Microbiology Zoonotic infection Bacteriology Veterinary Microbiology Explanation of Brucella pathogenesis of brucella important species

1. BRUCELLA
By
Zainab Shabbbir

2. General Features
• Causes brucellosis also known as Malta fever. Undulent fever and
meditranean fever.
• Small gram negative ,Coccobacilli
• Slow growing
• Aerobic , non-spore forming, non-motile
• No capsule
• Obligate intracellular parasite of human and animals (capable of surviving
and replicating within phagocytic cells)
• Complex nutritional requirements ( media containing amino acids,
vitamin, salts and glucose)
• Catalase and oxidase positive
• Brucella colonies become visible on suitable solid media in 2-3 days.
• Farrell medium (FM) and modified Thayer-Martin medium (mTM) are
selective media for Brucella.

3. Important Species
• Four common species include:
• B.abortus ( Effects cattle)
• B.suis ( Swine)
• B.canis ( dogs )
• Brucella melitensis ( goat)

4. In Humans
• Transmission
• Common routes of entry are gastrointestinal tract
(consumption of contaminated milk) mucous membrane and
skin (by contact with infected tissues of animal).
• Cheese made from unpasteurized goat milk is also common
vehicle.

5. Pathogenesis
• Brucellae are facultative intracellular parasites, multiplying mainly in monocyte-
macrophage cells.
• Portal of entry are conjuctiva, mouth respiratory tract and abraded skin.
• From portal of entry organism progress via lymphatic channels and regional
lymph nodes to the thoracic duct and blood stream and reaches to
parenchymatous organs ( kidney, spleen, liver, and pancrease).
• Granulomatous nodules that may develop into abscesses form in lymphatic tissue,
liver, spleen, bone marrow, and other parts of the reticuloendothelial system.
• The main histologic reaction in brucellosis consists of:
• Proliferation of mononuclear cells,
• Exudation of fibrin,
• Coagulation necrosis, and fibrosis.
• The granulomas consist of epithelioid and giant cells, with central necrosis and
peripheral fibrosis.
• There is no erythritol in human placentas, and abortion is not part of Brucella
infection of humans.

6. Infection cycle

7. • The brucellae that infect humans have apparent
differences in pathogenicity.
• B. abortus usually causes mild disease without
suppurative complications; noncaseating granulomas of
the reticuloendothelial system are found.
• B.canis also causes mild disease.
• B. suis infection tends to be chronic with suppurative
lesions and caseating granulomas
• B.melitensis infection is more acute and severe.

8. In Animals
• Placentas and fetal membranes of cattle, swine,
sheep, and goats contain erythritol, a growth factor
for brucellae.
• The proliferation of organisms in pregnant animals
leads to placentitis and abortion in these species.

9. Clinical Findings
• In the simplest case, the onset is influenza like with fever reaching 38 to 40°C.
Limb and back pains are unusually severe.
• The leukocyte count tends to be normal or reduced, with a relative lymphocytosis.
• The onset is insidious, with malaise, fever, weakness, aches, and sweats.
• The fever usually rises in the afternoon; it falls during the night and is accompanied
by drenching sweat therefore known as undulant fever.
• There may be gastrointestinal and nervous symptoms.
• Lymph nodes enlarge, and the spleen becomes palpable.
• Chronic stage is characterized by weakness, aches and pains, low-grade fever,
nervousness, and other nonspecific manifestations compatible with psychoneurotic
symptoms.
• Relapses are not uncommon, focal lesions may occur in bones joints, genitourinary
tract and other sites.
• Hypersensitivity reactions can follow occupational exposure.
• In contrast to animals, abortion is not a feature of brucellosis in pregnant women
which is due to absence of meso-erythritol in human while present in animals

10. Prevention
• Occupationally exposed individuals can be protected
by using impermeable gloves, rubber boots and face
mask.
• Pasteurization of milk for direct consumption or
preparation of dairy products can reduce risk of
infection.
• In eradication campaigns, the level of enzootic
disease can first be reduced by intensive use of live,
attenuated vaccines (B.abortus strain 19 in cattle,
B.melitensis strain Rev. 1 for sheep and goats)
particularly in immature animals.

11. Treatment
• The treatment of choice is tetracycline plus rifampin.
There is no significant resistance to these drugs.
• Combination of antibiotics for weeks.
• Doxycycline, rifampin and cotrimoxazole are
commonly used.

12. References
• https://www.ncbi.nlm.nih.gov/books/NBK8572/
• https://microbenotes.com/brucella-agar/
• https://en.wikipedia.org/wiki/Brucella