The genus Brucella consists of 8 or 9 species, four of which cause human brucellosis
Are all intracellular organisms
Brucella are small (0.4～0.8 Ч0.5～1.5μm), non-motile, non-capasulate, gram-negative coccobacilli. (very short rods) 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
Antigenic Structure and classificationTwo 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.canis no A & M antigen.
B. abortusBacteria is excreted in genital secretions (including semen), milk, colostrum.
Cheese at 4oC: 180 days !!!
Water at 25oC: 50 days
Meat and salted meat: 65 days
Manure at 12oC: 250 days !!!!
Widespread: Cattle, Bison, Elk, Deer, Moose, Horse, Sheep, Goat, Swine, Donkey, Dogs, Birds, Hares, Fox, Rats, mice, Camels and Human.
Spread of Brucella in the bodyIncubation 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
Portals of entryOral entry - most common route
Ingestion of contaminated animal products (often raw milk or its derivatives)
contact with contaminated fingers
Inhalation of bacteria
Contamination of the conjunctivae
Percutaneous infection through skin abrasions or by accidental inoculation
Clinical ManifestationsThe presentation of brucellosis is characteristically variable
The onset may be insidious or abrupt
Influenza-like with fever reaching 38 to 40oC
Limb and back pains are unusually severe, night sweating and fatigue are marked.
Anorexia, weakness, severe fatigue and loss of weight, depression
The leukocyte count tends to be normal or reduced, with a relative lymphocytosis
On physical examination, splenomegaly may be the only finding.
COURSE OF BRUCELLOSISIf the disease is not treated, the symptoms may continue for 2 to 4 weeks
Many patients will then recover spontaneously
Others may suffer a series of exacerbations
May produce an undulant fever in which the intensity of fever and symptoms recur and recede at about 10 day intervals.
BrucellosisCyprus fever/Gibraltar fever/Malta fever/Rock fever/Undulant fever
Most affected persons recover entirely within 3 to 12 months
Some will develop complications
involvement of various organs,
a few may enter an ill-defined chronic syndrome.
COMPLICATIONSArthritis, often sacroiliitis, and spondylitis (in about 10 percent of cases)
central nervous system involvement including meningitis (in about 5%)
Endocarditis very rare
In contrast to animals, abortion is not a feature of brucellosis in pregnant women.
Population riskThe main source of infection for the general population is dairy produce prepared from infected milk.
B. melitensis presents the greatest hazard.
The milk of infected sheep and goats may contain large numbers of viable organisms, which become concentrated in products such as soft cheeses.
Indeed, soft cheese has been recognized as a major vehicle of infection in the Mediterranean region, the Middle East and Latin America
Occupational hazardInfection arises from occupational or domestic contact with infected animals or with an environment contaminated by their discharges
Farmers and their families, abattoir workers, butchers and veterinarians are particularly at risk
Extending spectrum of zoonosisThe recent isolation of distinctive Brucella strains, tentatively named Brucella maris, from marine animals in the United Kingdom and the United States extends the ecologic range of the genus and, potentially, its scope as a zoonosis
seals, sea otters, dolphins and porpoises
An incident of laboratory-acquired infection suggests that this type is pathogenic for humans
Infection could result from occupational contact with infected seals or cetaceans.
CLINICAL DIAGNOSISLaboratory identification
The organism can be cultured from blood and other body fluids or from tissue specimens. Multiple blood specimens should be cultured. For plated materials, colonies may appear in 4 to 5 days, whereas longer times are required for blood cultures, and these are routinely examined for up to 1 month before being declared negative.
SanitaryPasteurization of dairy products and use of protective clothing prevent human infection. More importantly, systematic identification and elimination of infected animals and vaccination of animals reduces the reservoir.
PreventionEradication of brucellosis in cattle can be attempted by test and slaughter,active immunization of heifers with avirulent live strain 19, combined testing, segregation, and immunization. Cattle are examined by means of agglutination tests
Active immunization of humans against brucella infection is experimental. Control rests on limitation of spread and possible eradication of animal infection,pasteurization of milk and milk products, and reduction of occupational hazards wherever possible.