Avian influenza
Avian influenza (also known as
bird flu) is a type of
influenza virulent in
birds. It was first identified in
Italy in the early
1900s and is now known to exist worldwide.
Infection
The causative agent is the avian influenza (AI) virus. AI viruses all belong to the influenza virus A genus of the Orthomyxoviridae family and are negative-stranded, segmented RNA viruses.
Avian influenza spreads in the air and in manure. Wild fowl often act as resistant carriers, spreading it to more susceptible domestic stocks. It can also be transmitted by contaminated feed, water, equipment and clothing; however, there is no evidence that the virus can survive in well cooked meat.
The incubation period is 3 to 5 days. Symptoms in animals vary, but virulent strains can cause death within a few days.
Avian Influenza in Humans
While avian influenza spreads rapidly among birds, it does not infect humans easily, and there is no confirmed evidence of human-to-human transmission. Of the 15 subtypes known, only subtypes H5 and H7 are known to be capable of crossing the species barrier.
The symptoms of avian influenza in humans are akin to those of human influenza, ie. fever, sore throat, cough and in severe cases pneumonia. \nHuman deaths from avian influenza were unknown until 1997, when six people in Hong Kong died from the particularly virulent H5N1 strain.
In January 2004, a major new outbreak of H5N1 avian influenza surfaced again in Vietnam and Thailand's poultry industry, and within weeks spread to ten countries and regions in Asia, including Indonesia, South Korea, Japan and China. Intensive efforts were undertaken to slaughter chickens, ducks and geese, and the outbreak was contained by March, but the total human death toll in Vietnam and Thailand was 23 people.
It is feared that if the avian influenza virus undergoes antigenic shift with a human influenza virus, the new subtype created could be both highly contagious and highly lethal in humans. Such a subtype could cause a global influenza pandemic, similar to the Spanish Flu that killed over 20 million people in 1918. In February 2004, avian influenza virus was detected in pigs in Vietnam, increasing fears of the emergence of new variant strains.
Fresh outbreaks in poultry were confirmed in Ayutthaya and Pathumthani provinces of Thailand, and Chaohu city in Anhui, China, in July 2004.
In North America, the presence of avian influenza was confirmed at several poultry farms in British Columbia in February 2004. As of April 2004, 18 farms have been quarantined to halt the spread of the virus. Two cases of humans with avian influenza have been confirmed in that region.
Prevention and Treatment
Avian influenza in humans can be detected reliably with standard influenza tests. Antiviral drugs are clinically effective in both preventing and treating the disease. Vaccines, however, take at least four months to produce and must be prepared for each subtype.
Increasing Virulence
\nIn July 2004 researchers, headed by H. Deng of the Harbin Veterinary Research Institute, Harbin, China and Professor Robert Webster of the St Jude Children's Research Hospital, Memphis, Tennessee, reported results of experiments in which mice had been exposed to 21 isolates of confirmed H5N1 strains obtained from ducks in China between 1999 and 2002. They found "a clear temporal pattern of progressively increasing pathogenicity". [1]
External link
\n* WHO Avian Influenza Fact Sheet
\n\n\n\n\n\n\n\n\nzh-cn:禽流感/简\nzh-tw:禽流感/繁
