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Avian influenza has triggered an international alarm regarding its possible transformation into a deadly human killer.
The genetic phylogeny of avian influenza, caused by the type A influenza virus, H5N1, indicates that the genesis of all influenza viruses occurs among birds, such as ducks and other waterfowl. The majority of these viruses are highly species-specific and remain among their species of origin. On rare occasions, a virus may cross the species barrier and develop the capability of invading and infecting humans. Fortunately, most of the influenza viruses are similar and are considered to be weakly pathogenic to birds and to humans.
Avian flu has killed more than 150 million birds in Southeast Asia since 2003. In addition, Indonesia, Viet Nam, Thailand, and Cambodia have 61 confirmed human deaths from 118 cases of avian influenza A (H5N1) as of this writing. The apparent widespread nature of this avian virus and the human mortality figures suggest that there may be a direct risk of infection as the virus passes from poultry to humans.
Waterfowl and migratory birds act as natural reservoirs of the avian influenza virus, which is harbored in their intestinal tract and shed in their feces. Susceptible birds are infected through inhalation of the viral particles in nasal and respiratory secretions, and through contact with the feces of infected birds (Cardona, 2005). Similarly, the high density of human contact with birds and feces enables aspiration of the virus by handlers.
Before examining the human health implications of the H5N1 strain of avian influenza, it is important to note that influenza affects 20% of the United States population annually and typically more than 200,000 people are hospitalized each year due to flu symptoms. Globally, more than 1 million succumb annually due to influenza, and about 30,000–50,000 deaths occur in the U.S because of influenza virus infections. To put this into perspective, hunger affects more than 843 million people in developing and transition countries, and approximately 16,000 children die each day from hunger and malnutrition.
In 2003, 70–80 million people in the U.S. received the flu vaccine. Historical data indicate that flu vaccine is generally only 40–60% effective in preventing flu. The risk of human-to-human transmission of the bug du jour is questionable, and the effectiveness of antiviral medications such as oseltamivir (Roche Laboratories, Inc.'s Tamiflu oral tablet) and zanamivir (Glaxo Wellcome, Inc.'s Relenza inhaler) is uncertain.
Michael Osterholm, Associate Director of the National Center for Food Protection and Defense, recently commented that our capacity to produce vaccine is limited based on 1950s egg-based technology (Osterholm, 2005). For example, to make 300 million doses of influenza vaccine for global immunization programs, more than 350 million chicken eggs would be required and more than 6 months of production time would be needed after the initial isolation of the implicated viral strain. He said that new cell culture–based vaccines should be developed that include antigens present in all subtypes of influenza virus. This approach will reduce production time and increase production yield. There should also be an international approach to public funding that will pay for excess production capacity required during a pandemic.
Good management practices can prevent and control avian flu from affecting domestic poultry. These practices include cleaning and disinfecting surfaces, equipment, clothing, and environments that may be contaminated with excreta from wild birds.
Vaccinating domestic poultry to prevent clinical symptoms of a variety of influenza infections is not practical. Current vaccines are not cross-protective for the 15 virus subtypes that can infect poultry. Perhaps future biotechnology will produce effective vaccines to be incorporated into the feed of domestic poultry and thus reduce the risk of avian influenza.
With regard to avian flu, we cannot function as alarmist and ignorant Chicken Littles. The scientific community, health care professionals, public health officials, and food industry leadership must be Owl Wises who engage historical perspective, current evidence, and measured reasoning and action.
by Roger Clemens, Dr.P.H.,
Director, Analytical Research, Professor, Molecular Pharmacology & Toxicology, USC School of Pharmacy, Los Angeles, Calif.
by Peter Pressman, M.D.,
Attending Staff, Internal Medicine, Cedars-Sinai Medical Center, Los Angeles, Calif.
Cardona, C.J. 2005. Avian influenza. www.vetmed.ucdavis.edu/vetext/inf-po_avianinfluenzafs.html.
Osterholm, M. 2005. Preparing for the next pandemic. New Eng. J. Med. 352: 1839-1842.