Swine influenza (SI)

What is swine influenza?

Swine influenza is a contagious respiratory disease of pigs that occurs worldwide and is caused by infection with influenza A viruses.

Clinical signs

Infection can cause a range of clinical signs in pigs, from sudden onset severe respiratory illness that infects a large number of exposed pigs, often with few deaths, to less severe illness that may be characterised as a chronic respiratory disease syndrome, usually affecting groups of pigs. Breeding pigs can also suffer reproductive problems, and pigs can also be infected and not show signs of illness. Recovery in uncomplicated infections is usually quick, within 10-14 days.

Transmission

Short distance transmission between pigs can occur by droplets generated by infected pigs coughing or sneezing, by direct or indirect contact or by the movement and introduction of infected pigs not showing clinical signs.

Other factors, such as the presence of other infections, can also make disease appear more severe or seem to last longer.

The virus is normally found in pigs but human cases can and do happen. The current human influenza pandemic, caused by pandemic (H1N1) 2009 virus, was first reported in Mexico and the USA in April 2009, followed by rapid global spread. Transmission between people is thought to occur in the same way as seasonal flu.

Origins of pandemic (H1N1) 2009 virus

The pandemic (H1N1) 2009 virus causing the problem in people has genetic material from pig, bird and human influenza viruses. More is of pig origin and therefore people refer to it as ‘swine flu’. The World Health Organization (WHO) has named the virus 'pandemic (H1N1) 2009 virus'.

VLA's role

The VLA is an international reference laboratory for animal influenza for the World Organization for Animal Health (OIE), and has 35 years of experience on animal influenza viruses. VLA has various national and international programmes on the diagnosis, research and surveillance of influenza in pig populations.

We also have a close working relationship with the Health Protection Agency (HPA) on viruses that can infect animals and people and we have been providing information and reagents to HPA to support their response to the human pandemic.

VLA information