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Where the Bird Flu Got Its Infamous StartThe bird flu has technically been around for a very long time in aquatic bird species; however, the first H5N1 outbreak was first seen in geese in China in 1996.
Avian influenza is an infectious disease of birds caused by a type A strain of the influenza virus. Most species of wild birds that carry this disease show no apparent signs of infection or harm. This disease occurs worldwide, and other bird species, including domestic poultry, develop disease when infected with avian influenza virus.
These influenza viruses are usually species-specific, which means that viruses that infect an individual species stick to that species. Since 1959, instances of human infection with an avian influenza virus have been only documented on 10 occasions.
The first documented
outbreak among humans infected with H5N1 occurred in Hong Kong in 1997. There were 18 human cases, which coincided with an outbreak of highly pathogenic avian influenza, caused by an identical virus, in poultry farms and live markets. The source of infection was determined by extensive studies of the human cases to be the direct contact with diseased poultry. Studies carried out in family members, and social contacts of patients, health workers engaged in their care, and poultry cullers found that there was very limited, if any human to human transmission. Hong Kongs entire poultry population was immediately destroyed and within three days, human infections ceased. The destruction of almost 1.5 million birds has some experts believing that the drastic action may have averted an influenza pandemic.
The principal source of human infection with the H5N1 virus is shown by all evidence to date to be close contact with dead or sick birds. Particularly risky behaviors for risk of infection include slaughtering, defeathering, butchering, and preparation for consumption of infected birds. Children playing in an area frequented by free-ranging poultry, and exposure to the chickens feces, are thought to have been the source of infection in a few cases. Another possible source of infection is swimming in water bodies where the carcasses of dead infected birds have been discarded or which may have been contaminated by feces from infected animals.
In some cases, investigators have not been able to identify the exposure source, which suggests that there may be some as yet unknown environmental factor that could involve contamination with the deadly virus.
The flu virus can be found in nature with several types of wild aquatic birds and has persisted in these animals for millions of years. The virus does not typically cause illness, however the flu viruses that frequently mutate can easily jump the species barrier from these wild birds to domestic ducks and then chickens. Pigs can then be infected with the avian influenza and the form that infects the human population. If humans and pigs live together in close proximity, then a mutation can occur when a pig is infected with the avian and human flu resulting in a virus whose genes have been resorted and can now spread from pigs to humans. Depending on the precise assortment of bird flu proteins that make it into the human population, the resulting flu may be more or less severe.
In 1997 it was discovered by scientists that the bird influenza skipped the step where it would have to infect a pig, and went directly to infecting humans. This alarmed health officials to think that a pandemic was possible. Fortunately at that time the virus was not able to pass between people, and therefore did not cause an outbreak. Scientists are now speculating that chickens may be able to contract these human type viruses and cause the same problem.
The infamous type A avian influenza virus got its start in nature, but through the continuous mutation of the virus, coupled with the new forms of human infection methods, the bird flu has become a much more serious illness than when it first got its start.
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