Brucellosis is an infectious disease caused by a type of bacteria called Brucella. The bacteria can spread from animals to humans. There are several different strains of Brucella bacteria. Some types are seen in cows. Others occur in dogs, pigs, sheep, goats, and camels. Recently, scientists have seen new strains in the red fox and certain marine animals, including seals.
Brucella organisms, which are small aerobic intracellular coccobacilli, localize in the reproductive organs of host animals, causing abortions and sterility. They are shed in large numbers of animal’s urine, milk, placental fluid, and other fluids.
Magnified view of Brucella abortus
To date, 8 species have been identified, named primarily for the source animal or features of infection. Of these, the following 4 have moderate-to-significant human pathogenicity:
Brucella melitensis (from sheep; highest pathogenicity)
Brucella suis (from pigs; high pathogenicity)
Brucella abortus (from cattle; moderate pathogenicity)
Brucella canis (from dogs; moderate pathogenicity)
Origin of Brucella organisms from different sources
Brucellosis is a disease that is thought to have existed since ancient times, as it was first described more than 2,000 years ago by the Romans and Hippocrates. It was not until 1887 that a British physician, Dr. David Bruce, isolated the organism that causes brucellosis from several deceased patients from the island of Malta. This disease has had several names throughout its history, including Mediterranean fever, Malta fever, Crimean fever, Bang’s disease, and undulant fever (because of the relapsing nature of the fever associated with the disease).
In the mid-20th century, the Brucella bacteria was also developed for use as a biological weapon by the United States. The use of brucellosis for biological warfare purposes was later banned in 1969 by President Nixon.
Different species of Brucella tend to affect certain animal hosts and are more common in specific geographical locations.
Worldwide, B melitensis is the most common species to infect humans, although some studies have suggested that up to 73% of cases of brucellosis in certain areas of the US may be due to B abortus. The majority of cases reported in the US between 1979 and 2002 were in California and Texas, particularly among the Hispanic population and those travelling to and from Mexico.
Brucellosis tends to be an occupational disease predominantly affecting farmers, animal handlers, abattoir workers, and veterinarians. It may also occur in laboratory personnel working with cultures. Between 1979 and 1999, approximately 8% of laboratory-acquired infections in the US were due to Brucella species. Brucellosis continues to be a hazard in the laboratory in both endemic and non-endemic countries.
Brucellosis in humans occurs when a person comes into contact with an animal or animal product infected with the Brucella bacteria.
Very rarely, the bacteria may spread from person to person. Breastfeeding moms with brucellosis may pass the bacteria to their baby. Brucella may also be spread through sexual contact.
The bacteria can enter into the body:
Through a cut or scratch in the skin
When you breathe in contaminated air (rare)
When you eat or drink something contaminated with the bacteria, such as unpasteurized milk or undercooked meat
Risk factors of Brucellosis
Eating or drinking unpasteurized dairy products from cows, goats, or other animals that are infected with the bacteria
Eating other unpasteurized cheeses called “village cheeses.” These come from high-risk regions, including the Mediterranean
Traveling to areas where Brucella is common
Working in a meat-processing plant or slaughterhouse
Working in a farm
Signs and symptoms
Symptoms in humans are similar to having the flu. The symptoms may include:
Continuous or intermittent fever
The infection can affect the liver and spleen, and may last for days or months, and sometimes for a year or more if not treated
Joint complications and involvement of the testes and epididymis (storage tubes for sperm that are on top of the testes) are common. Recovery is usual but relapses can occur.
Death can occur from inflammation of the lining of the heart (endocarditis) but this is very rare.
If treatment isn’t successful, brucellosis can cause complications. These may include:
Encephalitis (inflammation of the brain)
Lesions on the bones and joints
Endocarditis (infection of the heart’s inner lining)
Meningitis (inflammation of the membranes around your brain)
Diagnosis and Test
Testing may include:
Bone marrow culture
Cerebrospinal fluid testing
Testing for antibodies to brucellosis
Other imaging studies and procedures may also be performed, depending on the individual’s signs and symptoms. These tests may include:
Lumbar puncture (spinal tap),
The cornerstone of treatment for brucellosis is antibiotics. Because of the high relapse rate associated with the disease, the use of a multidrug (two or more) antibiotic regimen is recommended. The antimicrobials most commonly used include:
Ciprofloxacin or ofloxacin
Trimethoprim-sulfamethoxazole (Bactrim, Septra)
The combination of antibiotics used will vary based on disease severity, age and pregnancy.
Exclusion from work is not necessary.
A vaccine is not available for use in humans.
Control is best achieved by eliminating the disease in animals.
Avoid drinking raw or unpasteurized milk and products made from raw or unpasteurized milk.
Educate farmers, abattoir workers and other occupational at risk groups on how to prevent infection when handling potentially infected animal products:
Cover open cuts and sores with dressings
Wear gloves, overalls and face masks when slaughtering animals or handling animal products
Thoroughly wash hands and arms after handling animals or their products
Take special care when handling animal birth products
Thoroughly clean all working areas