Learn More About a Disease

Swine influenza (SIV)

Swine flu, or swine influenza, is a respiratory disease that infects pigs and is caused by the influenza virus. An estimated 25% of animals are affected worldwide. The morbidity rate is high, but the mortality rate is low (less than 1 to 2%). The most common swine flu viruses belong to subtypes H1N1, H3N2 and H1N2, and pigs can be coinfected with more than one virus subtype at a time. This mixture of different subtypes can lead to the creation of a recombinant virus. Also, genetic drift occurs when the virus multiplies, which means that the new virus is slightly different from the previous one and that, over time, these differences become more marked.

Clinical Signs +

The disease, which is characterized by high fever, cough, anorexia, nasal discharge, conjunctivitis and difficulty breathing, heals on its own within 7 to 10 days. Asymptomatic forms of the disease are common. The virus can also survive in farms, leading to an endemic form of the disease, resulting in recurrent respiratory symptoms. 

Transmission +

The virus is transmitted by direct and indirect contact with animals with the disease or asymptomatic carriers of the disease. It is also airborne. Dissemination within a farm and from one farm to the next is very quick. These viruses usually only affect pigs, but they can sometimes cross the species barrier and cause disease in humans, generally those who come into close contact with pigs. Some cases of person-to-person transmission have also been reported. In 1976, the swine flu was responsible for one human death in the United States. In 2009, the known swine flu strains included type C and type A influenza viruses, in particular, those belonging to subtypes H1N1, H1N2, H3N1, H3N2 and H2N3.

Diagnosis +

The presence of flu syndrome does not necessarily mean that a person has “influenza”. Flu syndrome also occurs in certain viral infections such as the PCV2 or PRRS virus. Modern diagnostic techniques (a combination of histopathology and immunohistochemistry) make it possible to identify the type of virus in question. There is a quick test that can identify the presence of type A influenza virus in nasal secretions.

Treatment +

The administration of antipyretics in water limits the phase during which the pigs do not eat. The use of antibiotics limits the dissemination of concomitant bacteria.

Consult with your veterinarian before administering antibiotics and vaccines to animals.

Your veterinarian is the best person to talk to for recommendations that are right for your farm.

Prevention +

Vaccinating a sow will protect the piglets and, in some cases, eliminate the virus from the herd. Vaccination of fattening pigs must wait until the number of maternal antibodies drops. It is important to use a vaccine that includes the virus subtypes present on the farm. Commercial and autogenous vaccines must be frequently replaced.


1 Maladies d’élevage des porcs (Diseases of Swine), 2nd Edition, Guy Pierre Martineau