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The disease is caused by several different species of parasitic bacteria of the genus Brucella. B. abortus is found in cattle and can cause cows to abort their fetuses. B. suis is most often found in hogs and is more deadly when contracted by humans than the organism found in cattle. B. melitensis is found in goats and sheep and causes the most severe illness in humans. B. rangiferi infects reindeer and caribou, and B. canis is found in dogs.
A human contracts the disease by coming into contact with an infected animal and either allowing the bacteria to enter a cut, breathing in the bacteria, or by consuming unpasteurized milk or fresh goat cheese obtained from a contaminated animal. In the United States, the disease is primarily confined to slaughterhouse workers.
Scientists do not agree about whether brucellosis can be transmitted from one person to another, although some people have been infected from a tainted blood transfusion or bone marrow transplant. Newborn babies have also contracted the illness from their mothers during birth. Currently, it is believed that brucellosis can also be transmitted sexually.
The disease is not usually fatal, but the intermittent fevers (a source of its nickname, "undulant fever") can be exhausting. Symptoms usually appear between five days and a month after exposure and begin with a single bout of high fever accompanied by shivering, aching, and drenching sweats that last for a few days. Other symptoms may include headache, poor appetite, backache, weakness, and depression. Mental depression can be so severe that the patient may become suicidal.
In rare, untreated cases, the disease can become so severe that it leads to fatal complications, such as pneumonia or bacterial meningitis. B. melitensis can cause miscarriages, especially during the first three months of pregnancy. The condition can also occur in a chronic form, in which symptoms recur over a period of months or years.
— Carol A. Turkington
