World Trade and Infectious Disease
World Trade and Infectious Disease
History and Scientific Foundations
Introduction
World trade impacts the epidemiology of infectious diseases in numerous ways, including commercial travel by air and rail, shipping of contaminated goods, transportation of disease vectors with shipped goods or via commercial transportation, and the consumption of translocated plants and animals that have been infected with non-native pathogens.
The globalization of world commerce has brought about unprecedented contact between populations and exposure to foreign pathogenic organisms that is radically changing the distribution of communicable diseases worldwide. Consequently, the urgency of international collaboration on public health information and disease control has risen to a point where an outbreak of a serious communicable disease anywhere in the world raises alarms and spawns defensive activity everywhere. The limiting of the SARS outbreak in 2004 through quarantine and restriction of wild animal markets and social interaction provides an example of how such collective defense measures can be effective. However, lessons taken from that outbreak and sober reflection on the potential virulence of certain pathogens such as avian influenza, anthrax and tuberculosis have revealed gaps in international cooperation and preparedness for the consequences of possible pandemics that world trade could facilitate. The future of disease control and local public health will increasingly depend on the processes of globalization and their impact on the distribution of pathogens and on environmental change, which can create new ecological niches for pathogenic organisms.
History and Scientific Foundations
The Impact of Globalization
Human travel and movement have been the main source of epidemics throughout recorded history. Trade caravans, religious pilgrimages, and military maneuvers facilitated the spread of many diseases, including plague and smallpox. Smallpox is presumed to have spread from Egypt or India along historical trade routes, where it was first thought to have become adapted to humans sometime before 1000 BC. For most of history, human populations were relatively isolated. Only in recent centuries has there been extensive contact between the peoples, flora, and fauna of the Old and New Worlds. Contact between the European colonists and native American populations during trade and exploration led to the transmission of measles, influenza, mumps, smallpox, tuberculosis, and other infections from the crowded urban centers of Europe, which caused the suddenly exposed native American populations to drop by at least one-third.
Intensifying global trade, which entails deregulated trade and investment, can have a mixed impact on public health. When global trade brings economic growth and disseminates technologies such as antibiotics and other medications that enhance life expectancy, there are broad benefits to public health. However, some aspects of globalization erode public health infrastructure and jeopardize health by causing the deterioration of social and environmental conditions, undermining the livelihoods of certain population groups, and sowing some unhealthful lifestyle patterns. Global environmental changes, related to population growth and intensified economic activity, include air pollution, deforestation and desertification, depletion of terrestrial aquifers and ocean fisheries, and decreased biodiversity. Some of these processes pose public health risks.
On the positive side, improvements in the public health of industrializing countries have resulted from widespread social, nutritional, and material changes such as improved sanitation and other deliberate public-health interventions, including vaccination and disease vector eradication programs. Health gains have begun more recently in developing nations in the wake of population control efforts, application of knowledge about sanitation and vaccination, improved nutrition, vector control, and gradually improved treatment of infectious diseases. However, shifts in the ecology of local habitats brought about by environmental change related to globalization can have a profound impact on the distribution of infectious diseases.
Globalization and the Ecology of Infectious Disease
The main reason for the adverse effects of globalization is the disruption of traditional and largely self-contained agricultural societies that produce, consume, and trade on a local basis, using technologies that have a low impact on the environment. The social and environmental determinants of public health for these societies are predominantly local. Over the past century, industrialization and modernization have changed the amount of contact, influence, and trade between societies; created new hierarchical business associations; and have increased the impact of technology on the environment. The former balance between local populations and the pathogens in their environments is often disturbed and new pathogens are introduced into local regions, increasing the probability of serious disease outbreaks for which local people either lack herd immunity or the means for effective treatment.
Globalization of commerce and culture has also spurred an increase in human mobility. Much of this travel is voluntary, connected with business, tourism, and movement of labor. Some of this mobility is involuntary, caused by war (which is often connected with trade advantage or resource access issues), social breakdown, and natural disasters. A recent study found that the number of environmental and political refugees has increased about tenfold since 1980. The increased transnational movement of labor generally brings economic benefits to both developed and less developed economies, but also increases the transmission of ideas, values, and microbiological agents that affect disease patterns.
The globalization of world trade thus fundamentally changes the ecological context of infectious disease epidemiology by opening new opportunities for transmission and environmental niches for pathogens while also increasing the need for transnational public health information sharing and cooperation for disease prevention and treatment. Perhaps more than any other current trend, world trade brings home the importance of viewing epidemiology as more than the analysis of risk factors for disease, but rather as the study of ecological systems that mediate disease distribution and causation.
Global Trade and Travel
Global trade necessitates greatly increased travel for transactions, and travel is a major force in disease emergence and spread. According to the Centers for Disease Control (CDC), the current volume, speed, and reach of travel are unprecedented. Travel and trade facilitate the mixing of diverse genetic pools and harbored microorganisms at rates and in combinations unknown. Such massive mobility and other concomitant changes in social, political, climatic, environmental, and technologic factors have converged to favor the emergence of infectious diseases.
WORDS TO KNOW
BUSHMEAT: The meat of terrestrial wild and exotic animals, typically those that live in parts of Africa, Asia, and the Americas; also known as wild meat.
ENDEMIC: Present in a particular area or among a particular group of people.
EPIDEMIOLOGY: Epidemiology is the study of various factors that influence the occurrence, distribution, prevention, and control of disease, injury, and other health-related events in a defined human population. By the application of various analytical techniques including mathematical analysis of the data, the probable cause of an infectious outbreak can be pinpointed.
GLOBALIZATION: The integration of national and local systems into a global economy through increased trade, manufacturing, communications, and migration.
HERD IMMUNITY: Herd immunity is a resistance to disease that occurs in a population when a proportion of them have been immunized against it. The theory is that it is less likely that an infectious disease will spread in a group where some individuals are less likely to contract it.
PATHOGENIC: Something causing or capable of causing disease.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
ZOONOTIC: A zoonotic disease is a disease that can be transmitted between animals and humans. Examples of zoonotic diseases are anthrax, plague, and Q-fever.
Disease emergence or reemergence generally requires several simultaneous events. Travel introduces a potentially pathogenic microbe into a new geographic region. However, in order to become established and cause disease a microorganism must survive, proliferate, and find a way to enter a vulnerable host.
Global travel, changing patterns of resistance and susceptibility, and the emergence of infectious diseases also affect plants, animals, and insect vectors. Infectious diseases are dynamic. Most new infections are not caused by genuinely new pathogens. Agents involved in new and reemergent infections include viruses, bacteria, fungi, protozoa, and helminths. Human activities that provide new opportunities for the proliferation of these microbes are the most potent factors driving infectious disease emergence.
Travel is relevant in the emergence of disease if it changes an ecosystem in ways that promote the transmission of disease by introducing new organisms or by altering the ecosystem in ways that facilitate the proliferation of new or endemic pathogens. Travel introduces such organisms by transporting pathogens (in or on travelers’ bodies, including microbiologic flora or disease vectors) and carrying dormant infections that have been controlled by the travelers’ immune systems and genetic makeup but to which native populations are not immune. Pathogens are also introduced to new ecosystems by luggage and whatever it contains. Direct change of native ecosystems in ways that favor disease emergence can occur when trade brings about changes in cultural preferences, customs, behavioral patterns, and local technology.
Applications and Research
Trade in Wildlife—An Infectious Disease “Time Bomb”
Worldwide trade in wildlife creates opportunities for infectious disease transmission that cause outbreaks in both humans and livestock. In turn, these outbreaks threaten international trade, agriculture, native wildlife populations, and the integrity of local ecosystems. Disease outbreaks resulting from wildlife trade have caused hundreds of billions of dollars of economic destruction globally.
According to the CDC, estimating the volume of the global wildlife trade is extremely difficult because it encompasses activities ranging from local barter to major international commerce via ships, rail, and aircraft. A significant proportion of this trade is conducted either informally or illegally. It is estimated that 40,000 live primates, four million live birds, 640,000 live reptiles, and 350 million live tropical fish are traded globally each year. Guangzhou, China, has live wildlife markets that trade in masked palm civets, ferret badgers, barking deer, wild boars, hedgehogs, foxes, squirrels, bamboo rats, gerbils, snakes, and endangered leopards, as well as domesticated dogs, cats, and rabbits. Lacking precise trade data, the CDC conservatively estimates that in East and Southeast Asia, tens of millions of wild animals are shipped annually, both within the region and from around the world for food or use in traditional medicine.
The estimate for trade and regional consumption of wild animal meat in Central Africa is more than 2.2 billion lb (1 billion kg) per year, and estimates for consumption in the Amazon Basin are in the range of 220 million lb (100 million kg) annually. For mammals, this amounts to 6.4 million to 15.8 million individual animals. In Central Africa, estimates range over 500 million mammals.
Hunters, brokers/distributors, and consumers have some degree of contact as each animal is traded. Other wildlife in the trade is exposed, as are domestic animals and wild scavengers in villages and market areas that consume the remnants and wastes from the traded wildlife. The CDC calculates that multiple billions of direct and indirect contacts among wildlife, humans, and domestic animals result from the wildlife trade annually. The global scope of this trade, together with rapid modern transportation and the role of markets as network hubs rather than as final destinations, dramatically increases the movement and potential cross-species transmission of communicable pathogens that every animal naturally hosts. Since trade in wildlife functions as networks with the markets as major hubs, these markets provide control opportunities to maximize the effects of public health and other regulatory efforts.
Far from being a peripheral public health risk, trade in wild animals presents one of the most severe health threats facing modern society. Perhaps the most significant human disease outbreak in the past several years directly attributable to wildlife trade (specifically, trade in civet cats) was the epidemic of severe acute respiratory syndrome (SARS) in 2003. Control efforts in Guangzhou involved the confiscation of a reported 838,500 wild animals from the markets. A study of antibody evidence of exposure to the SARS Coronavirus demonstrated a dramatic rise from low or zero prevalence of civets at farms to an approximately 80% prevalence in civets tested in markets.
Since 1980, more than 35 new infectious diseases have emerged in humans, approximately one every eight months. The origin of HIV is likely linked to human consumption of nonhuman primates. Recent Ebola hemorrhagic fever outbreaks have been traced to index patient contact with infected great apes that are hunted for food.
The collateral transmission of infectious agents due to the wildlife trade is not limited to human pathogens but also involves pathogens of domestic animals and native wildlife. Ominously, H5N1 Type-A Influenza virus was recently isolated from two mountain hawk eagles illegally imported to Belgium from Thailand. Monkeypox was transmitted to a native rodent species and then to humans in the United States by imported wild African rodents for the United States pet trade. Chytridiomycosis, a fungal disease now identified as a major cause of the extinction of 30% of amphibian species worldwide, has been spread by the international trade in African clawed frogs.
Many domestic animal diseases are transmitted through the same species of parasites carried by imported animals. Ticks have been removed from nearly 100 shipments of wild animals inspected by the U.S. Department of Agriculture. Ticks carry many diseases that threaten livestock and human health, including heartwater disease, Lyme disease, and babesiosis.
CDC examination of epidemiological data indicates that the possibility of emerging infectious diseases spreading between persons and animals is rising due to human activities ranging from the handling of bushmeat and the trade in exotic animals to the destruction or disturbance of wild habitat. The majority (61%) of listed human pathogens is known to be zoonotic, and multiple host pathogens are twice as likely to be associated with an emerging human infectious disease. More than three-quarters of pathogens found in livestock are shared with other host species.
The sudden increase of emerging or reemerging livestock disease outbreaks around the world since the mid 1990s, including bovine spongiform encephalopathy (BSE), foot-and-mouth disease, avian influenza, and swine fever, has cost the world economy $80 billion. In early 2003, the United Nations reported that more than one third of the global meat trade was embargoed as a result of mad cow disease, avian influenza, and other livestock disease outbreaks. Efforts to control the spread of avian influenza in Asian countries since 2003 have required the culling of more than 140 million chickens.
Any attempt to eradicate the trade in wild species is doomed to failure. However, the experience of slowing the spread of SARS by regulating the market in Guangzhou shows that focusing efforts at wildlife markets to regulate, reduce, or in some cases, eliminate the trade in particular wildlife species could provide a cost-effective approach to decreasing the risks of disease for humans, domestic animals, wildlife, and ecosystems.
Impacts and Issues
Updating International Health Regulations
The International Health Regulations (IHR) are the only existing global regulations for infectious disease control. These regulations have not been appreciably changed since their original issuance in 1951. The World Health Organization (WHO) is currently attempting to modernize the IHR, in view of the many emerging global public health threats posed by international trade, travel, and other worldwide human activity.
In an article published in the Journal of the American Medical Association in 2004, Lawrence Gostin recommended IHR revisions to improve global health, including:
- Adopting a robust mission, emphasizing the WHO's core public health purposes, functions, and essential services
- Assuming a broad scope, flexibly covering various health threats
- Taking responsibility for global surveillance, developing information networks of official and informal data sources
- Evaluating the adequacy of national public health systems, setting performance criteria, measuring outcomes, and holding states accountable for public protection
- Ensuring the protection of human rights, setting science-based standards and fair procedures
- Promoting good governance, adopting the principles of fairness, objectivity, and transparency
Overall, recommendations are for according the WHO with sweeping responsibility for enforcing health norms and ensuring state compliance while providing generous economic and technical assistance to poorer countries. Enforcement options for the WHO remain unclear, but there is an implicit reliance in the recommendations upon the power of world public opinion, possibly backed up by sanctions imposed by influential countries against those that withhold cooperation. Given the intimacy with which the world is now connected in the struggle against infectious disease, the rich and poor nations have an equal stake in assuring that all nations have the tools to combat emerging and reemerging diseases that result from global trade.
See AlsoPublic Health and Infectious Disease; Travel and Infectious Disease.
BIBLIOGRAPHY
Books
Myers, N., and J. Kent. Environmental Exodus: An Emergent Crisis in the Global Arena. New York: Climate Institute, 1995.
Periodicals
Gostin, L.O. “International Infectious Disease Law: Revision of the World Health Organization's International Health Regulations.” Journal of the American Medical Association 291 (2004): 2623-2627. (Also available at <http://jama.ama-assn.org/cgi/content/full/291/21/2623>; accessed May 26, 2007).
Karesh, W.B., R.A. Cook, E.L. Bennett, and J. Newcomb. “Wildlife Trade and Global Disease Emergence.” Emerging Infectious Diseases 11, 7 (July 2005). Available at <http://www.cdc.gov/eid> (accessed May 26, 2007).
McMichael A., and R. Beaglehole. “The Changing Global Context of Public Health.” The Lancet 356, 9228 (August 2000): 495–499.
Kenneth T. LaPensee