Swine
Influenza
Frequently
Asked Questions
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| What
is swine influenza?
Swine influenza, or ¡°swine flu¡±, is a highly contagious
acute respiratory disease of pigs, caused by one of several
swine influenza A viruses. Morbidity tends to be high and mortality
low (1-4%). The virus is spread among pigs by aerosols, direct
and indirect contact, and asymptomatic carrier pigs. Outbreaks
in pigs occur year round, with an increased incidence in the
fall and winter in temperate zones. Many countries routinely
vaccinate swine populations against swine influenza.
Swine influenza viruses are most commonly of the H1N1 subtype,
but other subtypes are also circulating in pigs (e.g., H1N2,
H3N1, H3N2). Pigs can also be infected with avian influenza
viruses and human seasonal influenza viruses as well as swine
influenza viruses. The H3N2 swine virus was thought to have
been originally introduced into pigs by humans. Sometimes pigs
can be infected with more than one virus type at a time, which
can allow the genes from these viruses to mix. This can result
in an influenza virus containing genes from a number of sources,
called a "reassortant" virus. Although swine influenza
viruses are normally species specific and only infect pigs,
they do sometimes cross the species barrier to cause disease
in humans. |
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What
are the implications for human health?
Outbreaks and sporadic human infection with swine influenza
have been occasionally reported. Generally clinical symptoms
are similar to seasonal influenza but reported clinical presentation
ranges broadly from asymptomatic infection to severe pneumonia
resulting in death.
Since typical clinical presentation of swine influenza infection
in humans resembles seasonal influenza and other acute upper
respiratory tract infections, most of the cases have been detected
by chance through seasonal influenza surveillance. Mild or asymptomatic
cases may have escaped from recognition; therefore the true
extent of this disease among humans is unknown.
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Where
have human cases occurred?
Since the implementation of IHR(2005) <International Health
Regulation(2005)> in 2007, WHO has been notified of swine
influenza cases from the United States and Spain. |
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How
do people become infected?
People usually get swine influenza from infected pigs, however,
some human cases lack contact history with pigs or environments
where pigs have been located. Human-to-human transmission has
occurred in some instances but was limited to close contacts
and closed groups of people. |
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Is
it safe to eat pork meat and pork products?
Yes.
Swine influenza has not been shown to be transmissible to people
through eating properly handled and prepared pork (pig meat)
or other products derived from pigs. The swine influenza virus
is killed by cooking temperatures of 160¡ãF/70¡ãC, corresponding
to the general guidance for the preparation of pork and other
meat. |
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Which
countries have been affected by outbreaks in pigs?
Swine influenza is not notifiable to international animal health
authorities (OIE, www.oie.int), therefore its international
distribution in animals is not well known. The disease is considered
endemic in the United States. Outbreaks in pigs are also known
to have occurred in North America, South America, Europe (including
the UK, Sweden, and Italy), Africa (Kenya), and in parts of
eastern Asia including China and Japan. |
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What
about the pandemic risk?
It is likely that most of people, especially those who do not
have regular contact with pigs, do not have immunity to swine
influenza viruses that can prevent the virus infection. If a
swine virus establishes efficient human-to-human transmission,
it can cause an influenza pandemic. The impact of a pandemic
caused by such a virus is difficult to predict: it depends on
virulence of the virus, existing immunity among people, cross
protection by antibodies acquired from seasonal influenza infection
and host factors.
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Is
there a human vaccine to protect from swine influenza?
There are no vaccines that contain the current swine influenza
virus causing illness in humans. It is not known whether current
human seasonal influenza vaccines can provide any protection.
Influenza viruses change very quickly. It is important to develop
a vaccine against the currently circulating virus strain for
it to provide maximum protection to the vaccinated people. This
is why WHO needs access to as many viruses as possible in order
to select the most appropriate candidate vaccine virus. |
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What
drugs are available for treatment?
Antiviral drugs for seasonal influenza are available in some
countries and effectively prevent and treat the illness. There
are two classes of such medicines, 1) adamantanes (amantadine
and remantadine), and 2) inhibitors of influenza neuraminidase
(oseltamivir and zanamivir).
Most of the previously reported swine influenza cases recovered
fully from the disease without requiring medical attention and
without antiviral medicines.
Some influenza viruses develop resistance to the antiviral medicines,
limiting the effectiveness of chemoprophylaxis and treatment.
The viruses obtained from the recent human cases with swine
influenza in the United States were sensitive to oselatmivir
and zanamivir but resistant to amantadine and remantadine.
Information is insufficient to make recommendation on the use
of the antivirals in prevention and treatment of swine influenza
virus infection. Clinicians have to make decisions based on
the clinical
and epidemiological assessment and harms and benefit of the
prophylaxis/treatment of the patient. For the ongoing outbreak
of the swine influenza infection in the United States and Mexico,
the national and the local authorities are recommending to use
oseltamivir or zanamivir for treatment and prevention of the
disease based on the virus¡¯s susceptibility profile.
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¡î Above information was quoted
from WHO OFFICIAL WEBSITE
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