Syn:
Undulant
fever or Malta fever
Brucellosis, a zoonotic disease
caused by several species of the genus Brucella, may present as
an acute severe systemic disease or as a subacute or chronic disease.
Brucella are small , nonmotile , nonsporulating , gram-negative
coccobacilli , which may or may not be encapsulated.
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Four species infect humans, each from
its own animal reservoir.
Brucella melitensis
infects sheep and goats ; Brucella abortus , cattle ; Brucella
suis , swine ; and Brucella canis, dogs.
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The disease is
encountered worldwide and in all climates. Virtually every type of
domestic animal and many wild ones are affected.
The prevalence
relates to occupational exposure, cultural or socioeconomic conditions
resulting in close contact with animals, and consumption of
contaminated milk or milk products.
In much of the world the most common cause of infection
is unpasteurized dairy products.
In the arctic and subarctic regions
humans acquire brucellosis by eating raw bone marrow of infected
reindeer.
Infectious mastitis of cattle may persist for years after
recovery from the acute infection and remain a reservoir of Brucella.
Products of abortion may contain organisms and are infectious.
Urine, manure, and vaginal discharges are major sources of
contamination.
The incubation period is 5 days to
several months.
The onset of symptoms may be abrupt or insidious.
The
three clinical types of brucellosis are acute malignant, recurrent,and
chronic (intermittent).
The presenting features of acute malignant
brucellosis resemble those of influenza, and include the sudden onset
of high fever, chills, prostration, and somatic aches and pains.
Lymphadenopathy and a palpable spleen and liver are the only localized
findings.
Death may be sudden, within a few days of onset, or after a
few weeks of delirium and coma.
Recurrent brucellosis (undulant fever)
is characterized by influenza-like signs and symptoms that recur in
wavelike relapses.
The cycles may persist for weeks, gradually
decreasing in severity.
Chronic (intermittent) brucellosis is caused
primarily by B. abortus.
The onset may be acute or there may be
gradual increase in malaise, weakness, weight loss, and vague somatic
aches and pains. Fever is usually mild but weakness may be profound.
The most common complications of
brucellosis involve the bones and joints and include spondylitis of
the intervertebral area of the lumber spine and localized
suppuration in large joints.
In addition, peripheral neuritis,
meningitis, orchitis, suppurative endocarditis, and pulmonary lesions
may develop.
Bacteria enter through skin
abrasions, the conjunctiva, oropharynx, or lung and spread in the
bloodstream to the liver, spleen, lymph nodes, and bone marrow, where
they multiply in phagocytic cells.
A generalized histiocytic
hyperplasia ensues with conspicuous noncaseating granulomas, causing
lymphadenopathy and hepatosplenomegaly.
Patients with chronic
brucellosis may exhibit “coin” lesions in the lung resembling histoplasmomas
(infectious
granuloma of the lung caused by Histoplasma capsulatum)or the lesions of tuberculosis.
Histoplasmosis
Acute bacterial
endocarditis, myocardial abscesses
and focal suppurative
lesions in the myocardium are occasionally encountered.
Infective Endocarditis
The diagnosis must be confirmed by
isolating the organism in culture or by serologic testing.
Prolonged treatment with tetracycline
and streptomycin is usually effective.
Patients who recover from brucellosis
are immune.
Control of the disease depends on the
elimination of brucellosis in animal reservoirs.
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