Leptospirosis is zoonotic disease, which is caused by leptospira-bacteria. Leptospirosis is rare disease in Finland, but amount of leptospirosis cases can grow, when human and horses travel across the world. This thesis address diagnostic methods of leptospirosis, leptospirosis disease, symptoms, appearance, way of transmitting and treatment in horses. This thesis covers leptospira-bacteria's structure and genus.

Goal of this literature review was to compose a study, which can help to find information about diagnostic methods of leptospirosis in horses in Finnish language and that more information would be easier to find through the articles and studies. To this review was accepted 17 international research and review articles and one Finnish master´s thesis. These researches, review articles and master´s thesis were published during 2017–2022 to increase the reliability.

The most used diagnostic method was microscopic agglutination test. MAT was described to be the golden standard test. Other used method was PCR. In microscopic agglutination test, different titers for positive result were accepted. Most of the studies dilution of 1:100, where agglutination happened was the lowest limit for the positive result. Serum was the most used sample in the studies.

In the future the disease might spread easier in Finland. It would be good to do a study to find out what diagnostic methods would be the best to use in Finland and what methods can be expected to come. It would be necessary to understand and examine the most common serotypes, which cause the disease to horses in Finland. There is not enough current knowledge about them, because of the rareness of appearance in Finland.