Histopathological changes and expression of latency-related RNA in the central nervous systems of mice latently infected with a field isolate of EHV-1

Nine inbred BALB/c (H-2(d)) 4-week old female mice were intranasally infected with 2.5x10(5) CCID50 of EHV-1 strain isolated from an aborted foetus. Three mice died on days 3, 5 and 8. In 4 out of the 6 mice which survived, nested PCR with DNA extracted from the brains of the infected mice resulted 56 days post-infection in a single 1.29 kb band specific for EHV-1 observed after the second round of amplification. Histopathological examination of brains in PCR-positive mice showed the presence of mononuclear cells infiltration, degeneration of neurones and proliferation of glial cells. DNA/RNA in situ hybridization performed on brain sections using the biotin-labelled, purified genomic viral DNA revealed the probe bound to the nuclei of some neurones, presumably localized in the rhinencephalon.