Brucellosis

Queensland Health Guidelines for Public Health Units

Revision History

VersionDateChanges
1.0 August 2010 Full revision of guideline
2.0 June 2015 Full revision of guideline
3.0Dec 2022Full revision of guideline

Infectious Agent

Brucellosis is a zoonotic infection caused by small, intracellular gram-negative bacteria belonging to the genus Brucella. A number of Brucella species may cause brucellosis in humans. The species are named primarily after the source animal or features of infection. Of these, the following 4 have moderate-to-significant human pathogenicity:

Brucella melitensis (from sheep and goats; highest pathogenicity)
Brucella suis (from pigs; high pathogenicity)
Brucella abortus (from cattle; moderate pathogenicity)
Brucella canis (from dogs; moderate pathogenicity)

Other Brucella species such as Brucella ceti, novel Brucella pinnepedialis and atypical amphibian-like strains have also been reported to cause human infection. In Australia, Brucellasuis is the dominant disease-causing species and is usually associated with pig hunting.

Notification Criteria

Brucellosis is notifiable in Queensland on pathological diagnosis.

Clinical evidence
Clinically compatible illness (NB. clinical evidence is required for reporting probable cases to NOCS but does not by itself constitute a requirement for clinicians to notify).

Confirmed case
A confirmed case requires laboratory definitive evidence only.

Laboratory definitive evidence
1. Isolation of Brucella species

OR

2. Detection of Brucella species by nucleic acid testing from a blood sample.

OR

3. IgG seroconversion or a significant increase in lgG antibody level (e.g., fourfold or greater rise) to Brucella.

Probable case
A probable case requires laboratory suggestive and clinical evidence.

Laboratory suggestive evidence
1. A single high  agglutination titre to Brucella*

OR

2. Detection of Brucella species by nucleic acid testing from a normally sterile site other than blood.

*A single high Brucella agglutination titre (at least 1:64). Note: the numerical value is not specified in the national case definition and the titre considered significant varies by pathology laboratory.

Community Outbreak Criteria
Two or more associated cases.

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Notification Procedure

Pathology Laboratories
To notify by usual means if definitive or suggestive evidence.

Laboratory Aspects

Blood cultures are best performed on samples collected during a febrile episode, preferably while the person's temperature is still rising. The isolation rate is improved if several samples are taken over 24 hours.

Bacterial culture and isolation will identify the genus Brucella, but not differentiate species. Brucella in culture can be slow growing and may be subject to misidentification by laboratory systems including Vitek 2, Vitek MS and API 20NE. Queensland Health Forensic and Scientific Services (FSS) routinely perform speciation PCR testing on all Brucella isolates. B. suis, B. melitensis and B. abortus species can be identified with the current assay. Additional speciation can be performed by FSS using whole genome sequencing on isolates.

Reporting to NOCS

Report confirmed cases and probable cases.

Confirmed case

A confirmed case requires laboratory definitive evidence only.

Probable case
A probable case requires laboratory suggestive evidence AND clinical evidence.

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Objectives of Surveillance

1. To monitor the epidemiology of brucellosis in Queensland.

2. To identify and manage potentially co-exposed persons at risk of brucellosis.

3. To identify locally acquired human cases not exposed to feral pigs, so that animal health authorities can be alerted to the possibility of emerging infection in animal populations.

Public Health Significance and Occurrence

Brucellosis occurs worldwide and remains one of the world's major zoonotic pathogens. It is responsible for vast economic losses as well as considerable human morbidity in endemic areas, especially in developing areas of the Mediterranean region, the Middle East, India, central Asia and parts of Africa and Latin America. In such countries, it is predominately an occupational disease of those working with infected animals or their tissues, especially farm workers, veterinarians and abattoir workers. The consumption of unpasteurised milk and milk products from infected animals is also a major risk factor in these countries.

Notification rates for brucellosis in Queensland have decreased over the past two and a half decades, from an average rate of 0.8 per 100,000 during 1995–2012 to 0.2 per 100,000 population in 2013–2021 (75% decrease). Since 2013, the number of notifications has been relatively stable with approximately 10 cases notified annually. This reduction is reflected nationally with cases attributed to Queensland reducing from 83% in 1991–2011 to 58% in 2012–2016.

Clinical Features

The clinical features of brucellosis depend on the stage of disease, and the organs and systems involved. It is a systemic bacterial disease with acute or insidious onset, characterised by continued, intermittent or irregular fever of variable duration. Other common symptoms include:

  • sweats
  • anorexia and weight loss
  • fatigue and malaise
  • arthralgia, myalgia and back pain
  • headache
  • depression.

Depression is often severe, relative to other symptoms, and occurs in around 30% of patients.

Local suppurative infections of organs including the liver and spleen may occur, subclinical disease has been reported and chronic localised infections can occur. The disease can last for several days, months, or occasionally a year or more if not adequately treated. Osteoarticular complications occur in 30%–70% of cases and genitourinary involvement is seen in 2%–20% of cases.

Other rare complications of brucellosis include:

  • neurobrucellosis, usually presenting as acute or chronic lymphocytic meningitis
  • cardiovascular manifestations such as endocarditis, aneurysms, myocarditis or pericarditis (often the main cause of death from brucellosis)
  • respiratory complications, such as bronchopneumonia and pleural adhesions
  • endophthalmitis.

The case-fatality rate of untreated brucellosis is documented to be 2% or less.

Brucella sp. infections can also lead to spontaneous abortions and intrauterine foetal death in pregnant women but have not been associated with birth defects.

Reservoir

Swine brucellosis (caused by B. suis) is endemic in the feral pig population in Queensland and has also been reported in northern parts of the Northern Territory, New South Wales and Western Australia. B. suis has also been identified as the cause of several cases of brucellosis in pig dogs in northern NSW.

Bovine brucellosis (B. abortus) was eradicated from the Australian cattle herd in 1989 and is presently considered an exotic animal disease in Australia.

Caprine brucellosis (caused by B. melitensis) has never been reported in goats or sheep in Australia.

Ovine brucellosis (caused by B. ovis) occurs widely in sheep in Australia but does not pose a zoonotic risk.

Organisms originally misidentified as Ochrobactrum anthropi,  but now understood to be atypical Brucella spp., have been reported to cause spinal arthropathy in Australian cane toads. Atypical Brucella have also been described as causing disease in captive Australian green tree frogs. Queensland is the origin of other atypical Brucella spp. from wild native rodents.

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Mode of Transmission

Infection, particularly with B. suis, occurs principally from exposure to infected animals and animal products, through breaks in the skin and mucus membranes via contact with:

  • infected tissues
  • blood
  • urine
  • vaginal discharges
  • aborted animal foetuses and especially placentae
  • ingestion of raw milk or milk derived products
  • consumption of undercooked feral pig meat or other game meat overseas.

Airborne transmission from animal to humans is also possible, as the bacteria are highly infectious by aerosol. It has been estimated that only 10-100 organisms are needed to constitute an infectious aerosol for humans.

A small number of cases have resulted from accidental self-inoculation of B. abortus strain 19 vaccine used in livestock; the same risk is present when Rev-1 vaccine is handled. Limited data support vertical transmission of human brucellosis and transmission via breast milk. Further study is needed to substantiate these routes.

Person-to-person transmission is rare, but sexual transmission has been proposed in a small number of cases. In addition to possible transmission from mother to child as indicated above, risk may exist for medical personnel in endemic areas who have gross exposure to blood, tissues, or contaminated fomites.

The bacteria are sensitive to exposure to heat and most disinfectants but may survive in the environment for up to 2 years under specific conditions.

Risk Factors

Since the eradication of B. abortus in Australian livestock the most common risk groups are:

  • B. suis: hunters who have direct contact with feral pigs and blood via skin abrasions and mucous membranes during hunting and slaughtering. This is the main source of locally acquired brucellosis in Australia.
  • travellers to countries, or consumption of unpasteurised dairy products from countries, where B. melitensis and or B. abortus occur in animals.

Lesser risk groups:

  • B. suis: veterinarians and dog breeders who may be exposed when infected female dogs are birthing or during surgical procedures, such as desexing operations. Transmission to humans from casual contact with an infected dog has not been documented.
  • B. suis: people involved in processing, storage or transportation of feral pig carcasses.
  • B. meletensis and/or B. abortus: farmers, abattoir workers and other animal handlers who have a history of working in other countries where these organisms are present in animals and present with clinical signs after they return/arrive in Australia.
  • people who work in laboratories who handle Brucella cultures.

Brucella, particularly B. melitensis and B. suis, has been historically considered a potential biological weapon, however it is considered low risk due to its extended inoculation period and many treatment options.

Incubation Period

Variable and difficult to ascertain but is usually 5–60 days, occasionally extending to several months. The incubation period may be shorter if the bacteria have been aerosolised for use as a biological weapon.

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Susceptibility and Resistance

Severity and duration of clinical illness are subject to wide variation. Duration of acquired immunity is uncertain.

Management

Cases

Investigation
If notified on the basis of a single high agglutination titre, consult with the attending medical practitioner to attempt to confirm the diagnosis by the presence of a clinically compatible illness, and/or a further sample for laboratory confirmation.

In consultation with the attending medical practitioner and case, attempt to identify the source of infection. Especially inquire about exposure to feral pigs. Ascertain whether the person has been overseas in the past 2 months or has imported an animal product from overseas.

Restriction
Nil; use standard precautions if dealing with draining lesions. Disinfect purulent discharges.

Treatment
Antibiotic treatment is available, however effective treatment may involve a combination of antibiotics for at least 6 weeks, sometimes months. Refer to latest edition of Therapeutic Guidelines: Antibiotic.

Relapses can occur in up to 10% of cases and are usually a result of sequestered rather than resistant organisms. Expert advice should be sought regarding longer duration of therapy or alternative combination regimens if indicated for relapse, osteoarticular disease, neurobrucellosis or endocarditis.

Counselling
The case should be advised of the nature of the infection and its mode of transmission.

Contacts

Contact Tracing
Identify possible cases among co-exposed persons, provide them with information about the disease, and advise to seek medical attention should symptoms develop.

Definition
Persons having exposure to the same possible source of infection as the case.

Investigation
If workplace acquired, contact the occupational health officer in the workplace to inquire if there are any other cases (i.e. common exposure).

New, non-imported, human cases of brucellosis with no history of exposure to feral pigs should be reported to Biosecurity Queensland so that appropriate investigation and control measures can occur if required.

Prophylaxis
No controlled studies have been performed to assess the value of administering post-exposure prophylaxis (PEP) to persons at risk. Anecdotal evidence suggests that PEP may reduce the risk of developing clinical disease. PEP should be considered for all persons after an obvious exposure to living brucellae (e.g. following laboratory exposure). Regimens reported in the literature are:

  • a combination of oral doxycycline 100mg bd and rifampicin 600mg once daily for 3 weeks commenced as soon as exposure is confirmed
  • for pregnant women, use trimethoprim-sulfamethoxazole 160/800mg bd for 3 weeks.

Consultation with an infectious diseases physician is recommended to provide additional risk assessment and, if PEP is indicated, selection of agents most suited to the individual.

In addition, increased surveillance for clinical signs of disease is recommended for at least 6 months, and serological testing for subclinical disease is suggested every 1–2 weeks for the first 3 months and then monthly for the next 3–9 months.

Counselling
Co-exposed persons should be advised of the nature of the infection and its mode of transmission. Advice on possible side effects from PEP should be given if PEP is recommended.


Other Control Measures
Ultimate control of human brucellosis depends on the elimination of the disease in animals; therefore, reservoir animals need to be identified and contained. Elimination of Brucella suis from feral pigs is unlikely.


Community Outbreaks/Epidemics
Trace source of infection.  Recall incriminated products and implement remedial measures in production process.

Depending on the circumstances, a Multi-Agency Threat Assessment Team (MATAT) may be convened by the lead agency involved in order to undertake an effective assessment of the threat, its credibility and the potential consequences based on information provided by the various team members/organisations. A Technical or Expert Advisory Group may also be convened to inform the health response.

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Preventive Measures

There is currently no vaccine available for humans.

Educate farmers, pig shooters, and handlers of potentially infected animals, particularly feral pigs, to reduce exposure and exercise care in the handling and disposal of placenta, discharges, foetuses and aborted animals. Protective clothing and gloves should be worn during risk activities; and hand hygiene measures taken as soon as possible after contamination with potentially infected substances.

Educate the public against drinking unpasteurised milk, particularly if travelling overseas.  Boiling milk is effective when pasteurisation is not available. As cattle, sheep and goats in Australia are free of zoonotic forms of brucellosis, unpasteurised milk and milk products produced in Australia from these animals do not pose a risk of brucellosis.

Educate dog owners to prevent dogs from consuming raw feral pig products.

The following precautions should be considered if there is a release of Brucella sp., for example, from a biological attack or an accidental laboratory exposure:

  • airborne precautions are required
  • once persons are removed from the contaminated area, clothing, skin and other surfaces can be decontaminated with an appropriate disinfectant
  • exposed persons should be medically assessed to determine if post-exposure prophylaxis is required.

Summary

Prepare a report of any outbreak investigation for the Communicable Diseases Branch, Queensland Health, on request.

Provide a copy of the Case Report Form to the Communicable Diseases Branch, Queensland Health.

References

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Bennett N.J.B, Bronze M.S.B. (22 April, 2021) Brucellosis. Medscape.  http://emedicine.medscape.com/article/213430-overview

Bossi P, Tegnell A, Van Loock F, et al. 2004. BICHAT guidelines for the clinical management of brucellosis and bioterrorism-related brucellosis (2010). Euro Surveill 9(12). http://www.eurosurveillance.org/em/v09n12/0912-237.asp Accessed 22/02/10

Centers for Disease Control and Prevention. (2019). Brucellosis [Internet]. [cited 24 February 2022]. Available from: https://www.cdc.gov/brucellosis/index.html

Brucellosis Reference Guide: Exposures, Testing, and Prevention [Internet]. Centers for Disease Control and Prevention; 2017 [cited 2017 July 1]. Available from: https://www.cdc.gov/brucellosis/pdf/brucellosi-reference-guide.pdf

Department of Health. National notifiable diseases surveillance system. Canberra: DoH, 2017. www9.health.gov.au/cda/source/cda-index.cfm

Therapeutic Guidelines (2019). eTG. e-Therapeutic Guidelines – Antibiotic: Brucellosis. https://tgldcdp.tg.org.au/viewTopic?topicfile=brucellosis&guidelineName=Antibiotic&topicNavigation=navigateTopic#MPS_d1e149

Heymann DL, editor. Control of communicable diseases manual. 21st ed. Brucellosis. Washington, DC: American Public Health Association; 2022. https://ccdm.aphapublications.org/doi/book/10.2105/CCDM.2745

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Traxler, R. M., Lehman, M. W., Bosserman, E. A., Guerra, M. A., & Smith, T. L. (2013). A literature review of laboratory-acquired brucellosis. Journal of Clinical Microbiology, 51(9), 3055-3062.

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Last updated: 5 December 2022