Brucellosis (undulant fever, Malta fever)
Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information
Victorian statutory requirement
Brucellosis (Group B disease) must be notified in writing within five days of diagnosis.
School exclusion is not required.
Infectious agent
The following infectious agents cause brucellosis:
- Brucella abortus (biovars 1–6 and 9)
- Brucella melitensis (biovars 1–3)
- Brucella suis (biovars 1–5)
- Brucella canis
Identification
Clinical features
Brucellosis is a systemic bacterial disease with acute or insidious onset. Localised suppurative infections may occur. Subclinical and unrecognised infections are frequent.
Fever is the most common symptom and may be associated with a variety of other complaints.
Osteoarticular complications are common. Orchitis, epididymitis, osteomyelitis and endocarditis are less common. The case-fatality rate in untreated brucellosis is approximately 2%, mostly due to endocarditis from B. melitensis infections.
Method of diagnosis
Laboratory confirmation of the diagnosis is made by isolating the infectious agent from blood, bone marrow, other tissues or discharges of the patient. Serological testing for Brucella is useful but often difficult to interpret. Current serological tests allow a precise diagnosis in over 95% of cases, but it is necessary to combine a test (Rose Bengal and seroagglutination) detecting agglutinating antibodies (IgM, IgG and IgA) with others detecting non-agglutinating antibodies (Coombs-IgG or ELISA-IgG) developing in later stages. Except in the case of B. canis, where diagnosis requires tests detecting antibodies to rough-lipolysaccharide antigens.
Incubation period
The incubation period is highly variable. It is most commonly one to two months but ranges from five to sixty days.
Public health significance & occurrence
B. abortus was successfully eradicated from Australian cattle herds during the national eradication campaign in 1989. B. suis is still isolated occasionally from feral pigs in Queensland and represents a risk to people who hunt and butcher feral pigs. Notifications of brucellosis in Victoria are now rare and generally represent imported infections or undiagnosed chronic infections.
Brucellosis occurs worldwide. The sources of infection and responsible organism vary according to geographic area. Affected regions include the Mediterranean countries, North and East Africa, Western Africa, the Middle East, India and Central and South America.
Reservoir
The most important reservoirs for human infection are cattle, swine, goats, sheep and dogs. Infections may also occur in other wild ungulates. B. canis has occasionally been identified in laboratory dogs.
Mode of transmission
Brucellosis can be transmitted by contact with infected tissues, blood, urine, vaginal discharges, aborted animal foetuses and especially placentae. It can also be transmitted by ingestion of raw milk and dairy products from infected animals.
Outbreaks are generally attributed to inhalation of aerosols which may occur in animal pens and stables, abattoirs and laboratories, or through ingestion of unpasteurised milk products. A small number of cases have occurred following accidental self-inoculation of the strain 19 animal Brucella vaccine.
Period of communicability
There is no evidence of communicability from person to person.
Susceptibility & resistance
Everyone is susceptible to infection. Severity and duration of clinical illness are subject to wide variation. Duration of acquired immunity is uncertain.
Control measures
Preventive measures
Educate the public, particularly travellers, against drinking unpasteurised milk or eating dairy products produced from such milk. Boiling milk is effective in killing the organisms when pasteurisation is not available.
Educate farmers and handlers of potentially infected animals such as feral pigs to reduce exposure and exercise care in handling placentae, discharges and foetuses. Search for and investigate livestock at risk of infection.
Control of case
Treatment should be age appropriate. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited) and seek expert infectious diseases.
Control of contacts
Although there is no person to person transmission of brucellosis, contact tracing is done as part of the case investigation to identify those people who have been exposed to the same implicated source of Brucella infection as the case. These people are advised of the early signs and symptoms of brucellosis to aid early diagnosis and treatment.
Control of environment
The Department of Primary Industries is notified of any new, non-imported case of brucellosis so that appropriate animal investigations and control measures can commence.
All incriminated products are recalled. Restriction on the distribution of unpasteurised milk and milk products is enforced.
Outbreak measures
Trace source of infection such as contaminated unpasteurised milk products and institute appropriate control measures.
Related information