Swine influenza virus

Swine influenza (SI) viruses infect a wide range of hosts, but are endemic in pigs. SI viruses are members of the family Orthmyxoviridae, and fall into the Type A and C categories. These are subdivided into categories (strains) depending on the outer proteins H (Haemagglutinin) and N (Neuraminidase). These outer proteins can be combined to create different strains, for example H1N1, H1N2. Influenza viruses have a single stranded RNA genome that is spilt into eight different segments.

  • Swine influenza is a notifiable disease and should be reported.
    Please see the Defra website for advice on how to spot and report the disease.

Associated diseases:

SI is highly infectious in pigs although the levels of mortality are low. It can also be transferred to humans, for example in 2009 the H1N1 strain caused an outbreak which spread globally, killing over 18,000 people.

Clinical signs:

  • Fever
  • Lethargy
  • Sneezing
  • Coughing
  • Difficulty breathing
  • Decreased appetite
  • In some cases the infection can cause abortion
  • Weight loss
  • Poor growth

Disease transmission:

The disease spreads by direct contact or through contaminated faeces and body fluids. New SI virus strains are created frequently which means that there is a constant risk that one of the new strains may spread easily among people. Thankfully no recent strains of SI have been proven to spread between people, only from pigs to people.

Disease prevalence:

Outbreaks of SI occur regularly during the winters of North America and Europe. They have also been reported in South Africa, Kenya, India, China, Hong Kong, Japan, Singapore and South America.

Impact for Society – what are we doing?

Influenza viruses are a major threat to health in livestock and humans. Weight loss and poor growth can cause economic loss to farmers as infected pigs can lose up to 12 pounds of body weight over a three to four week period. SI viruses are implicated in human influenza as sources of new influenza strains that are transmitted to humans by occupational exposure. Groups at the Institute are therefore researching how the immune system protects against SI and using this information to develop a 'universal' vaccine. It is hoped this vaccine will be able to protect against all strains of SI.


Downloadable factsheet

* Image by C. Goldsmith and D. Rollin courtesy of Public Health Image Library (PHIL)

Research papers

Martini V, Edmans M, Gubbins S, Jayaraman S, Paudyal B, Morgan S, McNee A, Morin T, Rijal P, Gerner W, Sewell A K, Inoue R, Bailey M, Connelley T, Charleston B, Townsend A, Beverley P, Tchilian E (2022)

Mucosal Immunology 15 (3) , 428-422
Paudyal B, McNee A, Rijal P, Carr B V, Nunez A, McCauley J, Daniels R S, Townsend A R, Hammond J A, Tchilian E (2021)

Frontiers in Immunology 12 , 790918
Chrun T, Maze E A, Vatzia E, Martini V, Paudyal B, Edmans M D, McNee A, Manjegowda T, Salguero F J, Wanasen N, Koonpaew S, Graham S P, Tchilian E (2021)

Frontiers in Immunology 12 , 758368
Vatzia E, Allen E R, Manjegowda T, Morris S, McNee A, Martini V, Kaliath R, Ulaszewska M, Boyd A, Paudyal B, Carr V B, Chrun T, Maze E, MacLoughlin R, van Diemen P M, Everett H E, Lambe T, Gilbert S C, Tchilian E (2021)

Frontiers in Immunology 12 , 763912


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