TOLERANCE STATE IN ANIMALS WITH LEPTOSPIROSIS
Tolerance to Leptospira in piglets may be induced on purpose by introducing avirulent Leptospira of certain serogroups to the new-born animals before first sucking of beestings. Experiments were executed on piglets. Five pregnant sows and one sow with 14 days old piglets were selected for the experiment at a leptospirosis-free farm. The sows were quarantined and examined for Leptospira and antibodies to Leptospira. The results were negative. Right after farrowing and before first sucking of beestings the piglets were isolated and intraperitoneally inoculated with avirulent Leptospira antigen of Pomona serogroup. The piglets were raised on artificial feeding. Twenty five days after the first inoculation each piglet was intraperitoneally inoculated with 2 ml of virulent Pomona serogroup culture. Challenged piglets were observed for 20 days more. It was found that introduction of 2 ml of live avirulent Leptospira culture (gr. 3) resulted in tolerance in up to 33% piglets while the same dose of dead Leptospira generated tolerance in 25% of piglets. Introduction of avirulent antigen on the 14th day after birth resulted in tolerance in 14.3% of piglets only. High ratio of Leptospira carriage (18.2%) among areactive (tolerant) animals is a substantially hazardous source of infection. It is necessary to screen for Leptospira carriage all pigs transferred to other farms for breeding purposes, including animals seronegative to leptospirosis. This requirement must be mandatory for all farms with history of leptospirosis.