This study aimed at clarifying the course and infectivity of EHV-9 in BALB/c-nu/nu and their immunocompetent counterpart (BALB/c). Following intranasal inoculation with 105 PFU, specimens were collected at different hours postinoculation (h PI) to assess histopathology and conduct quantitative analysis of immunohistochemical reactions and quantitative real-time polymerase chain reaction, paraffin-embedded specimens were used for examination of ORF30 gene expression. In BALB/c-nu/nu, marked detection of EHV-9 antigen in the olfactory epithelia of all inoculated animals. Viral antigen was detected in the olfactory bulb of 1 animal. Unlike BALB/c-nu/nu, there was minimal rhinitis in only 1 normal BALB/c mouse, faced 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 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 slowdown in expression level until the end of experiment. In contrast, the expression level in brains showed no differences between mice strain except at 96 h PI. In both strains, the highest messenger RNA expression 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.