Swine influenza: how to spot and report the disease

Advice on what to do if you suspect there is an outbreak of this infectious disease.    

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Swine influenza (swine flu) in pigs is an acute, highly contagious, respiratory disease that results from infection with type A influenza virus.

H1N1, H3N2 and H1N2 are the most commonly found serotypes, but pigs can be infected by other subtypes. The disease in pigs occurs commonly in the mid-western USA (and occasionally in other states), Mexico, Canada, South America, Europe, and parts of eastern Asia.

Swine influenza is not notifiable because it causes transient infection with low mortality in pigs.

Latest situation: there are no reports of swine flu in pigs in Scotland.

Clinical signs

Symptoms are often sudden in onset. Pigs of all ages can be affected, although pigs with immunity from previous exposure to influenza, maternal immunity to vaccination often do not show symptoms. Recovery generally takes five to seven days and the mortality rate is very low unless another infection is present and or very young pigs are affected. In severe cases, some pigs can have difficulty breathing, especially if they are forced to move.

Classical signs of swine influenza in pigs may include:

  • fever
  • dullness and lethargy
  • going off feed
  • coughing and sneezing
  • discharge from the eyes or nose
  • eye redness or inflamation

How swine flu is spread

Usually, an outbreak is preceded by one or two indvidual cases and then spreads rapidly within a herd, mainly by aerosol and pig to pig contact. The virus survives in carrier pigs for up to 3 months.  Whilst other forms of respiratory disease are common in pigs the explosive nature of the diseae should be recognized by alert stockmen and veterinary surgeons.

A classic acute outbreak is characterized by sudden onset and rapid spread through the entire herd, often within 1 to 3 days. The disease usually lasts around 3 to 7 days, with clinical recovery of the herd almost as sudden as the onset. Some pigs may become chronically affected.  

Human health implications

Swine influenza viruses are not transmitted through properly cooked food.

Code of practice

A code of practice for Swine Influenza in pigs has been produced by Government and Industry for Pig Keepers.


Biosecurity is about being aware of the ways disease can spread and taking every practical measure to minimise the risk of disease spreading. The advice details practical things you can do on your farm to help prevent the introduction and spread of swine flu to and from your animals.

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