Effect of Mouse Strain on Equine Herpesvirus 9 Infection

The infectivity of equine herpesvirus (EHV)-9 has been studied in different animal models including immunocompromised animals. The current study focused on the infectivity of EHV-9 in different mouse strains (C3H, C57BL, DBA, BALB/c-nu/nu, BALB/c and ICR) by intranasal inoculation of 2 × 10⁶ plaque forming units (PFU). Various organs, including head and lungs, were collected 7 days post infection (dpi) to investigate microscopical lesions and the distribution of EHV-9 antigen. Immunopositivity of tissue sections was scored using ImageJ software. Open reading frame (ORF) 30 expression in lung tissues was quantified using quantitative reverse transcriptase polymerase chain reaction. Pathological examination revealed different degrees of rhinitis in the different mouse strains. Severe rhinitis was detected in C3H and BALB/c-nu/nu strains, moderate rhinitis was observed in C57BL and DBA strains and no lesions were detected in BALB/c mice. Immunopositivity for EHV-9 antigens was detected in the olfactory epithelium of C3H and BALB/c-nu/nu strains. Compared with C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, the C3H strain showed greater expression of EHV-9 antigens in the brain. The proportion of areas with high positive to positive immunoreactivity for EHV-9 were 7.57, 3.42, 3.12, 2.51, 1.79 and 0.03% for C3H, C57BL, DBA, BALB/c-nu/nu, ICR and BALB/c strains, respectively. The proportions of areas with low positive to negative immunoreactivity were 92.42, 96.70, 96.87, 97.48, 98.16 and 99.96%, respectively. The highest relative expression levels for EHV-9 ORF30 in the lungs were in C3H mice. No significant differences in the expression of ORF30 were observed in other strains. In conclusion, of the strains examined, C3H, C57BL, DBA, BALB/c-nu/nu and ICR were the most susceptible to EHV-9 infection, and the BALB/c strain was less susceptible.