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Summary

The pathogenesis of equine recurrent uveitis (ERU) is not completely understood. Persistent infection of pathogenic leptospires in the eyes is the probable primary cause. Consistently, we isolated and characterized in this study leptospires from 32.2% of the intraocular samples collected from 501 horses from the following Western European countries: Germany, Switzerland, Austria, The Netherlands, Luxembourg, Great Britain, Italy and Poland. The vast majority of the leptospiral isolates belonged to serogroup Grippotyphosa (78.2%). The other isolates belonged to the Australis group (14.2%), the Sejroe group (3.6%), the Pomona group (2.5%) and the Javanica group (1.5%). Apart from three isolates that likely belong to Leptospira kirschneri, serovar Dadas, all Grippotyphosa group isolates belonged to L. kirschneri, serovar Grippotyphosa. Analysis with monoclonal antibodies revealed that the isolates differed from Moskva V, the reference strain of serovar Grippotyphosa. However, the Grippotyphosa isolates closely resembled serovar Grippotyphosa, strain Duyster, which has been isolated from a Dutch patient. Because of apparent phenotypic and genotypic differences between the strains Moskva V and Duyster, we propose two different types within serovar Grippotyphosa, namely type Moskva and type Duyster. Distribution of type Duyster is restricted to Western Europe. Strikingly, only a few serovars were isolated from the eyes of horses with ERU. A number of other commonly occurring serovars, such as Copenhageni, were not found, whereas the presence of antibodies in blood and eye fluids against such serovars suggests that infection occurs. Therefore, we hypothesize that, while many pathogenic serovars might be able to penetrate the eyes, only few are capable to persist.