Kenneth H Mayer and HF Pizer

Infectious disease is one of the great tragedies of Jiving things - the struggle for existence between different forms of life. Man sees it from his own prejudiced point of view; but clams, oysters, insects, fish, flowers, tobacco, potatoes, tomatoes, fruit, shrubs, trees, have their own varieties of smallpox, measles, cancer, or tuberculosis. Incessantly, the pitiless war goes on, without quarter or armistice - a nationalism of species against species ... The important point is that infectious disease is merely a disagreeable instance of a widely prevalent tendency of all living creatures to save themselves the bother of building, by their own efforts, the things they require. Whenever they find it possible to take advantage of the constructive labors of others, this is the direction of the least resistance ... About the only genuine sporting proposition that remains unimpaired by the relentless domestication of a once free-living human species is the war against these ferocious littie fellow creatures, which lurk in the dark corners and stalk us in the bodies of rats, mice, and all kinds of domestic animals; which fly and crawl with the insects, and waylay us in our food and drink and even in our love.

Hans Zinsser, 1935, in Rats, Lice and History

Most people associate ecology with efforts to preserve nature, to recycle waste products and conserve resources and heal or prevent the wounds people inflict upon the world's ecosystems. But although these are important results of ecological thinking, ecology itself is much more. In its original sense, it is the science of connections. It seeks to describe the vast web of interrelationships that tie living things to their environmente, its fundamental premise being that a change in any part of one of the

"tangled banks" of life we call ecosystems can have broad and often unexpected implications for any living thing seeking to survive within them.

Gabriel Rotello, 1997, in Sexual Ecology AIDS and the Destiny ofGay Men

This book was conceived to expand upon previous efforts to explore the social ecology of infectious diseases, which we define as the scientific study of the ways by which human activities enable microbes to disseminate and evolve, creating favorable conditions for the diverse manifestations of communicable diseases. Despite advances in living standards, public health, and medical technologies (including antimicrobial drugs and vaccines), infectious and parasitic diseases cause about a third of deaths worldwide and are the second leading cause of mortality and disability (Fauci, 2001). The rapidity by which changes in human behavior can result in severe epidemics is well illustrated by HIV, the cause of AIDS, which is spread primarily by sexual activity and injecting drugs using unsterile equipment. But AIDS is only one of multiple microbial threats, and other human activities can cause devastating infectious epidemics. The goal of this text is to analyze the wide range of activities and behaviors that influence the evolution and dissemination of infectious disease epidemics. They include the migration of people and the transport of goods; the production and distribution of food; human-influenced changes in demography and the environment; advances in medical technologies; and patterns of governance, conflict, natural disaster and the dislocation of populations. Taken together, we believe these diverse activities are essential determinants of the prevalence and incidence of the current array of infectious diseases that continue to be major causes of morbidity and mortality across the planet.

In the electronic media era, on almost any given day, it seems the news is highlighting a new infectious disease pathogen as the next great threat to humanity. In 2003 it was SARS. In 2006 it was avian influenza. Before that there were Legionnaires' disease and Toxic Shock Syndrome, and earlier tuberculosis was (as coined by Rene and Jean Dubos) known as "the white plague" (Dubos and Dubos, 1952). While the battle between humans and constantly evolving microbes is continuous, it would be wrong to be unduly pessimistic about the future. The microbes adapt to their hosts and humans respond. Each year, more people have access to modern medicines. Health programs expand to more communities, and more young professionals are trained in clinical care and public health. In response to the AIDS epidemic, the international health workforce is expanding and improving at an unprecedented pace. While more always needs to be done, there now is a historic commitment to improving health, especially in the developing world. What is different now from the unwarranted optimism of the 1960s is the realization that medical technology by itself will not prevent or fully contain infectious diseases. Vaccines have been effective for some diseases, but many microbial pathogens are highly adaptable and human activities are often amenable to creating niches and opportunities for the spread of infectious diseases. This is demonstrated by the re-emergence of old diseases like dengue fever, yellow fever, measles, cholera, leishmaniasis, and malaria, and the appearance of new ones like AIDS, the hemorrhagic fevers, SARS, and avian influenza. Although new antimicrobial agents continue to be developed, as they become increasingly used by humans and in veterinary medicine, pathogens often develop resistance. Some vectors have become resistant to insecticides, complicating the control of several common diseases, such as malaria.

Advances in medical technology create new opportunities for nosocomial pathogens to proliferate in immunocompromised hosts and prosthetic tissues. Although secondary spread of these opportunistic infections is uncommon, nosocomial outbreaks of multi-resistant bacteria and fungi have plagued many intensive care units and cancer treatment centers. Advances in surgery and life support create new niches for microbes to proliferate, ranging from in-dwelling catheters to surgical wounds. As life-saving advances such as organ transplants, immunosuppressive therapy of autoimmune diseases like rheumatoid arthritis, and chemotherapy for malignancies become more accessible in under-resourced communities, the ability of a diverse array of microbes to create new clinical challenges will grow.

Moreover, the continued existence of millions of impoverished and malnourished individuals throughout the world creates a vast reservoir for the development and dissemination of new plagues. The elimination of poverty through strategies to promote human development would not eradicate all infectious diseases, but could certainly decrease global morbidity and mortality substantially. We believe the contributors to this text make forceful arguments that protection against new infectious disease epidemics necessitates the use of traditional, as well as innovative, public health strategies that include:

• conducting continuous, concerted epidemiological surveillance

• ensuring that communities have clean and safe water supplies, proper sanitation, housing and vector control

• effective oversight over travel and the transport of goods

• government regulation of food and blood supplies, as well as pharmaceuticals

• vaccination of children and regulation of health-care and day-care facilities

• identification and treatment of sexually transmitted infections and, where appropriate, partner notification.

There is a need to emphasize public health in medical and other clinical education, to expand the international health workforce, and to improve global responsiveness to natural and man-made disasters, as well as to take advantage of newer technologies - such as computerized surveillance, web links to report new outbreaks, and videoconferencing - to share relevant outbreak information.

These strategies can provide valuable new tools to address the intractable, as well as emerging, epidemics of the twenty-first century.

We begin the text with a discussion of the role modern travel plays in infectious diseases. Population migrations and trade have always spread epidemics, but the speed, scope, and volume of modern travel is qualitatively different from any period before in history. Over the last half-century, international travel grew 32-fold. Two million people cross international borders every day, and many more travel within their country's borders but still over significant distances. In the last 200 years, the average daily distance a Frenchman now travels has increased 1000-fold. The world is covered and linked by an efficient network of roads, and rail, water, and air routes. In March and April 2003 a businessman flew from Hong Kong to Frankfurt, and then took seven flights within Europe, before returning to Hong Kong, where he was diagnosed with SARS. Travelers invariably and inadvertently expose themselves and others to new microbes, and today's fast and efficient travel network has created a global gene pool that links even the remote regions of the world.

In the United States and other developed nations, a sexual revolution began in the 1960s. An unprecedented number of young people started to leave home for college. Effective hormonal contraception freed them from the fear of unplanned pregnancy. Young people delayed marriage. Women gained new independence through increased workforce participation. A new literature on lovemaking became popular, encouraging heterosexual men to become more competent lovers and women to be orgasmic and assertive about their sexual desires. Meanwhile, the divorce rate increased, and with it the number of sexually experienced unmarried adults available for intimate relationships. From 1971 to 1988, the number of never-married women in the United States between the ages of 15 and 19 that had had sexual intercourse increased from 28 percent to over 50 percent. The gay pride and sexual liberation movements created vastly expanded opportunities for homosexually active men to meet and have sex. All of these social changes helped set the stage for epidemics of AIDS and hepatitis A and B, as well as the resurgence of other sexually transmitted infections, such as syphilis. The Internet now offers a new, efficient, inexpensive, and anonymous tool for sexually active individuals to communicate and then meet for sex, abetted by the ease of rapid travel.

International drug epidemics have contributed to the widespread transmission of HIV, hepatitis B and C, malaria, tetanus, and syphilis and other sexually transmitted infections. Drug trafficking and drug injecting flourish where people encounter adverse economic and social conditions, and where there is political unrest and societal disruption. While different patterns of recreational drug use may be associated with a range of health risks (for example, non-parenteral drug use is associated with behavioral disinhibition leading to sexually transmitted infections), drug injecting and needle sharing may still account for 10 percent of all new AIDS cases worldwide. The editors of this book and the authors of the chapter on substance use believe that prohibitionist approaches exacerbate drug problems and their health consequences. Limiting drug supplies makes drugs more expensive and encourages injecting, which is the most efficient route of pathogen administration. Harsh legislation and law enforcement drive injecting drug users away from testing, education, and treatment programs. Another option is to combat the adverse downstream effects of drug use with education, drug treatment, and drug substitution therapy, access to clean needles and syringes, and routine screening for, and treatment of, sexually transmitted infections in drug users.

Over the past half-century, humankind has gone through a revolutionary historic shift from rural to urban living. Two hundred years ago, Beijing was the only city in the world with a population of more than a million; now there are at least 400. Most of the growth has been in tropical zones and in congested, sprawling urban environments rife with neighborhoods that lack adequate electricity, drinking water, sewage systems, and waste management. Public health and infectious disease control generally are under-funded or absent. At some point a critical threshold is reached where there are enough susceptible individuals who have not been previously exposed to a particular infectious agent, and an outbreak occurs. Uncontrolled urbanization across the developing world is now a major factor in the eruption of epidemics of old and new infectious diseases, and provides hubs for their spread to nearby communities and to distant countries and continents. Our contributors focus on dengue fever to discuss this phenomenon, but their observations also apply to other well-characterized diseases like yellow fever, as well as newly recognized and emerging infectious diseases. The social ecology of dengue fever involves the interaction of humans and the mosquito vector Aedes aegytpi, which over time evolved from its origins in the tropical rainforest to thriving on humans in sprawling tropical cities. In overcrowded, impoverished urban centers, every water container and domestic animal can be a potential source for maintaining and propagating A. aegypti, and each mosquito bite has the potential for spreading dengue within urban neighbourhoods, which then radiates out from the city by the continuous flow of inter-city commuters, urban-rural migrants, animal reservoirs, and vectors. Between 2.5 and 3 billion people, half the world's population, now live in areas at risk for dengue, and each year an estimated 50-100 million people are infected with dengue flaviruses. At least four dengue serotypes that cause human disease have been isolated, and infection with one subtype does not confer immunity to the other subtypes. While it is not possible to kill every mosquito, prior success at controlling dengue provides lessons for the future - better laboratory-based epidemiological surveillance and improved training for frontline health practitioners; community-based public strategies such as targeting open-air water reservoirs and installing air conditioning and screens on windows; targeted spraying; and educating the public to avoiding peak exposure hours, especially when surveillance has provided early warning of an outbreak.

For more than half a century the suburbs of affluent nations have been replacing farms and forest with lawns and parks - so, for example, over the past 20 years the greater Chicago area has sprawled out by 46 percent, even though the population has grown by only 4 percent. While the net amount of forest in the country may not have changed significantly in the last two decades, expanding suburbanization has created a huge patchwork of forest interspersed with residential communities where more than half the US population now lives. This is the ideal set-up for putting humans, wildlife, and ticks in close proximity. Conservation efforts, including the protection of tick-infected deer, have expanded the pool of potential vectors for several infectious pathogens. The result has been a rapid increase in the number of humans who have developed Lyme disease, caused by a spirochete, and now the most common tick-borne disease in the word. It came to public attention in the late 1970s, in large part through the efforts of two suburban mothers in Connecticut. Almost 17,000 cases are reported each year in the United States alone by individuals who may suffer serious joint, nervous system, and cardiac involvement. However, seroepidemiological studies suggest even greater prevalence of Lyme spirochetal infection. Areas of high exposure risk include parks and the mowed back lawns of single-family suburban homes that abut woodlands. Meanwhile, general public opposition to widespread insecticide application and to measures to reduce the deer population have helped to expand the pool of infected ticks. Thus the responsibility for preventing exposure to Lyme disease largely falls on the individual through behavior modification, insect repellent use, and prompt removal of attached ticks. However, these measures have had limited effectiveness, so the incidence of Lyme disease continues to rise.

Changes in child-rearing practices, ranging from decreased breastfeeding to leaving children in day care while mothers work, can alter the natural history of communicable diseases. For example, in affluent societies it is now common for women of childbearing age to work, and for young children to be in group day care where they are exposed to common viruses and bacteria. There have been many infectious agents associated with group day care, such as Hemophilus influenzae b (prior to the advent of an effective vaccine), cytomegalovirus, Sreptococcus pneumoniae, Neisseria meningitides, rotavirus, Salmonella, Shigella, Giardia lamblia, E. coli, respiratory viruses, varicella, hepatitis A, and parvovirus B 19. Children are often separated by age and cared for in a single room, and each year a new group of children with limited prior exposure to infectious diseases enters the day-care center. Until they acquire immunity to common infectious agents, children in group day care experience a higher incidence of diarrhea, otitis media, and respiratory tract infections than children who stay home. Studies of hepatitis A outbreaks have illustrated how an infectious agent spreads in group day-care settings and then from the day-care center to the home and even to the wider community. Another well-studied example is CMV infection, which is heavily influenced by both breastfeeding and the group care of children. Once infected with CMV, a child can shed virus for years in saliva and urine. Because young children cannot control their body fluids, day-care centers have become ideal settings for the transmission of CMV between children, and from children to adult caregivers and to family members. The prevalence of CMV infection among day-care workers ranges from 8 percent to 20 percent, while the average is about 2 percent among adults in general. Until recently, relatively few infants were breastfed or attended group day care, so many of today's mothers have no immunity to CMV. If a pregnant woman without immunity sends her child to day care and that child becomes infected with CMV, the mother is then at risk for having her next newborn develop congenital CMV, which can cause hearing loss, mental retardation, or cerebral palsy.

Modern medical care would not be possible without a safe and available blood supply. With the population aging and more medical uses for blood each year, the demand for safe blood and blood products continues to grow. Even though millions of blood units are collected each year, more seems always to be needed in developed nations, and the need is even greater in developing nations, which typically do not have well-regulated and well-organized national voluntary donor systems. Voluntary donation is the proven key to a safe blood supply. For example, from 1970 to 2000 the United States instituted a national voluntary system and the overall risk of acquiring a transfusion-transmitted infection dropped from 1 in 70,000 to 1 in 11.15 million units transfused. For hepatitis B, the risk dropped from one in 855 to one in 138,700 units transfused. (Compare this with the risk of dying from motorcycling, which is one in 50 per person per year, and from playing soccer, which is one in 5000 per person per year.) Regardless of whether a blood unit is contaminated with a well-characterized infectious agent such as malaria or a newly recognized one like HIV or Babesia microti, the likely causes of the human infection and entry into the blood supply include intravenous drug use with needle sharing, high-risk multiple-partner sexual activity, exposure to insect vectors, travel, population migration, and medical negligence. Each of these factors may be influenced by economic, political, and social conditions. While laboratory testing to uncover infectious agents in the blood supply is constantly improving, there probably never will be a fully effective laboratory test for every infectious disease that can be transmitted by blood transfusion, particularly if the infections are very recent with a low micro-organism burden. Moreover, the next infectious threat is likely to be present in asymptomatic blood donors before an effective diagnostic test is developed for it. The blood system's safety therefore is based on relatively low-cost, low-technology public health strategies: altruistic donation, public education, rigorous professional training, continuous epidemiological surveillance, and consistent frontline screening of prospective donors before they give blood.

The mass production and distribution of food is one of the great triumphs of the twentieth century. A hundred years ago, about 40 percent of the population in the United States lived and worked on family farms where food animals were raised in small herds, slaughtered locally, and, without refrigeration, could be transported only a short distance. Now food production and distribution are highly industrialized, and an unprecedented variety and quantity of products are transported over large distances. While safer and less expensive than ever before, the mass production, co-mingling and shipment of food products over large distances and across international borders has the potential for producing large-scale outbreaks of infectious diseases. For example, a single contaminated batch of mozzarella cheese from one small producer shredded into products by four other manufacturers created a multi-state outbreak of salmonellosis. One hamburger patty can have meat from hundreds of different cows. Even though agricultural products require extensive handling, at present the United States does not have microbiological regulatory criteria for fresh produce. Between 1977 and 1997, outbreaks due to fresh produce increased 10-fold. While food contamination is most common and serious in developing nations, it should be no surprise that even in a developed one like the United States about 20 percent of the population contracts acute gastroenteritis each year. While most cases of diarrhea are self-limited, there also are serious cases of hepatitis, sepsis, meningitis, and even paralysis. The spread of well-known food-borne diseases like typhoid fever by cooks and food handlers (for example, Typhoid Mary) have largely been eliminated in the developed world, but serious new pathogens have emerged such as non-typhoidal, drug-resistant strains of S. yphimurium. New and emerging food-borne pathogens continue to be recognized, and almost surely more will arise in the future.

The discovery and widespread use of antibiotics is one of the most important advances in humankind's history, but it also has had the unavoidable downside of creating an environment for drug-resistant bacteria developing a selective advantage. Antibiotic resistance and nosocomial infection are now significant threats to global health. Hospitals are a major source of the problem because they must use antibiotics regularly to care for increasingly ill and elderly patients. Another factor is the inappropriate outpatient use of antibiotics to treat self-limited illnesses such as viral upper respiratory infections. The overuse and misuse of antibiotics is also common where they are sold without a prescription. Drug pricing is another factor - for example, France has some of the lowest drug prices in Europe but also one of the highest per capita rates of use of antibiotics. Some believe that the most significant problem is in agriculture, where millions of pounds of antibiotics are used each year to treat sick animals, prevent infection in herds raised in close proximity, and promote growth. Animal husbandry has found that sub-therapeutic use of oral antibiotics is associated with rapid animal growth, but these doses are ideal for selecting resistant bacterial mutants.

There is no alternative to using antibiomicrobial drugs, and no single strategy for stopping the ability of micro-organisms to adapt to them. Hospitals can probably do a better job with infection control, surveillance, professional education, encouraging the use of less expensive antibiotics that are targeted to microbio-logically-diagnosed infections, using computers, and requiring infectious disease consultant's approval before more expensive antibiotics are prescribed. Despite understandable professional concern about prescribing restrictions, studies have shown that sensible limits on provider prescribing have not produced adverse patient outcomes. Similar efforts are needed to improve outpatient prescribing practices, and the public needs to be more aware that taking antibiotics is not always in an individual's interest or in the interest of public health. Legal and economic forces that encourage unnecessary antibiotic use must be addressed -especially in developing countries, where antibiotics often can be purchased without a prescription, there is a ready black market for them; and pharmacists with limited medical training regularly prescribe antibiotics or refill prescriptions without physician approval. With increasing numbers of immunocompromised patients living after chemotherapy or organ transplants, wider use of antibiotics and the subsequent evolution of resistance will be inevitable, even if judicious policies are put in place.

The development of safe, effective, and cost-effective vaccines is one of the great medical achievements in history. It has had enormous impact on society by dramatically increasing childhood survival, and decreasing morbidity and disability. Smallpox was eradicated, and previously common childhood diseases like diphtheria, whooping cough, measles, and tetanus are so rare that many physicians have never seen a case. Since the late 1980s, the global incidence of polio has been reduced by 99 percent. There are now vaccines against 15 infectious diseases in the US childhood immunization schedule, and national immunization programs currently reach 80 percent of the world's children. Perversely, some parents in the developed world now refuse to immunize their children, refusing to tolerate even a very small risk of side effects. Moreover, urban myths about the association of vaccinations with the development of childhood autism and other chronic diseases have been abetted by the proliferation of disinformation on the Internet. Mass immunization programs raise thorny issues of individual rights versus public good, the risks and rewards of inaction, and social justice. New vaccines continue to be developed, like those against human papillomavirus (which is thought to account for about 70 percent of cervical cancer cases) and against rotavirus (which causes an estimated 600,000 deaths and 2 million hospitalizations, primarily in children due to diarrheal disease, mainly in poor countries). Two main challenges lie ahead: one is to discover new vaccines against the most important infectious agents, especially HIV; and the other is to make vaccines available to the poor in developing nations, which is a complex matter of cost, access to health-care, education, culture, and infrastructure. There is a worldwide consensus that the problems of both new vaccine development and expanding access must be tackled and solved through international public-private partnerships. Historically, vaccines have been developed through collaboration between academia, government, and industry, with non-profit foundations such as the Rockefeller Foundation playing an important role. Unfortunately, the cost of developing new vaccines has been rising faster than the ability of individuals and governments (especially in developing nations) to pay for them, which is why the increasing involvement of newer groups, such as the Bill and Melinda Gates Foundation, offers great promise. Even in a wealthy country like the United States, the Federal Government purchases more than half of all childhood vaccines. The primary body in Latin America is the Pan American Health Organization, and UNICEF covers much of the rest of the developing world. A bright spot is that local pharmaceutical companies are now manufacturing vaccines in developing nations. Meanwhile, there is an unprecedented commitment to support vaccine research, manufacture, and distribution. For example, in November 2005 the Bill and Melinda Gates Foundation and the country of Norway announced a 10-year $1-billion commitment to support childhood vaccinations globally. The WHO and UNICEF have their ambitious Global Immunization Vision and Strategy (GIVS) to immunize more people, especially children in low-income countries; to introduce new vaccines and technologies; and to provide basic health-care services in tandem with immunization. The GIVS goal is for each country to be immunizing at least 80 percent of its population by 2010.

Bioterrorism is the deliberate and malicious use of microbial agents or their toxins as weapons of mass destruction. Bioweapons are relatively inexpensive, simple, available, easy to conceal and produce, and easy to disseminate in a stealth attack. In 1972, under the auspices of the United Nations, more than 100 nations agreed to prohibit the development, production, and stockpiling of biological WMD, but at least 11 nations are known to have programs to develop them. Open societies are vulnerable, and a bioterrorism attack would most likely come without specific warning. Biological agents have an incubation period of days or weeks before symptoms arise, so infected persons might travel over long distances before their status is known. Initial symptoms also might not be diagnostic, and it is likely there would be additional delay in recognition because most medical professionals have never seen a patient infected with a biological WMD. The technology to produce these weapons is "dual use," which means it can serve legitimate scientific and medical purposes, or malicious ones. This serves to insulate rogue states from international scrutiny. While advances in molecular biology and biotechnology provide the possibilities to develop protective vaccines, medications, and diagnostics, they are also the tools for producing ever more lethal weapons of hybrid organisms and drug-resistant and/or particularly virulent mutants. A WHO study modeled the release of 50 kg of aerosolized anthrax spores in a city of 500,000. Depending on whether this were to occur in a developed or developing setting, the agent would likely spread at least 20 km downwind and kill or injure between 84,000 and 210,000 people. In an age of global terrorism, bioterrorism and its state sponsorship must be taken seriously.

Climate sets geographic and seasonal limits on the expression of infectious agents. The current consensus projection among climate scientists is that Earth will warm by 2-3°C this century in response to human activities, in particular the burning of fossil fuels that produce greenhouse gases. Among the numerous possible impacts of climate change on the environment are alterations in the natural systems that affect microbes, vectors, and hosts. The reproduction rate of many common pathogens and arthropod vectors, like mosquitoes and ticks, increases with rising temperatures. Demography, land use, human migration, industry, technology, and other factors also interact with climate, so that the relationship of temperature change and infectious disease transmission is not likely to be linear. While it is not possible to predict with certainty where and when a disease outbreak will occur, it is possible to model probabilities based on what is known about the effect of temperature on specific pathogens, vectors, and hosts. For example, if the "freeze line" moves north in places where schistosomiasis (a worm parasite of humans in tropical climates) is endemic, it is reasonable to predict that more people would be at risk. Malaria, which is carried by mosquitoes, is likely to spread more rapidly in warmer temperatures. Cholera thrives in warmer waters. The risk of food poisoning from salmonella and other common agents also increases as temperature and humidity rise. Because climate is affected by a wide array of economic and social activities, interdisciplinary effort will be needed to understand how climate change may affect infectious diseases. One concern is that the more rapid the pace of climate change, the more difficult it may be for humans to adapt with new technologies and public health strategies.

In the aftermath of the atrocities committed by Nazi scientists during World War II, the United Nations adopted the Universal Declaration of Human Rights, which proclaims each individual's right to the highest attainable level of health. Subsequent proclamations obligate governments to provide high-quality health services and prevent rights abuses that would have negative impacts on public health. Measures of health status - like life expectancy, maternal and infant mortality, immunization, and the prevalence of preventable and treatable infectious diseases - can be used to assess the health of populations. They may also be reasonably used to assess how well governments are fulfilling their responsibilities to populations. There is an increasing awareness that there is a link between personal economic and health status, including infectious diseases, and how governments behave with regard to public accountability, adherence to the rule of law, tolerance of an independent civil society, social stability, and respect for human rights. While more solid research in this area needs to be done, organizations like Freedom House and the World Bank have made efforts to document these links. It is clear that infectious disease risks are not spread evenly across populations and countries. Poverty leading to crowding and malnutrition, the subordination of women and minorities, as well as the mistreatment of or denial of services to other socially vulnerable populations (like injecting drug users and sex workers), are factors known to increase the risk for infectious disease transmission. For example, in Russia today there is large and growing disparity in income and employment between Moscow and a few other large cities, and the vast geographic area of the Russian federation. With the demise of the former Soviet Union and widening income disparities, there has been a sizeable increase in the number of women migrating to Moscow to perform sex work at truck stops, in hotel lobbies, and through escort services. While prostitution is legal, it takes a special permit to live in Moscow, and these women live illegally in the city. In effect, they are stateless in their own country, and thus unable to access basic health and social services. The police, their pimps, and anyone else who realizes they are not legal residents can "shake them down". This is a set-up for the transmission of HIV and other sexually transmitted infections, as well as the continued exploitation of the women. While more research is needed to document the impact of governance and poverty elimination on infectious diseases, it seems likely that these links are real.

Throughout history, poverty, war, civil unrest, political violence, social dislocation, and natural catastrophe have been responsible for establishing the underlying conditions that promote infectious epidemics. These events produce hunger and malnutrition, exposure to extremes of heat and cold, injuries and wounds, the disruption of sanitation and clean water supplies, and the abrupt dislocation of peoples leading to refugee populations. In the fifth century BCE, a plague killed one-quarter to one-third of the population of Athens because residents were crowded into and largely confined to the city as a consequence of the Peloponnesian War. Spanish conquistadors brought smallpox and measles from Europe to the New World and devastated the Incas and Aztecs. In 1741, Prague surrendered to the French, in large part because 30,000 defending Austrian soldiers were stricken with typhus. Between 1917 and 1923, millions in Europe were infected with typhus carried by soldiers from the battlefront. Conditions during World War I almost certainly facilitated the great influenza pandemic of 1918. War, civil strife, social dislocation, and natural disasters have cause millions of deaths since World War II as a direct or indirect consequence of infectious diseases such as HIV/AIDS, hepatitis A, cholera, shigella, leptospirosis, trypanosomiasis, malaria, tuberculosis, influenza, dengue, typhoid, pneumocystis carinii, pseudomonas species, and other pathogens. The fact that major infectious epidemics did not occur in the wake of the enormous undersea earthquake and resulting massive Asian tsunami that struck Indonesia, Thailand, India, and Sri Lanka in December 2004 provides important lessons for dealing with future man-made and natural disasters. Loss of life due to infectious disease can be prevented with prompt and massive international response based on providing clean water, sanitation, and shelter; limiting the size and population density of refugee camps; conducting extensive immunization campaigns; and treating diarrheal and other infectious illnesses promptly and on an empirical basis.

For both humanitarian reasons and self-preservation in an age where pathogens can so readily be transported across the globe, there is an immediate need to close the enormous health-care training gap between wealthy and poor nations. While many of the health-worker shortages in Africa are because of the advent of AIDS, other diseases and settings also urgently need highly trained health professionals. Compounding the lack of training opportunities in their home country, skilled health-care professionals in developing nations are often motivated to migrate to developed ones in order to enjoy expanded career opportunities, avoid civil strife, and enjoy an improved lifestyle for themselves and their families. Training the next generation of health professionals for practice in resource-constrained settings requires awareness of, and a multidisciplinary approach towards, the social, ecological, and political factors that impact infectious diseases. Fortunately, new cooperative training ventures are being developed to serve both poor and rich nations, so the need and rewards are mutual. Collaborative training programs build bridges across nations and cultures, students from affluent countries are enriched in their medical knowledge and understanding of the world, and linked programs provide essential venues for conducting research. There are bilateral training programs supported through US governmental organizations such as the NIH, CDC, USAID, and PEPFAR, as well as multilateral programs supported by the United Nations, the Pan American Health Organization, the Global Fund to Fight AIDS, TB and Malaria, and non-profit foundations such as the Gates and Clinton Foundations. Two examples of the effort to expand a trained international health workforce are the NIH's Fogarty International Center's Clinical Scholars Program and the US Centers for Disease Control's Epidemiology Intelligence Service, which now collaborates with 60 countries. Graduates form a core of committed individuals with clinical skills, and training in public health, public policy, government, and education. One of the first programs to recognize the need for expanding international training is the Epidemic Intelligence Service (EIS) of the Centers for Disease Control. Its mission is to train future frontline responders to assist local and state health departments in the United States and overseas to conduct epidemiological investigations, research, and public health surveillance; and to publish and present their work to the academic community, the media, and the public. There are educational opportunities in surveillance, communication, coordination, and the prompt application of public health principles to curtail remote epidemics. EIS emphasizes practical skills in areas such as computers, biostatistics, and epidemiology through day-to-day access to experienced epidemiologists who act as mentors and primary supervisors. Since the program began in the early 1950s, EIS has worked on more than 10,000 projects and expanded its geographic scope and areas of investigation. Recent infectious disease projects include polio eradication in Africa and Asia, investigation of a Hantavirus outbreak in the south-western United States, and training in bioterrorism. There are EIS field programs on every continent except Antarctica.

The Fogarty International Center has used its resources to train a large cadre of both domestic and international clinical investigators, many of whose insights have advanced global health, often with very practical public health implications. Observations that short courses of antiretroviral therapy can dramatically decrease mother-to-child HIV transmission have created moral imperatives that have facilitated treatment scale-up programs in sub Saharan Africa and other heavily affected, low-resource countries. The training of international medical and public health professionals in the conduct of clinical trials and related research will have beneficial effects for many years, based on the assumption that those trained will train other local colleagues. At the same time, the reality of "brain drain" and the limitation in dedicated resources to support clinical care and public health infrastructure in developing countries means that the implementation of new research insights may not be able to be immediately translated into appreciable benefits for those who are most in need.

The response to an infectious disease outbreak almost always begins at the local level. In a poor nation, the first responder might be a community health worker in a refugee camp or a health-care professional in the emergency room of a hospital in a large city. If the situation is grave, help will be needed from the outside. WHO regulations require nations to report outbreaks promptly and take measures to prevent their spread, while minimizing the negative impacts on trade and travel. Compliance depends largely on the action of individual governments. While the World Health Organization and the US CDC have made great strides in improving coordination, the international organizational response network remains largely a loose collection of multinational organizations, national, regional and local governments, private health-care institutions, health and education ministries, local and international NGOs, religious groups, research centers and universities, and UN programs, agencies, and funders. And there are more programs and partnerships for dealing with long-term health problems. Capacity on paper does not always translate into effective action, even in an affluent country like the United States - as evidenced when Hurricane Katrina hit the Gulf Coast in August 2005. The WHO currently is the first and leading multilateral organization for dealing with infectious disease threats. It has separate divisions for dealing with AIDS, TB, malaria, and childhood immunization, while all other infectious diseases come under Communicable Diseases. There is a global emergency response division. WHO relies on its member nations to conduct research. With at least 160 staff in more than 43 countries, the US CDC is the global swat team; after receiving an invitation from a government, they come in and help with surveillance, epidemic investigations, laboratory and epidemio-logical research, and training and public education to prevent and control communicable diseases. As fast travel and widening trade make the world smaller, there is an increasing need to improve the international response to infectious diseases. Hurricane Katrina showed that even in a wealthy nation the capacity on paper to respond to a disaster does not always easily translate to effective action in real life. Also, the system needs to move past emphasizing current disease threats to improving local primary-care medical and public health systems.

Descriptions of the social determinants of infectious diseases date back to antiquity. Ovid wrote: "What timid man does not avoid contact with the sick, fearing lest he contract a disease so near?" (Pontic Epistles, Ill.ii. 13). Humankind has been perpetually aware of the presence of invisible agents that could devastate communities with great rapidity. However, until the development of the germ theory of microbiology, the understanding of the transmission of infectious agents was based on empirical observations - such as John Snow's recognition that people who obtained their water from the High Street pump in London were more likely to become ill with cholera. Advances in microbiology enabled nineteenth-century investigators to identify etiological agents of communicable disease outbreaks and to develop more rational approaches to disease prevention and treatment. Ironically, during this recent era of impressive advances in the understanding of the pathogenesis and transmission of infectious diseases, which have led to evidence-based approaches to treatment and prevention, new epidemics have emerged that have taken advantage of diverse technological breakthroughs, ranging from rapid global travel to blood transfusions and immunosuppression after organ transplants. Ultimately, humans must recognize that we live in a global gene pool, with any microbe within days of potential contact with any population. As human activities change, microbial evolution will continue to occur to enable organisms to take advantage of newly available niches and opportunities for replication. It is neither feasible nor desirable to live in a sterile world. Although microbes can cause devastating diseases, and plagues have altered the course of human history, some, like lactobacilli in the female genital tract, are commensual and assist in keeping pathogens at bay. Others have been domesticated to allow humans to enjoy cheese, beer, and wine. The ultimate purpose of this text is to enable the reader to become more knowledgeable about some of the most recent ways that micro-organisms have evolved in the modern era, and to stimulate thinking about how the clinical and public health communities can use the rapidly evolving tools of enhanced communication technologies, such as the Internet, to disseminate information as new epidemics emerge, and to share insights that may mitigate the harm that infectious disease pathogens may cause. Some of the best ways to avoid epidemics do not rely on new technologies, but derive from insights as old as humankind: people who are well-fed and not crowded are less likely to be sick, and destructive wars provide a milieu for contagious disease to spread rapidly. Thus, if we can learn from the past and utilize some of the amazing panoply of new technologies for information dissemination, infectious diseases will not disappear but their dissemination may be most efficiently curtailed.

Caring For Your Lawn

Caring For Your Lawn

The Secret of A Great Lawn Without Needing a Professional You Can Do It And I Can Show You How. A Great Looking Lawn Doesn't Have To Cost Hundreds Of Dollars Or Require The Use Of A Professional Lawn Care Service. All You Need Is This Incredible Book.

Get My Free Ebook


Post a comment