individuals, as well.

Water-vectored diseases

As previously noted, malaria, one of the most well-known diseases, causes more cases of morbidity and mortality than any other tropical infectious disease around the world. Malaria is widely distributed in the tropics, and is a particularly serious health risk in developing countries. Human infection is caused by Plasmodium falciparum (most common and virulent), P. malariae, P. vivax, or P. ovale. It is a vector-borne disease, where an intermediate vector organism is needed to pass the infectious parasite to and between humans. Malaria infections are caused by the bite of an infected female Anopheles mosquito. Water plays a crucial role in transmission; mosquitoes require high humidity and standing water in which to breed. Thus, disease rates are largely determined by flooding or heavy rainfalls. However, global environmental change is affecting the virulence of the parasite and the life cycle of the intermediate host. Climate is an important factor affecting the incidence of disease outbreak. As global temperatures rise, malaria may spread into new regions of the globe, for example North America or Europe.

Water-based diseases

One of the most commonly known water-based diseases is dracunculiasis or guinea worm disease. It is caused by the parasite Dracunculus medinensis. The disease is contracted by drinking water sources contaminated with the infected intermediate hosts of the parasite, called cyclops. Due to significant multi-lateral aid and research efforts, it is close to being eradicated, but remains a significant threat in Sub-Saharan Africa. Ensuring safe water supplies is key to controlling dracunculiasis.

Controlling infectious diseases

There are many success stories in the control of infectious diseases in the past. As Figure 5 illustrates, deaths from infectious diseases declined markedly in the US throughout the twentieth century; so much so that the leading causes of death in 1997 were heart disease and various cancers, whereas in 1900, they were pneumonia, tuberculosis, and diarrhea and enteritis; a set of causes with a well-known ring to it. As the National Center for Environmental Health (1999) points out, improvements in sanitation and hygiene, the discovery of antibiotics and the implementation of childhood immunization programs, built on the scientific discovery of microorganisms, were key components of public health action. Specifically, sewage disposal, waste treatment, food safety, organized solid waste disposal, and housing improvements all helped reduce the incidence and spread of infectious diseases. Animal and pest control were important too. Yet, influenza and HIV/AIDS illustrate the unpredictability of all infectious diseases. The actions to control the development and spread of most infectious diseases have been identified. The policies and programs of countries, like the US and Canada, point to their efficacy. What is different today?

Figure 5. Crude death rate1 for infectious diseases               - United States, 1990 - 19962 1 Per 100,000 population per year 2 Adapted from Armstrong GL, Conn LA, Pinner RW. Trends in infectious diseases morality in the United States during the 20th century. JAMA 1999:281;61-6 3 American Water Works Association. Water chlorination principles and practices: AWWA manual M20. Denver, Colorado: American Water Works Association, 1973 Source: National Center for Environmental Health, 1999. Back

As noted in the introduction, the world has been transformed. It is qualitatively different from early in the twentieth century and indeed up to 20-25 years ago when nations seemed to be in greater control of their destinies than now. The emergence of the global village has created potent opportunities for wealth and prosperity, but at the cost of a world more polarized by differences in life circumstances and opportunities. Complacency is also a factor in controlling disease - the victories of the past over infectious diseases and their agents seemed to have been won forever. This is not the case - the differential impact of global economic change, environmental change, the easy movement of people, goods, and ideas, and policy myopia combine to make control of infectious diseases difficult today.

This rings true for most nations. So, what is to be done?

Future directions

There are some encouraging signs for the future. Demonstration projects are a vital way of showing what can be done to reduce the impact of infectious diseases. Satcher (1998) reports on the case reduction in meningitis in sub-Saharan Africa through vaccination carried out in partnerships with national governments, the WHO, US agencies, and several NGOs. There is evidence too that many controls are relatively inexpensive and effective. For example, child deaths from malaria in Gambia, Ghana, Kenya, and Burkina Faso were reduced by the use of regularly treated bed-nets (WHO, 1998a). There are also developments in surveillance and monitoring systems that will allow for early diagnosis and prompt treatment, as with malaria. The WHO (2000c) sees surveillance as one element in the strategy for effective infectious disease control. For TB control, the WHO has developed a five-element strategy, called DOTS (Directly Observed Treatment, Short-course). This strategy has produced cure rates of up to 95% in some situations, even in the poorest countries. DOTS is a cost-effective intervention, which prevents the development of multi-drug resistant TB. Its five elements are microscopy services, drug supplies, use of highly efficacious regimes with direct observation of treatment, surveillance and monitoring systems, and political commitment.

However, for any control system to be effective, action is required at the national and international level. There is also a need for linkages to be made between global incidence rates or data sets and local field studies, which relate specifically to local social, behavioral, and cultural circumstances. It is hoped that future research agendas will allow key individuals from various disciplines and geographical areas to come together and not only share, but build upon current information from a bottom-up, local community driven perspective. The WHO (1997) points to the need for strengthening health systems through integrated policies, especially bringing a strong health focus to national and local planning within nations, as well as international efforts to ensure effective use of resources and programs based on the best available research. Yet, many countries struggle with outdated control measures (e.g., annual screening of children for TB in much of eastern Europe). Further, investments in health are low - wealthier countries spend significantly more on health than the poorer ones, where the need is greatest. Moreover, in developing countries, economic issues, such as poverty are much higher priorities than health issues, so that infectious diseases are a neglected concern within a neglected sector. Prioritizing policies, such as those of structural adjustment and trade aimed at economic transformation, adversely affect health and well-being in poorer countries, at least in the short- to medium-term. It is possible that the policies of some international agencies conflict with the aims of others, especially with respect to economic development and health protection and disease prevention.

For the future, these possible conflicts must be understood and, if necessary resolved. Extending G20 deliberations beyond finance may be a start in the right direction. While surveillance, monitoring, research, and training with respect to infectious diseases remain vital, they are necessary but not sufficient conditions for controlling such diseases. Malnutrition, unclean water, poorly disposed of sewage and waste, unsafe sex and the use of biomass fuel remain, among other things, implicated in the growing spread of infectious diseases. International partnerships, targeted donor assistance, and equitable trade relationships are required as means to achieve infrastructure changes in the environments that breed diseases. The movement of people, goods, and ideas means that industrialized nations are not only part of the solution but are potential victims in the globalization of infectious diseases. While, through Gro Harlem Brundtland, the WHO (1999) has called for healthy development and the need for partnerships to ensure this occurs; industrialized nations are only now participating in these discussions. Global dialogue must lead to appropriate structures of governance to ensure infrastructure changes and adequate surveillance - we need to move forward within a changing environmental and health context. There is much to build on but much to do.

John Eyles,
McMaster Institute of Environment and Health

Ranu Sharma,
University of Victoria

References, Key Readings, and Key Websites

Borroto R.J. and R. Martinez-Piedra (2000). Geographical patterns of cholera in Mexico, 1991-1996. International Journal of Epidemiology 29, 764-772.

Chatterjee P., M. Pai and A. Zachariah (1999). Back with a vengeance. http://www.humanscapeindia.org/hs0599/hs59910t.htm

Garrett L. (1994). The Coming Plague. New York: Penguin.

Garrett L. (2000). Betrayal of Trust. New York: Hyperion.

Last J.M. (1995). A Dictionary of Epidemiology. New York: Oxford UP.

Murray C.J.L. And A.D. Lopez (1996). The Global Burden of Disease. Cambridge Mass: Harvard School of Public Health.

National Center for Environmental Health (1999). Achievements in public health 1900-1999. Mortality and Morbidity Weekly Reports 48, 621-629.

Platonov A.E., G.A. Shipulin, O.Y. Shipulina et al. (2001). Outbreak of West Nile virus infection, Volgograd region, Russia, 1999. Emerging Infectious Diseases 7, 128-132.

Satcher D. (1998). Testimony on global health. http://www.hhs.gov/progorg/asl/testify/t980303d.html

Sibanda A. (2000). A nation in pain. International Journal of Health Services 30, 717-738.

UNAIDS (2000). Report on the Global HIV/AIDS Epidemic. Geneva: UNAIDS.
http://www.unaids.org/wac/2000/wad00/files/WAD_epidemic_report.PDF

WHO (1997). Health and Environment in Sustainable Development. Geneva: WHO.

WHO (1998a). Malaria. http://www.who.int/inf-fs/en/fact094.html

WHO (1998b). Dengue and dengue haemorrhagic fever.
http://www.who.int/info-fs/en/fact117.html

WHO (1999). Report on infectious diseases.
http://www.who.int/infectious-disease-report/pages/textonly.html

WHO (2000a). The urgency of a massive effort against infectious diseases,
a statement by David L. Heymann.
http://www.who.int/infectious-disease-report/dlh-testimony/testmo.pdf

WHO (2000b). Tuberculosis. http://www.who.int/inf-fs/en/fact104.html

WHO (2000c). WHO report on global surveillance of epidemic-prone infectious diseases.
http://www.who.int/emc-documents/surveillance/docs/
whocdscsrisr2001.html/cholera/cholera.htm

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