Effect of streptomycin treatment on the shedding of and the serologic responses to Leptospira interrogans serovar hardjo subtype hardjobovis in experimentally infected cows.

Shedding patterns of and serologic responses to Leptospira interrogans serovar hardjo subtype hardjobovis (L. hardjobovis) have been studied in experimentally infected cows treated with streptomycin in comparison to experimentally infected cows receiving no such treatment. Fourteen cows were experimentally infected with L. hardjobovis, and blood and urine samples were collected weekly for 24 weeks. The microscopic agglutination test (MAT) and enzyme-linked immunosorbent assay (ELISA) were used to determine serologic responses. The polymerase chain reaction (PCR) was used to determine bacterial shedding in urine. Six weeks after infection six cows were treated with the antibiotic streptomycin (25 mg/kg body weight/day); three cows were treated only once, and the remaining three were treated for five consecutive days. After treatment all six cows had lower serologic responses compared to the untreated cows. The treated cows became also PCR-negative two days after the first treatment, whereas the eight untreated cows remained PCR-positive for at least 70 days. Cows that stopped shedding did not resume shedding within the observation period. Since streptomycin treatment reduces the period of shedding, transmission of leptospira via contaminated urine might be prevented by a single treatment of an infected herd.