Bird flu, or Avian flu, is an illness in birds caused by type A influenza virus. The form that passes to humans is an H5N1 strain known sometimes as Asian bird flu. In 2008, some experts expressed concern about an outbreak of this flu among humans due to increasing numbers of infected individuals since 2003, as well as the high mortality (approximately 60 percent) among the few hundred who were confirmed to be infected. Most cases were confined to Asia and the Middle East, with no confirmed cases in birds or humans in the United States (see Flu.gov).
The origin of the word “influenza” is Italian, specifically in 1743 (Oxford Dictionary), the location of the first reported influenza epidemic. The first historical cases of avian flu were also in Italy, among chickens in 1878, which was called fowl plague (SFGate). In 1997, chicken flocks were once again in danger from the virus, this time in Hong Kong, with another outbreak in 2003.
The outbreak of influenza among birds was extensive in the first decade of the 21st century and resulted in the culling or death of thousands of birds by 2008. Because the transmission of the specific strain was not found to occur between people, birds were the reasonable culprit for the nearly 400 human infections that occurred between 2003 (when surveillance started, confirmed human cases did not appear until 2005) and 2008 (avianinfluenza.org), and the additional ~100 that occurred between 2008 and 2010 (Flu.gov). However, these numbers are very low as some human populations live in close contact with poultry and wild fowl.
The first human cases of bird flu in the 21st century were documented in the open farm markets of Vietnam, China, and Indonesia. In 2005, the World Health Organization (WHO) laid the origin of human infection at the feet of birds, specifically their droppings. The ingestion of bird feces contaminated food or contact with feces contaminated objects and surfaces is thought to be the point of spread to humans. Wild waterfowl are the natural reservoir of avian type A influenza viruses and may also be responsible for the spread of H5N1 bird flu.
The theory is that, as infected wild birds migrate, they share type A influenza viruses with domestic populations across the globe, as well as native wild birds in other regions, causing avian flu. The domestic birds then spread the virus among human inhabitants when it mutates enough to infect the human respiratory epithelium, causing Asian bird flu. However, some dispute that migratory pathways are to blame and offer a theory about airplane travel, which would allow human carriers to spread the disease. What is currently known about the ability of H5N1 to infect humans (based on a genetic analysis published in The Lancet in 2008, see the BBC for a synopsis) does not indicate that this is possible. Meanwhile, the migration theory is supported by the deahts of 6000 migratory birds that began at the Qinghai Lake nature reserve in central China in late April 2005. Accumulated evidence also pointed to the virus following trade routes, likely among birds being transported for sale.