Background:
Bucellosis is caused by a bacteria from the genus Brucella. There are a few different species that cause disease in animals and humans. For humans, the three species that usually cause disease are suis, abortus, and melitensis.
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| Brucella colonies on blood agar. Image from Pixnio. |
Brucella species are small, anaerobic, gram negative coccobacilli, meaning that they do not require oxygen and do not have peptidoglycan in their cell walls and stain red/pink on a gram stain (bacteria that stain purple are gram positive). Coccobacilli describes the shape--they are between cocci (round) and baccili (rod-shaped).
They are facultative intracellular organisms, which means that they have to be inside another cell for part of their life cycle, but can also live outside of another cell. In the case of Brucella species, the cell they tend to invade is the macrophage. Macrophages are important cells in your immune system. Briefly, they usually "eat" things that are dangerous, like bacteria, and break it up into pieces. Then they take those pieces and display them on the surface of their cells using special cell receptors that will signal other immune cells to look for them. That way, the rest of your immune system can respond to the invaders. Brucella bacteria hiding in these cells, it makes it much more difficult for your body to find and fight off.
How is it spread?
Humans usually get this disease either by being in close contact with an infected animal or by eating contaminated animal products. Namely unpasteurized milk, which is contaminated with the bacteria when an animal is infected (this is why drinking unpasteurized milk is so dangerous). The bacteria can cause infection if inhaled, ingested, or through the skin. Most commonly, it infects via mucous membranes (for example: the eyes, throat, or respiratory tract).
According to the CDC, person-to-person spread is rare, but is most common if a mother is infected, she can infect her breastfeeding infant.
This disease is most worrisome in animals, both wild and agricultural. It is also found world-wide.
The bacteria are not especially hardy, they don't form spores and they can be killed with heat. However, they manage to survive in the environment for several years, if the conditions are right.
The incubation period for this bacteria is about two to four weeks, so there can be quite a delay between getting infected and showing symptoms.
Symptoms:
Many of the symptoms are flu-like: fatigue, fever, sweating, headache, body aches, anorexia, nausea, and malaise (generally not feeling well). According to the CDC, some symptoms can be recurring or persist for a longer period of time. Most commonly these symptoms are: recurrent fever, arthritis, swelling of the heart, neurological problems, chronic fatigue, swelling of the male reproductive system (namely the testes and scrotum), and swelling of the spleen and/or liver.
The good news is that brucellosis is rarely fatal in humans, but it is still considered a potential bioweapon because it can be easily spread and incapacitate people.
The chronic symptoms that are so common with this microbe are due to a couple things: incomplete antibiotic treatment, which causes relapses, and persistent infection by the bacteria in tissues (like bone, spleen, liver, et cetera). It can be difficult to get rid of.
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| Brucella colonies on serum dextrose. Credit: Royal Veterinary College and Wellcome Collection |
Prevention and Treatment:
One way to prevent human infection is by pasteurizing milk and other dairy products. Eating under-cooked meat is not recommended as it could be contaminated with Brucella. There is also a vaccine for herd animals to B. abortus.
People who work with animals like cattle, pigs, goats, and sheep should wear protective clothing, like gloves and goggles.
Because the bacteria hides inside cells, antibiotic treatments can last a long time (often 6 weeks) and often more than one antibiotic is needed. Doxycycline with with rifampicin can be used, or doxycycline with gentamicin. Trimethoprim-sulfamethoxazole can be used for women who are pregnant or for young children.
Miscellaneous Information:
What I find super interesting about this bacteria is that it causes abortion (and infertility), which can lead to further infections in animals. It almost plays off of the maternal instinct. For example, if a cow is infected and it causes the cow to have an abortion, the cow may survive. However, the aborted fetus is infectious. Other cows may come into contact with the aborted fetus as they inspect it and then the bacteria can infect the new animal. A bit evil and fascinating.
Brucellosis is known by many other names, including: Malta fever, Mediterranean fever, Cyprus fever, goat fever, Gibralter fever, to name a few.
Sources:
The Centers for Disease Control: Brucellosis
Microorganisms and Bioterrorism edited by Burt Anderson, Herman Friedman, and Mauro Bendinelli
Emerging Infectious Diseases by Lisa A. Beltz
Medical Microbiology 6th edition by Patrick R. Murray, Ken S. Rosenthal, and Michael A Pfaller
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