04-29-2009, 10:57 AM
The 2009 swine flu outbreak or H1N1 outbreak is the spread of a new strain of H1N1 influenza virus that was first detected by public health agencies in March 2009. Local outbreaks of an influenza-like illness were first detected in three areas of Mexico, but the new strain was not clinically identified as such until a month later in Texas and California, whereupon its presence was swiftly confirmed in various Mexican states and Mexico City; within days isolated cases elsewhere in Mexico, the U.S., and several other Northern Hemisphere countries were also identified. By April 28, the new strain was confirmed in Canada, Spain, the United Kingdom, New Zealand and Israel and suspected in many other nations, including South Korea and Austria, with over 2,500 candidate cases, prompting the World Health Organization (WHO) to raise their pandemic alert level to 4.level 4 warning means that the WHO considers that there is "sustained human to human transmission"; whereas levels 5 and 6 represent "widespread human infection".
The new strain is an apparent reassortment of several strains of influenza A virus subtype H1N1, which analysis at the United States Centers for Disease Control and Prevention (CDC) identified as a strain endemic in humans, a strain endemic in birds, and two strains endemic in American and Eurasian pigs (swine).
In late April both the United Nations WHO and the U.S. CDC expressed serious concern about the situation, as it had the potential to become a flu pandemic due to the novelty of the influenza strain, its transmission from human to human, and the unusually high mortality rate in Mexico. On April 25, 2009, the WHO determined the situation to be a formal "public health emergency of international concern", with knowledge lacking in regard to "the clinical features, epidemiology, and virology of reported cases and the appropriate responses". Government health agencies around the world also expressed concerns over the outbreak and are monitoring the situation closely.
On April 24, 2009, Mexico's schools, universities, and all public events were closed or suspendedwhile other schools in the U.S. closed due to confirmed cases in students. Schools in Mexico were then announced to be closed until May 6, 2009
![[Image: 180px-Symptoms_of_swine_flu.svg.png]](http://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Symptoms_of_swine_flu.svg/180px-Symptoms_of_swine_flu.svg.png)
![[Image: 180px-Sow_with_piglet.jpg]](http://upload.wikimedia.org/wikipedia/commons/thumb/5/59/Sow_with_piglet.jpg/180px-Sow_with_piglet.jpg)
![[Image: 180px-InfluenzaNomenclatureDiagram.svg.png]](http://upload.wikimedia.org/wikipedia/en/thumb/1/11/InfluenzaNomenclatureDiagram.svg/180px-InfluenzaNomenclatureDiagram.svg.png)
Genetics and effects
The CDC has confirmed that U.S. cases were found to be made up of genetic elements from four different flu viruses – North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."Pigs have been shown to act as a potential "mixing vessel" in which reassortment can occur between flu viruses of several species.This new strain appears to be a result of the reassortment of two swine influenza viruses, which themselves are descended from previous reassortments in pigs.Influenza viruses readily undergo reassortment because their genome is split between eight pieces of RNA (see Orthomyxoviridae).
The virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).
Several complete genome sequences for U.S. flu cases were rapidly made available through the Global Initiative on Sharing Avian Influenza Data (GISAID). 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.[78][79] 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. The seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection.
The CDC does not understand why the U.S. cases were primarily mild disease 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.Differences in the viruses or co-infection are also being considered as possible causes. Only fourteen samples from Mexico had been tested by the CDC, with seven found to match the American strain. The virus likely passes through several cycles of infection with no known linkages between patients in Texas and California, and that containment of the virus is "not very likely". The U.S. embassy reported that a CDC investigative team arrived in Mexico City on April 25 to work with Mexican counterparts to study the virus.
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."
Unlike what usually happens in cases of influenza, which inflict a greater number of deaths between the elderly and the children, this strain has, so far, resulted in deaths in people between the ages of 25 and 50. One reason why this might be is that the virus produces a damaging cytokine storm in young people with an active and healthy immune system.
![[Image: 180px-Swine_Flu_Masked_Train_Passengers_...o_City.jpg]](http://upload.wikimedia.org/wikipedia/commons/thumb/6/66/Swine_Flu_Masked_Train_Passengers_in_Mexico_City.jpg/180px-Swine_Flu_Masked_Train_Passengers_in_Mexico_City.jpg)
Prevention and 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. People should avoid touching their mouth, nose or eyes with their hands unless they've washed their hands. If people do cough, they should either cough into a tissue and throw it in the garbage immediately or, if they cough in their hand, they should wash their hands immediately.
There is no risk of flu transmission from consumption of pork.
Many countries confirmed that inbound international passengers will be screened. Typical airport health screening involves asking passengers which countries they have visited and checking whether they feel or look particularly unwell. Thermographic equipment was put into use at a number of airports to screen passengers. In the USA, two confirmed cases were detected through their border infectious disease surveillance.A number of countries advised against travel to known affected regions.
To maintain a secure household during a pandemic flu, the Water Quality & Health Council recommends keeping as supplies food and bottled water, portable power sources and chlorine bleach as an emergency water purifier and surface sanitizer.
Train commuters in Mexico City wearing surgical masks.
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.Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months.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.
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.Baxter has patented a cell-based technology that may allow the company to develop a vaccine in half the time it usually takes, possibly cutting development time from six months to three.
An alternative to vaccination used in the 1918 flu pandemic was the direct transfusion of blood, plasma, or serum from recovered patients. Though medical experiments of the era lacked some procedural refinements, eight publications from 1918-1925 reported that the treatment could approximately halve the mortality in hospitalized severe cases with an average case-fatality rate of 37% when untreated.
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)and zanamivir (Relenza) but resistant to amantadine and rimantadine. Tamiflu and Relenza also have a preventative effect against Influenzavirus A.
On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain.Roche and the U.S. government had already extended the shelf-life of federally stock-piled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.
Some physicians in the U.S. are recommending the use of masks when in public.The purpose of a face mask is to effectively cover a person's mouth and nose so that if a person is around someone who is infected, there is a decreased likelihood of transmission. Recommendations to protect against the avian flu indicated that using a face mask with a rating of N99, N100 or P100 in the United States or a rating of FFP3 in Europe should be effective in protecting against transmission.While face masks with these ratings provide 99% or greater efficiency in protecting against flu transmission, N95 or FFP2 face masks provide about 94% efficiency.N95 and FFP2 rated face masks may therefore also be effective.
On April 28, the WHO flu expert Keiji Fukuda pointed out that it is too late to contain the swine flu. "Containment is not a feasible operation. Countries should now focus on mitigating the effect of the virus," he said.He also stressed that the experts did not recommend closing borders or restricting travel. "With the virus being widespread... closing borders or restricting travel really has very little effects in stopping the movement of this virus."However, on April 28, the U.S. CDC began "recommending that people avoid non-essential travel to Mexico."
Dr. Ira Longin, a specialist in the mathematical and statistical theory of epidemics, suggests that if those infected stay at home or seek medical care, public meeting places are closed, and anti-flu medications are made widely available, then in simulations the sickness is reduced by nearly two-thirds. "The name of the game is to slow transmission until a well-matched vaccine can be made and distributed. I am fairly optimistic we can do that". In the northern hemisphere the flu season will soon end. However, "Timing is terrible for people in the Southern Hemisphere -- places like New Zealand, Australia, South Africa, parts of South America. They are just coming into their flu season."
Ref: http://en.wikipedia.org/wiki/2009_swine_flu_outbreak
The new strain is an apparent reassortment of several strains of influenza A virus subtype H1N1, which analysis at the United States Centers for Disease Control and Prevention (CDC) identified as a strain endemic in humans, a strain endemic in birds, and two strains endemic in American and Eurasian pigs (swine).
In late April both the United Nations WHO and the U.S. CDC expressed serious concern about the situation, as it had the potential to become a flu pandemic due to the novelty of the influenza strain, its transmission from human to human, and the unusually high mortality rate in Mexico. On April 25, 2009, the WHO determined the situation to be a formal "public health emergency of international concern", with knowledge lacking in regard to "the clinical features, epidemiology, and virology of reported cases and the appropriate responses". Government health agencies around the world also expressed concerns over the outbreak and are monitoring the situation closely.
On April 24, 2009, Mexico's schools, universities, and all public events were closed or suspendedwhile other schools in the U.S. closed due to confirmed cases in students. Schools in Mexico were then announced to be closed until May 6, 2009
Genetics and effects
The CDC has confirmed that U.S. cases were found to be made up of genetic elements from four different flu viruses – North American swine influenza, North American avian influenza, human influenza, and swine influenza virus typically found in Asia and Europe – "an unusually mongrelised mix of genetic sequences."Pigs have been shown to act as a potential "mixing vessel" in which reassortment can occur between flu viruses of several species.This new strain appears to be a result of the reassortment of two swine influenza viruses, which themselves are descended from previous reassortments in pigs.Influenza viruses readily undergo reassortment because their genome is split between eight pieces of RNA (see Orthomyxoviridae).
The virus was resistant to amantadine and rimantadine, but susceptible to oseltamivir (Tamiflu) and zanamivir (Relenza).
Several complete genome sequences for U.S. flu cases were rapidly made available through the Global Initiative on Sharing Avian Influenza Data (GISAID). 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.[78][79] 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. The seasonal influenza strain H1N1 vaccine is thought to be unlikely to provide protection.
The CDC does not understand why the U.S. cases were primarily mild disease 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.Differences in the viruses or co-infection are also being considered as possible causes. Only fourteen samples from Mexico had been tested by the CDC, with seven found to match the American strain. The virus likely passes through several cycles of infection with no known linkages between patients in Texas and California, and that containment of the virus is "not very likely". The U.S. embassy reported that a CDC investigative team arrived in Mexico City on April 25 to work with Mexican counterparts to study the virus.
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."
Unlike what usually happens in cases of influenza, which inflict a greater number of deaths between the elderly and the children, this strain has, so far, resulted in deaths in people between the ages of 25 and 50. One reason why this might be is that the virus produces a damaging cytokine storm in young people with an active and healthy immune system.
Prevention and 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. People should avoid touching their mouth, nose or eyes with their hands unless they've washed their hands. If people do cough, they should either cough into a tissue and throw it in the garbage immediately or, if they cough in their hand, they should wash their hands immediately.
There is no risk of flu transmission from consumption of pork.
Many countries confirmed that inbound international passengers will be screened. Typical airport health screening involves asking passengers which countries they have visited and checking whether they feel or look particularly unwell. Thermographic equipment was put into use at a number of airports to screen passengers. In the USA, two confirmed cases were detected through their border infectious disease surveillance.A number of countries advised against travel to known affected regions.
To maintain a secure household during a pandemic flu, the Water Quality & Health Council recommends keeping as supplies food and bottled water, portable power sources and chlorine bleach as an emergency water purifier and surface sanitizer.
Train commuters in Mexico City wearing surgical masks.
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.Current development, large-scale manufacturing, distribution and delivery of a new vaccine takes several months.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.
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.Baxter has patented a cell-based technology that may allow the company to develop a vaccine in half the time it usually takes, possibly cutting development time from six months to three.
An alternative to vaccination used in the 1918 flu pandemic was the direct transfusion of blood, plasma, or serum from recovered patients. Though medical experiments of the era lacked some procedural refinements, eight publications from 1918-1925 reported that the treatment could approximately halve the mortality in hospitalized severe cases with an average case-fatality rate of 37% when untreated.
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)and zanamivir (Relenza) but resistant to amantadine and rimantadine. Tamiflu and Relenza also have a preventative effect against Influenzavirus A.
On April 27, the CDC recommended the use of Tamiflu and Relenza for both treatment and prevention of the new strain.Roche and the U.S. government had already extended the shelf-life of federally stock-piled Tamiflu from the original five years to seven years because studies indicated that the medication continues to maintain its effectiveness.
Some physicians in the U.S. are recommending the use of masks when in public.The purpose of a face mask is to effectively cover a person's mouth and nose so that if a person is around someone who is infected, there is a decreased likelihood of transmission. Recommendations to protect against the avian flu indicated that using a face mask with a rating of N99, N100 or P100 in the United States or a rating of FFP3 in Europe should be effective in protecting against transmission.While face masks with these ratings provide 99% or greater efficiency in protecting against flu transmission, N95 or FFP2 face masks provide about 94% efficiency.N95 and FFP2 rated face masks may therefore also be effective.
On April 28, the WHO flu expert Keiji Fukuda pointed out that it is too late to contain the swine flu. "Containment is not a feasible operation. Countries should now focus on mitigating the effect of the virus," he said.He also stressed that the experts did not recommend closing borders or restricting travel. "With the virus being widespread... closing borders or restricting travel really has very little effects in stopping the movement of this virus."However, on April 28, the U.S. CDC began "recommending that people avoid non-essential travel to Mexico."
Dr. Ira Longin, a specialist in the mathematical and statistical theory of epidemics, suggests that if those infected stay at home or seek medical care, public meeting places are closed, and anti-flu medications are made widely available, then in simulations the sickness is reduced by nearly two-thirds. "The name of the game is to slow transmission until a well-matched vaccine can be made and distributed. I am fairly optimistic we can do that". In the northern hemisphere the flu season will soon end. However, "Timing is terrible for people in the Southern Hemisphere -- places like New Zealand, Australia, South Africa, parts of South America. They are just coming into their flu season."
Ref: http://en.wikipedia.org/wiki/2009_swine_flu_outbreak