16 - Brucella The genus Brucella consists of six species...

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Brucella The genus Brucella consists of six species, four of which cause human brucellosis 布布布布 Brucella melitensis 布布布布 , Brucella suis 布布布 , Brucella abortus 布布布布 , and Brucella canis 布布布布 Are all intracellular organisms B. neotomae; B. ovis
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Brucella are small (0.4 ~ 0.8 ×0.5 ~ 1.5μm), non-motile, non-capasulate, gram- negative coccobacilli. The organism is aerobic, and their nutritional requirements are complex. All strains grow best in a medium enrich with animal serum and glucose 5-10% carbon dioxide
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Antigenic Structure and classification Two main antigen: A and M The three main Brucella differ from one another in the amount or the two main antigen they have in common : B.abortus : A:M=20:1 B.melitensis: A:M=1:20 B.suis: A:M=2:1
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B. abortus Bacteria is excreted in genital secretions (including semen), milk, colostrum. Survival time : Cheese at 4 o C: 180 days !!! Water at 25 o C: 50 days Meat and salted meat: 65 days Manure at 12 o C: 250 days !!!! Widespread: Cattle, Bison, Elk, Deer, Moose, Horse, Sheep, Goat, Swine, Donkey, Dogs, Birds, Hares, Fox, Rats, mice, Camels and Human.
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B. abortus Sources of Human Infection: Raw milk and products /Direct contact Portal of entry : oral mucosa, nasopharynx and conjunctivae, genital then X in regional lymph node and spread to RES (nodes of udder, uterus, erythritol...). Placentitis with endometritis. Fetus die with edema /congestion of lung, dissimenated hemorrhages of epicardium and splenic capsule. Bacteria in lung and digestive tract of the fetus. B. abortus Bacteria is excreted in genital secretions (including semen), milk, colostrum. Survival time : Cheese at 4 o C: 180 days !!! Water at 25 o C: 50 days Meat and salted meat: 65 days Manure at 12 o C: 250 days !!!! Widespread: Cattle, Bison, Elk, Deer, Moose, Horse, Sheep, Goat, Swine, Donkey, Dogs, Birds, Hares, Fox, Rats, mice, Camels and Human. B. melitensis Goat (1886), Sheep, Cow (1905 in Malta), Swine, Hares, Camels, Buffalo, Impala . B. suis Wild pigs, Rats, Swine. Abortion,metritis, bursitis, spondylitis (Lumbar and sacral), arthritis, orchitis, paralysis. Brucella canis Brucella canis was first described as a cause of abortion in beagles in the USA It was subsequently shown to infect dogs in many other countries, irrespective of breed An occasional cause of brucellosis in humans
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Spread of Brucella in the body
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Incubation period Acute or subacute disease follows an incubation period which can vary from 1 week to 6 or more months . In most patients for whom the time of exposure can be identified, the incubation period is between 2 and 6 weeks The length of the incubation period may be influenced by many factors virulence of the infecting strain size of the inoculum route of infection resistance of the host
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Portals of entry Oral entry - most common route Ingestion of contaminated animal products (often raw milk or its derivatives) contact with contaminated fingers Aerosols Inhalation of bacteria Contamination of the conjunctivae Percutaneous infection through skin abrasions or by accidental inoculation
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