Influenza A virus subtype H1N1, also known as A(H1N1), is a subtype of influenzavirus A and the most common cause of influenza (flu) in humans. Some strains of H1N1 are endemic in humans, including the strain(s) responsible for the 1918 flu pandemic which killed 50–100 million people worldwide. Less virulent H1N1 strains still exist in the wild today, worldwide, causing a small fraction of all influenza-like illness and a large fraction of all seasonal influenza. H1N1 strains caused roughly half of all flu infections in 2006.[1] Other strains of H1N1 are endemic in pigs and in birds.
In March and April 2009, hundreds of laboratory-confirmed infections and a number of deaths were caused by an outbreak of a new strain of H1N1.[2]
In March and April 2009, hundreds of laboratory-confirmed infections and a number of deaths were caused by an outbreak of a new strain of H1N1.[2]
In the 2009 swine flu outbreak, the virus isolated from patients in the United States was found to be made up of genetic elements from four different flu viruses – North American Mexican influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."[14] This new strain appears to be a result of reassortment of human influenza and swine influenza viruses, in all four different strains of subtype H1N1. However, as the virus has not yet been isolated in animals to date and also for historical naming reasons, the World Organisation for Animal Health (OIE) suggests it be called "North-American influenza".[15] On April 30, 2009 the World Health Organization began referring to the outbreak as "Influenza A (H1N1)" instead of "swine flu".[16] Swine flu cases worldwide top 1,000 Several complete genome sequences for U.S. flu cases were rapidly made available through the Global Initiative on Sharing Avian Influenza Data (GISAID).[17][18] Preliminary genetic characterization found that the hemagglutinin (HA) gene was similar to that of swine flu viruses present in U.S. pigs since 1999, but the neuraminidase (NA) and matrix protein (M) genes resembled versions present in European swine flu isolates. The six genes from American swine flu are themselves mixtures of swine flu, bird flu, and human flu viruses.[19][20] While viruses with this genetic makeup had not previously been found to be circulating in humans or pigs, there is no formal national surveillance system to determine what viruses are circulating in pigs in the U.S.[21]
Black Area - Confirmed cases followed by death
Red Area - Confirmed cases
Orange Area - Unconfirmed or suspected cases
See also: Live map of swineflu, H1N1 live map
Symptoms and severity
See also: Swine_influenza#In_humans, for symptoms in previous cases.
The CDC does not fully understand why the U.S. cases' symptoms were primarily mild while the Mexican cases had led to multiple deaths. However, research on previous pandemic strains has suggested that mortality can vary widely between different countries, with mortality being concentrated in the developing world.[144] Differences in the viruses or co-infection are also being considered as possible causes. In 1918, influenza weakened the infected, and it was then lung infections such as pneumonia which killed 3% of them. Such co-infection can be reduced by the use of antibiotics. In the current outbreak, the first death (13 and 21 April) were diagnosed as 'atypical pneumonias', a pneumonia which, helped by the flu, becomes more dangerous. The CDC's flu chief Nancy Cox said that genetic analysis of the swine flu strain did not reveal the markers for virulence found in the 1918 flu virus.[145]
At a press briefing on April 27, acting CDC director Dr. Richard Besser stated that out of 40 confirmed cases in the United States at that point, only one individual was hospitalized. He also revealed that the median age was 16 years "with a range in age of 7 to 54 years"[146]. By April 29, the U.S. had 91 confirmed cases with 5 hospitalizations and one death.[147]
Whereas most influenza strains affect the elderly and young children worst, this strain has primarily caused deaths in people between the ages of 25 and 50.[148]
Prevention and treatment
Further information: Influenza: Prevention and Influenza treatment
Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public. The CDC advises not touching the mouth, nose or eyes, as these are primary modes of transmission. When coughing, they recommend coughing into a tissue and disposing of the tissue, then immediately washing the hands.[149]
There is no risk of flu transmission from the consumption of properly-cooked pork products.[150]
The previously recommended influenza vaccines for the southern and northern hemispheres, including that for the 2009/2010 flu season, are ineffective against the new strain.[151] Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months.[152][153] The WHO Director-General announced that production of the unchanged seasonal vaccine should continue for now, and that the WHO would assist the development process for an effective vaccine.[110] U.S.-based medical product company Baxter International has requested a virus sample from the WHO in order to begin development of a new vaccine.[154] Sanofi-Aventis (Sanofi-Pasteur) is manufacturing the conventional seasonal flu vaccine and has not been asked to produce a vaccine against the new H1N1 strain, which would be difficult to manufacture without diverting facilities from current production.[155]
Of the available antiviral treatments for influenza, the WHO stated that the viruses obtained from the human cases with swine influenza in the United States were sensitive to oseltamivir (Tamiflu)[156] and zanamivir (Relenza) but resistant to amantadine and rimantadine.[157] Tamiflu and Relenza also have a preventative effect against Influenzavirus A.[158] On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain.[159] Roche and the U.S. government had already extended the shelf life of federally stockpiled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.[160]
Due to a more convenient method of administration, treatment with oseltamivir is typically preferred, but in H3N2 flu treatment leads to resistance in 0.4% of adult cases and 5.5% of children. The resistant strains are typically less transmissible, but that is not certain, and resistant human H1N1 viruses have become widely established. Fortunately, simulations reveal that using a second effective antiviral such as zanamivir (Relenza) to treat even 1% of cases will delay the spread of resistant strains. Even a drug such as amantadine (Symmetrel) for which resistance frequently emerges may be useful in combination therapy.[161][162]
Source: http://en.wikipedia.org/wiki/2009_swine_flu_outbreak
See also: Swine_influenza#In_humans, for symptoms in previous cases.
The CDC does not fully understand why the U.S. cases' symptoms were primarily mild while the Mexican cases had led to multiple deaths. However, research on previous pandemic strains has suggested that mortality can vary widely between different countries, with mortality being concentrated in the developing world.[144] Differences in the viruses or co-infection are also being considered as possible causes. In 1918, influenza weakened the infected, and it was then lung infections such as pneumonia which killed 3% of them. Such co-infection can be reduced by the use of antibiotics. In the current outbreak, the first death (13 and 21 April) were diagnosed as 'atypical pneumonias', a pneumonia which, helped by the flu, becomes more dangerous. The CDC's flu chief Nancy Cox said that genetic analysis of the swine flu strain did not reveal the markers for virulence found in the 1918 flu virus.[145]
At a press briefing on April 27, acting CDC director Dr. Richard Besser stated that out of 40 confirmed cases in the United States at that point, only one individual was hospitalized. He also revealed that the median age was 16 years "with a range in age of 7 to 54 years"[146]. By April 29, the U.S. had 91 confirmed cases with 5 hospitalizations and one death.[147]
Whereas most influenza strains affect the elderly and young children worst, this strain has primarily caused deaths in people between the ages of 25 and 50.[148]
Prevention and treatment
Further information: Influenza: Prevention and Influenza treatment
Recommendations to prevent infection by the virus consist of the standard personal precautions against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public. The CDC advises not touching the mouth, nose or eyes, as these are primary modes of transmission. When coughing, they recommend coughing into a tissue and disposing of the tissue, then immediately washing the hands.[149]
There is no risk of flu transmission from the consumption of properly-cooked pork products.[150]
The previously recommended influenza vaccines for the southern and northern hemispheres, including that for the 2009/2010 flu season, are ineffective against the new strain.[151] Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months.[152][153] The WHO Director-General announced that production of the unchanged seasonal vaccine should continue for now, and that the WHO would assist the development process for an effective vaccine.[110] U.S.-based medical product company Baxter International has requested a virus sample from the WHO in order to begin development of a new vaccine.[154] Sanofi-Aventis (Sanofi-Pasteur) is manufacturing the conventional seasonal flu vaccine and has not been asked to produce a vaccine against the new H1N1 strain, which would be difficult to manufacture without diverting facilities from current production.[155]
Of the available antiviral treatments for influenza, the WHO stated that the viruses obtained from the human cases with swine influenza in the United States were sensitive to oseltamivir (Tamiflu)[156] and zanamivir (Relenza) but resistant to amantadine and rimantadine.[157] Tamiflu and Relenza also have a preventative effect against Influenzavirus A.[158] On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain.[159] Roche and the U.S. government had already extended the shelf life of federally stockpiled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.[160]
Due to a more convenient method of administration, treatment with oseltamivir is typically preferred, but in H3N2 flu treatment leads to resistance in 0.4% of adult cases and 5.5% of children. The resistant strains are typically less transmissible, but that is not certain, and resistant human H1N1 viruses have become widely established. Fortunately, simulations reveal that using a second effective antiviral such as zanamivir (Relenza) to treat even 1% of cases will delay the spread of resistant strains. Even a drug such as amantadine (Symmetrel) for which resistance frequently emerges may be useful in combination therapy.[161][162]
Source: http://en.wikipedia.org/wiki/2009_swine_flu_outbreak
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