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Brucellosis --- a flu-like disease

Introduction

Brucellosis, also known as undulant fever, Mediterranean fever is a zoonosis and the infection is almost invariably transmitted by direct or indirect contact with infected animals or their products. Expansion of animal industries and urbanization, and the lack of hygienic measures in animal husbandry and in food handling partly account for brucellosis remaining a public health hazard. Expansion of international travel which stimulates the taste for exotic dairy goods such as fresh cheeses which may be contaminated, and the importation of such foods into Brucella-free regions, also contribute to the ever-increasing concern over human brucellosis.

Clinical manifestation

a) Brucellosis infects many species, especially cattle, sheep, goats and pigs.
b) Different Brucella types infect different species preferentially.
c) Brucellosis presents typically as abortion in animals.
d) Diagnosis can only be confirmed by laboratory tests.

Host B.abortus B.melitensis B.suis B.canis B.ovis
Cattle + + + - -
Buffaloes + + - - -
Bison + - - - -
Sheep + + + - +
Goats + + - - -
Swine + + + - -
Dogs + + + + -
Camels + + - - -
Caribou/Reindeer - - + - -
Elk + - - - -
Horses + + + - -
Rodents + + + - -

Epidemiology

1) B.abortus causes most brucellosis in cattle, but B.melitensis and B.suis can also cause bovine infection.
2) B.melitensis is the main cause of brucellosis in sheep and goats and B.suis in swine.
3) Transmission occurs by direct contact and environmental contamination following abortion.
4) Sexual transmission and/or artificial insemination are also important.
5) Seronegative latent infections can occur.

Diagnosis

1) Bacteriological methods

Bacteriological methods Stained smears
Culture

The isolation and identification of Brucella offers a definitive diagnosis of brucellosis and may be useful for epidemiological purposes and to monitor the progress of a vaccination programme. It should be noted that all infected materials present a serious hazard, and they must be handled with adequate precautions during collection, transport and processing.

2) Serological methods

Serological methods Rose Bengal plate test (RBT)
ELISA tests
Serum agglutination test (SAT)
Complement fixation test (CFT)

The detection of specific antibody in serum or milk remains the most practical means of diagnosis of brucellosis. The most efficient and cost-effective method is usually screening all samples using a cheap and rapid test which is sensitive enough to detect a high proportion of infected animals. Samples positive to screening are then tested using more sophisticated, specific confirmatory tests for the final diagnosis to be made.

3) Supplementary tests

Supplementary tests Milk testing
Milk ring test
Milk ELISA
Fluorescence polarization assay
Intradermal test

a) Culture of Brucella from abortion material, milk or tissues collected at autopsy provides a definitive diagnosis.
b) Serology is usually the most practicable method.
c) Cattle: the RBT is recommended for screening; ELISA or complement fixation are recommended for confirmation of infection in individual animals. Screening of milk samples by milk ring test or ELISA is useful for surveillance.
d) Sheep, goats and pigs: no single serological test is reliable for confirmation of infection in individual animals. Serological tests should be used on a herd or flock basis. Similarly, the skin test is useful for screening at the herd or flock level, especially if vaccination is not used.
e) A “rough-specific” antigen must be used for B.canis serology.

Prevention, control and eradication of animal brucellosis

1) Animal brucellosis is best prevented by careful herd management and hygiene.
2) Vaccination is useful for prevention and control of infection.
3) B.abortus strains 19 and RB 51 are recommended for prevention of bovine brucellosis.
4) B.melitensis Rev 1 is recommended for prevention of B.melitensis infection in sheep and goats.
5) Vaccine efficacy may be limited in the face of heavy exposure.
6) Control and prevention schemes require effective collaboration between all sections of the community.
7) Control programmes must be properly planned, coordinated and resourced.
8) Education and information programmes are essential to ensure cooperation at all levels in the community.
9) Eradication can only be achieved by test and slaughter combined with effective prevention measures and control of animal movements.

References

FAO

Information Category