What is the role of avian H5N1 influenza virus in the etiology of viral pneumonia?

Updated: Mar 24, 2021
  • Author: Zab Mosenifar, MD, FACP, FCCP; Chief Editor: John J Oppenheimer, MD  more...
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In Hong Kong in 1997, an influenza virus (H5N1 virus) previously known to infect only birds was found to infect humans. Manifestations included pneumonia, which in some cases led to fatal acute respiratory distress syndrome (ARDS) or multisystem organ failure.

Prior to the human outbreak, the H5N1 virus caused widespread deaths in chickens on three farms in Hong Kong. Epidemiologic investigations of this outbreak demonstrated that individuals in close contact with the index case or with exposure to poultry were at risk of being infected.

Concern is growing that avian influenza, which is a subtype of influenza A, may result in a worldwide pandemic in the near future. The avian influenza virus A/H5N1 has several ominous characteristics, including increased virulence and human-to-human transmission in several cases, rather than bird-to-human transmission, as is usually necessary. The disease causes high mortality as a result of pneumonia and respiratory failure.

The 1997 outbreak in Hong Kong was thought to be controlled by depopulating 1.5 million chickens in local farms and markets. However, human infections occurred in 2001 through 2003 in other parts of Asia, and the virus has been found in poultry and birds in Europe.

The rising incidence and widespread reporting of disease from H5N1 influenza viruses can probably be attributed to the increasing spread of the virus from existing reservoirs in domestic waterfowl and live bird markets, leading to greater environmental contamination. As of January 2014, 650 cases of H5N1 human infections have been reported from 16 countries since 2003, with 386 deaths (59% mortality). [30]

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