ABORTION IN HEIFERS INOCULATED WITH A THYMIDINE KINASE-NEGATIVE RECOMBINANT OF BOVINE HERPESVIRUS-1

The Cooper isolate of bovine herpesvirus 1 (BHV-1) was used to produce a thymidine kinase-negative ( TK-) recombinant by insertion of a beta -galactosidase (bgal) expression cassette into the TK coding region. T he recombinant virus (TK(-)bgal+) was tested for abortifacient activit y in cattle by inoculation of 5 pregnant heifers at 25 to 29 weeks ges tation. Five additional heifers were inoculated with the Cooper TK-pos itive ( TK+) virus to serve as controls. After inoculation, both group s of heifers developed similar febrile responses and neutralizing anti body titers. Virus was isolated from blood of all heifers during the f irst postinoculation (PI) week, and isolation frequencies were similar for both groups. Ln contrast, whereas virus was isolated from many of the nasal and vaginal swab specimens of heifers inoculated with TK+ v irus, only rare virus isolations were made from the heifers given TK- bgal+ virus. All heifers inoculated with TK+ virus aborted between PI days 19 and 35. The finding of characteristic microscopic lesions and viral antigen in fetal tissues indicated that the abortions were cause d by BHV-1 infection. Virus was isolated from 3 fetuses, and all isola tes were TK+. Two heifers inoculated with TK- bgal+ virus aborted at P I days 25 and 39. Fetal tissues had typical BHV-1 microscopic lesions and viral antigen. Virus was isolated from blood of both fetuses, and the isolates were TK- bgal+. Results of this study indicate that inact ivation of the TK gene reduces, but does not eliminate, the abortifaci ent activity of BHV-1.