Experimental myelitis in BALB/cN and C57BL/6N mice caused by herpes simplex virus type 1 compared with herpes simplex virus type 2

Intraperitoneal and footpad inoculations of herpes simplex virus type 1 (HSV) into BALB/cN (HSV-susceptible) and C57BL/6N (HSV-resistant) mice were carried out to induce experimental myelitis. Standard laboratory strains (McIntyre, F, RK, and recently Okinawa strain R1) were inoculated in mice. As a control, the HSV 2 standard laboratory strain SAV was also inoculated. The McIntyre strain was the most virulent, while the F strain was the least. RK and R1 were both moderately virulent. Myelitis was induced in BALB/cN mice after intraperitoneal and footpad inoculations of low to high doses of the McIntyre strain, and intraperitoneal inoculation of moderate and high doses of the RK and R1 strains. Symptoms of paraplegia of the hind legs and rectal and urinary incontinence were observed, but not until 3-5 hours before death. The symptoms caused by footpad inoculation were slightly different from those following intraperitoneal inoculation; rectal incontinence, in particular, was inconspicuous in the former. In the case of footpad inoculation of RK and R1, only one mouse inoculated with R1 showed symptoms and histology of myelitis. The F strain caused no symptoms. In the case of C57BL/6N mice, high dose intraperitoneal and footpad inoculations of the McIntyre strain also caused myelitis, and the symptoms were observed about 6-7 hours before death. In only one C57BL/6N mouse intraperitoneally inoculated with a high dose of R1 did symptoms appear about 6 hours before death. The same symptoms caused by intraperitoneal and footpad inoculations of HSV 2 (SAV) were observed more clearly and for a longer period (half to one day) than those caused by HSV 1 inoculation. Spinal cord necrosis was noted with McIntyre, RK and R1 inoculations, but it was not marked with randomly located foci, when compared with that caused by SAV. Further, the foci of necrosis in C57BL/6N mice were smaller than in BALB/cN mice, even when high dose McIntyre strain was used. Nuclear pyknosis and edema of the brain in the dead mice following HSV 1 inoculation were more marked than in those killed by SAV.