Persistence of Brucella abortus infection in six herds of cattle under brucellosis eradication

Authors: Cordes DO, Carter ME
Publication: New Zealand Veterinary Journal, Volume 27, Issue 12, pp 255-259, Dec 1979
Publisher: Taylor and Francis

Animal type: Cattle, Livestock, Production animal, Ruminant
Subject Terms: Bacterial, Biosecurity, Disease/defect, Infectious disease, Clinical pathology, Diagnostic procedures, Disease control/eradication, Disease surveillance, Epidemiology, Notifiable organisms/exotic disease, Reproduction, Zoonosis, Public health
Article class: Scientific Article

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Abstract: Six herds of dairy cattle, in which infection had persisted after measures had been employed to eradicate brucellosis, were investigated in detail. One hundred and two animals out of 700 (14.6%) had evidence of the disease from cultural or serological tests. Only 4 infected animals aborted; the remaining 98 animals with brucellosis exhibited no clinical sign of the disease, and 52 were heifers calving for the first time. Sixty-five of the 700 animals (9.3%) produced brucella-infected vaginal discharges at the end of a normal period of gestation, and another 17 (2.4%) were detected only by the brucellosis (Brewer) card test (BCT) or complement fixation test (CFT). All the infected animals were removed from the herds immediately after detection. About 2 weeks after all the cows had calved, 20 of the remaining 510 animals (3.9%) in 4 of the herds became positive to one or more tests and 8 excreted brucellae in their milk. The pregnancy of three 2-year-old primiparous heifers terminated normally and one aborted. All four discharged brucellae until they were slaughtered 20 to 35 days after parturition. Twenty-five of the 102 infected animals were detected by bacteriological, and 29 by serological, means only. A comparison was made of the results of the tests from 73 culturally positive animals; 4.1% of the sera were CFT positive but BCT negative, and 5.5% were BCT positive but CFT negative. An attempt has been made to explain the large numbers (34.2%) of infected animals that were serologically negative.

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