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
- Facultatice 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
- 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 and lymphatic tissue of non-pregnant animals
- Occasionally causes arthritis
- Isolated from closed cases of 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