Difference between revisions of "Brucella species"

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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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#REDIRECT[[:Category:Brucella species]]
<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
 
 
 
 
 
 
 
===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 - Anatomy & Physiology|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===
 
 
 
*Bovine brucellosis:
 
**Caused by ''Brucella abortus''
 
**Eradicated in many countries including UK
 
**Infection usually by ingestions but also venereal, skin abrasions, inhalation, transplacental
 
**Abortion storms in susceptible herds
 
**Abortion after fifth month of gestation due to placentitis
 
**Brucellae excreted in foetal fluids for 2-4 weeks following abortion and at subsequent parturitions without abortion
 
**Infection of mammary glands and lymph nodes persists for years
 
**Excreted intermittently in milk for years
 
**Seminal vesicles, ampullae, testicles and epididymus infected in bulls; necrotising orchitis
 
**Decreased fertility in cows and bulls; decreased milk production
 
**Localisation in [[Spleen - Anatomy & Physiology|spleen]] and lymphatic tissue of non-pregnant animals
 
**Occasionally causes [[Joints Inflammatory - Pathology#In Cattle|arthritis]]
 
*Isolated from closed cases of [[Bursae and Tendons - inflammatory#Poll Evil and Fistulous Withers|poll evil and fistulous withers]] in horses
 
*Caprine and ovine brucellosis:
 
**Caused by ''B. melitensis''
 
**Goats more susceptible
 
**Abortion, orchitis in males, arthritis, hygromas
 
**May not have protective immunity following abortion
 
**Rose Bengal agglutination test and complement fixation test
 
**Test and slaughter where exotic
 
*Ovine epididymitis
 
**Caused by ''B. ovis''
 
**Epididymitis in rams and placentitis in ewes
 
**Reduced fertility in rams, sporadic abortion and peinatal mortality
 
**Venereal transmission
 
**Long latent period in rams following infection (present in semen 5 weeks after infection)
 
**Premating checks on rams - serological tests and scrotal palpation
 
**Testicular atrophy and swollen epididymis in chronically-infected rams
 
**Agar gel immunodiffusion test, complement fixation test and indirect ELISA
 
**Vaccination of young rams with ''B. melitensis'' vaccine or ''B. ovis'' bacterin
 
*Porcine brucellosis:
 
**Caused by ''B. suis''
 
**Prolonged bacteraemia
 
**Chronic inflammation in reproductive organs of boars and sows; also in joints and bones
 
**Routes of infection: ingestion or venereal
 
**Abortion, still birth, neonatal mortality, temporary sterility
 
**Boars excreting bacteria in semen may have testicular abnormalities or be normal
 
**Lameness, incoordination and posterior paralysis in joint and bone involvement
 
**Rose Bengal and indirect ELISA for diagnosis
 
**Test and slaughter where exotic
 
**Modified live ''B. suis'' vaccine
 
*Canine brucellosis:
 
**Caused by ''B. canis''
 
**Rough therefore lower virulence - mild or asymptomatic infections
 
**Abortions, decreased fertility, reduced litter sizes, neonatal mortality
 
**Orchitis and epididymitis causing infertility in male dogs
 
**Infertility may be permanent if chronic infection
 
**Slide agglutination, ELISA, agar gel immunodiffusion
 
**Neuter infected animals
 
*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''
 

Latest revision as of 21:06, 10 May 2010