A foreign agent that invades sovereign territory, evades detection, kills civilians, and disrupts the economy is a security threat by most definitions. Not all new diseases are highly lethal, contagious, and able to spread internationally, inciting panic as they do. But those that can are international threats to health security. We live in a world where threats to health arise from the speed and volume of air travel, the way we produce and trade food, the way we use and misuse antibiotics, and the way we manage the environment. All of these activities affect one of the greatest direct threats to health security: outbreaks of emerging and epidemic-prone diseases. Outbreaks are unique public health events because of their ability to cross national borders, undetected and undeterred. Traditional defenses at national borders are no protection against a microbe incubating in an unsuspecting traveller or an insect hiding in a cargo hold. All nations are at risk. This universal vulnerability creates a need for collective defenses and for shared responsibility in making these defenses work. Outbreaks are a much larger menace today than they were just three decades ago. They are larger in two ways. First, changes in the way humanity inhabits the planet have led to the emergence of new diseases in unprecedented numbers. In the thirty years from 1973 to 2003, when SARS appeared, 39 pathogenic agents capable of causing human disease were newly identified. The names of some are notoriously well-known: Ebola, HIV/AIDS, and the organisms responsible for toxic shock syndrome and legionnaire's disease. Others include new forms of epidemic cholera and meningitis, Hanta virus, Hendra virus, Nipah virus, and H5N1 avian influenza. This is an ominous trend. It is historically unprecedented, and it is certain to continue. Second, the unique conditions of the 21st century have amplified the invasive and disruptive power of outbreaks. We are highly mobile. Airlines now carry almost two billion passengers a year. SARS taught us how quickly a new disease can spread along the routes of international air travel. Financial markets are closely intertwined. Businesses use global sourcing and just-in-time production. These trends mean that the disruption caused by an outbreak in one part of the world can quickly ricochet throughout the global financial and business systems. Finally, our electronic interconnectedness spreads panic just as far and just as fast. This has made all nations vulnerable - not just to invasion of their territories by pathogens, but also to the economic and social shocks of outbreaks elsewhere. Some experts have gone so far as to state that there is no such thing as a "localized outbreak anymore. If the disease is lethal, frightening, or spreading in an explosive way, there will always be international repercussions. On the positive side, our world's electronic transparency has made it difficult for any country to hide an outbreak. News will always seep out and be picked up. Last year, media reports were the first alert to more than 52 percent of the 197 outbreaks verified - in just that year - by the World Health Organization (WHO). In June of this year, the revised International Health Regulations will come into force. For the first time, WHO is authorized to act on media reports to request verification and offer collaboration to an affected country. If this offer is refused, WHO can alert the world to an emergency of international concern using information other than official government notifications. This is a significant step forward for our collective security. The best defense against emerging and epidemic-prone diseases is not passive barriers at borders, airports and seaports. It is proactive risk management that seeks to detect an outbreak early and stop it at its source - before it has a chance to become an international threat. We are now in a good position to act in this pre-emptive way. I have mentioned the role of changes in the way humanity inhabits the planet. A list of some of these helps us understand the multiple dimensions of health security. Constant evolution is the survival mechanism of the microbial world. Organisms that can replicate more than a million times a day are well-equipped to exploit any opportunities we give them to adapt, invade, and evade. The opportunities are multiple. The pressures of population growth push people into previously uninhabited areas, disrupting the delicate equilibrium between microbes and their natural reservoirs. This creates opportunities for new diseases to emerge. Population growth also puts people in close proximity to domestic animals, creating evolutionary pressures and opportunities for pathogens to jump the species barrier. Of the emerging pathogens capable of infecting humans, around 75 percent originated as diseases of animals. Urbanization has encouraged insect vectors to adapt their breeding habits. They have learned how to thrive in urban litter and filth. Urban crowding under unsanitary conditions also creates ideal conditions for explosive epidemics of well-known diseases, such as yellow fever and dengue. Environmental degradation and changing weather patterns allow known diseases to flare up in unexpected places, at unexpected times, and in unprecedented numbers of cases. Intensive food production, including the use of antibiotics in animals, creates additional pressures on the microbial world, leading to mutations and adaptations, including drug resistance. In humans, our misuse of antimicrobials is causing mainstay drugs to fail much faster than the pace of development of replacement drugs. If this trend continues, we can begin to think of a world where mainstay antibiotics are no longer effective. And we must not forget: drug-resistant strains of viruses and bacteria also travel well internationally. World Health Day, devoted this year to international health security, focuses attention on these complex and interrelated threats to our collective security. In our mobile, interdependent, and interconnected world, threats arising from emerging and epidemic-prone diseases affect all countries. They reinforce our need for shared responsibility and collective action in the face of universal vulnerability, in sectors well beyond health. Dr Margaret Chan is the Director-General of the World Health Organization Singapore.
