Brucellosis

Brucellosis is a highly contagious zoonotic disease caused by Gram-negative bacteria of the genus Brucella. It affects various species of animals and can be transmitted to humans primarily through direct or indirect contact with infected animals or their products. The disease is endemic in many parts of the world and represents a significant public health and economic burden in regions with underdeveloped livestock management and veterinary care. The most significant species responsible for human infection are: 

• Brucella melitensis: The most virulent and common species causing brucellosis in humans, primarily associated with sheep and goats.
• Brucella abortus: Primarily affects cattle but can also cause zoonotic infection.
• Brucella suis: Primarily affects pigs and can cause severe, chronic human infections.
• Brucella canis: Infects dogs and rarely causes zoonotic disease but can lead to chronic infections in humans when it does 

The World Organisation for Animal Health (WOAH) categorises brucellosis as a notifiable disease, due to its zoonotic potential and significant economic impact on livestock production. 

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation. 

As with zoonotic diseases, the control of brucellosis among humans is highly dependent on the control systems in the veterinary sector. The following include case definitions for human surveillance and exclude case definitions for veterinary surveillance. For more information on veterinary surveillance or clinical presentations, please visit WOAH’s page on brucellosis.  

Clinical description: It is characterised by 2 clinical forms   

• Acute Phase
  • Fever, often fluctuating (undulant fever)
  • Sweating, particularly at night
  • Fatigue and general weakness
  • Muscle and joint pain
  • Headaches
• Chronic Phase
  • Persistent or recurrent fevers
  • Arthritis and joint pain
  • Swelling of the testicles and scrotum area
  • Neurological symptoms such as depression, fatigue, and headaches 

Suspected case: A case that is compatible with the clinical description and has an epidemiological link to confirmed or suspected animal cases or contaminated animal products. 

Probable case: A suspected case that has symptoms compatible with disease and is positive in the Rose Bengal test, but negative in blood culture and showing low titres in the confirmatory tests. 

Confirmed case: A suspected case that is laboratory-confirmed  

Source of information: (FAO) 

Determined based on local contexts and is influenced by; seasonal trends and yearly incidence rates. 

• People who work with animals (farmers, veterinarians, livestock breeders) or animal products such as wool, hides or hair (butchers, weavers).
• People who eat raw or undercooked meat from infected animals.
• Hunters who hunt wild animals in forests
• People living in known brucellosis endemic areas and/or with lack of infection, prevention and control measures during and after a known outbreak are at higher risk. 

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities. 

• Generally low and depends on the type of exposure. 

• Older people.
• People with weakened immune systems.
• Immunosuppressed persons such as those receiving chemotherapy, transplant recipients or HIV carriers.
• People with chronic diseases such as renal disease, cancer, chronic lung or liver disease and diabetes. 

Brucellosis is a zoonotic disease. The most significant species responsible for human infection are: 

• Brucella melitensis: The most virulent and common species causing brucellosis in humans, primarily associated with sheep and goats.
• Brucella abortus: Primarily affects cattle but can also cause zoonotic infection.
• Brucella suis: Primarily affects pigs and can cause severe, chronic human infections. 

Brucella canis: Infects dogs and rarely causes zoonotic disease but can lead to chronic infections in humans when it does. 

The final hosts for Brucella spp. are cattle, goats, sheep, pigs, camels, and humans. Wild animals such as (deer, bison, elk, wild boars, and some rodents) are also known to carry the disease as reservoir hosts.  

People get infected with brucellosis when infected with the causative organisms. This can happen via: 

1. Direct and Indirect Animal Contact: Individuals working on livestock farms, slaughterhouses, veterinary clinics, or meat processing plants are at increased risk. This includes direct contact with animal blood, placenta, urine, or other tissues during birthing, slaughter, or veterinary procedures. Also, contaminated animal waste can serve as a source of transmission through skin abrasions or mucosal exposure. 

2. Ingestion: Brucella spp. can persist in raw milk, cheese, and other dairy products, especially in areas where pasteurisation standards are not enforced. 

3. Aerosolization: Laboratory personnel handling Brucella cultures without adequate biosafety measures are at risk of aerosol transmission. Animal handlers and abattoir workers may also inhale aerosolized bacteria during slaughter or animal birthing processes. 

4. Vertical Transmission: Rare cases of mother-to-child transmission have been documented, either during childbirth or breastfeeding.

It is usually 2–4 weeks (but can range from 5 days–6 months) 

Human-to-human transmission is very rare and it has been recorded that women have passed the disease to their children during birth or through their breast milk. 

• The acute phase of brucellosis typically occurs 2-4 weeks after infection and it is characterised by: 
  • Fever, often fluctuating (undulant fever)
  • Sweating, particularly at night
  • Fatigue and general weakness
  • Muscle and joint pain
  • Headaches  
     
• Brucellosis can progress to the chronic phase If left untreated, and it can persist for months or even years. This phase is marked by; 
  • Persistent or recurrent fevers
  • Arthritis and joint pain
  • Swelling of the testicles and scrotum area
  • Neurological symptoms such as depression, fatigue, and headaches 

Typhoid fever, Q fever, Tuberculosis, Malaria, Lyme disease, Dengue fever, Leptospirosis 

• Isolation of Brucella spp. from clinical specimens (note that repeated attempts may be necessary); or
• Brucella agglutination titre, e.g. standard tube agglutination tests: SAT³160 in one or more specimens obtained after onset of symptoms; or
• ELISA (IgA, IgG, IgM), 2-Mercaptoethanol test, Complement fixation test, Combs, fluorescent antibody test.
• In small laboratories or clinics, a Rose Bengal screening test may be used. Positive results should always be confirmed by the tests listed above. 

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of a treatment or vaccine should be conducted by a health professional.  

• Brucellosis can be prevented and treated with antibiotics. 
• There is no approved vaccine for brucellosis in humans. 

Brucellosis infection results in long-term immunity.