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    Influenza (Flu)

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    Hager
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    عدد المساهمات : 5
    تاريخ التسجيل : 03/01/2010

    Influenza (Flu)

    مُساهمة  Hager في الأربعاء 6 يناير 2010 - 17:27

    Influenza
    (Flu
    )



    of several types of swine influenza virus. Swine influenza
    virus
    (SIV) or S-OIV (swine-origin influenza virus) 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



    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. 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 because of reassortment
    there have been transfers of genes among strains crossing swine, avian, and
    human species boundaries.




    Influenza C



    Influenza C viruses
    infect both humans and pigs, but do not infect birds. Transmission between pigs
    and humans have occurred in the past For example, influenza C caused small
    outbreaks of a mild form of influenza amongst children in Japan and California.
    Because of its limited host range and the lack of genetic diversity in
    influenza C, this form of influenza does not cause pandemics in humans.



    Influenza A



    Swine influenza is known
    to be caused by influenza A subtypes H1N1, H1N2,
    H2N3, H3N1, and H3N2. In pigs, three
    influenza A virus subtypes (H1N1, H1N2, and H3N2) are the most common strains
    worldwide. 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.



    Surveillance



    Although there is no
    formal national surveillance system in the United
    States to determine what viruses are circulating in pigs,
    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.



    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. The first
    identification of an influenza virus as a cause of disease in pigs occurred
    about ten years later, in 1930. 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.



    The H1N1 form of swine flu is
    one of the descendants of the strain that caused the 1918 flu
    pandemic
    . 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. However, direct transmission from
    pigs to humans is rare, with only 12 cases in the U.S. since 2005. 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.



    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 1918 flu
    pandemic
    in humans was associated with H1N1 and influenza appearing
    in pigs; this may reflect a zoonosis either from swine to humans, or from
    humans to



    1976 U.S. outbreak 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. Genetic components of these 1998
    triple-hybrid stains would later form six out of the eight viral gene segments
    in the 2009 flu outbreak.2007 Philippine
    outbreak in swine



    Transmission between pigs



    Influenza is quite
    common in pigs, with about half of breeding pigs having been exposed to the
    virus in the US Antibodies to the virus are also common in pigs in other
    countries.



    The main route of
    transmission is through direct contact between infected and uninfected animals.
    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. 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. The virus usually spreads quickly through
    a herd, infecting all the pigs within just a few days. Transmission may also
    occur through wild animals, such as wild boar,
    which can spread the disease between farms.





    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. Vaccination of these workers against influenza and surveillance
    for new influenza strains among this population may therefore be an important
    public health measure. 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. 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. 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



    Interaction with avian
    H5N1 in pigs
    In swine Pigs are unusual as they can be infected with
    influenza strains that usually infect three different species: pigs, birds and
    humans This makes pigs a host where influenza viruses might exchange producing
    new and dangerous strains 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. H3N2
    evolved from H2N2
    by antigenic shift. In August 2004, researchers in
    China
    found H5N1
    in pigs.



    In pigs influenza infection produces fever, lethargy,
    sneezing,
    coughing,
    difficulty
    breathing
    and decreased appetite In some cases the infection can
    cause abortion.
    Although mortality is usually low (around 1–4%), the virus can produce weight loss
    and poor growth,
    causing economic loss to farmers. Infected pigs can lose up to 12 pounds
    of body weight over a 3 to 4 week period.



    In human









    Main symptoms of swine flu in human



    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. Of
    these six people, one was pregnant, one had leukemia,
    one had Hodgkin disease and two were known to be
    previously healthy. 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.



    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.



    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 Swine
    flu cannot be spread by pork products, since the virus is not transmitted through
    food. 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.


    Treatment



    In swine





    As swine influenza is rarely fatal to pigs, little treatment beyond
    rest and supportive care is required Instead veterinary efforts are focused on
    preventing the spread of the virus throughout the farm, or to other farms.
    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.


    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. The virus isolates in the 2009
    outbreak have been found resistant to amantadine
    and rimantadine.



    In the U.S., on April 27, 2009, the 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.



      الوقت/التاريخ الآن هو الخميس 23 نوفمبر 2017 - 15:03