Results suggest that persistent ocular infection with L interrogans is common in horses with recurrent uveitis. A 4-fold increase in vitreous humor versus serum antibody titers may not be a sensitive test for the diagnosis of L interrogans-induced recurrent uveitis. We hypothesize that the immune component of recurrent uveitis can be directly induced and maintained by persistent infection of the eye with L interrogans.

This study documents the examination of 17 horses (both sexes, 3-18 years old) suffering from spontaneous equine recurrent uveitis (ERU). Vitreal samples obtained by pars plana vitrectomy were examined macroscopically and ultrastructurally, and in most cases also by cultural examination, by microscopic agglutination test (MAT) and by polymerase chain reaction. In 24% (4/17) of the animals, ultrastructural examination by electron microscopy revealed intact leptospiral bacteria in the vitreous. The leptospires were detected freely in the vitreous and also incorporated by a phagocyte. They were surrounded by a rim of proteinaceous material which was reduced around a phagocytosed leptospira. Ninety-four per cent (16/17) of the vitreal samples presented significant antibody levels in the MAT, mostly against leptospiral serovar Grippotyphosa. Seventy-five per cent (9/12) of bacterial culture examinations were positive for leptospira. Polymerase chain reaction was positive in all (16/16) examinations performed. Our findings support previous reports suggesting that leptospires play an important role in the pathogenesis of ERU. Interestingly, this study found leptospires after secondary and later acute episodes. A persistent leptospiral infection is therefore suggested as the cause of ERU.

ZusammenfassungDie Literatur zur Ätiologie der equinen rezidivierenden Uveitis (ERU) erscheint seit Jahrzehnten verwirrend, da einerseits wegen nachweisbaren Autoimmunreaktionen eine "Autoimmunkrankheit" beschrieben wird, andererseits jedoch wiederholt Nachweise einer intraokularen Leptospireninfektion erfolgt sind. Die Etablierung der Vitrektomie bei an ERU erkrankten Pferden ermöglicht erstmals die routinemäßige Entnahme von Glaskörperproben aus vielen der betroffenen Augen. Diese im Rahmen der Vitrektomie gewonnen Glaskörperproben können sowohl zur Untersuchung auf zelluläre und humorale Autoimmunphänomene als auch zu mikrobiologischen Studien verwendet werden und zur Klärung der Ätiologie und Pathogenese der ERU dienen. Neben Serumproben von 724 an ERU erkrankten und von 132 augengesunden Pferden konnten von 1998 bis 2001 bei Vitrektomien von 426 eindeutig an ERU erkrankten Augen unverdünnte Glaskörperproben unter sterilen Kautelen entnommen werden. Als Kontrolle dienten 54 Glaskörperproben aus gesunden Pferdeaugen. Alle Proben (Serum und Glaskörper) wurden mittels Mikroagglutinationsreaktion (MAR) auf Antikörper gegen Leptospiren getestet. Für die Berechnung des Goldmann-Witmer-Koeffizienten (C) wurden bei 36 Glaskörper-und Serumprobenpaaren Elektrophoresen durchgeführt. Zur Anzüchtung von Leptospiren wurden 41 Glaskörperproben aus gesunden und 358 Glaskörperproben aus an ERU erkrankten Augen kultiviert. Von den Glaskörperproben aus an ERU erkrankten Augen wurden zudem 55 mittels PCR auf Leptospiren-DNA untersucht. Aus 6 vitrektomierten Augen konnten in unterschiedlichen Abständen nach der Operation erneut Proben entnommen und mittels MAR untersucht werden. Der Krankheitsverlauf von 150 der operierten Pferdeaugen wurde im Mittel bis 2,7 Jahre nach der Vitrektomie weiter verfolgt. Zwischen Höhe und Vorkommen von Antikörpertitern gegen Leptospiren im Serum von augengesunden und an ERU erkrankten Pferden bestand ein geringer, jedoch nicht signifikanter Unterschied. Die MAR konnte in 3/54 (6 %) der Glaskörperproben aus gesunden Pferdeaugen sowie in 382/426 (90 %) der Glaskörperproben aus an ERU erkrankten Augen Antikörper gegen Leptospiren nachweisen. Die Berechnung des Goldmann-Witmer-Koeffizienten konnte für 34/36 (94 %) der Probenpaare eine intraokulare Antikörperproduktion nachweisen (C > 8). In 189/358 (53 %) Glaskörperproben aus an ERU erkrankten Pferdeaugen und in keiner der 41 Glaskörperproben aus gesunden Augen konnten kulturell Leptospiren nachgewiesen werden. Die positiven Kulturergebnisse konnten sowohl aus Augen erzielt werden, die erst wenige Wochen erkrankt waren, als auch aus Augen, die schon über viele Jahre rezidivierende Entzündungen gehabt hatten. Bei 18/189 (9,5 %) der Serum-und Glaskörperprobenpaare mit positivem Kulturbefund in den Glaskörperproben konnten in den zugehörigen Serumproben keine Antikörper gegen Leptospiren mehr nachgewiesen werden. Die Polymerase-Ketten-Reaktion (PCR) wies in 39/55 (71 %) Glaskörperproben aus an ERU erkrankten Augen Leptospiren-DNA nach. In den 6 Glaskörper...

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.

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans, but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.