Growth and protective potentials of attenuated strains of equid herpesvirus 1 in the lungs of mice.

Attenuated equid herpesvirus 1 (EHV-1) strains with different passage histories in bovine kidney cells (BKC), i.e. BK77, BK161, BK271 and BK343, were examined for their growth in mouse lungs after intranasal inoculation. BK77 and BK161 were recovered from lungs with almost the same titres, and were found to be about 100 times lower than that of the parent HH1 strain. The growth abilities of high-passaged BK271 and BK343 were markedly reduced. Although partial growth of BK343 in the lungs of athymic nude mice was observed, the virus was almost eradicated from their lungs within 1 week. By contrast, the parent HH1 persisted in the lungs of nude mice for at least 1 week. The mice immunized with the BKC-passaged viruses were partially protected against subsequent challenge with the parent HH1. Antibodies were detected by ELISA. These results demonstrate that, although serial BKC-passage lowered the growth ability of the parent HH1, the descendant viruses still have a partial protective potential in mice.