Brucellosis (undulant fever, Malta fever)

Notification requirement for brucellosis

Brucellosis is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for brucellosis

Exclusion is not required.

Infectious agent of brucellosis

The following infectious agents cause brucellosis:

• Brucella abortus (biovars 1–6 and 9) – cattle
• B. melitensis (biovars 1–3) – goats
• B. suis (biovars 1–5) – pigs
• B. canis – dogs
• B. ceti – seals
• B. pinnepedialis – whales, dolphins and porpoises.

B. suis is the only species occurring in Australia that can cause human disease.

Identification of brucellosis

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, which may be continuous, intermittent or irregular and of variable duration, is the most common symptom. It may be associated with a variety of other complaints, including headache, weakness, profuse sweating, chills, arthralgia, depression and weight loss. Recovery is usual but disability can be pronounced and relapses may occur.

Osteoarticular complications are common. Orchitis, epididymitis, osteomyelitis and endocarditis are less common. The case–fatality rate in untreated brucellosis is approximately 2 per cent, mostly due to endocarditis from B. melitensis infections.

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. A confirmed case requires IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre in Brucella agglutination titres or complement fixation titres between acute and convalescent phase serum samples. Where possible, these tests should be conducted in parallel at the same laboratory.

Incubation period of Brucella

The incubation period is highly variable. It is most commonly 1–2 months but ranges from 5 days to 60 days.

Public health significance and occurrence of brucellosis

B. abortus was successfully eradicated from Australian cattle herds during the national eradication campaign between 1970 and 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 the responsible organism vary according to geographical area. Affected regions include the Mediterranean countries, North and East Africa, Western Africa, the Middle East, India and Central and South America.

Reservoir of Brucella

The most important reservoirs for human infection are cattle, swine and goats. In Australia, feral pigs in Queensland account for most newly acquired infections.

Mode of transmission of Brucella

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 the ingestion of raw milk and milk products from infected animals.

Outbreaks are generally attributed to the inhalation of aerosols, which may occur in animal pens and stables, abattoirs and laboratories, or through the 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 of brucellosis

There is no evidence of communicability from person to person.

Susceptibility and resistance to brucellosis

Everyone is susceptible to infection. The severity and duration of clinical illness are subject to wide variation. The duration of acquired immunity is uncertain.

Control measures for brucellosis

Preventive measures

Educate the public, particularly international 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 their 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 and seek advice from an expert in 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 potentially been exposed to the same implicated source of Brucella infection as the case. Those people are advised of the early signs and symptoms of brucellosis to aid early diagnosis and treatment. Laboratory exposures should be assessed for risk and those potentially exposed may be advised to take chemoprophylaxis.

Control of environment

The Department of Environment, Land, Water and Planning is notified of any new, non-imported case of brucellosis so that appropriate animal investigations and control measures can commence.

All implicated milk products are recalled. A restriction on the distribution of unpasteurised milk and milk products is enforced.

Outbreak measures for brucellosis

Trace the source of infection, such as contaminated unpasteurised milk products, and institute appropriate control measures.