Brucellae is a bacterium named after David Bruce, a surgeon who first isolated it in 1887. The bacterium is the cause of the disease called Brucellosis. This disease is sometimes known as “undulant fever,” as well as Malta, Mediterranean, or Gibraltar fevers because of research done by the British in those areas in the late 1800s.
The bacterium is normally found in lower animals. Humans become infected after coming in contact with contaminated animal products or ingesting contaminated milk or milk products. Brucellae are small, Gram-negative, pleomorthic (its form widely varies), coccobacillary-shaped bacterium that can survive for several days to several weeks when excreted in animal body fluids.
The most common Brucellae species that can infect humans are as follows:
- B. abortus is found in cattle and can cause spontaneous abortions.
- B. melitensis (Malta fever) is found in sheep or goats and causing the most severe illness in humans.
- B. canis is found in dogs.
- B. suis (Bang’s disease) infects swine, but is more virulent in humans.
- B. rangiferi reside in reindeer or caribou.
Many other animals, including horses, also carry the Brucellae bacterium. There is no person to person contagion, only animal to person.
Brucellae enters the body via lesions or cuts on the skin, ingestion of infected products, or inhaling the organism. The bacteria are readily phagocytized by white blood cells, but are able to survive inside both the phagocyte and the macrophage. The bacteria are then carried through the lymphatic system to the blood and into such organs as the liver and spleen, which often become enlarged. Circulating antibodies are produced, but are unable to neutralize the bacteria because of their location inside human white blood cells.
The onset of the disease is gradual, occurring weeks or months after exposure. Clinical symptoms include generalized flu-like symptoms with a fever that may occur in cycles. It is this cycle that gave the disease the name of “undulant fever”. The disease is so gradual in its progression that it often goes unnoticed. Recovery is just as gradual. Although brucellosis induces abortions in animals, it does not seem to be a factor in humans. However, B. melitensis is known to cause abortions in women, especially in the first trimester. Fevers from this bacterium have been known to be recurrent for as long as twenty years. B. abortus causes abortions in animals because the bacterium thrives on the nutrient erythritol found in calf placenta, which is not found in human placenta.
Infections in humans are most often seen in those who work closely with animals or in meat-processing plants, as well as those who drink unpasteurized milk. In the US, brucellosis is largely confined to fresh goat cheese. There does not seem to be a problem with aged cheese. Tetracyclines are the drugs of choice in treating the disease, but must be taken for a prolonged period of three to four weeks, causing serious side effects. Streptomycin is sometimes used in conjuction with the tetracyclines.