This disease affects all age groups. The key clinical signs include abortions; vulval discharges with pus or occasionally blood; swollen testicles. This disease is notifiable – contact your vet and local authorities if you believe this disease is affecting your herd.
calendar icon 13 November 2018
clock icon 10 minute read

Background and history

This disease is caused by the bacterium Brucella suis, which is one of the six different species of brucella. B. 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. Pigs can also be infected via the conjunctiva, through the nose or by mouth.

When a female becomes infected, the organism is plentiful in the blood, causing a bacteraemia, which persists over a period of 3–6 weeks. It is during this period of time that the organism establishes itself in the placenta, causing inflammation and ultimately abortion. B. suis infects the testicles and accessory reproductive glands, and can be excreted via semen.

The hare in Northern Europe can also be infected and is considered a natural host. Biotype 4 is enzootic in reindeer and caribou in Siberia, Alaska and Canada. Type 4 is thought not to be very pathogenic to pigs.

B. suis is not a highly epizootic infectious organism like, say, transmissible gastro enteritis (TGE) or foot-and-mouth disease (FMD). It spreads slowly between and within herds and you should be able to keep it out of your herd if you take sensible precautions. But it should always be considered a serious disease.

If it gets into your herd, it is difficult to eliminate. It causes long term reproductive losses and some biotypes (1 and 3 particularly) also cause severe disease in people.

Human health

Brucellosis in people, also called undulant fever, is a serious long-lasting disease which does not respond well to treatment. Infected people get recurrent attacks of clinical disease over many years. It causes a variety of symptoms including severe headaches, meningitis and bad dreams, severe back-ache, depression and lack of energy and interest, damaged testicles and changes of personality. It is therefore essential that if the organism infects your herd, you take every precaution against people becoming infected.

  • Wear protective clothing and take it off and wash your hands before eating.
  • Wear rubber gloves when handling affected pigs or infected materials.
  • Protect your eyes against splashing infected materials into them.
  • Do not touch your eyes or put your fingers or any instruments on or in your mouth when working with affected pigs.
  • Protect any bare skin on your arms or face that might have cuts and abrasions.
  • Get rid of the disease as soon as possible.

Clinical signs


  • Bacteraemia (bacteria in the blood).
  • Infertility.
    • The infection in the sows' reproductive tracts is not permanent and eventually clears up spontaneously.


  • Swollen/painful testicles.
    • The infection in the boars' reproductive tract is usually permanent, the damage that it does is irreversible.


  • Paralysis of hind legs.

Weaners and growers

  • Swollen testicles.
  • Lameness.
  • High return to service.
  • Abnormal oestrus.
  • Abortions at any time.
  • Vulval discharges with pus or occasionally blood.
  • Delayed returns.
  • Lameness.


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.

Enzyme-linked immunosorbent assay (ELISAs) and card and plate tests are also used.

The complement fixation test (CFT) is often used in conjunction with the SAT for export testing purposes within the EU.

Best samples to submit are aborted piglets, swabs of vaginal discharges, dead pigs and blood samples from at least 10 sows, preferably from those which have aborted or returned to service.

The most sensitive and accurate laboratory method is to culture and identify the organism on selective medium. The products of abortion are teeming with organisms. The organism can also be cultured from semen, testicles and accessory organs, lymph nodes, fluid from swollen joints and in the early stages, from blood.

It would be risky to carry out a post-mortem to look for lesions. In the early stages of the disease the organism is spread throughout the pig's body. Even in the later stages it is fairly widespread. It can infect you through tiny cuts and abrasions on your hands or by being splashed or rubbed into your eye or mouth.

Standards used with the EU for intra community trade:

  • SAT – More than 31iu classified as a failure.
  • CFT – More than 25iu classified as a failure.


  • Spread by venereal infection.
  • The boar is a major source either by direct contact at mating or via artificial insemination.
  • Via the conjunctiva, through the nose or by mouth.
  • Spread by other carriers (e.g. hare in Northern Europe).
  • Carrier sows.
  • Eating or rooting of aborted piglets, dead piglets, aborted afterbirths or materials contaminated by vaginal discharges from aborted sows.
  • Exposure of cut or abraded skin to infected materials.
  • Suckling sows also shed the organism in milk which then infects their piglets.


  • This is based on identifying herds free from B. suis infection and maintaining them by purchasing pigs only from herds free of disease.
  • Eradication programmes – identifying infected herds and removing them.
  • Serological testing of imported breeding stock.
  • Repeated herd blood tests with removal of positive reactors. This may be effective if only a few pigs are infected but is likely to be unsuccessful if many pigs are positive.


  • Treatment with antibiotics is not very effective and generally should not be attempted.
  • Affected pigs should be destroyed.
  • If your herd becomes infected the most reliable method of control is to slaughter the herd, clean up the premises and restock with brucella-free pigs. This is also the safest procedure from the pig attendants' and public's stand-point and in the long term is usually the least costly. Depending upon the country in which you work, it may mandatory to do so.

Emily Houghton

Editor, The Pig Site

Emily Houghton is a Zoology graduate from Cardiff University and was the editor of The Pig Site from October 2017 to May 2020. Emily has worked in livestock husbandry, and has written, conducted and assisted with research projects regarding the synthesis of welfare and productivity of free-range food species.

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