Brucella abortus

Brucella abortus is an intracellular, blood-borne parasite. It is a Gram-negative coccobacillus that causes an infectious and contagious disease called Brucellosis. The disease primarily affects cattle but it can also be transmitted to humans from infected animals and consuming their products. The disease can lead to great economic loss especially in the dairy and agricultural industry. The Brucella abortus genome contains two DNA chromosomes in a circular confirmation; the first chromosome is approximately 2.1 Mb and the second chromosome is approximately 1.2Mb. Unusually it does not contain any plasmids or genomic islands that relate to pathogenicity and lacks many other genes that code for common virulence factors including capsules, fimbriae, exotoxins, cytolysins, resistance forms, or antigenic variation. The most common mode of transmission to humans is through the ingestion of unpasteurized milk and cheese products as the bacteria are present in the milk glands of infected female cows. In cattle transmission can also be through ingestion but in addition, the bacteria can persist in the reproductive tracts of males, namely seminal vesicles, ampullae, testicles, and epididymides, allowing sexual transmission. In humans the bacteria enter macrophages by phagocytosis and then live in compartments of vacuolar space along the endoplasmic reticulum. They persist by inhibiting host apoptosis and go onto form chronic disease causing lesions in the liver, spleen, bone marrow and kidneys. In cattle the bacteria additionally infect the trophoblast epithelial cells, which provide nutrition to the embryo. The trophoblast cells eventually lyse, releasing further bacteria into the blood stream of the embryo. The B. abortus cells in the blood stream go on to colonize the placenta and fetus in pregnant female cows, resulting in abortion of the fetus. Abortion can also result from insufficient anti-Brucella activity in the amniotic fluid. In humans, the disease can be either acute or chronic and some of the symptoms include fluctuating fever, chills, sweating, headache, muscle pain and weight loss. Once a person becomes infected they are prescribed a combination of tetracycline and streptomycin for 3-6 weeks. In cattle, additional symptoms include arthritic joints and retained after-birth.