Medical Definition of Fever, undulant

Reviewed on 3/29/2021

Fever, undulant: An infectious disease due to the bacteria Brucella that characteristically causes rising and falling fevers, sweats, malaise, weakness, anorexia, headache, myalgia (muscle pain) and back pain.

The disease is called undulant fever because the fever is typically undulant, rising and falling like a wave. It is also called brucellosis after its bacterial cause.

The disease is transmitted through contaminated and untreated milk and milk products and by direct contact with infected animals (cattle, sheep, goats, pigs, camels, buffaloes, wild ruminants and, very recently, seals), and animal carcasses. Transmission can be through abrasions of the skin from handling infected animals. In the US, infection occurs more frequently by ingesting contaminated milk and dairy products. Groups at elevated risk include abattoir (slaughterhouse) workers, meat inspectors, animal handlers, veterinarians, and laboratory workers.

The incubation period of brucellosis is usually one to three weeks, but sometimes may be several months after exposure.

The symptoms are like those with many other febrile diseases, but with a marked effect on the musculoskeletal system evidenced by generalized aches and pains and associated with fatigue, prostration and mental depression. Urogenital symptoms may dominate the clinical presentation in some patients. The duration of the disease can vary from a few weeks to many months.

Undulant fever (brucellosis) is an extremely variable disease. In the acute form (less than 8 weeks from the onset of illness), the features are nonspecific and "flu-like." In the undulant form (8 weeks to a year after onset), the symptoms include undulant fevers, arthritis, and orchiepididymitis (inflammation of the testis and epididymis) in young males. In the chronic form (more than a year after onset), symptoms may include chronic fatigue syndrome-like, depressive episodes.

The sequelae (long-term consequences) of undulant fever (brucellosis) are also very variable. They may include granulomatous hepatitis, arthritis, spondylitis, anemia, leukopenia (low white blood cells), thrombocytopenia (low platelets), meningitis, uveitis (inflammation of the uvea of the eye), optic neuritis (inflammation of the nerve to the retina of the eye), and endocarditis (inflammation of the lining of the heart, heart valves and great blood vessels).

Millions of people worldwide are at risk for the disease, especially in developing countries where the infection in animals has not been brought under control, heat treatment procedures of milk (e.g. pasteurization) are not routinely applied, and food habits such as consumption of raw milk and poor hygienic conditions favor human infection. In the US, there are fewer than 0.5 cases per 100,000 population. Most cases are reported from California, Florida, Texas, and Virginia.

Antibiotics (such as doxycycline and rifampin) are effective against Brucella. However, Brucella is localized intracellularly (within cells) and requires the use of more than one antibiotic for several weeks.

Undulant fever can be prevented in people by controlling, or better, eliminating the disease in animals and avoiding consumption of raw milk and raw milk products. Proper heat treatment of milk or milk products is important for effective prevention of brucellosis in humans.

Bioterrorism -- There has been concern about brucellosis as a possible weapon for bioterrorism. The General Accounting Office, the investigative arm of the US Congress, in a 1999 report, however, considered brucellosis "not likely" to be a biologic threat for terrorism, because of the difficulty acquiring the seed stock of the agent (Brucella), the moderate difficulty in processing it, the long incubation period, and the "very low" lethal effects of the agent.



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