Experimental leptospiral infections in pregnant cattle with organisms of the Hebdomadis serogroup.

The clinical and pathologic implications of leptospirosis caused by organisms of the Hebdomadis serogroup were tested on 8 pregnant cows. The animals were inoculated after their 5th month of pregnancy, 2 with serovar szwajizak and 6 with serovar hardjo. During the acute phase of the infection, the cows had mild signs of clinical illness; however, mastitis was observed in all cows that calved. One cow aborted, and 2 delivered premature and weak calves. By bacteriologic cultural examination, a short leptospiremic phase was observed. Leptospires were isolated from milk of 5 cows during early phases of mastitis; these isolations were obtained only when using solid media. Leptospiruria was determined by culture and direct examination. Only hardjo-inoculated cows had detectable urinary shedding which was observed to extend past 450 days in 1 cow. Leptospires were isolated from tissues of all cows and from 2 calves at necropsy. Interstitial nephritis was observed in all cows necropsied. Histologically, leptospires were demonstrated in silver-stained sections of kidney, liver, and lung of most calves. Leptospires were also observed in sections of kidney of all cows necropsied and in the cotyledons, placenta, and liver of some. Agglutinating titers were detected in the serum of cows as early as 4 days after inoculation and reached maximum titer (81,920) after 20 days. Significant serum titers persisted for the duration of the experiment only in hardjo-inoculated cows. At birth, all calves had no detectable agglutinins, but seroconverted within 24 hours; the serum titers were similar to those found in the dam's milk.