Wednesday, September 2, 2009
United States
The new strain was first diagnosed in two children, neither of whom had been in contact with pigs, by the CDC, first on April 14, 2009 in San Diego County, California and a few days later in nearby Imperial County, California[27] (it was not identified as a new strain in Mexico until 24 April
Response
The Public Health Agency of Canada announced that their National Microbiology Laboratory (NML) had mapped the genetic code of the swine flu virus, the first time that was done.[29]
U.S officials noted that six years of worrying about H5N1 avian flu did much to prepare for the current swine flu outbreak, noting that after H5N1 emerged in Asia, ultimately killing about 60 percent of the few hundred people infected by it over the years, many countries took steps to try to prevent any similar crisis from spreading further.[30][31] The CDC would now use the current lull to take stock of the United States's response to the new H1N1 flu and attempt to patch any gaps in the public health safety net before flu season starts this autumn.
U.S officials noted that six years of worrying about H5N1 avian flu did much to prepare for the current swine flu outbreak, noting that after H5N1 emerged in Asia, ultimately killing about 60 percent of the few hundred people infected by it over the years, many countries took steps to try to prevent any similar crisis from spreading further.[30][31] The CDC would now use the current lull to take stock of the United States's response to the new H1N1 flu and attempt to patch any gaps in the public health safety net before flu season starts this autumn.
Pigs and food safety
The novel H1N1 virus is a type of swine influenza, derived originally from a strain that lived in pigs and this origin gave rise to the common name of "swine flu", largely used today by mass media. Despite this origin, however, the current strain is transmitted between people and not from swine.[33] The U.S. agriculture secretary has made it clear that despite its common name, "swine flu," there is no risk in eating cooked pork products and the virus has not been found in American hogs
Initial outbreaks
It is not known where the virus originated.[20][21] Analysis has suggested that the H1N1 strain responsible for the current outbreak first evolved around September 2008 and circulated in the human population for several months before the first cases were identified as being due to a new strain.
Mexico
The virus was first reported in two U.S. children in March, but health officials have said that it apparently infected people as early as last January in Mexico.[24] The outbreak was first detected in Mexico City on March 18, 2009,[25] Immediately after the outbreak was officially announced, Mexico requested material support from the U.S., and within days of the outbreak Mexico City was "effectively shut down." Some countries canceled flights to Mexico while others halted trade. Calls to close the border to contain the spread were rejected.
Some experts today assume that Mexico already had hundreds of thousands, and possibly millions, of cases before the outbreak was officially recognized, and was therefore in the midst of a "silent epidemic".[26] As a result, Mexico was reporting only the most serious cases, possibly leading to a skewed initial estimate of the case fatality rate.
Some experts today assume that Mexico already had hundreds of thousands, and possibly millions, of cases before the outbreak was officially recognized, and was therefore in the midst of a "silent epidemic".[26] As a result, Mexico was reporting only the most serious cases, possibly leading to a skewed initial estimate of the case fatality rate.
Historical context
Annual influenza epidemics are estimated to affect 5–15% of the global population. Although most cases are mild, this still causes severe illness in 3–5 million people and around 250,000–500,000 deaths worldwide. In industrialized countries severe illness and deaths occur mainly in the high-risk populations of infants, the elderly, and chronically ill patients.[7]
In addition to these annual epidemics, Influenza A virus strains caused three major global epidemics during the 20th century: the Spanish flu in 1918, Asian flu in 1957 and Hong Kong flu in 1968–69. These pandemics were caused by strains of Influenza A virus that had undergone major genetic changes and for which the population did not possess significant immunity.[7][8] The overall effects of these pandemics and epidemics are summarized in the table below.
In addition to these annual epidemics, Influenza A virus strains caused three major global epidemics during the 20th century: the Spanish flu in 1918, Asian flu in 1957 and Hong Kong flu in 1968–69. These pandemics were caused by strains of Influenza A virus that had undergone major genetic changes and for which the population did not possess significant immunity.[7][8] The overall effects of these pandemics and epidemics are summarized in the table below.
Historical context 2
The influenza virus has also caused several pandemic threats over the past century, including the pseudo-pandemic of 1947, the 1976 swine flu outbreak and the 1977 Russian flu, all caused by the H1N1 subtype.[8] The world has been at an increased level of alert since the SARS epidemic in Southeast Asia (caused by the SARS coronavirus).[16] The level of preparedness was further increased and sustained with the advent of the H5N1 bird flu outbreaks because of H5N1's high fatality rate, although the strains currently prevalent have limited human-to-human transmission (anthroponotic) capability, or epidemicity.[9][17]
People who have contracted flu prior to 1957 may have some immunity. A May 20, 2009 New York Times article stated: “Tests on blood serum from older people showed that they had antibodies that attacked the new virus, Dr. Daniel Jernigan, chief flu epidemiologist at the Centers for Disease Control and Prevention, said in a telephone news conference. That does not mean that everyone over 52 is immune, since some Americans and Mexicans older than that have died of the new flu
People who have contracted flu prior to 1957 may have some immunity. A May 20, 2009 New York Times article stated: “Tests on blood serum from older people showed that they had antibodies that attacked the new virus, Dr. Daniel Jernigan, chief flu epidemiologist at the Centers for Disease Control and Prevention, said in a telephone news conference. That does not mean that everyone over 52 is immune, since some Americans and Mexicans older than that have died of the new flu
In humans
If a person becomes sick with swine flu, antiviral drugs can make the illness milder and make the patient feel better faster. They may also prevent serious flu complications. For treatment, antiviral drugs work best if started soon after getting sick (within 2 days of symptoms). Beside antivirals, supportive care at home or in hospital, focuses on controlling fevers, relieving pain and maintaining fluid balance, as well as identifying and treating any secondary infections or other medical problems. The U.S. Centers for Disease Control and Prevention recommends the use of Tamiflu (oseltamivir) or Relenza (zanamivir) for the treatment and/or prevention of infection with swine influenza viruses; however, the majority of people infected with the virus make a full recovery without requiring medical attention or antiviral drugs.[86] The virus isolates in the 2009 outbreak have been found resistant to amantadine and rimantadine.[87]
In the U.S., on April 27, 2009, the Food and Drug Administration (FDA) issued Emergency Use Authorizations to make available Relenza and Tamiflu antiviral drugs to treat the swine influenza virus in cases for which they are currently unapproved. The agency issued these EUAs to allow treatment of patients younger than the current approval allows and to allow the widespread distribution of the drugs, including by non-licensed volunteers.[88]
In the U.S., on April 27, 2009, the Food and Drug Administration (FDA) issued Emergency Use Authorizations to make available Relenza and Tamiflu antiviral drugs to treat the swine influenza virus in cases for which they are currently unapproved. The agency issued these EUAs to allow treatment of patients younger than the current approval allows and to allow the widespread distribution of the drugs, including by non-licensed volunteers.[88]
2009 flu pandemic
The 2009 flu pandemic is a global outbreak of a new strain of an influenza A virus subtype H1N1, referred to as the "novel H1N1"[1] first identified in April 2009, and commonly called "swine flu." It is thought to be a reassortment of four known strains of influenza A virus[2]: one endemic in (normally infecting) humans, one endemic in birds, and two endemic in pigs (swine). Transmission of the new strain is human-to-human, with cooked pork products safe to eat as the virus cannot be transmitted by eating foods.
The outbreak began in Mexico, with evidence that Mexico was already in the midst of an epidemic for months before the outbreak was recognized. Soon after, its government closed down most of Mexico City's public and private offices and facilities to help contain the spread. In early June, as the virus spread globally, the World Health Organization (WHO) declared the outbreak to be a pandemic, but also noted that most illnesses were of moderate severity. The virus has since spread to the Southern Hemisphere which entered its winter flu season, and to many less developed countries with limited healthcare systems. Because the virus was spreading with unprecedented speed, and many clinics were overwhelmed testing and treating patients, WHO stopped requiring countries to report all cases, but is still monitoring unusually large outbreaks.[3][4]
The virus typically spread via coughing, sneezing or touching contaminated surfaces and then touching the nose or mouth. Symptoms, which could last up to a week, were similar to those of seasonal flu, and may have included fever, sneezes, sore throat, coughs, headache, and muscle or joint pains. The U.S. Centers for Disease Control and Prevention (CDC) noted that although this was a very serious virus, cases worldwide were usually mild, and most hospitalizations and deaths had been of persons that also had underlying conditions such as asthma, diabetes, obesity, heart disease, or a weakened immune system.[5] As the virus spreads easily between people, through the air or surface contact, those who get the flu are recommended to stay home from school or work and avoid crowds to avoid spreading the infection further. Wearing facial masks is of limited benefit as they are designed for industrial use and do not filter out viral or other biological agents.[6]
In an attempt to slow the spread of the illness, a number of countries, especially in Asia, quarantined airline passengers with flu symptoms, while some also pre-screened passengers. As of August 2009, WHO did not expect to have a full vaccine before the end of 2009, and vaccines available sooner would be limited and given first to healthcare workers, pregnant women, and other higher risk groups. Two or three injections would be required for maximum immunity from both the swine flu and seasonal flu. There was also concern if the new virus mutated further, it could become more virulent and less susceptible to any new vaccine.
The outbreak began in Mexico, with evidence that Mexico was already in the midst of an epidemic for months before the outbreak was recognized. Soon after, its government closed down most of Mexico City's public and private offices and facilities to help contain the spread. In early June, as the virus spread globally, the World Health Organization (WHO) declared the outbreak to be a pandemic, but also noted that most illnesses were of moderate severity. The virus has since spread to the Southern Hemisphere which entered its winter flu season, and to many less developed countries with limited healthcare systems. Because the virus was spreading with unprecedented speed, and many clinics were overwhelmed testing and treating patients, WHO stopped requiring countries to report all cases, but is still monitoring unusually large outbreaks.[3][4]
The virus typically spread via coughing, sneezing or touching contaminated surfaces and then touching the nose or mouth. Symptoms, which could last up to a week, were similar to those of seasonal flu, and may have included fever, sneezes, sore throat, coughs, headache, and muscle or joint pains. The U.S. Centers for Disease Control and Prevention (CDC) noted that although this was a very serious virus, cases worldwide were usually mild, and most hospitalizations and deaths had been of persons that also had underlying conditions such as asthma, diabetes, obesity, heart disease, or a weakened immune system.[5] As the virus spreads easily between people, through the air or surface contact, those who get the flu are recommended to stay home from school or work and avoid crowds to avoid spreading the infection further. Wearing facial masks is of limited benefit as they are designed for industrial use and do not filter out viral or other biological agents.[6]
In an attempt to slow the spread of the illness, a number of countries, especially in Asia, quarantined airline passengers with flu symptoms, while some also pre-screened passengers. As of August 2009, WHO did not expect to have a full vaccine before the end of 2009, and vaccines available sooner would be limited and given first to healthcare workers, pregnant women, and other higher risk groups. Two or three injections would be required for maximum immunity from both the swine flu and seasonal flu. There was also concern if the new virus mutated further, it could become more virulent and less susceptible to any new vaccine.
Treatment
As swine influenza is rarely fatal to pigs, little treatment beyond rest and supportive care is required.[54] Instead veterinary efforts are focused on preventing the spread of the virus throughout the farm, or to other farms.[11] Vaccination and animal management techniques are most important in these efforts. Antibiotics are also used to treat this disease, which although they have no effect against the influenza virus, do help prevent bacterial pneumonia and other secondary infections in influenza-weakened herds.[5
Prevention in swine
Methods of preventing the spread of influenza among swine include facility management, herd management, and vaccination (ATCvet code: QI09AA03). Because much of the illness and death associated with swine flu involves secondary infection by other pathogens, control strategies that rely on vaccination may be insufficient.
Control of swine influenza by vaccination has become more difficult in recent decades, as the evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the infection when the virus strains match enough to have significant cross-protection, and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.[74][75] Present vaccination strategies for SIV control and prevention in swine farms typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses.[76][77] The United States Department of Agriculture researchers say that while pig vaccination keeps pigs from getting sick, it does not block infection or shedding of the virus.[78]
Facility management includes using disinfectants and ambient temperature to control virus in the environment. The virus is unlikely to survive outside living cells for more than two weeks, except in cold (but above freezing) conditions, and it is readily inactivated by disinfectants.[2] Herd management includes not adding pigs carrying influenza to herds that have not been exposed to the virus. The virus survives in healthy carrier pigs for up to 3 months and can be recovered from them between outbreaks. Carrier pigs are usually responsible for the introduction of SIV into previously uninfected herds and countries, so new animals should be quarantined.[54] After an outbreak, as immunity in exposed pigs wanes, new outbreaks of the same strain can occur.[2]
Control of swine influenza by vaccination has become more difficult in recent decades, as the evolution of the virus has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the infection when the virus strains match enough to have significant cross-protection, and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.[74][75] Present vaccination strategies for SIV control and prevention in swine farms typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests that current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses.[76][77] The United States Department of Agriculture researchers say that while pig vaccination keeps pigs from getting sick, it does not block infection or shedding of the virus.[78]
Facility management includes using disinfectants and ambient temperature to control virus in the environment. The virus is unlikely to survive outside living cells for more than two weeks, except in cold (but above freezing) conditions, and it is readily inactivated by disinfectants.[2] Herd management includes not adding pigs carrying influenza to herds that have not been exposed to the virus. The virus survives in healthy carrier pigs for up to 3 months and can be recovered from them between outbreaks. Carrier pigs are usually responsible for the introduction of SIV into previously uninfected herds and countries, so new animals should be quarantined.[54] After an outbreak, as immunity in exposed pigs wanes, new outbreaks of the same strain can occur.[2]
Prevention in humans
Prevention in humans
Prevention of pig to human transmission
Swine can be infected by both avian and human influenza strains of influenza, and therefore are hosts where the antigenic shifts can occur that create new influenza strains.
The transmission from swine to human is believed to occur mainly in swine farms where farmers are in close contact with live pigs. Although strains of swine influenza are usually not able to infect humans this may occasionally happen, so farmers and veterinarians are encouraged to use a face mask when dealing with infected animals. The use of vaccines on swine to prevent their infection is a major method of limiting swine to human transmission. Risk factors that may contribute to swine-to-human transmission include smoking and not wearing gloves when working with sick animals.[79]
Prevention of human to human transmission
Influenza spreads between humans through coughing or sneezing and people touching something with the virus on it and then touching their own nose or mouth.[80] Swine flu cannot be spread by pork products, since the virus is not transmitted through food.[80] The swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children, can remain contagious for up to ten days. Diagnosis can be made by sending a specimen, collected during the first five days for analysis.[81]
Recommendations to prevent spread of the virus among humans include using standard infection control against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public.[82] Chance of transmission is also reduced by disinfecting household surfaces, which can be done effectively with a diluted chlorine bleach solution.[83]
Experts agree that hand-washing can help prevent viral infections, including ordinary influenza and the swine flu virus. Also avoiding touching eyes, nose and mouth with hands prevents flu. [3] Influenza can spread in coughs or sneezes, but an increasing body of evidence shows small droplets containing the virus can linger on tabletops, telephones and other surfaces and be transferred via the fingers to the mouth, nose or eyes. Alcohol-based gel or foam hand sanitizers work well to destroy viruses and bacteria. Anyone with flu-like symptoms such as a sudden fever, cough or muscle aches should stay away from work or public transportation and should contact a doctor for advice.
Social distancing is another tactic. It means staying away from other people who might be infected and can include avoiding large gatherings, spreading out a little at work, or perhaps staying home and lying low if an infection is spreading in a community. Public health and other responsible authorities have action plans which may request or require social distancing actions depending on the severity of the outbreak.
Vaccination
Vaccines are available for different kinds of swine flu. Although the current trivalent influenza vaccine is unlikely to provide protection against the new 2009 H1N1 strain,[84] vaccines against the new strain are being developed and could be ready as early as November 2009.[85]
Prevention of pig to human transmission
Swine can be infected by both avian and human influenza strains of influenza, and therefore are hosts where the antigenic shifts can occur that create new influenza strains.
The transmission from swine to human is believed to occur mainly in swine farms where farmers are in close contact with live pigs. Although strains of swine influenza are usually not able to infect humans this may occasionally happen, so farmers and veterinarians are encouraged to use a face mask when dealing with infected animals. The use of vaccines on swine to prevent their infection is a major method of limiting swine to human transmission. Risk factors that may contribute to swine-to-human transmission include smoking and not wearing gloves when working with sick animals.[79]
Prevention of human to human transmission
Influenza spreads between humans through coughing or sneezing and people touching something with the virus on it and then touching their own nose or mouth.[80] Swine flu cannot be spread by pork products, since the virus is not transmitted through food.[80] The swine flu in humans is most contagious during the first five days of the illness although some people, most commonly children, can remain contagious for up to ten days. Diagnosis can be made by sending a specimen, collected during the first five days for analysis.[81]
Recommendations to prevent spread of the virus among humans include using standard infection control against influenza. This includes frequent washing of hands with soap and water or with alcohol-based hand sanitizers, especially after being out in public.[82] Chance of transmission is also reduced by disinfecting household surfaces, which can be done effectively with a diluted chlorine bleach solution.[83]
Experts agree that hand-washing can help prevent viral infections, including ordinary influenza and the swine flu virus. Also avoiding touching eyes, nose and mouth with hands prevents flu. [3] Influenza can spread in coughs or sneezes, but an increasing body of evidence shows small droplets containing the virus can linger on tabletops, telephones and other surfaces and be transferred via the fingers to the mouth, nose or eyes. Alcohol-based gel or foam hand sanitizers work well to destroy viruses and bacteria. Anyone with flu-like symptoms such as a sudden fever, cough or muscle aches should stay away from work or public transportation and should contact a doctor for advice.
Social distancing is another tactic. It means staying away from other people who might be infected and can include avoiding large gatherings, spreading out a little at work, or perhaps staying home and lying low if an infection is spreading in a community. Public health and other responsible authorities have action plans which may request or require social distancing actions depending on the severity of the outbreak.
Vaccination
Vaccines are available for different kinds of swine flu. Although the current trivalent influenza vaccine is unlikely to provide protection against the new 2009 H1N1 strain,[84] vaccines against the new strain are being developed and could be ready as early as November 2009.[85]
Diagnosis
Different medical kits are available for diagnosis of swine flu.[73]
The two major tests that are being used are the nasopharyngeal (or back of the throat) swab for viral culture, the gold standard, and the indirect evidence test by detection of antibodies to novel H1N1 with PCR studies.
The two major tests that are being used are the nasopharyngeal (or back of the throat) swab for viral culture, the gold standard, and the indirect evidence test by detection of antibodies to novel H1N1 with PCR studies.
Prevention
Prevention of swine influenza has three components: prevention in swine, prevention of transmission to humans, and prevention of its spread among humans.
In humans
Direct transmission of a swine flu virus from pigs to humans is occasionally possible (called zoonotic swine flu). In all, 50 cases are known to have occurred since the first report in medical literature in 1958, which have resulted in a total of six deaths.[69] Of these six people, one was pregnant, one had leukemia, one had Hodgkin disease and two were known to be previously healthy.[69] Despite these apparently low numbers of infections, the true rate of infection may be higher, since most cases only cause a very mild disease, and will probably never be reported or diagnosed.[69]
Video xo.ogv
Play video
In this video, Dr. Joe Bresee, with CDC's Influenza Division, describes the symptoms of swine flu and warning signs to look for that indicate the need for urgent medical attention.
See also: See this video with subtitles on YouTube [2]
According to the Centers for Disease Control and Prevention (CDC), in humans the symptoms of the 2009 "swine flu" H1N1 virus are similar to those of influenza and of influenza-like illness in general. Symptoms include fever, cough, sore throat, body aches, headache, chills and fatigue. The 2009 outbreak has shown an increased percentage of patients reporting diarrhea and vomiting.[70] The 2009 H1N1 virus is not zoonotic swine flu, as it is not transmitted from pigs to humans, but from person to person.
Because these symptoms are not specific to swine flu, a differential diagnosis of probable swine flu requires not only symptoms but also a high likelihood of swine flu due to the person's recent history. For example, during the 2009 swine flu outbreak in the United States, CDC advised physicians to "consider swine influenza infection in the differential diagnosis of patients with acute febrile respiratory illness who have either been in contact with persons with confirmed swine flu, or who were in one of the five U.S. states that have reported swine flu cases or in Mexico during the 7 days preceding their illness onset."[71] A diagnosis of confirmed swine flu requires laboratory testing of a respiratory sample (a simple nose and throat swab).[71]
The most common cause of death is respiratory failure. Other causes of death are pneumonia (leading to sepsis)[72], high fever (leading to neurological problems), dehydration (from excessive vomiting and diarrhea) and electrolyte imbalance. Fatalities are more likely in young children and the elderly.
Video xo.ogv
Play video
In this video, Dr. Joe Bresee, with CDC's Influenza Division, describes the symptoms of swine flu and warning signs to look for that indicate the need for urgent medical attention.
See also: See this video with subtitles on YouTube [2]
According to the Centers for Disease Control and Prevention (CDC), in humans the symptoms of the 2009 "swine flu" H1N1 virus are similar to those of influenza and of influenza-like illness in general. Symptoms include fever, cough, sore throat, body aches, headache, chills and fatigue. The 2009 outbreak has shown an increased percentage of patients reporting diarrhea and vomiting.[70] The 2009 H1N1 virus is not zoonotic swine flu, as it is not transmitted from pigs to humans, but from person to person.
Because these symptoms are not specific to swine flu, a differential diagnosis of probable swine flu requires not only symptoms but also a high likelihood of swine flu due to the person's recent history. For example, during the 2009 swine flu outbreak in the United States, CDC advised physicians to "consider swine influenza infection in the differential diagnosis of patients with acute febrile respiratory illness who have either been in contact with persons with confirmed swine flu, or who were in one of the five U.S. states that have reported swine flu cases or in Mexico during the 7 days preceding their illness onset."[71] A diagnosis of confirmed swine flu requires laboratory testing of a respiratory sample (a simple nose and throat swab).[71]
The most common cause of death is respiratory failure. Other causes of death are pneumonia (leading to sepsis)[72], high fever (leading to neurological problems), dehydration (from excessive vomiting and diarrhea) and electrolyte imbalance. Fatalities are more likely in young children and the elderly.
In swine
In pigs influenza infection produces fever, lethargy, sneezing, coughing, difficulty breathing and decreased appetite.[11] In some cases the infection can cause abortion. Although mortality is usually low (around 1-4%),[2] the virus can produce weight loss and poor growth, causing economic loss to farmers.[11] Infected pigs can lose up to 12 pounds of body weight over a 3 to 4 week period
Interaction with avian H5N1 in pigs
Pigs are unusual as they can be infected with influenza strains that usually infect three different species: pigs, birds and humans.[62] This makes pigs a host where influenza viruses might exchange genes, producing new and dangerous strains.[62] Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains.[63] H3N2 evolved from H2N2 by antigenic shift.[64] In August 2004, researchers in China found H5N1 in pigs.[65]These H5N1 infections may be quite common: in a survey of 10 apparently healthy pigs housed near poultry farms in West Java, where avian flu had broken out, five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region. Additional tests of 150 pigs outside the area were negative.[66][67]
Transmission to humans
People who work with poultry and swine, especially people with intense exposures, are at increased risk of zoonotic infection with influenza virus endemic in these animals, and constitute a population of human hosts in which zoonosis and reassortment can co-occur.[58] Vaccination of these workers against influenza and surveillance for new influenza strains among this population may therefore be an important public health measure.[59] Transmission of influenza from swine to humans who work with swine was documented in a small surveillance study performed in 2004 at the University of Iowa.[60] This study among others forms the basis of a recommendation that people whose jobs involve handling poultry and swine be the focus of increased public health surveillance.[58] Other professions at particular risk of infection are veterinarians and meat processing workers, although the risk of infection for both of these groups is lower than that of farm workers
2009 outbreak in humans
The H1N1 viral strain implicated in the 2009 flu pandemic among humans often is called "swine flu" because initial testing showed many of the genes in the virus were similar to influenza viruses normally occurring in North American swine.[46] But further research has shown that the outbreak is due to a new strain of H1N1 not previously reported in pigs.
In late April, Margaret Chan, the World Health Organization's director-general, declared a "public health emergency of international concern" under the rules of the WHO's new International Health Regulations when the first cases of the H1N1 virus were reported in the United States.[47] [48] Following the outbreak, on May 2, 2009, it was reported in pigs at a farm in Alberta, Canada, with a link to the outbreak in Mexico. The pigs are suspected to have caught this new strain of virus from a farm worker who recently returned from Mexico, then showed symptoms of an influenza-like illness.[49] These are probable cases, pending confirmation by laboratory testing.
The new strain was initially described as an apparent reassortment of at least four strains of influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two endemic in swine.[46] Subsequent analysis suggested it was a reassortment of just two strains, both found in swine.[50] Although initial reports identified the new strain as swine influenza (i.e., a zoonosis originating in swine), its origin is unknown. Several countries took precautionary measures to reduce the chances for a global pandemic of the disease.[51] The 2009 swine flu has been compared to other similar types of influenza virus in terms of mortality: "in the US it appears that for every 1000 people who get infected, about 40 people need admission to hospital and about one person dies".[52]. There are fears that swine flu will become a major global pandemic in the winter months, with many countries planning major vaccination campaigns.
In late April, Margaret Chan, the World Health Organization's director-general, declared a "public health emergency of international concern" under the rules of the WHO's new International Health Regulations when the first cases of the H1N1 virus were reported in the United States.[47] [48] Following the outbreak, on May 2, 2009, it was reported in pigs at a farm in Alberta, Canada, with a link to the outbreak in Mexico. The pigs are suspected to have caught this new strain of virus from a farm worker who recently returned from Mexico, then showed symptoms of an influenza-like illness.[49] These are probable cases, pending confirmation by laboratory testing.
The new strain was initially described as an apparent reassortment of at least four strains of influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two endemic in swine.[46] Subsequent analysis suggested it was a reassortment of just two strains, both found in swine.[50] Although initial reports identified the new strain as swine influenza (i.e., a zoonosis originating in swine), its origin is unknown. Several countries took precautionary measures to reduce the chances for a global pandemic of the disease.[51] The 2009 swine flu has been compared to other similar types of influenza virus in terms of mortality: "in the US it appears that for every 1000 people who get infected, about 40 people need admission to hospital and about one person dies".[52]. There are fears that swine flu will become a major global pandemic in the winter months, with many countries planning major vaccination campaigns.
Transmission between pigs
Influenza is quite common in pigs, with about half of breeding pigs having been exposed to the virus in the US.[54] Antibodies to the virus are also common in pigs in other countries.[54]
The main route of transmission is through direct contact between infected and uninfected animals.[11] These close contacts are particularly common during animal transport. Intensive farming may also increase the risk of transmission, as the pigs are raised in very close proximity to each other.[55][56] The direct transfer of the virus probably occurs either by pigs touching noses, or through dried mucus. Airborne transmission through the aerosols produced by pigs coughing or sneezing are also an important means of infection.[11] The virus usually spreads quickly through a herd, infecting all the pigs within just a few days.[2] Transmission may also occur through wild animals, such as wild boar, which can spread the disease between farms.
The main route of transmission is through direct contact between infected and uninfected animals.[11] These close contacts are particularly common during animal transport. Intensive farming may also increase the risk of transmission, as the pigs are raised in very close proximity to each other.[55][56] The direct transfer of the virus probably occurs either by pigs touching noses, or through dried mucus. Airborne transmission through the aerosols produced by pigs coughing or sneezing are also an important means of infection.[11] The virus usually spreads quickly through a herd, infecting all the pigs within just a few days.[2] Transmission may also occur through wild animals, such as wild boar, which can spread the disease between farms.
1998 US outbreak in swine
In 1998, swine flu was found in pigs in four U.S. states. Within a year, it had spread through pig populations across the United States. Scientists found that this virus had originated in pigs as a recombinant form of flu strains from birds and humans. This outbreak confirmed that pigs can serve as a crucible where novel influenza viruses emerge as a result of the reassortment of genes from different strains.
2007 Philippine outbreak in swine
On August 20, 2007 Department of Agriculture officers investigated the outbreak (epizootic) of swine flu in Nueva Ecija and Central Luzon, Philippines. The mortality rate is less than 10% for swine flu, unless there are complications like hog cholera. On July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "red alert" warning over Metro Manila and 5 regions of Luzon after the disease spread to backyard pig farms in Bulacan and Pampanga, even if these tested negative for the swine flu virus
1976 swine flu outbreak
The 1976 swine flu outbreak, also known as the swine flu fiasco, or the swine flu debacle, was a strain of H1N1 influenza virus that appeared in 1976. Infections were only detected from January 19 to February 9, and were not found outside Fort Dix.[1] The outbreak is most remembered for the mass immunization that it prompted in the United States. The strain itself killed one person and hospitalized 13. However, side-effects from the vaccine caused 25 deaths.
On February 15, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease. The vaccination program was plagued by delays and public relations problems, but about 24% of the population had been vaccinated by the time the program was canceled. Only one person, the Fort Dix army recruit, died from the flu.[2]
There were reports of Guillain-Barré syndrome, a paralyzing neuromuscular disorder, affecting some people who had received swine flu immunizations. This syndrome is a rare side-effect of modern influenza vaccines, with an incidence of about one case per million vaccinations.[3] As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, less than 33 percent of the population had been immunized by the end of 1976. The National Influenza Immunization Program was effectively halted on December 16.
Overall, about 500 cases of Guillain-Barré syndrome (GBS), resulting in death from severe pulmonary complications for 25 people, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to Guillain-Barré syndrome, though caution is advised for certain individuals, particularly those with a history of GBS.
On February 15, 1976, an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that swine flu was the cause of death and that this strain of flu appeared to be closely related to the strain involved in the 1918 flu pandemic. Alarmed public-health officials decided that action must be taken to head off another major pandemic, and they urged President Gerald Ford that every person in the U.S. be vaccinated for the disease. The vaccination program was plagued by delays and public relations problems, but about 24% of the population had been vaccinated by the time the program was canceled. Only one person, the Fort Dix army recruit, died from the flu.[2]
There were reports of Guillain-Barré syndrome, a paralyzing neuromuscular disorder, affecting some people who had received swine flu immunizations. This syndrome is a rare side-effect of modern influenza vaccines, with an incidence of about one case per million vaccinations.[3] As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, less than 33 percent of the population had been immunized by the end of 1976. The National Influenza Immunization Program was effectively halted on December 16.
Overall, about 500 cases of Guillain-Barré syndrome (GBS), resulting in death from severe pulmonary complications for 25 people, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to Guillain-Barré syndrome, though caution is advised for certain individuals, particularly those with a history of GBS.
1988 zoonosis
In September 1988, a swine flu virus killed one woman and infected others. 32-year old Barbara Ann Wieners was eight months pregnant when she and her husband, Ed, became ill after visiting the hog barn at a county fair in Walworth County, Wisconsin. Barbara died eight days later, after developing pneumonia.[37] The only pathogen identified was an H1N1 strain of swine influenza virus.[38] Doctors were able to induce labor and deliver a healthy daughter before she died. Her husband recovered from his symptoms.
Influenza-like illness (ILI) was reportedly widespread among the pigs exhibited at the fair. 76% of 25 swine exhibitors aged 9 to 19 tested positive for antibody to SIV, but no serious illnesses were detected among this group. Additional studies suggested between one and three health care personnel who had contact with the patient developed mild influenza-like illnesses with antibody evidence of swine flu infection. However, there was no community outbreak.[
Influenza-like illness (ILI) was reportedly widespread among the pigs exhibited at the fair. 76% of 25 swine exhibitors aged 9 to 19 tested positive for antibody to SIV, but no serious illnesses were detected among this group. Additional studies suggested between one and three health care personnel who had contact with the patient developed mild influenza-like illnesses with antibody evidence of swine flu infection. However, there was no community outbreak.[
1976 U.S. outbreak
On February 5, 1976, in the United States an army recruit at Fort Dix said he felt tired and weak. He died the next day and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced that the cause of death was a new strain of swine flu. The strain, a variant of H1N1, is known as A/New Jersey/1976 (H1N1). It was detected only from January 19 to February 9 and did not spread beyond Fort Dix.[26]This new strain appeared to be closely related to the strain involved in the 1918 flu pandemic. Moreover, the ensuing increased surveillance uncovered another strain in circulation in the U.S.: A/Victoria/75 (H3N2) spread simultaneously, also caused illness, and persisted until March.[26] Alarmed public-health officials decided action must be taken to head off another major pandemic, and urged President Gerald Ford that every person in the U.S. be vaccinated for the disease.[27]
The vaccination program was plagued by delays and public relations problems.[28] On October 1, 1976, the immunization program began. That same day, three senior citizens died soon after receiving their swine flu shots and there was a media outcry linking the deaths to the immunizations, despite the lack of positive proof. According to science writer Patrick Di Justo, however, by the time the truth was known—that the deaths were not proven to be related to the vaccine—it was too late. "The government had long feared mass panic about swine flu—now they feared mass panic about the swine flu vaccinations." This became a strong setback to the program.[29]
There were reports of Guillain-Barré syndrome, a paralyzing neuromuscular disorder, affecting some people who had received swine flu immunizations. This syndrome is a rare side-effect of modern influenza vaccines, with an incidence of about one case per million vaccinations.[30] As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, 48,161,019 Americans, or just over 22% of the population, had been immunized by the time the National Influenza Immunization Program (NIIP) was effectively halted on December 16, 1976.[31] [32]
Overall, there were 1098 cases of Guillain-Barré Syndrome (GBS) recorded nationwide by CDC surveillance, 532 of which were linked to the NIIP vaccination, resulting in death from severe pulmonary complications for 25 people, which, according to Dr. P. Haber, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to GBS, though caution is advised for certain individuals, particularly those with a history of GBS. [33] [34][35] Still, as observed by a participant in the immunization program, the vaccine killed more Americans than the disease did.[36]
The vaccination program was plagued by delays and public relations problems.[28] On October 1, 1976, the immunization program began. That same day, three senior citizens died soon after receiving their swine flu shots and there was a media outcry linking the deaths to the immunizations, despite the lack of positive proof. According to science writer Patrick Di Justo, however, by the time the truth was known—that the deaths were not proven to be related to the vaccine—it was too late. "The government had long feared mass panic about swine flu—now they feared mass panic about the swine flu vaccinations." This became a strong setback to the program.[29]
There were reports of Guillain-Barré syndrome, a paralyzing neuromuscular disorder, affecting some people who had received swine flu immunizations. This syndrome is a rare side-effect of modern influenza vaccines, with an incidence of about one case per million vaccinations.[30] As a result, Di Justo writes that "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, 48,161,019 Americans, or just over 22% of the population, had been immunized by the time the National Influenza Immunization Program (NIIP) was effectively halted on December 16, 1976.[31] [32]
Overall, there were 1098 cases of Guillain-Barré Syndrome (GBS) recorded nationwide by CDC surveillance, 532 of which were linked to the NIIP vaccination, resulting in death from severe pulmonary complications for 25 people, which, according to Dr. P. Haber, were probably caused by an immunopathological reaction to the 1976 vaccine. Other influenza vaccines have not been linked to GBS, though caution is advised for certain individuals, particularly those with a history of GBS. [33] [34][35] Still, as observed by a participant in the immunization program, the vaccine killed more Americans than the disease did.[36]
History
Swine influenza was first proposed to be a disease related to human influenza during the 1918 flu pandemic, when pigs became sick at the same time as humans.[16] The first identification of an influenza virus as a cause of disease in pigs occurred about ten years later, in 1930.[17] For the following 60 years, swine influenza strains were almost exclusively H1N1. Then, between 1997 and 2002, new strains of three different subtypes and five different genotypes emerged as causes of influenza among pigs in North America. In 1997-1998, H3N2 strains emerged. These strains, which include genes derived by reassortment from human, swine and avian viruses, have become a major cause of swine influenza in North America. Reassortment between H1N1 and H3N2 produced H1N2. In 1999 in Canada, a strain of H4N6 crossed the species barrier from birds to pigs, but was contained on a single farm.[17]
The H1N1 form of swine flu is one of the descendants of the strain that caused the 1918 flu pandemic.[18][19] As well as persisting in pigs, the descendants of the 1918 virus have also circulated in humans through the 20th century, contributing to the normal seasonal epidemics of influenza.[19] However, direct transmission from pigs to humans is rare, with only 12 cases in the U.S. since 2005.[20] Nevertheless, the retention of influenza strains in pigs after these strains have disappeared from the human population might make pigs a reservoir where influenza viruses could persist, later emerging to reinfect humans once human immunity to these strains has waned.[21]
Swine flu has been reported numerous times as a zoonosis in humans, usually with limited distribution, rarely with a widespread distribution. Outbreaks in swine are common and cause significant economic losses in industry, primarily by causing stunting and extended time to market. For example, this disease costs the British meat industry about £65 million every year
The H1N1 form of swine flu is one of the descendants of the strain that caused the 1918 flu pandemic.[18][19] As well as persisting in pigs, the descendants of the 1918 virus have also circulated in humans through the 20th century, contributing to the normal seasonal epidemics of influenza.[19] However, direct transmission from pigs to humans is rare, with only 12 cases in the U.S. since 2005.[20] Nevertheless, the retention of influenza strains in pigs after these strains have disappeared from the human population might make pigs a reservoir where influenza viruses could persist, later emerging to reinfect humans once human immunity to these strains has waned.[21]
Swine flu has been reported numerous times as a zoonosis in humans, usually with limited distribution, rarely with a widespread distribution. Outbreaks in swine are common and cause significant economic losses in industry, primarily by causing stunting and extended time to market. For example, this disease costs the British meat industry about £65 million every year
1918 pandemic in humans
The 1918 flu pandemic in humans was associated with H1N1 and influenza appearing in pigs;[19] this may reflect a zoonosis either from swine to humans, or from humans to swine. Although it is not certain in which direction the virus was transferred, some evidence suggests that, in this case, pigs caught the disease from humans.[16] For instance, swine influenza was only noted as a new disease of pigs in 1918, after the first large outbreaks of influenza amongst people.[16] Although a recent phylogenetic analysis of more recent strains of influenza in humans, birds, and swine suggests that the 1918 outbreak in humans followed a reassortment event within a mammal,[23] the exact origin of the 1918 strain remains elusive.[24] It is estimated that anywhere from 50 to 100 million people were killed worldwide
Influenza A
Swine influenza is known to be caused by influenza A subtypes H1N1,[8] H1N2,[8] H2N3,[9] H3N1,[10] and H3N2.[8] In pigs, three influenza A virus subtypes (H1N1, H1N2, and H3N2) are the most common strains worldwide.[11] In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.[12]
Surveillance
Although there is no formal national surveillance system in the United States to determine what viruses are circulating in pigs,[13] there is an informal surveillance network in the United States that is part of a world surveillance network.
Veterinary medical pathologist, Tracey McNamara, set up a national disease surveillance system in zoos because the zoos do active disease surveillance and many of the exotic animals housed there have broad susceptibilities. Many species fall below the radar of any federal agencies (including dogs, cats, pet prairie dogs, zoo animals, and urban wildlife), even though they may be important in the early detection of human disease outbreaks.
Veterinary medical pathologist, Tracey McNamara, set up a national disease surveillance system in zoos because the zoos do active disease surveillance and many of the exotic animals housed there have broad susceptibilities. Many species fall below the radar of any federal agencies (including dogs, cats, pet prairie dogs, zoo animals, and urban wildlife), even though they may be important in the early detection of human disease outbreaks.
Influenza C
Influenza C viruses infect both humans and pigs, but do not infect birds.[4] Transmission between pigs and humans have occurred in the past.[5] For example, influenza C caused small outbreaks of a mild form of influenza amongst children in Japan[6] and California Due to its limited host range and the lack of genetic diversity in influenza C, this form of influenza does not cause pandemics in humans.
Swine influenza
Swine influenza (also called swine flu, hog flu, and pig flu) is an infection by any one of several types of swine influenza virus. Swine influenza virus (SIV) is any strain of the influenza family of viruses that is endemic in pigs.[2] As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3.
Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked.
During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.
Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked.
During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of influenza and of influenza-like illness in general, namely chills, fever, sore throat, muscle pains, severe headache, coughing, weakness and general discomfort.
Classification
Of the three genera of influenza viruses that cause human flu, two also cause influenza in pigs, with influenza A being common in pigs and influenza C being rare.[3] Influenza B has not been reported in pigs. Within influenza A and influenza C, the strains found in pigs and humans are largely distinct, although due to reassortment there have been transfers of genes among strains crossing swine, avian, and human species boundaries.
Tuesday, September 1, 2009
When will the vaccine be available?
As of now, it looks as though vaccination for high-risk groups will begin in mid- to late October. Once the high-risk groups have been immunized, vaccination of the general population will begin, most likely in November or early December. Announcements regarding when and where to get the vaccine will be made on a regular basis this fall, so pay close attention to your news sources for updated information
What is the typical incubation period of swine flu?
This is difficult to estimate, but it appears that it takes one to three days for symptoms to develop after exposure to the virus. Remember that the most important thing is what you do after you feel the first symptoms: Stay home and limit your contact with people, practice good cough and sneeze hygiene (cough or sneeze into disposable tissues or your sleeve) and wash your hands and the surfaces you come in contact with frequently.
I got a swine flu vaccine in 1976. Am I protected from this strain?
No, you are not. The 1976 and 2009 H1N1 viruses are different, and the immune responses from the 1976 vaccine lasted only about a year.
Swine Flu
In the Health section's special report on swine flu last week, we posed some common questions to Andrew Pekosz, an associate professor of molecular microbiology and immunology at Johns Hopkins University's Bloomberg School of Public Health in Baltimore. As readers submit further questions, he will continue to offer answers.
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