A BACTERIAL INFECTION, brucellosis is transmitted to humans through contact with contaminated animals or animal products such as unpasteurized milk and cheese. It is also known as remitting fever, undulant fever, Mediterranean fever, Malta fever, and goat fever.1 Although only about 150 cases are reported in the US annually, approximately 500,000 cases occur globally each year, making it the most common zoonotic bacterial infection in the world.2-4
The Brucella species includes multiple strains of the Gram-negative coccobacilli that can infect humans, of which Brucella melitensis is the most virulent (see Infectious strains of Brucella).1 Brucella can be found in the saliva, nasal secretions, reproductive secretions, and urine of farm animals and dogs.2,5 The bacteria can remain viable for up to 48 hours in unpasteurized milk, weeks in frozen meat, and months in nonpasteurized cheese or on contaminated fomites such as dust.3,6 Transmission of bacteria from animals to humans typically occurs through ingestion of infected food products and direct contact with an infected animal, but it can also be transmitted by inhalation of aerosols.6
Who is at risk?
Individuals with a history of working with or processing animals, including those who work on farms or in kennels and those who hunt or process meat, are at increased risk for infection.2,5 The disease burden is highest in animals that have not been vaccinated, spayed, or neutered, as well as in those that roam freely such as stray dogs.5 Although brucellosis is uncommon in the US, recent reports of infections related to pet ownership among children and immunosuppressed patients have highlighted concerns for these populations.5 In pregnant women, infection can lead to miscarriage, preterm birth, and fetal mortality, and the infection may be transmitted to an infant during delivery or in breastmilk.2,7
Brucella is a major cause of lab-acquired infection in the US, and potentially positive samples must be handled in a level 3 biosafety lab.8 These labs test dangerous samples in contained, biohazard environments, and the staff receives special training and supervision to handle infectious and pathogenic specimens.9 Because it is easily converted to an aerosol and can survive for long periods in this state, it was developed into a biological weapon by several countries, including the US in the 1950s, as well as the Soviet Union and Japan.10 Although the mortality risk is fairly low, it is now considered a potential bioterrorism agent that could cause widespread illness and extended disability because patients generally require a minimum of 6 weeks of combination antibiotic therapy and monitoring.1
Signs and symptoms
The incubation period for brucellosis can range from 5 days to 6 months after exposure.11 Signs and symptoms are nonspecific and may include cyclical fever that is typically worse in the afternoon, chills, weight loss, headache, lymphadenopathy, splenomegaly, hepatomegaly, and fatigue. Some patients are asymptomatic while others become severely ill. Severe presentations include encephalitis, septic arthritis, epididymo-orchitis, and neurologic disorders such as meningitis and Guillain-Barré syndrome.1,3 Some patients experience fever and night sweats with a strong moldy or wet hay odor.1 Others develop chronic signs and symptoms lasting more than 6 months, including arthralgia, testicular swelling edema, nervous system impairment, uveitis, endocarditis, spondylitis, and/or flulike symptoms.3,12 Mortality occurs in 2% of cases, typically secondary to endocarditis.13
Brucellosis is diagnosed based on clinical presentation, confirmation culture, serologic testing such as enzyme-linked immunosorbent assays, or polymerase chain reaction testing.7 A prompt diagnosis and immediate treatment can significantly improve the prognosis, but the infection is easy to miss due to a lack of characteristic signs and symptoms and a low index of clinical suspicion.5,13
Cultures may not indicate a positive result for a week or more.1 Providers should alert lab personnel of potentially infectious samples to ensure that they take appropriate precautions and allow adequate time for accurate culture results.7
Patients with suspected Brucella infection, fever, abnormal hematology results, and negative brucellosis serology should be assessed with a bone marrow culture.7 With a sensitivity between 65% and 95%, bone marrow cultures are most accurate during the early stages of infection, but the invasive nature of these tests makes them less feasible in many clinical settings.3 A presumptive diagnosis is also supported by rising Brucella agglutination titers. Examining immunoglobulin G and immunoglobulin M titers may be helpful in distinguishing acute from chronic infections.3,7
Management and prevention
Patients with Brucella infection should receive 6 weeks of combination antibiotic therapy due to the bacteria's intracellular location and slow doubling time. The bacteria typically respond to various antibiotics. For example, doxycycline may be administered in combination with rifampin, streptomycin, gentamicin, or sulfamethoxazole/trimethoprim.1,7 More complex cases may require a combination of three antibiotics for up to 12 weeks.7
Nurses and providers should be aware of the characteristics that may place individuals at an increased risk of zoonotic infections, such as Brucella, and conduct appropriate screening (see Risk factor screening questions). Early detection and treatment efforts can help prevent chronic infection and the continued spread of the disease. Brucella is killed by common disinfectants and heat, so routine housekeeping is appropriate in inpatient settings.12
Pasteurization also plays an important role in preventing Brucella infection in humans.12 All meat products should be thoroughly cooked to an internal temperature between 145 and 165 degrees.1 Travelers should avoid raw dairy products or meat from street vendors and order all meat well done.
When working with animals or animal products, people should wear gloves and practice appropriate hand hygiene.12 Although no human vaccine is available, annual testing of dairy cows and livestock vaccinations may help to decrease risk.1,7 However, some veterinarians have reportedly become infected due to accidental exposure to the live vaccine.1
Healthcare and lab staff should be aware of the risks and follow the appropriate protocols while handling potentially infectious samples. Because person-to-person transmission is rare, standard precautions are appropriate and patients do not need to be isolated.12 Personal protective equipment such as gloves and closed footwear help nurses minimize direct contact with skin, body fluids, and mucous membranes. Additional protective gear may be appropriate in cases that involve a risk of aerosol or spraying exposure to the eyes, nose, or mouth. Depending on the procedure, this includes eye protection, face shields, and respiratory protection.11
Patients should be monitored for symptoms weekly and instructed to take their temperature daily for 6 months after direct exposure to Brucella.7 Postexposure prophylaxis may be warranted in pregnant or immunocompromised patients, as well as those with high-risk exposure to Brucella; for example, following direct exposure to infected body fluids including spraying into the eyes, nose, or mouth.7
Teach patients diagnosed with a strain of Brucella about the importance of completing a full course of the prescribed antibiotics. Up to 15% of infected patients may relapse due to an inadequate length or dose of treatment, as well as inconsistent adherence to the recommended treatment.3 Also educate patients about any common adverse drug reactions and how to manage them. Though person-to-person spread is unlikely, it is important to teach infected patients how to limit exposure to others. This includes prevention of body fluid exchange through sexual activity or breastfeeding. More than half of the cases of brucellosis that are transmitted person-to-person occur in children under age 1 who acquire the infection in utero, during delivery, or while breastfeeding.14 Infected patients should also be advised against donating blood, tissue, or bone marrow to avoid further spread.11,14,15 Warn patients about the risk of contracting brucellosis from raw milk and raw milk products.16
Brucellosis is a notifiable infection in the US, and nurses, healthcare providers, and lab staff must follow the appropriate reporting procedures.5 This allows for proper investigation and control of potential outbreaks or bioterrorism concerns.
Risk factor screening questions12
- Do you work in a slaughterhouse or meat-packing environment?
- Have you recently traveled overseas? If so, where?
- While traveling, did you consume any undercooked meat or unpasteurized dairy products?
- Do you hunt? If so, have you come into contact with moose, elk, caribou, bison, or wild hogs (feral swine)?
- Have you assisted animals giving birth?
- Do you work in a lab? If so, does the lab handle Brucella specimens?
1. Smith ME, Shorman M. Brucellosis
. StatPearls. Treasure Island, FL: StatPearls Publishing; 2018.
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5. Hensel ME, Negron M, Arenas-Gamboa AM. Brucellosis in dogs and public health risk. Emerg Infect Dis
6. Elfaki MG, Alaidan AA, Al-Hokail AA. Host response to Brucella infection: review and future perspective. J Infect Dev Ctries
7. Bosilkovski M. Brucellosis: clinical manifestations, diagnosis, treatment, and prevention. UpToDate. 2019. http://www.uptodate.com
8. Garofolo G, Fasanella A, Di Giannatale E, et al Cases of human brucellosis in Sweden linked to Middle East and Africa. BMC Res Notes
9. Mourya DT, Yadav PD, Majumdar TD, Chauhan DS, Katoch VM. Establishment of Biosafety Level-3 (BSL-3) laboratory: important criteria to consider while designing, constructing, commissioning & operating the facility in Indian setting. Indian J Med Res
10. Pappas G, Panagopoulou P, Christou L, Akritidis N. Brucella as a biological weapon. Cell Mol Life Sci
14. Tuon FF, Gondolfo RB, Cerchiari N. Human-to-human transmission of Brucella—a systematic review. Trop Med Int Health
17. Suárez-Esquivel M, Ruiz-Villalobos N, Jiménez-Rojas C, et al Brucella neotomae infection in humans, Costa Rica. Emerg Infect Dis