Brucella

Brucella is a genus of gram negative, small, non-encapsulated coccobacilli which are strict aerobes.

Route of entry

• Ingestion of contaminated milk products
• Through the skin by direct contact
• Inhaled in aerosols

Pathogenesis

• Majority are killed by macrophages, rest survive in macrophages
• Invade the body through mucous of upper intestinal and respiratory tracts or skin lesions.
• Enter sub serosa and are transported by macrophages to lymph nodes of liver, spleen and bone marrow
• Enter bloodstream
• Host response is granulomatous, which progresses to focal abscesses
• Produce endotoxin but no exotoxin

Virulence factors
• Endotoxin

Predisposing factors
• Inflected animals
• Unpasteurized milk

Clinical symptoms
• Incubation period is 01-03 weeks
• Fever is seen in minority of cases and it is undulating fever
• Chills
• Fatigue
• Malaise
• Anorexia
• Weight loss
• Enlarged spleen, liver, lymph nodes
• Pancytopenia
• Osteomyelitis –a complication

Lab Diagnosis

Specimen
• Blood
• Bone marrow

Microscopy
• Gram negative
• Small, coccobacilli
• Non-encapsulated
• Strict aerobes

Culture
Strict aerobes, requiring 5-10% CO2

Tryptone soya diphase medium
Produce variety of colonies, e.g smooth, mucoid, colourless or grey, white colonies

TSI agar
No H2S is produced

Biochemical Tests
• Catalase +ve
• Oxidase +ve
• Indole -ve
• Hydrolyze urea

Serological tests
• Slide agglutination test with Brucella antiserum.
• Rapid IgM/IgG immunochromatographic assay
• PCR

Treatment

• Tetracycline
• No vaccine is available