Leptospirosis is a worldwide zoonotic disease of domestic animals and wildlife. It is caused by a spirochete bacteria classified under the genus Leptospira. The taxonomy of the genus is confusing, with a number of species and serovars. In cattle leptospirosis is primarily due to Leptospira borgpetersenii serovar hardjo (L. hardjo) and Leptospira interrogans serovar pomona (L. pomona). Both serovars may affect cattle of all ages but clinical signs greatly vary depending on the serovar and the age of the animals.
L. pomona may cause acute infections especially in calves. Calves may demonstrate high fever, anorexia, dyspnea, hemolytic anemia, hemoglobinuria, icterus, and high mortalities. Acute infections of naive cattle with L. hardjo are characterized by a sudden drop in milk production. The milk is thick, yellow, and blood-tinged. The udder is typically soft and flabby. L. hardjo causes the milker’s fever syndrome. Moreover both serotypes may cause abortion which generally occurs in late pregnancy. Stillbirths and birth of premature or weak infected calves also occur.
The diagnosis of leptospirosis especially in adult cattle may be difficult. Culture in special media, PCR, immunohistochemistry techniques and serology may be used. Antibody titers may peak before abortion because the acute infection occurred several weeks previously. Abortion due to L. hardjo infections may occur with low or negative serologic titers.