Swine Influenza or ‘flu’
Swine Influenza is a virus more commonly known as flu. The virus affects both humans and animals, and can be introduced by infected people, pigs who are ‘carriers’ of the virus and water birds.
Signs of Swine Influenza
The signs of Swine Influenza can be sudden and severe. Incubation is less than 48 hours and pigs often appear fine one day and are found prostrate and breathing heavily the next. However, mortality is low, and recovery is usually swift. In sows you may also see high temperatures which could cause abortions and other reproductive problems. Piglets are unlikely to be affected – this is believed to be due to the protective antibodies in their mother’s colostrum. Outbreaks are seen throughout the year but peak in the winter months.
Once infected, pigs often recover without intervention within two to six days, if no other pig respiratory disease is present. However, when combined with other infections such as Porcine Pleuropneumonia or Porcine Reproductive and Respiratory Syndrome (PRRS) a chronic respiratory disease syndrome can develop. The strain of the virus and the immune status of the herd also influence the severity of the infection.
Swine Influenza may be responsible for continuing pig respiratory disease with milder clinical signs – particularly in small groups of weaners.
Treatment of Swine Influenza
There is no treatment specifically for Swine Influenza, however antibiotic cover may be necessary to prevent or treat secondary bacterial infections.
To prevent Swine Influenza and other pig respiratory disease, a proactive approach to animal health is recommended. This includes biosecurity and following general good management procedures. Inactivated vaccines are available to protect against swine influenza.
Understanding the virus
Influenza A viruses infect a wide range of avian and mammalian species, with the latter group including man, pigs, horses and aquatic mammals. Type A viruses are known for their ability to change their antigenic structure and create new strains.
The type A viruses are further divided into serotypes, or variations, based on the antigenic nature of their surface glycoproteins haemagglutinin and neuraminidase. The three common strains that affect the pig are described as H1 N1, H1 N2, and H3 N2. There are also different strains within these serotypes varying in pathogenicity.
Swine Influenza is endemic worldwide. It is virtually impossible to maintain a population of pigs that is influenza virus free. In large herds influenza may continue to occur with intermittent bouts of disease and infertility due to different influenza strains circulating. Immunity to influenza viruses can last as little as six months and the immunity profile in the breeding herd varies considerably with time.
Public health implications
Pigs might be responsible for the transmission of influenza viruses to humans in the following ways:
- Directly transferring avian influenza viruses to humans.
- Acting as an intermediate host and ‘mixing pot’ for genetic re-assortment between human and avian viruses. This can cause a new strain of virus transmissible to humans.
- Be responsible for the re-emergence of a virus that caused an epidemic previously. Pigs can act as reservoir for old human influenza viruses.