Category:Brucella species

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Overview

  • Important zoonoses worldwide
  • Cause chronic granulomatous diseases
  • 6 species
  • Target reproductive organs of certain species
  • Infected animals act as reservoir of infection
  • Organisms can remain viable in moist environment for months
  • Cause undulant fever in humans


Characteristics

  • Small, non-moltile, Gram negative coccobacilli
  • Facultative intracellular pathogens
  • Modified Ziehl-Neelsen positive - clusters of red coccobacilli on smears
  • Aerobic and capnophilic
  • Catalase positive; oxidase and urease positive except for Brucella ovis
  • Some species require enriched media for growth
  • Non-haemolytic
  • Smooth colonies of B. abortus, B. melitensis and B. suis are small, glistening, blue and translucent after incubation for 3-5 days, and become opaque with age
  • Rough colonies of B. ovis and B. canis are dull, yellow, opaque and friable
  • Slide agglutination with speicific antisera detect important antigens
  • B. abortus lysed by specific bacterophages
  • Oxidative metaboloic rates can differentiate species

Pathogenesis and pathogenicity

  • Brucellae that lack outer membrane LPS (rough colonies) are less virulent than those which possess it
  • Penetrate nasal, oral or pharyngeal mucosa
  • Phagocytosed and carried to regional lymph nodes
  • Smooth organisms survive and multiply in cells of the reticulo-endothelial system
  • Inhibit lysosome-phagosome fusion
  • Superoxide dismutase and catalase production may resist oxidative killing
  • Lymph nodes enlarge (lymphatic and lymphoreticular hyperplasia) and inflammation is induced
  • Surviving organisms spread to other organs (liver, spleen, placenta) and cause granulomatous reactions
  • Eythritol is a growth stimulant and attracts the bacteria to the placenta of cattle, sheep, goats and pigs; also found in mammary gland and epididymis, targets for brucellae
  • Infection of foetus and abortion
  • May localise in joints or intervertebral discs in chronic infections


Clinical disease

  • Human brucellosis:
    • Susceptible to B. abortus, B. suis, B. melitensis and B. canis
    • Transmission via contact with secretions from infected animals
    • Routes of infection: skin abrasions, inhalation, ingestion
    • Unpasteurised milk source of infection
    • Undulant fever - fluctuating pyrexia, malaise, fatigue, muscle and joint pains, osteomyelitis
    • Can become chronic
    • B melitensis and B. suis cause most severe infections
    • Antimicrobials

Diagnosis

  • Serological testing of milk (Milk Ring Test) and beef cattle (Rose Bengal Plate Test)
  • Serological tests detect anti-lipopolysaccharide antibodies
  • LPS antigen present in virulent as well as some vaccine strains therefore vaccination may confuse serological testing
  • False positives due to cross-reaction with LPS in other bacteria
  • Modified Ziehl-Neelson stains reveal organisms in samples from cotyledons, uterine discharge and foetal abomasal contents
  • PCR for detection in tissue
  • Brucellin for intradermal testing for B. abortus
  • Enriched media for isolation
  • Complement fixation test
  • Indirect and competitive ELISA
  • Serum agglutination test
  • Antiglobulin test


Control

  • Test and slaughter program has eradicated bovine brucellosis in the UK
  • Vaccination of heifers against B. abortus in endemic regions:
    • Strain S19, a live attenuated vaccine, stimulating a cell-mediated immune response; vaccination of young animals; interferes with serological testing
    • 45/20 bacterin vaccine less effective
    • Newer RB51 vaccine has no LPS O-antigen therefore not detected by serological tests and gives good protection
  • Live attenuated Brucella melitensis vaccine to protect lambs and kids against B. melitensis

Pages in category "Brucella species"

The following 6 pages are in this category, out of 6 total.