Avian influenza is an infection caused by avian (bird) influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, avian influenza is very contagious among birds and can affect some of the domesticated birds, including chickens, ducks, and turkeys, and kill them.1Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they come in contact with contaminated secretions or excretions or with surfaces that are contaminated with secretions or excretions from infected birds. Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the virus.1 Epidemiology Avian influenza disease which was first identified in Italy more then 100 year ago occurs worldwide. In 1997, the first cases of human infection with the avian influenza A (H5N1) virus were reported in China, Hong Kong Special Administrative Region (Hong Kong SAR). These 18 cases included 6 deaths and coincided with outbreaks of highly pathogenic H5N1 in poultry on farms and in markets selling live poultry. 1 Now this disease is spreading to Thailand, Vietnam, Korea, and Pakistan. Therefore, it poses a sufficient threat to India too! In mid-2003, the highly pathogenic H5N1 virus began to circulate widely in poultry in parts of south-east Asia, spreading within months to affect 8 countries in an outbreak unprecedented in its geographical extent and is therefore of particular public health concern. The disease remained confined to animals and humans in South-East Asia until mid-2005, when the virus expanded its geographical range through parts of central Asia to Europe, Africa and the Middle East. Between 1 December 2003 and 30 April 2006, 205 laboratory-confirmed cases and 113 deaths were reported to WHO from 9 countries. During that same period, the World Organisation for Animal Health reported outbreaks of H5N1 infection in domestic or wild birds in approximately 50 countries. H5N1 variants have demonstrated a capacity to directly infect humans in 1997, and have done so again in Vietnam in January, 2004. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to highly contagious and rapidly fatal disease resulting in severe epidemics. 2,3 Transmission from avian to humanTransmission to humans occurs only when they come in contact with the surfaces contaminated with the secretions from infected birds. Severity of Clinical symptoms depends on the virulence of the pathogenic forms of the virus which may vary from low to high pathogenic form.Virulence caused by influenza virusInfection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The “low pathogenic” form may go undetected and usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the highly pathogenic form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours.Human infection with avian influenza virusesThere are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds.Usually, “avian influenza virus” refers to influenza A viruses found chiefly in
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