RESUMO
Investigations were carried out on the presence of carriers and the excretion of the virulent swine fever virus in pigs vaccinated with the lapinized vaccine strain K. On the 15th, 25th, and 35th day following injection with the virulent virus a pig was killed each time and material was taken for morphologic studies and immunofluorescence microscopy. The results of the investigations were negative except for two pigs the cerebrum of which showed perivascular, slightly to moderately expressed lymphoid-cell agglomerations as well as a weakly manifested perivascular edema. Material of the killed animals was used to infect unvaccinated susceptible pigs in which the presence of the virus had not been demonstrated. No clinical and morphologic data or immunofluorescence microscopy demonstration proved the presence of a virus upon exposure of animals to pigs that were injected with a virulent virus. Hematologic studies revealed leukopenia, lower percent of hemoglobin, and a drop in the erythrocyte count following injection with the virulent virus. After a certain period of time this condition was overcome. These experiments showed that when a virulent virus gains access to pigs that have become immune after vaccination with the K vaccinal strain of the swine fever virus does not persist longer than the seventh day and does not cause the development of latent or a clinically manifested infectious process.