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| Credit: wikipedia.org |
Brucellosis, Bang's disease, Crimean
fever, Gibraltar fever, Malta fever, Maltese fever, Mediterranean
fever,rock fever, or undulant fever, is a
highly contagious zoönosis caused by ingestion of unpasteurized milk or
undercooked meat from
infected animals, or close contact with their secretions.
Brucella species
are small, gram-negative, nonmotile, nonspore-forming, rod-shaped
(coccobacilli)
bacteria. They function as facultative intracellular
parasites, causing chronic disease, which usually persists for
life. Four species infect humans: B. abortus, B. canis, B.
melitensis, and B. suis. B. abortus is less virulent than B.
melitensis and is primarily a disease of cattle. B. canisaffects
dogs. B. melitensis is the most virulent and invasive species; it
usually infects goats and occasionally sheep. B. suis is of
intermediate virulence and chiefly infects pigs. Symptoms include profuse sweating
and joint and muscle pain. Brucellosis has been recognized in animals and
humans since the 20th century.
Signs and symptoms
The symptoms
are like those associated with many other febrile diseases, but
with emphasis on muscular pain and sweating. The duration of the disease can
vary from a few weeks to many months or even years.
In the first
stage of the disease, septicaemia occurs and leads to the classic triad of
undulant fevers, sweating (often with characteristic smell, likened to wet
hay), and migratory arthralgia and myalgia (joint
and muscle pain). Blood tests characteristically reveal leukopenia andanemia, show some
elevation of AST and ALT, and demonstrate positive Bengal Rose and Huddleston
reactions.
This complex
is, at least in Portugal, Palestine , and Jordan, known as Malta fever. During
episodes of Malta fever, melitococcemia (presence of brucellae in blood) can
usually be demonstrated by means of blood culture in tryptose medium or Albini
medium. If untreated, the disease can give origin to focalizations or become
chronic. The focalizations of brucellosis occur usually in bones and joints and spondylodiscitis of
the lumbar spine accompanied by sacroiliitis is
very characteristic of this disease. Orchitis is
also common in men.
Diagnosis of
brucellosis relies on:
- Demonstration of the agent: blood cultures in tryptose broth, bone marrow cultures. The growth of brucellae is extremely slow (they can take up to two months to grow) and the culture poses a risk to laboratory personnel due to high infectivity of brucellae.
- Demonstration of antibodies against the agent either with the classic Huddleson, Wright, and/or Bengal Rose reactions, either with ELISA or the 2-mercaptoethanol assay for IgM antibodies associated with chronic disease
- Histologic evidence of granulomatous hepatitis on hepatic biopsy
- Radiologic alterations in infected vertebrae: the Pedro Pons sign (preferential erosion of the anterosuperior corner of lumbar vertebrae) and marked osteophytosis are suspicious of brucellic spondylitis.
The
disease's sequelae are highly variable and may include granulomatous
hepatitis, arthritis, spondylitis, anaemia, leukopenia, thrombocytopenia, meningitis, uveitis, optic
neuritis, endocarditis, and various neurological disorders
collectively known as neurobrucellosis.
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Cause
Brucellosis
in humans is usually associated with the consumption of unpasteurized milk and
soft cheeses made from the milk of infected animals, primarily goats, infected
with Brucella melitensis and with occupational exposure of laboratory
workers, veterinarians, and slaughterhouse workers. Some vaccines used in
livestock, most notably B. abortus strain 19, also cause disease in
humans if accidentally injected. Brucellosis induces inconstant fevers, miscarriage,
sweating, weakness, anaemia, headaches, depression, and muscular and bodily pain. The
other strains, B. suis and B. canis, cause infection in pigs and
dogs, respectively.
Diagnosis
Definite
diagnosis of brucellosis requires the isolation of the organism from the blood,
body fluids, or tissues, but serological methods may be the only tests
available in many settings. Positive blood culture yield ranges between 40% and
70% and is less commonly positive for B. abortus than B. melitensis or B. suis.
Identification of specific antibodies against bacterial lipopolysaccharide and other antigens can
be detected by the standard agglutination test (SAT), rose Bengal,
2-mercaptoethanol (2-ME), antihuman globulin (Coombs’) and indirect
enzymelinked immunosorbent assay (ELISA). SAT is the most commonly used serology in
endemic areas. An
agglutination titre greater than 1:160 is considered significant in nonendemic
areas and greater than 1:320 in endemic areas. Due to the similarity of the O
polysaccharide of Brucella to that of various other Gram-negative bacteria (e.g. Francisella tularensis, Escherichia
coli, Salmonella urbana, Yersinia enterocolitica, Vibrio
cholerae, and Stenotrophomonas maltophilia) the
appearance of cross-reactions of class M immunoglobulins may occur. The
inability to diagnose B. canis by SAT due to lack of cross-reaction
is another drawback. False-negative SAT may be caused by the presence of
blocking antibodies (the prozone phenomenon) in the α2-globulin (IgA) and in
the α-globulin (IgG) fractions. Dipstick assays are new and promising, based on
the binding of Brucella IgM antibodies, and found to be simple,
accurate, and rapid. ELISA typically uses cytoplasmic proteins as antigens. It
measures IgM, IgG, and IgA with better sensitivity and specificity than the SAT
in most recent comparative studies. The
commercial Brucellacapt test, a single-step immunocapture assay for the
detection of total anti-Brucella antibodies, is an increasingly used
adjunctive test when resources permit. PCR is fast and should be specific. Many
varieties of PCR have been developed (e.g. nested PCR, realtime PCR and
PCR-ELISA) and found to have superior specificity and sensitivity in detecting
both primary infection and relapse after treatment. Unfortunately,
these have yet to be standardized for routine use, and some centres have
reported persistent PCR positivity after clinically successful treatment,
fuelling the controversy about the existence of prolonged chronic brucellosis.
Other laboratory findings include normal peripheral white cell count, and
occasional leucopenia with relative lymphocytosis. The serum biochemical
profiles are commonly normal. Read more >>
Source: https://en.wikipedia.org/wiki/Brucellosis
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