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Bird Flu (Avian Flu)
By John A.D. Leake, M.D.
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Colorized transmission electron micrograph of Avian influenza A H5N1 viruses (seen in gold) grown in MDCK cells (seen in green).
Avian influenza A viruses do not usually infect humans; however, several instances of human infections and outbreaks have been reported since 1997. When such infections occur, public health authorities monitor these situations closely.
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Influenza viruses circulate around the world, and birds are the main hosts of several highly adapted, bird-specific influenza virus strains. All influenza viruses need specialized molecules to circulate within a given host species, and thus far avian (bird) influenza viruses have not adapted these molecules to allow for efficient transmission between humans. Such bird-to-human adaptation has happened in the past, however, and many experts anticipate that it may occur again. There is virtually no immunity among humans to avian strains of influenza, and in the relatively few humans infected thus far, severe illness has developed.
For these reasons, there has been considerable recent discussion concerning the possibility of a future human worldwide influenza outbreak caused by a newly emerging avian influenza strain, H5N1. “H” and “N” designate proteins needed for viral replication and transmission which are also useful for virologic classification. The World Health Organization reports that from 2003 though mid-December 2005, 138 human influenza H5N1 infections have occurred (with 71 deaths). Such infections have so far been limited to Cambodia, China, Indonesia, Thailand, and Vietnam, and nearly all human cases had direct contact with infected birds. Nearly all H5N1-infected birds live in Asia, but some have now been found in Eastern Europe.
Scientists perform careful worldwide surveillance for human and avian influenza, closely monitoring yearly influenza virus activity via a coordinated global surveillance and laboratory network. In San Diego, Rady Children's Hospital and other hospitals and medical providers participate in influenza surveillance to assist the State of California (Department of Health Services) and San Diego County (Division of Community Epidemiology). Information is provided to these agencies on hospitalized cases of influenza, on the specific types of virus circulating in a given season, and on other disease aspects.
A specific vaccine is being developed to protect against H5N1 influenza, and increased supplies of anti-influenza medications are being produced and distributed. Selected influenza medications are active against avian strains, but like all medications, they have potential side effects. These medications are best used either to treat people with early, active influenza illness, or to decrease the chance of illness among close (e.g., family) contacts of actively ill persons. It is not appropriate to request a prescription for anti-influenza medications “just in case” H5N1 becomes more transmissible from person to person in the future.
It is important to remember that every year “regular” human strains of influenza cause tens of thousands of persons to become ill and result in many deaths in the United States alone, especially among older adults and young children. We have reasonably effective vaccines for these “regular” strains. The Centers for Disease Control and Prevention recently reported 153 influenza-associated deaths among children in a survey conducted in 40 U.S. states during the two most recent influenza seasons. Yearly influenza vaccination should be provided to young children aged 6–23 months, children and adults with chronic medical conditions, household contacts of infants aged less than 6 months, and others who wish to reduce their risk of getting influenza. Washing hands frequently and teaching children to cover their mouths when they cough or sneeze are also important means to decrease influenza at home and in the community.
 CSSD Division of Infectious Disease
© Children's Specialists of San Diego | Medical News Archive
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