A backgrounder on swine influenza put together by the Science Media Centre in London.
What is it?
· Swine flu is a highly contagious acute respiratory disease affecting pigs, caused by one of several influenza A viruses
· Four subtypes of the virus have been identified: H1N1, H1N2, H3N2, and H3N1, though most recently identified cases have been of the H1N1 type
· H1N1 has been shown to be common throughout pig populations worldwide – studies have shown that between around 30-50% of pigs in the north central US show evidence of infection by H1N1
· Outbreaks occur in pig herds all year round, with increased incidence in autumn and winter and after the introduction of new pigs to herds
· The virus causes high rates of illness and low rates of mortality (1-4%)
Does it affect humans?
· Swine flu viruses do not normally infect humans, and H1N1 infections in humans are rare.
· However, some infections have occurred, usually in people who work in close proximity to pigs
· The extent of swine flu infection among humans is unknown, as many cases resemble normal human flu or are asymptomatic and thus go undetected
How does it spread?
· The virus spreads among pigs through both direct contact (animal-to-animal) and indirect contact (via contaminated objects and surfaces)
· It can be spread between humans and pigs, most likely to people who have been in close physical proximity to pigs (such as livestock workers)
· It can also spread between humans, in a similar manner to human seasonal influenza (via direct contact and contaminated surfaces – doorknobs, etc.)
· Viruses can survive for up to 2 hours on contaminated surfaces – frequent handwashing can reduce risk of contamination from these sources
· Swine flu viruses are not transmitted by food – you cannot get swine flu from eating pork or pork products
What are the symptoms?
· In pigs: sudden onset of fever, depression, barking cough, discharge from nose or eyes, sneezing, breathing difficulties, eye redness or inflammation, going of feed
· In humans: similar to regular flu – fever, cough, sore throat, aches and pains, chills, fatigue. Diarrhoea and vomiting have also been reported
· Severity in humans can vary from asymptomatic infection to severe, sometimes fatal pneumonia
What treatments are available?
· Two antiviral treatments are available in the US and are recommended by CDC: oseltamivir and zanamivir
· Antivirals work by preventing the virus from reproducing in the body. They have greatest benefit when given within two days of onset of symptoms
Is there a vaccine?
· There are no swine flu vaccines currently available for humans, as the swine flu virus is genetically very different from that which affects humans
· Vaccines for human seasonal flu do not protect against swine flu for the same reason
Sources / further information
New Zealand Ministry of Health
World Health Organisation:
US Centers for Disease Control and Prevention:
American Veterinary Medical Association
Center for Infectious Disease Research & Policy has current updates: