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  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 • • •