Susceptibility of the wild-derived inbred CAST/Ei mouse to infection by orthopoxviruses analyzed by live bioluminescence imaging

•Wild-derived inbred CAST/Ei mice are susceptible to vaccinia virus and cowpox virus.•Morbidity and mortality from orthopoxviruses are greater in CAST/Ei than BALB/c mice.•Morbidity and mortality from herpes simplex virus type 1 are similar in both mice.•Imaging shows virus spread from nose to lungs, abdominal organs and brain.•Vaccinia virus spreads more rapidly than cowpox virus.

Classical inbred mice are extensively used for virus research. However, we recently found that some wild-derived inbred mouse strains are more susceptible than classical strains to monkeypox virus. Experiments described here indicated that the 50% lethal dose of vaccinia virus (VACV) and cowpox virus (CPXV) were two logs lower in wild-derived inbred CAST/Ei mice than classical inbred BALB/c mice, whereas there was little difference in the susceptibility of the mouse strains to herpes simplex virus. Live bioluminescence imaging was used to follow spread of pathogenic and attenuated VACV strains and CPXV virus from nasal passages to organs in the chest and abdomen of CAST/Ei mice. Luminescence increased first in the head and then simultaneously in the chest and abdomen in a dose-dependent manner. The spreading kinetics was more rapid with VACV than CPXV although the peak photon flux was similar. These data suggest advantages of CAST/Ei mice for orthopoxvirus studies.