Effective treatment with dihydrostreptomycin of naturally infected cows shedding Leptospira interrogans serovar hardjo subtype hardjobovis.

The efficacy of dihydrostreptomycin in stopping the shedding of Leptospira hardjo subtype hardjobovis was studied in naturally infected cows. Blood and urine samples were collected from dairy cows kept on a farm where the farmer had contracted L hardjobovis infection. A microscopic agglutination test and an ELISA were used to determine specific antibody responses in serum. Polymerase chain reaction was used to detect bacterial shedding in urine. On the first sample collection date, 6 cows were seropositive, and 3 of those shed leptospires in the urine. These 3 cows were treated once with 25 mg of dihydrostreptomycin/kg of body weight. Within 1 week, the 3 cows stopped shedding leptospires. Six weeks later, 8 more lactating cows were found to be shedding leptospires. These cows were also treated once with dihydrostreptomycin, and they too stopped shedding leptospires within 1 week. From then on, the whole herd was examined weekly for a period of 2 months, and all cows Leptospira-positive by polymerase chain reaction were treated once with dihydrostreptomycin. Again, all cows stopped shedding leptospires in the urine within 1 week after treatment with dihydrostreptomycin. After a single treatment of the whole herd at the same time, new infections were not seen.