The response of pigs inoculated with a thymidine kinase-negative (TK-) pseudorabies virus to challenge infection with virulent virus

12 Large-White-Landrace piglets were subdivided in four groups of 3 and hou sed in separate units. The: piglets of three groups were inoculated with th e 86/27V 6C2 thymidine kinase negative (TK-) mutant of pseudorabies virus ( PRV), by different routes. A second inoculation with the same mutant was gi ven to the pigs 21 days later. The animals of a fourth group were left as u ninoculated controls. 21 days following the second inoculation with the TK- mutant all pigs were challenge infected with the virulent PRV. On post cha llenge day (PCD) 30 all pigs were killed and samples for virus detection an d histology were taken from several organs. The inoculated TK- mutant of PRV did not induce any ill effects in the pigs except a transient febrile reaction in some animals. Virus was recovered f rom nasal swabbings from one pig 2 days after the first inoculation of the mutant. After challenge exposure with virulent PRV, the TK- mutant-inoculated pigs were apparently protected, whereas the control pigs all were severely affec ted and recovered very slowly over 3 weeks. Virus was isolated from the nas al swabbings from the TK- mutant-inoculated pigs on PCDs 2 and 4, whereas t he nasal swabbings from the control piglets were all positive for virus fro m PCD 2 through PCD 10. PNA analysis of the virus recovered showed a patter n identical to that of the virulent PRV. Histologic lesions were found in t he respiratory and the central nervous systems, however, the lesions in the TK- mutant-inoculated pigs were much milder compared to those registered f or the control pigs. Virus was not isolated from any of the tissue samples that were tested, hut viral DNA with sequences typical of PRV genome was detected by PCR in all. samples of trigeminal ganglia from either the TK- mutant-inoculated pies o r from the controls. (C) 1999 Elsevier Science Ltd. All rights reserved.