Disease: (Swine) brucellosis

This page provides general information about  this condition; reveal the text by clicking on  the green headers. Press releases, results from DWHC investigations as well as other useful documents and relevant literature can be found at the bottom of the page.

Pathogen

Brucellosis is the disease caused by infection with members of the Brucellaceae family of bacteria. Brucella suis is the cause of brucellosis in wild and domestic swine and is can also cause disease in humans (zoonotic).

Susceptible species

There are 5 strains of B. suis and these strains can affect other animals in addition to domestic and wild swine. Biovar 1 is seen in feral pigs in America and Australia; biovar 2 is found predominantly in wild boar and hares in Europe; biovar 3 is restricted to pigs in South East Asia (where the bacteria has not been eradicated from domestic pigs) and in America; biovar 4 (also known as rangiferine brucellosis) occurs predominantly in reindeer and caribou (and less in swine); and in Eastern Europe, biovar 5 (also known as murine brucellosis) is found in rodents.

Other species of Brucella can cause disease in cattle (B. abortus); sheep and goats (B.melitensis, and ovis); and, dogs (B. canis). Although they are generally not seen in wildlife there have been reports of B. melitensis infection in European chamois and infection with B. abortus, suis and the recently identified genus B. microti in foxes and voles. To date, B. neotomae has only been seen in desert rats in the United States.

Recently brucellosis has been identified in sea mammals, with the detection of two ‘novel’ species; B. ceti in dolphins, whales and porpoises and B.pinnipedialis seals.

Excepting B. ovis, all have the potential to cause disease in humans.

 

Signs in animals

In pigs, clinical signs are usually abortion and the birth of weak or still-born piglets. Sows may develop infection of the uterus and in boars testicular infection can occur. Less commonly abscess formation and swollen joints can be seen. Whilst some animals recover, others may remain persistently infected.

Similar signs, in the reproductive organs and around the joints may be seen in wildlife with brucellosis. For example, abortion and mastitis is seen in reindeer and caribou infected with biovar 4. Hares infected with biovar 2 may develop small abscesses in many organs (particularly the reproductive organs) as well as in the skin and muscle.

Infection of animals

In pigs, B. suis  occurs in the fetus and placental tissues, typically resulting in abortion; transmission can occur via ingestion of, and to a lesser extent via mucous membranes that come into contact with, aborted material and vaginal secretions. Venereal transmission in the semen of infected boars is also reported. The bacteria survives freezing and drying and can also survive in organic matter so transmission can also occur indirectly via contaminated feed, bedding and water.

Symptoms in people

Brucellosis infection in humans,can be caused by any of the members of the Brucellaceae and can cause serious illness although signs are  non-specific. Clinical signs of human brucellosis include recurrent fever and chills, joint and muscle pain, night sweats, headaches and general fatigue.

Infection of people

People can become infected with Brucella bacteria via direct contact with infected animals (typically with aborted fetal material), inhalation of bacteria-containing droplets in the air or consumption of contaminated (unpasteurized) dairy or meat (under-cooked) products.

Geographical distribution

Whilst B. suis has been eradicated from domestic pig populations in many countries including the United States, Canada and some European countries it persists in wild swine in some areas and this can sometimes result in outbreaks occurring in pig herds and humans. Whilst biovars 1 and 3 have a worldwide distribution, biovar 2 is predominantly found in European wild boar populations. Biovars 4 and 5 are restricted to Arctic regions and Eastern Europe, respectively.

Preventative measures

It is not clear as to whether cases of wildlife brucellosis arise from a sustained infection within wildlife populations or from new infections following contact with domestic livestock. Even in countries in which livestock is considered to be brucellosis-free, outbreaks of this disease can occur. People that may be exposed to infected animals in their work (abattoir workers, butchers, farmers, hunters, vets, laboratory staff) should be vigilant for signs of disease and work in a hygienic manner.

 

References

  1. Center for Food Security and Public Health, Iowa state University Veterinary Medical School, Brucella Factsheet
  2. J. Godfroid, B. Garin-Bastuji, C. Saegerman & J.M. Blasco. Brucellosis in terrestrial wildlife. Rev. sci. tech. Off. int. Epiz., 2013, 32 (1), 27-42

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