The Latest News on the H5N1 Type A Influenza

The H5N1 is a type A influenza virus, also known as the avian influenza or the Bird Flu. It is naturally found in specific species of shorebirds and waterfowl. Currently, the discovery of the highly pathogenic avian influenza and its subtype, the H5N1 avian influenza, have raised a lot of concern for wild birds, domestic poultry, as well as the health of humans around the world, as well as in the United States. There are many ways this virus could make its way into the United States. These include illegal movement of domestic or wild birds, as well as the migration of infected wild birds. Also of concern would be the contamination of products, making their way into the US via an infected traveler, possibly as a bioterrorism event.

Officials are focusing on many methods of detection and one recent plan includes the detection of a potential introduction of the H5N1 avian influenza by migratory birds. These types of viruses are classified by two proteins, hemagglutinin (H) and neuraminidase (N), which are found on the surface of the virus. Each possible combination has one of the 16 H proteins, and one of the 9 N proteins resulting in 144 different possible combinations. It is these combinations that determine how pathogenic the virus is to an infected host.

Wild birds are considered to be the natural reservoirs for all the different subtypes, especially waterfowl and shorebirds. These animals can survive with these subtypes and have adapted to cause little or no disease. However, a mutation can occur and one of those subtypes can infect other species of wild and domestic birds. This is called a gradual genetic drift. Although this mutation allows the virus to infect other species, it rarely causes illness in this new host. This change can also occur is a host is infected with another type A influenza at the same time. This can cause the genetic material to mix and can result in an entirely new strain of the virus. The combination of these mutations and rapid changes in the strain results in the production of a virus that now can cause death and severe illness. If this is significant enough, the new virus is classified as a highly pathogenic avian influenza (HPAI) virus.

One such drift or mutation occurred in an avian influenza virus of wild birds in 1995-96, which allowed a virus to infect chickens in China. This highly pathogenic H5N1 influenza has been traveling though Asian poultry and domestic fowl since that time and has caused significant mortality to these species. It is believed that this H5N1 virus mutated even further which has allowed the infection of additional species of birds, mammals, and now humans. The virus has recently moved back into wild birds and caused the death of many of these animals in China.

Although the spread of this virus has been mostly due to the movement of domestic birds, the movement of the virus into wild birds has caused concern that these species will spread the virus. There is increased concern that migrating species may introduce the virus to new regions of the world including North America. Therefore, the USDA and DOI are developing a coordinated National Strategic Plan for the early detection of the HPAI onto this continent by wild birds. The immediate concern is the introduction of the H5N1 avian influenza virus via migratory birds into Alaska and the Pacific Flyway (including Hawaii and other Pacific Islands). This group will also work on the detection of the virus in all the North American flyways.

The U.S. Governments concern that the ongoing outbreaks of the avian influenza in birds will lead to a human influenza pandemic, has prompted President Bush to request $251 million in funds to aid in the detection of this virus and to contain outbreaks before they spread around the world. These outbreaks would have significant global, health, economic, and social consequences.

The Latest News on the H5N1 Type A Influenza

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