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Epidemiology Corner

June 4, 2004

Avian influenza outbreaks

Avian flu was in the news earlier this year with an outbreak in Asia and cases reported in the United States. Avianflu is caused by influenza A viruses that primarily infect bird populations worldwide. Certain strains of avian flu arehighly contagious and possibly deadly for some birds, especially domesticated chickens. The virus is spreadamong susceptible birds when they have contact with nasal, respiratory or fecal material from infected birds. There are several subtypes of avian influenza viruses but, BirdFlu.org reports that only three subtypes are known to cause severe illness in humans: H5N1, H9N2 and H7N7. Influenza A subtypes are given names based on two surface proteins, Hemagglutinin and Neuraminidase, thus the strain is identified as H#N#.

The recent outbreak of avian flu in Asia was attributed to the H5N1 strain, which can cause illness and even death in humans. However, the isolated outbreaks in the United States were not related to the Asian H5N1 outbreak.The strains recently identified in the United States were H5N2, H7N2 and H7N3. These strains are not considered fatal to humans though they can be devastating to domestic chicken populations.

The Asian Outbreak
The first instance of direct bird-to-human transmission of H5N1 occurred during an outbreak of avian influenza among poultry in Hong Kong in 1997, according to reports from the Centers for Disease Control (CDC). The virus caused severe respiratory illness in 18 people and resulted in six deaths.

Human cases during the latest outbreak occurred only after direct contact with infected chickens or their drop-pings. However, in rare circumstances, people who catch the virus from birds can pass it on to other humans,although the disease is generally milder in those who caught it from an infected person rather than from infected birds.

Symptoms of avian influenza in humans range from typical influenza-like symptoms such as fever, cough, sore throat and muscle aches to eye infections, pneumonia, acute respiratory distress, viral pneumonia and other severe and life-threatening complications.

As a way of preventing a major outbreak of avian flu, the World Health Organization recommends that all infected or exposed flocks of chickens and other birds be killed to help prevent further spread of the virus and reduce opportunities for human infection. Rapid detection and elimination of the avian flu strain is essential. People working with potentially infected bird populations need take precautions to prevent disease transmission.

People traveling to areas affected by avian flu need to avoid poultry farms, live animal markets and contact with areas contaminated with animal or bird excrement.

For more information on avian flu strains and current outbreak information, visit the Centers for Disease Controversies at www.cdc.gov/flu, www.birdflu.org/birdflu_info.htm and the University of Texas Health Science Center at Houston’s online magazine at http://publicaffairs.uth.tmc.edu/hLeader/archive/