Swine influenza: how to spot the disease

How to spot swine influenza in pigs and humans, and what to do to prevent it and control its spread.

Applies to England, Scotland and Wales

Swine influenza is a disease of pigs caused by influenza viruses.

There are many different types of influenza viruses. They can also affect humans and birds, though these strains of the virus are usually different from those that affect pigs.

Swine influenza is present in pigs in most countries around the world, including the UK.

Pigs can carry many different types of the disease.

Swine influenza should not be confused with either classical swine fever or African swine fever, which are different diseases.

Swine influenza is not a notifiable disease but if you spot signs of this disease in animals you should contact your vet.

How to spot swine influenza

Swine flu infection usually results in respiratory disease.

The severity of the disease depends on the strain of virus involved and the age of the affected pigs.

The clinical signs can include:

  • sneezing, coughing and difficulty breathing
  • abortions (in some cases)
  • increased discharge from eyes or nose
  • high temperature
  • loss of appetite
  • weakness
  • swollen and red eyes

The disease can affect many pigs in a herd at the same time, but not all of them will show signs of illness.

Pigs are unlikely to die from swine influenza, unless they are very young or have other infections. Infected animals will usually recover in 5 to 7 days.

If infected pigs are suffering from other respiratory diseases, the symptoms may be worse and they may take longer to recover.

Risk to humans

Swine influenza may occasionally pass to humans, but this depends on the strain of the virus.

It causes similar symptoms to a seasonal flu. It is not usually a life-threatening illness.

If you or your employees work with pigs, you should read the Health and Safety Executive’s guide to zoonoses (animal diseases which can affect humans).

How swine influenza spreads

The infection is spread through direct contact between pigs.

When infected pigs sneeze or cough, they can spread the disease to nearby pigs.

The virus may survive in carrier pigs for several weeks without them showing any clinical signs. These carrier pigs can then be a source of infection for other pigs.

It can also be spread by wild animals and birds or indirectly via contaminated equipment, clothing, feed or water.

Preventing swine influenza

Follow the influenza in pigs code of practice (PDF, 315 KB, 13 pages) to reduce the risk of your animals getting infected and to minimise the spread of the disease.

You can also help prevent swine influenza by practising strict biosecurity on your premises.

Some other viral and bacterial pig diseases may cause similar disease signs, so a laboratory diagnosis may be required to confirm swine flu.

If you suspect swine influenza, you should talk to your vet.

They can arrange to have samples tested for swine influenza by the Animal and Plant Health Agency (APHA).

Published 26 August 2014
Last updated 27 November 2023 + show all updates
  1. Updated the section 'Preventing swine influenza'. Updated the link to the influenza in pigs code of practice.

  2. AHVLA documents have been re-assigned to the new Animal and Plant Health Agency (APHA).

  3. First published.