Where the Wild Things Are

The rapid emergence of the H1N1 strain of influenza in North America and its subsequent global spread have reminded the world that viruses and other microbes are often not limited to specific species and have little regard for international boundaries. While the world was watching to see if the highly pathogenic H5N1 influenza, the so-called bird flu, in Asia and Africa would mutate to make transmission easy among humans, the new H1N1 influenza -- first called swine flu because it shares several gene sequences with influenza viruses found in pigs -- seems to have already made that transition.

Changes to influenza viruses can happen as a result of quick mutations or as the end result of a slower drift in genetic material. At the same time, different influenza viruses exchange entire genetic segments with one another when they simultaneously infect the same person or animal. One of the virus's genetic segments controls the hemagglutinin antigen, which sits on the surface of the virus and allows it to attach itself to the cells of the host. Another segment controls neuraminidase, a protein that enables the virus's release from the host cell after multiplying. The combination of H's and N's provides the name used for strains of influenza viruses such as H5N1 and H1N2.

The host, whether it is a person, bird, or pig, provides a place for influenzas to make contact, exchange genetic material, and form new viruses. Such genetic intermixing is not uncommon: the new H1N1 influenza virus, for example, appears to have formed from components of previously circulating viruses with a mix of influenza genes for three different host groups: birds, pigs, and humans.

This specific H1N1 virus rapidly circulating around the world, then, is not a new phenomenon but simply a new strain of influenza. This does not, however, mean that there is no need for concern. Each new strain of influenza has the potential to cause mild to very serious disease, and when new strains first emerge, it is extremely difficult to predict a trajectory for infection or its consequences.

As I described in a 2005 article in Foreign Affairs, the health sciences are segregated into many specialty areas, such as human medicine, livestock disease, and wildlife health. The compartmentalization of these fields has hampered efforts to effectively control or prevent the emergence and spread of diseases that move among species, which together represent approximately 60 percent of all infectious organisms.

Even as national and global health agencies are scrambling to react to the continuing spread of the H1NI virus, a major influenza virus that emerged in the last decade has not been adequately addressed. The highly pathogenic avian influenza, subtype H5N1, is still killing millions of domestic chickens and ducks in Asia and Africa. This has caused economic hardship for people and has hit many poor countries with trade restrictions, especially Bangladesh, Egypt, Indonesia, and Vietnam. Avian flu still presents the ongoing threat of a potential human pandemic, with more than 400 cases reported as of April 2009, resulting in at least 250 human deaths.

Although collaboration among health organizations and local governments has vastly improved since H5N1 first emerged, much remains to be done to implement better control mechanisms in the poultry industry, such as improved sanitation and good vaccination programs. In East Asia, where the highly pathogenic H5N1 influenza first developed in domestic ducks, chickens, and geese, the virus has spread not only to other farms and flocks but also to wetlands, where it can live for years and infect wild bird populations.

In many countries where contact between domestic and wild animals is commonplace, early disease-detection systems are still not as good as they could or should be. In the case of H5N1, new vaccines developed in the last few years for both humans and birds may help to reduce risks, but local capabilities to vaccinate people are often lacking. Even the United States has yet to approve new vaccine production technologies that would cut the wait time for producing massive quantities of human-influenza vaccines from the current minimum of eight months or so to just half of that or less.

A broader understanding of the connection between human and animal health demands a more unified approach such as that offered by the One World-One Health program, an ongoing series of multidisciplinary dialogues led by the Wildlife Conservation Society. The resulting programs bring together experts ranging from biologists and sociologists to economists and natural-resource managers. The rapid partnering of animal- and human-influenza specialists on the current H1N1 outbreak is an example of how a more comprehensive approach can speed the response to a potential pandemic.   

Over the last few years, the One World-One Health concept has gained wide acceptance in the scientific community as well as the attention of policymakers and the development community. International bodies such as the World Health Organization and the World Bank have adopted the One World-One Health approach in their collaborative efforts to control avian and pandemic influenza and other diseases of global concern.