Pathogenesis of mouse hepatitis virus infection. The role of nasal epithelial cells as a primary target of low-virulence virus, MHV-S.

The pathogenesis of mouse hepatitis virus (MHV‐S) infection in suckling and weanling mice was comparatively studied after intranasal inoculation. In sucklings, infectious virus as well as specific antigen was first detected in the nasal mucosa at 12 hr, then in the nerve cells of the olfactory bulbs. At this stage viral particles were demonstrated both in the supporting cells and olfactory cells of the nasal mucosa. In the posterior part of the brain and spinal cord, virus was detected on days 3 to 4 postinoculation when viral growth was clearly demonstrable in the liver, spleen and intestines. In weanlings too, infection was first established in the nasal mucosa, shedding infectious virus in the nasal washing until day 6 postinoculation, and later infection spread to the brain and spinal cord. In weanling mice, however, neither infectious virus nor viral antigen was detected in the liver or other visceral organs, while serum neutralizing antibody became detectable on day 5 postinoculation, increasing in titer thereafter. Histopathologically degenerative and necrotic changes were observed in the nasal mucosa and central nervous system of both age groups of animals coincidentally with the presence of viral specific antigen, while inflammatory response was much less prominent in sucklings. In the liver, spleen and intestines, however, some lesions were observed only in sucklings.