Brucellosis is an important zoonosis, and serological surveillance is essential to its control. However, cross‐reactions of attenuated live cells of Brucella abortus strain S‐19 and B. melitensis strain Rev‐1 with Yersinia enterocolitica O9 or vaccinated animal sera interfere with accurate serological diagnosis by the Rose Bengal test (RBT). Therefore, we used ELISA with sarcosine extracts from the virulent B. abortus strain 544 to eliminate false‐positives among RBT positive‐sera. A total of 697 serum samples were collected in Mongolia from humans and animals in 23 nomadic herds. The herds were classified into three groups as brucellosis‐endemic (BE), brucellosis‐suspected (BS), or Brucella‐vaccinated (BV). The number of 295 animals (43.0%) was positive by RBT, but 206 (69.8%) of these were positive according to ELISA; therefore, 30.2% of the RBT‐positive sera were found to be false positives. The false positive samples for RTB represent 4.1%, 27.4%, and 68.2% of the animals from the BE, BS, and BV herds, respectively. In addition, 32% of RBT‐positive human sera were also false positives. Thus, our ELISA would be more specific than RTB and useful for epidemiological surveillance for brucellosis.
ABSTRACT. To investigate Brucella infection in cattle, sheep, goat, reindeer and yak in Mongolia, serological reactions of Brucella-infected and -vaccinated domestic animals were compared by the agar gel immunodiffusion (AGID) test with a polysaccharide (poly-B) of the B. Abortus strain S-19. The sensitivity and specificity were compared with conventional serological tests that are commonly used in Mongolia, such as the rose Bengal test, the tube agglutination test and the compliment fixation test. A total of 73.3, 100, 100, 95.8 and 61.9% of the sera from suspected cattle, yak, goat, sheep and reindeer, respectively, that were positive in the compliment fixation test, were also positive in the AGID test. Sera from vaccinated cattle, sheep and goat were positive over 90% by conventional tests 3 months after vaccination, but were negative by the AGID. These results suggest that the AGID test may be useful to differentiate infected and vaccinated animals in the field. KEY WORDS: AGID test, Brucellosis, poly-B.J. Vet. Med. Sci. 64(9): 839-841, 2002 Brucella Abortus and Brucella Melitensis are bacteria that can cause abortions in domestic animals and undulant fever that may persist intermittently for years in humans. In Mongolia, young and adult domestic animals such as calves, sheep and goats have been vaccinated with attenuated live cells of B. Abortus strain S-19 and B. Melitensis strain Rev-1 to protect against brucellosis, but the protection is not an absolute [1] because brucellosis occurs every year in Mongolia. However, diagnosing brucellosis is difficult because vaccine strains have antigenicity similar to virulent strains of Brucella [2,6], and consequently differentiating infected and vaccinated animals is very hard. Reports exist that vaccinated and infected animals that have checked by the agar gel immunodiffusion (AGID) test using Brucella polysaccharide can be differentiated [2][3][4]6]. In this study, we show that the AGID test using polysaccharide (poly-B) antigen isolated from the B. Abortus vaccine strain S-19 can be useful in epidemiological studies to differentiate vaccinated and infected animals in Mongolia.Poly-B antigen was prepared by the method of DiazAparicio et al. [3]. Briefly, washed cells of B. Abortus strain S-19 were extracted with 2.0% acetic acid-10% NaCl at 120°C for 30 min. The cell debris was removed by centrifugation, and the supernatant was precipitated with methanol-1.0% sodium acetate. The precipitate was then chromatographed on Sphadex G-50 (Pharmacia, Uppsala, Sweden). We could not use wild-type strain for antigen preparation because of bio-safety problems in Mongolia, therefore B. Abortus strain S-19 was used for antigen preparation. The specificity of the AGID test using poly-B antigen was checked by using serum samples collected from 114 cattle and 42 sheep, which were selected from unvaccinated and brucellosis-free farms in Mongolia. All serum samples were negative by the rose Bengal test (RBT), the tube agglutination test (TAT) and the compliment fixation test (CFT...
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