Abortion induced by cell-associated pseudorabies virus in vaccinated sows

Summary Pregnant sows, immune against pseudorabies after vaccination, were inoculated at 70 days of gestation either with autologous blood mononuclear cells that had been infected in vitro with pseudorabies virus (prv) or with cell-free prv. The infected cells or cell-free prv were inoculated surgically into the arteria uterina. Eight sows (A to H) had been vaccinated with an inactivated vaccine. The titer of seroneutralizing antibodies in their serum varied between 12 and 48. Five sows (A to E) were inoculated with autologous mononuclear cells, infected either with a Belgian prv field strain or with the Northern Ireland prv strain NIA3. These 5 sows aborted their fetuses: 2 of them (B and C) 3 days after inoculation, and the other 3 (A, D, and E) 10, 11, and 12 days after inoculation, respectively. Sows F, G, and H were inoculated with a cell-free prv field strain. They farrowed healthy litters after normal gestation. Neutralizing antibodies were absent against prv in the sera of the newborn pigs, which were obtained prior to the uptake of colostrum. The 23 fetuses that were aborted in sows B and C 3 days after the inoculation were homogeneous in appearance and size. Foci of necrosis were not detected in the liver. Viral antigens were located by immunofluorescence in individual cells in lungs, liver, and spleen of 15 fetuses. Virus was isolated from the liver, lungs, or body fluids of 12 fetuses. The 39 fetuses that were aborted in sows A, D, and E between 10 and 12 days after inoculation were of 2 types: 17 were mummified and 22 were normal-appearing. Foci of necrosis were found in the liver of all mummified fetuses and 13 of the normal-appearing fetuses. In fetuses with foci of necrosis in the liver, viral antigens were located in groups of cells in the liver, lungs, and spleen. Virus was isolated from 16 normal-appearing fetuses and from 11 mummified fetuses. Pseudorabies virus was isolated from vaginal excretions of sows A and D until 1 and 2 days after abortion, respectively, and of sows B and C until 4 and 5 days after abortion, respectively. Virus was not isolated from sow E. It was concluded that prv can reach the uterine and fetal tissues, via infected mononuclear cells, in the presence of circulating antibodies induced on vaccination. This cell-associated spread led to abortion. Cell-free virus did not induce abortion under similar circumstances.