Leptospiral abortions of sows: new data

In an immunization experiment, 460 sows at 7-60 days of gestation were inoculated with a rodent-adapted live strain of Leptospira interrogans serovar tarassovi at a large swine farm previously affected by this serovar. The inoculum consisted of a haemoculture prepared from the 52nd guinea-pig passage and the dose was 2 X 10(7) leptospires per sow. Over the period from the 48th to the 73rd day after inoculation 54 out of 283 sows having been inoculated at 32-60 days of gestation, aborted or delivered weak piglets. At the same time, 177 sows inoculated at days 7-32 of gestation farrowed normal litters. Altogether 18 underdeveloped piglets 2-5 weeks old derived from naturally infected litters were killed, but leptospires were not demonstrated or cultivated from their swollen and pale kidneys. It seems that L. interrogans serovar tarassovi is able to cause foetal damage in susceptible sows at one-two months of pregnancy and that previous adaptation of this serovar to rodents does not reduce its pathogenicity for porcine foetuses.