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This study aimed to clarify the timing and infectivity of equine herpesvirus 9 (EHV-9) infection in BALB/c-nu/nu mice and their immunocompetent counterpart (BALB/c). Following intranasal inoculation with 105 PFU of EHV-9, specimens from 8 mice per group were collected at different times postinoculation (PI) and assessed using histopathology, immunohistochemistry for viral antigen, and quantitative real-time polymerase chain reaction for ORF30 gene expression. In BALB/c-nu/nu mice, EHV-9 antigen was abundant in olfactory epithelia of all inoculated animals, and in the olfactory bulb of 1 animal. In contrast, only 1 BALB/c mouse per time point had rhinitis, with mild to moderate immunopositivity starting from 12 to 48 h PI, followed by a gradual virus clearance at 72 h PI. Statistically, significant differences were noted in the immunohistochemistry reactions between the 2 mouse strains, indicating that BALB/c-nu/nu is more susceptible to infection. Relative expression levels of ORF30 gene in olfactory epithelia were significantly different between the 2 groups, with the exception of 12 h PI, when BALB/c-nu/nu animals showed dramatic increases in ORF30 gene expression level until 48 h PI, followed by a decline in expression level until the end of experiment. In contrast, the expression level in brains showed no differences between mouse strain except at 96 h PI. In both strains, the highest messenger RNA expression was detected at 48 h PI, followed by a decline in BALB/c mice, proving a rapid clearance of virus in BALB/c and a gradual slowing down of the increased expression levels in BALB/c-nu/nu. [ABSTRACT FROM PUBLISHER]

Equine herpesvirus type 1 (EHV-1) UL11 is a 74-amino-acid tegument protein encoded by ORF51 of the EHV-1 genome. EHV-1 UL11 was previously reported by other researchers using the RacL22 and RacH strains to be nonessential for viral replication in cultured cells. Here, we constructed UL11 mutant viruses including a UL11 null mutant and three C-terminal truncated mutants, for further characterization of EHV-1 UL11 using bacterial artificial chromosome (BAC) technology based on the neuropathogenic strain Ab4p. EHV-1 Ab4p UL11 was localized to juxtanuclear and Golgi regions as reported by other researchers. We found that no progeny viruses were produced by transfection of fetal equine kidney cells and rabbit kidney (RK-13) cells with the UL11 null mutant and truncation mutant BAC DNAs. However, mutant viruses were generated after transfection of RK13-UL11 cells constitutively expressing EHV-1 UL11 with the mutant BAC DNAs. In conclusion, UL11 of EHV-1 Ab4p is essential for replication in cultured cells.