Wednesday, May 6, 2009

Swine flu - novel influenza A

The current outbreak of influenza virus will be easier to understand once we know how influenza viruses are named and catalogued.

The classification and naming of influenza viruses depends on several elements—the nucleoprotein of the virus, the geographic location from which it is first isolated, its surface antigens, the year when it was first isolated in a laboratory, the adaptation of the virus to animals other than humans (such as birds, dogs, pigs or horses), and its strain number.

Whether an influenza virus is called “Influenza A,” or “Influenza B” depends on its nucleoprotein. This is a protein within the nucleus of the virus, that packages the viral ribonucleic acid (RNA) and helps transcribe its genetic contents.

The location where the virus is first identified (the viral geographic source) is usually the name of a city, state, or country, e.g., Stockholm, Texas, or Panama.

If the virus was first identified as a cause of disease in 2009, it is a 2009 virus. This identifier is the viral year.

The next feature in the naming system is linked to the proteins the virus uses to enter and bud out of infected cells in the respiratory tract. These proteins are called hemagglutinin and neuraminidase respectively; they are abbreviated H and N in alphanumeric descriptions of the virus (i.e., H1N1), or more formally as HA and NA in some documents.

Fifteen hemagglutinins have been identified. Most of these infect water fowl (geese and ducks, for example). Four of them (H1, H2, H3, and H5) most readily infect people. Several of them can infect both birds and people (and other animals like swine). Nine neuraminidase variants have been identified of which N1 and N2 commonly infect humans. The influenza A viruses that most commonly infect people, listed by their H and N antigens are known as H1N1, H3N2, and H5N1.

When an animal cell (for example, in a pig) is infected with more than one influenza virus at the same time, reassortment of viral genes can occur, and mutated viruses with new mixtures of disease-causing proteins can emerge. The influenza virus has eight major components, where pieces of one virus may link with pieces of others to form novel, and occasionally deadly, combinations. A virus that emerges from a pig (after it has been infected with an avian virus and a human virus) with parts that are normally found in pigs is called a “swine flu” virus. Similarly, a virus that mutates on its own within a pig and becomes infectious to people is called a swine flu. Newly mutated and reassorted viruses appear fairly frequently around the world every year and are carried (by migration) rapidly from one place to another. People can carry influenza viruses from one location to another, if they travel when they are actively infected.

Public health data clearly have shown that about 30,000 people die of infection with influenza each year.

Each year when scientists and public health officials identify new, potentially hazardous strains of influenza virus, they create new vaccines against them to try to prevent influenza from infecting and killing people.

In 2009, a new virus capable of infecting human beings emerged from swine in North America. The first people identified with the virus were from San Diego and Imperial County, California. Soon after, a large number of infected people were found in Mexico, and clusters of infections have been found in many other locations around the U.S. Some people infected by the 2009 virus have died as a result of the infection. The virus is an H1N1 strain (as are many pandemic influenza viruses—see the accompanying table) and it contains genes that normally appear in both swine from North America and Eurasia, as well as in birds and people. It is therefore known as a quadruple reassortment virus, with many components normally seen in swine flu and a smaller number that are found in humans and birds.

The formal name for this virus currently is: Influenza A/North America/H1N1/2009 or in the popular press: “swine flu,” or “H1N1.”

The status of the virus and its spread around the globe are changing rapidly. Up-to-date information on the virus, its dissemination, prevention, and treatment is available on websites like that of the Centers for Disease Control and Prevention at http://www.cdc.gov/h1n1flu/swineflu_you.htm









Year of PandemicAntigenic MarkersCommon nameNumber of DeathsHistorical features
1918H1N1Spanish influenza40,000,000, approximatelyThe deadliest influenza of modern times, it was much deadlier than the World War (WWI) which it accompanied.
1957H2N2Asian influenza1,000,000 – 4,000,000, approximatelyMortality was especially high among older adults.
1968H3N2Hong Kong flu1,000,000 approximatelyMortality was especially high among older adults.
1976H1N1Swine fluA small number of people in Fort Dix, New JerseyAn outbreak of Guillain-Barre syndrome followed vaccination against the Swine flu, discouraging some people from future influenza vaccination
2009H1N1Swine flu1,000 approximatelyIdentified in Southern California and Mexico (where it proved most deadly). It spread rapidly to numerous other locations around the world
?H5N1Avian influenza?Potential unknown


Legend: Influenza viruses are identified by their primary host (humans, birds, pigs, dogs, or horses), as well as by their hemagglutinin and neuraminidase proteins (H and N in the table above). Although there are 15 known hemagglutinins, only types 1, 2, 3, 5, and possibly 7 and 9 are known to cause serious illnesses in humans. Of the nine known neuraminidases, only two N1 and N2 are involved currently in human disease. Viruses that primarily infect species other than humans can sometimes mutate to become pathogenic in people, especially people who have close contact with animals.

2 comments:

Tabers 21 said...

Latest news on swine flu or H1N1 ...Now called novel influenza A

T21 Marketing said...

The Swine Flu is now considered a pandemic according to WHO. Go here fore more info...
http://www.reuters.com/article/worldNews/idUSTRE55A1U720090611?feedType=RSS&feedName=worldNews&rpc=22&sp=true