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.
How do I protect myself?
The flu virus can live on a hard surface for up to 24 hours, and a soft surface
for around 20 minutes. The main way to protect oneself from infection is frequent
hand washing, effective surface disinfection in your environment, and avoid
contact with people who display flu-like symptoms.
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 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°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?
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.