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2can Case Study - Bird Flu (Avian Influenza)
Current - World Situation on Bird Flu (Avian Influenza)
As of March 2005 many countries are stock piling antiviral drugs to prevent widespread devastation which could be caused by a flu pandemic.
Experts say a pandemic is inevitable and will probably emerge in Asia if bird flu mutates with human flu, creating a highly pathogenic new virus.
Bird flu viruses normally infect only birds and pigs. There are 15 different strains of the bird flu virus. Since 1959 viruses of the H5, H7 and H9 subtypes have crossed the species barrier to infect humans on 10 occasions.
Most bird flu viruses affecting humans have caused mild respiratory symptoms or conjunctivitis, with one exception the H5N1 strain.
The H5N1 strain has caused severe disease with high fatality in 1997, 2003, 2005 and 2005. Studies have shown that the H5N1 strain
has, over the years, become progressively more pathogenic and is now much hardier than in the past
. It also seems to be expanding its host range to other mammals including species not previously thought to be susceptible to the virus such as tigers
and leopards.
The outbreaks of highly pathogenic H5N1 bird flu in poultry that began in Asia in 2003 have to date (end of October 2005), The H5N1 strain has killed more than 60 people in South East Asia since 2003. However, of those only one is suspected to have died after catching the virus from another human.
The majority of the cases have occurred in previously healthy children and young adults.
The H5N1 strain remained largely in South-East Asia until this summer, when Russia and Kazakhstan both reported outbreaks
Scientists fear it may be carried by migrating birds to Europe and Africa but say it is hard to prove a direct link with bird migration, although more swans have been found with bird flu in the Danube delta area in Romania.
The reports for where the flu has reached are very dynamic and are reported in the news stories in the right column.
29 May 2007 - Scientists find bird flu antibody
Antibodies that could protect against bird flu in humans have been isolated by an international team of scientists... more
As of 1st May 2007:
- Bird flu outbreaks have been confirmed in
Albania,
Afghanistan,
Austria,
Africa,
Azerbaijan,
Bulgaria,
Burma,
Canada,
Cambodia,
China,
Croatia,
Cyprus,
Czech Republic,
Denmark,
Egypt,
Estonia,
France,
Gaza,
Germany,
Greece,
India,
Indonesia,
Iran,
Israel,
Italy,
Jordan,
Japan,
Korea,
Kuwait,
Malaysia,
Pakistan,
Nigeria,
Poland,
Philippines,
Romania,
Russia,
Siberia,
Sicily,
Slovenia,
Sweden,
Switzerland,
Thailand,
Turkey,
Taiwan,
UK,
Vietnam.
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Bird flu in the Genomic/Proteomic/literature Databases
View all bird flu (avian influenza) sequences available in the protein and nucleotide sequence/structure databases:
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History of the Influenza Virus
There are 3 types of the influenza virus, type A, B and C.
- Influenza Type A viruses can infect people, birds, pigs, horses, seals, whales and other animals.
Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are called hemagglutinin (HA) and neuraminidase (NA). There are 15 different HA subtypes and 9 different NA subtypes. Many different combinations of HA and NA proteins are possible. Only some influenza A subtypes (i.e., H1N1, H1N2, and H3N2) are currently in general circulation among people. Other subtypes are found most commonly in other animal species. For example, H7N7 and H3N8 viruses cause illness in horses.
Subtypes of influenza A virus are named according to their HA and NA surface proteins. For example, an "H7N2 virus" designates an influenza A subtype that has an HA 7 protein and an NA 2 protein. Similarly an "H5N1" virus has an HA 5 protein and an NA 1 protein.
- Influenza Type B viruses are normally found only in humans. Unlike influenza A viruses, these viruses are not classified according to subtype. Although influenza type B viruses can cause human epidemics, they have not caused pandemics.
- Influenza Type C viruses cause mild illness in humans and do not cause epidemics or pandemics. These viruses are not classified according to subtype.
Influenza B viruses and subtypes of influenza A virus are further characterised into strains. There are many different strains of influenza B viruses and of influenza A subtypes. New strains of influenza viruses appear and replace older strains. This process occurs through a type of change called "drift".
When a new strain of human influenza virus emerges, antibody protection that may have developed after infection or vaccination with an older strain may not provide protection against the new strain. Thus, the influenza vaccine is updated on a yearly basis to keep up with the changes in influenza viruses.
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How Influenza Viruses Change: Drift and Shift
Influenza viruses can change in two different ways:
- Antigenic drift - this type of change occurs through small changes in the virus that happen continually over time. Antigenic drift produces new virus strains that may not be recognised by antibodies to earlier influenza strains. This process works as follows: a person infected with a particular flu virus strain develops antibodies against that virus. As newer virus strains appear, the antibodies against the older strains no longer recognise the "newer" virus, and infection with a new strain can occur. This is one of the main reasons why people can get the flu more than once. In most years, one or two of the three virus strains in the influenza vaccine are updated to keep up with the changes in the circulating flu viruses. For this reason, people who want to be immunised against influenza need to receive a flu vaccination every year.
- Antigenic shift - this type of change is an abrupt, major change in the influenza A viruses, resulting in a new influenza virus that can infect humans and has a hemagglutinin protein or hemagglutinin and neuraminidase protein combination that has not been seen in humans for many years. Antigenic shift results in a new influenza A subtype. If a new subtype of influenza A virus is introduced into the human population most people will have little or no protection against the new virus and if the virus can spread easily from person to person, a pandemic (worldwide spread) may occur (see Influenza Pandemics).
Influenza viruses are changing by antigenic drift all the time, but antigenic shift happens only occasionally. Influenza type A viruses undergo both kinds of changes; influenza type B viruses change only by the more gradual process of antigenic drift.
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Influenza Pandemics During the 20th Century
During the 20th century, the emergence of new influenza A virus subtypes caused three pandemics, all of which spread around the world within 1 year of being detected.
- 1918-19 "Spanish flu" - [A (H1N1)], caused the highest number of known influenza deaths. The name of Spanish Flu came from the early affliction and large mortalities in Spain where it allegedly killed 8 million in May (1918). More than 500,000 people died in the United States, and up to 50 million people may have died worldwide. Many people died within the first few days after infection, and others died of complications later. Nearly half of those who died were young, healthy adults. Influenza A (H1N1) viruses still circulate today after being introduced again into the human population in the 1970s.
- 1957-58 "Asian flu" - [A (H2N2)], caused about 70,000 deaths in the United States. First identified in China in late February 1957, the Asian flu spread to the United States by June 1957.
- 1968-69 " Hong Kong flu" - [A (H3N2)], caused about 34,000 deaths in the United States. This virus was first detected in Hong Kong in early 1968 and spread to the United States later that year. Influenza A (H3N2) viruses still circulate today.
Both the 1957-58 and 1968-69 pandemics were caused by viruses containing a combination of genes from a human influenza virus and an avian influenza virus. The origin of the 1918-19 pandemic virus is not clear.
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