A cross-sectional study was carried out in the Basque Country of Spain to determine the seroprevalence of 10 Leptospira serovars in a population of dairy cattle with poor fertility, and a case-control study was carried out in another northern area to investigate the role of Leptospira interrogans serovar Bratislava in abortions. L Bratislava was the most prevalent serovar in the cross-sectional study, with 25·4 per cent of the cows testing positive in the microagglutination test when a cut-off of 1:10 or higher was applied, followed by Leptospira Hardjo (8·2 per cent), Leptospira Pomona (7·7 per cent), Leptospira Autumnalis (0·7 per cent) and Leptospira Copenhageni (0·1 per cent). In the case-control study the seroprevalence of L Bratislava was significantly higher among the cows which had aborted when a titre of 1:300 or more was used as a cut-off (9·7 per cent v 3·4 per cent, P=0·008); 69 per cent of the L Bratislava-infected cows that had aborted apparently aborted as a result of the infection.
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