Why bru­cel­losis vac­ci­na­tion is vi­tal

Be­cause bovine bru­cel­losis causes abor­tions, it has a se­vere im­pact on calv­ing per­cent­age. All live­stock farm­ers should play their part in erad­i­cat­ing the dis­ease by vac­ci­nat­ing their herds.

Farmer's Weekly (South Africa) - - Promotional Article -

Bovine bru­cel­losis has been iden­ti­fied as the sin­gle great­est threat to the red meat in­dus­try, apart from footand-mouth dis­ease. Bru­cel­losis is es­pe­cially dan­ger­ous as it is a zoono­sis, which means that hu­mans can also be­come in­fected.

Bru­cel­losis re­sults in abor­tions in cat­tle, and can cause dev­as­tat­ing losses for a farmer. The dis­ease is chronic and, once in­tro­duced, is without cure. Farm­ers are there­fore com­pelled by law to vac­ci­nate all their heifers once be­tween four and eight months of age with ei­ther S19 or RB51.

Bru­cel­losis is caused by the Bru­cella abor­tus bac­terium and is most com­monly spread be­tween herds by the move­ment of in­fected an­i­mals. In par­tic­u­lar, the dis­ease can be spread when healthy cat­tle lick or eat the dis­charge of in­fected an­i­mals dur­ing calv­ing or abor­tion, and for one month there­after. This can re­sult in an acute out­break of the dis­ease in a herd, dur­ing which 30% to 40% of in-calf fe­males may abort (a so-called abor­tion storm).

Abor­tions usu­ally oc­cur be­tween five months’ ges­ta­tion and full term. Hy­groma (fluid ac­cu­mu­la­tion in the knee joint) may ap­pear in some cases.

WHAT TO DO FOL­LOW­ING AN OUT­BREAK

• Send spec­i­mens to a lab­o­ra­tory Spec­i­mens of the foetal abo­masal fluid, lung, spleen, liver and foetal mem­branes should be taken from aborted foe­tuses. Smears should also be made of the abort­ing cow’s lochia and the cotyle­dons of the pla­centa. Th­ese sam­ples should be sent to a lab­o­ra­tory on ice as soon as pos­si­ble af­ter abor­tion, with each or­gan packed sep­a­rately in a ster­ile jar.

• Sero­log­i­cal tests

Blood sam­ples are col­lected by a vet­eri­nar­ian or a registered, au­tho­rised tech­ni­cian in vac­uum tubes prop­erly marked with the an­i­mal’s iden­ti­fi­ca­tion num­ber. The sam­ples are sent to a South African Na­tional Ac­cred­i­ta­tion Sys­tem lab­o­ra­tory for test­ing. A neg­a­tive re­sult im­me­di­ately af­ter abor­tion may be false, as the an­i­mal’s im­mune sys­tem might not yet have de­vel­oped an­ti­bod­ies, so a re­peat sero­log­i­cal test af­ter two weeks or more will pro­vide a more re­li­able re­sult.

La­tent heifers are a par­tic­u­larly dan­ger­ous threat as they can trans­mit bru­cel­losis and are car­ri­ers of the dis­ease, but do not yet show up pos­i­tive in sero­log­i­cal tests.

• Herd test

Bru­cel­losis di­ag­nos­tics should be in­ter­preted ac­cord­ing to the sta­tus of the herd of ori­gin, as bru­cel­losis is a herd dis­ease. A neg­a­tive test re­sult for an in­di­vid­ual an­i­mal means noth­ing without the herd sta­tus. If an in­di­vid­ual an­i­mal tests pos­i­tive, how­ever, the en­tire herd is seen as po­ten­tially pos­i­tive and has to un­dergo fur­ther test­ing un­der quar­an­tine.

Test­ing and retest­ing at herd level will also help to clar­ify sus­pi­cious re­ac­tions or re­ac­tions caused by late S19 vac­ci­na­tion.

COM­MU­NAL HERDS

Com­bat­ing bru­cel­losis in com­mu­nal herds is a chal­lenge as th­ese an­i­mals are reared in a farm­ing sys­tem where mul­ti­ple own­ers use common pas­tures and wa­ter­ing points. The cat­tle ef­fec­tively form a ho­moge­nous herd with sim­i­lar dis­ease sta­tus even though the var­i­ous own­ers do not nec­es­sar­ily make common de­ci­sions on their an­i­mals. Com­pli­ance with heifer vac­ci­na­tion as pre­scribed in the An­i­mal Dis­eases Act No. 35 of 1984 is usu­ally poor, there­fore th­ese cat­tle herds tend to be sus­cep­ti­ble to bru­cel­losis in­fec­tion when placed in con­tam­i­nated com­mu­nal graz­ing.

The pub­lic per­cep­tion of bru­cel­losis is also prob­lem­atic as the dis­ease is usu­ally not plainly ap­par­ent, so own­ers find it hard to ac­cept that their an­i­mals are af­fected or in­fected. To cull in­fected cat­tle has an un­de­sir­able im­pact on the so­cial stand­ing of the owner in the com­mu­nity. It is also dif­fi­cult to reach con­sen­sus on whose cat­tle are ‘re­spon­si­ble’ for the dis­ease and there­fore whose an­i­mals must be slaugh­tered for the ben­e­fit of all.

• Visit nahf.co.za, click on ‘Info Cen­tre’, then on Dis­eases.

• Phone the RPO on

012 349 1102/1103, or email [email protected]­tic.net.

FW AR­CHIVE

ABOVE: Cat­tle usu­ally be­come in­fected with bru­cel­losis by lick­ing or eat­ing in­fected af­ter­birth, eat­ing in­fected feed or grass, or drink­ing in­fected wa­ter.

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