Avian influenza is an infection caused by avian or bird viruses and occurs worldwide. Wild migratory birds-notably ducks, geese and swans-harbor the viruses in their intestines and are thought to be the source of infection.
These birds are the natural reservoir of avian influenza viruses, but they are most resistant to infection. However, avian flu is widespread in the bird population and is highly contagious among domesticated birds, such as chickens, ducks and turkeys.
A wide spectrum of symptoms is observed in birds, ranging from mild symptoms, which often go undetected, to a highly pathogenic avian influenza that could affect multiple internal organs, causing severe illness and a mortality rate of 90-100 percent within 48 hours.1
Research shows that viruses of low pathogenicity could mutate into highly pathogenic viruses and cause an epidemic.
The avian flu virus is found in the saliva, feces and nasal secretions of infected birds. The virus can be transmitted when other birds come in contact with contaminated water or feed, or infected bird droppings on surfaces. Under normal conditions, bird flu viruses do not infect humans, but cases of human infection have been reported since 1997.2
During an outbreak of bird flu among poultry, humans can become infected when they come in direct contact with infected birds or contaminated surfaces. Almost all reported cases have been linked to close contact with household flocks that were diseased; during slaughtering, butchering and defeathering poultry for consumption.
Symptoms in infected humans are similar to those of the common flu, such as sore throat, fever, cough and sore muscles, as the avian flu is an influenza virus. In severe cases, watery diarrhea, respiratory failure, pneumonia, multiple lung infections and, ultimately, death can occur.
Avian influenza viruses compose the influenza virus A genus of the Orthomyxoviridae family and are negative-sense, single-stranded, segmented RNA viruses. Influenza virus A is not the same as avian influenza. The former is a genus of viruses, the latter is an illness. Only influenza A viruses infect birds and all known subtypes of influenza A virus can infect birds.3
Fifteen subtypes of influenza virus are known to infect birds, and according to studies, all outbreaks of the highly pathogenic form have been caused by influenza virus of subtypes H5 and H7.4 The subtypes differ because of changes in certain proteins on the surface of the influenza A virus hemagglutinin and neuraminidase. The avian flu virus subtypes are labeled according to an "H" number and an "N" number.
Under normal conditions, influenza viruses are species-specific, but at times can cross over and infect other species. Influenza viruses are H5N1-a subtype of the avian flu virus that is highly pathogenic, has the ability to mutate rapidly and has a tendency to acquire genes from viruses infecting different species of animals.
All the influenza viruses have the ability to change, and this is why the avian influenza is of grave concern to scientists. Influenza A viruses-including subtypes from different species-manages to exchange or "reassort" genetic material and merge. This process is referred to as the "antigenic shift," and it results in a subtype which is different from the parent virus.4
Such a change would hasten the transmission process from human to human. Since this virus does not normally infect humans, there will be no immunity against the virus. The current strain is, therefore, very unusual in being able to cause death in so many species, and, according to studies, under the right conditions, could start a pandemic.
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