Swine influenza frequently asked questions
27 April 2009
What is swine
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
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
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.
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
What about the
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
Most of the previously reported swine influenza cases recovered fully
from the disease without requiring medical attention and without
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
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
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 160oF/70oC 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
• 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
• 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
If you are living in a country where swine influenza has caused disease
in humans, follow additional advice from national and local health
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
• 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
If you need
• 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.