27 April 2009
Swine influenza frequently asked questions
• What is swine influenza?
• What are the implications for human health?
• Where have human cases occurred?
• How do people become infected?
• Is it safe to eat pork and pork products?
• Which countries have been affected by outbreaks in pigs?
• What about the pandemic risk?
• Is there a human vaccine to protect from swine influenza?
• What drugs are available for treatment?
• What should I do if I am in regular contact with pigs?
• How can I protect myself from getting swine influenza from infected
people?
• What should I do if I think I have swine influenza?
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.
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.
Where have human cases occurred?
Since the implementation of IHR(2005)1 in 2007, WHO has been notified of
swine influenza cases from the United States and Spain.
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.
Is it safe to eat pork 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°F/70°C, corresponding to the general guidance for the
preparation of pork and other meat.
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.
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.
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.
What drugs are available for treatment?
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 treatment. The viruses obtained from the recent human
cases with swine influenza in the United States are sensitive to oselatmivir
and zanamivir but resistant to amantadine and remantadine.
Information is insufficient to make recommendation on the use of the
antivirals in treatment of swine influenza virus infection. Clinicians have to
make decisions based on the clinical and epidemiological assessment and
harms and benefit of the treatment of the patient2. 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 of the disease based on the virus’s susceptibility profile.
What should I do if I am in regular contact with pigs?
Even though there is no clear indication that the current human cases with
swine influenza infection are related to recent or ongoing influenza-like
disease events in pigs, it would be advisable to minimize contact with sick
pigs and report such animals to relevant animal health authorities.
Most people are infected through prolonged, close contact with infected pigs.
Good hygiene practices are essential in all contact with animals and are
especially important during slaughter and post-slaughter handling to prevent
exposure to disease agents. Sick animals or animals that died from disease
should not be undergoing slaughtering procedures. Follow further advice
from relevant national authorities.
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°F/70°C corresponding to the general guidance for the
preparation of pork and other meat.
How can I protect myself from getting swine influenza from infected
people?
In the past, human infection with swine influenza was generally mild but is
known to have caused severe illness such as pneumonia for the current
outbreaks in the United States and Mexico however, the clinical pictures
have been different. None of the confirmed cases in the United States have
had the severe form of the disease and the patients recovered from illness
without requiring medical care. In Mexico, some patients reportedly had the
severe form of the disease.
To protect yourself, practice general preventive measures for influenza:
• Avoid close contact with people who appear unwell and who have fever
and cough.
• Wash your hands with soap and water frequently and thoroughly.
• Practice good health habits including adequate sleep, eating nutritious
food, and keeping physically active.
If there is an ill person at home:
• Try to provide the ill person a separate section in the house. If this is
not possible, keep the patient at least 1 meter in distance from others.
• Cover mouth and nose when caring for the ill person. Masks can be
bought commercially or made using the readily available materials as
long as they are disposed of or cleaned properly.
• Wash your hands with soap and water thoroughly after each contact
with the ill person.
• Try to improve the air flow in the area where the ill person stays. Use
doors and windows to take advantage of breezes.
• Keep the environment clean with readily available household cleaning
agents.
If you are living in a country where swine influenza has caused disease in
humans, follow additional advice from national and local health authorities.
What should I do if I think I have swine influenza?
If you feel unwell, have high fever, cough and/or sore throat:
• Stay at home and keep away from work, school or crowds as much as
possible.
• Rest and take plenty of fluids.
• Cover your mouth and nose with disposable tissues when coughing
and sneezing and dispose of the used tissues properly.
• Wash your hands with soap and water frequently and thoroughly,
especially after coughing or sneezing.
• Inform family and friends about your illness and seek help for
household chores that require contact with other people such as
shopping.
If you need medical attention:
• Contact your doctor or healthcare provider before travelling to see
them and report your symptoms. Explain why you think you have
swine influenza (for example, if you have recently travelled to a
country where there is a swine influenza outbreak in humans). Follow
the advice given to you for care.
• If it is not possible to contact your healthcare provider in advance,
communicate your suspicion of having swine influenza immediately
upon arrival at the healthcare facility.
• Take care to cover your nose and mouth during travel.
