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This disease is caused by the bacterium Brucella suis, which is one of the six different species of brucella. Brucella suis does not exist in the UK, Ireland and in some other EU countries, Canada and most states of the USA but is widespread through most of the rest of the pig rearing world. It is an important disease not least because some strains of it can be transmitted to people where it can cause serious illness. A carrier state persists for long periods of time.

It can be spread by venereal infection and the boar is a major source either by direct contact at mating or via artificial insemination. The organism can survive outside the pig for long periods of time particularly at or near freezing temperatures. The hare in Northern Europe can also be infected where it is considered a natural host. It can be an important source of infection to the pig.

When a female becomes infected, the organism establishes itself in the placenta, causing inflammation and ultimately abortion. B. suis infects the testicles and accessory reproductive glands of the boar, and can be excreted via semen.


  • Bacteraemia (bacteria in the blood).
  • Infertility.
  • Abnormal oestrus
  • Abortions at any time.
  • Vulval discharges with pus or occasionally blood.
  • Delayed returns.
  • Lameness
  • Swollen/ painful testicles (boar only).
  • Paralysis of hind legs.
Weaners & Growers
  • Swollen testicles.
  • Lameness

Causes / Contributing factors

  • Spread by venereal infection.
  • The boar is a major source either by direct contact at mating or via artificial insemination.
  • Pigs can also be infected via the conjunctiva, through the nose or by mouth.
  • The hare in Northern Europe can also be infected and is considered a natural host.
  • Carrier sows.


This can be readily carried out by isolation of the organism. Serology is used to detect carrier sows but cross reactions can occur quite extensively due to another organism called Yersinia enterocolitica. If the serum agglutination test (SAT) is used results of 31 international units (iu) or more are considered positive. The complement fixation test (CFT) is often used in conjunction with the SAT for export testing purposes.

Further Reading

Click on the links below to find out more about this disease, including treatment, management control and prevention information. The top link is the main article on this disease.