Brucella

Brucella

Brucella
The genus Brucella consists of 8 or 9 species, four of which cause human brucellosis Brucella melitensis, Brucella abortus Brucella suis Brucella canis Are all intracellular organisms B. neotomae B. ovis


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 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 B.canis no A & M antigen.

B. abortus

Bacteria is excreted in genital secretions (including semen), milk, colostrum. Survival time: 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 body

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

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

Clinical Manifestations

The 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 Headache The leukocyte count tends to be normal or reduced, with a relative lymphocytosis Relative leukopenia On physical examination, splenomegaly may be the only finding.

COURSE OF BRUCELLOSIS

If 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.

Brucellosis

Cyprus 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.

COMPLICATIONS

Arthritis, often sacroiliitis, and spondylitis (in about 10 percent of cases) central nervous system involvement including meningitis (in about 5%) Uveitis, epididymo-orchitis Endocarditis very rare In contrast to animals, abortion is not a feature of brucellosis in pregnant women.


Population risk
The 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 hazard

Infection 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 zoonosis

The 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 DIAGNOSIS

Laboratory 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.

Sanitary

Pasteurization 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.


Prevention
Eradication 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.