About Avian Influenza
Avian influenza (AI) is caused by the Influenza A virus and can affect all bird species. It is believed that wild birds, especially migratory waterfowl, carry the virus and they may or may not show signs of having the virus. The problems arise when the virus infects bird species such as chickens and turkeys.
The different subtypes for the AI virus are assigned based on surface antigens on the virus HA and NA subtypes. H stands for Hemagglutinin of which there are 15 types. N stands for Neuraminidase of which there are 9 types. In theory, there are 135 different subtypes of the virus that cause Avian Influenza. The more severe viruses with higher mortality rates for birds are called highly pathogenic Avian Influenza (HP AI) and the less severe viruses that cause milder illnesses are low pathogenic Avian Influenza (LP AI). Although most H5 and H7 viruses are low path, so far highly pathogenic strains have only arisen from H5 and H7 virus types. Since viruses are made up of genetic material and undergo mutations, it is possible for the viruses to mutate from a LP AI to a HP AI form. For that reason, the detection of any AI outbreak requires that producers, veterinarians, and government officials work quickly to contain and control the virus.
History of Highly Pathogenic AI Outbreaks
The last major outbreak of highly pathogenic avian influenza (HP AI) affecting the poultry industry in the United States was in 1983-84 when H5N2 was found in Pennsylvania and Virginia. A small outbreak of H5N2 HP AI occurred outbreak in Texas in 2004 in broilers. The AI strain in Texas was not clinically highly pathogenic in the birds; however, it was genetically similar to other highly pathogenic strains and was classified as HP AI. H5N2 has not been associated with any human illnesses.
In recent years, outbreaks of HP AI have occurred in other countries including H5N1 in Hong Kong in 1997, H7N7 in the Netherlands and Belgium in 2003, and H7N3 in British Columbia, Canada, in 2004. An outbreak of H5N1 HP AI has been ongoing in Asia for several. The concerns about the ongoingAsian outbreak are related to possibility that the avian virus could mutate and more easily infect humans. At this time, the H5N1 virus does not easily infect humans, and the H5N1 highly pathogenic virus does not exist in the United States.
Does Avian Influenza affect humans?
The outbreak of highly pathogenic H5N1 in Asia has been associated with more than 200 human illnesses and more than 100 deaths from 2003-2006. Outside of this situation, it is very rare for humans to experience health problems due to AI. In the United States, the only known illnesses have been conjunctivitis of the eyes when people handling sick birds have then touched their eyes. In 1997, it was reported in Hong Kong that eighteen people became ill and six people died after contracting H5N1 HP AI after direct contact with sick birds. In 2003, one fatal human case was reported in the Netherlands due to H7N7, involving a veterinarian with prolonged direct contact with infected birds. The outbreak in British Columbia, Canada in 2004 was also associated with some cases of human illness when there was close contact with sick birds. It is important that farm workers and animal health professionals use proper protective clothing and equipment when working with birds infected with AI or other diseases.