Interstitial pneumonia and subclinical infection after intranasal inoculation of murine cytomegalovirus

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Abstract
Although cytomegalovirus (CMV) infections are common throughout the world, little is known about the means of person-to-person transmission. To determine whether infection is established by a respiratory route, studies were conducted in a murine CMV (MCMV) model by using intranasal inoculation. The infectious dose which resulted in pulmonary and systemic infection of half the mice was 100 plaque-forming units [PFU] of MCMV. Infection was subclinical, but virus replicated in the lungs and subsequently disseminated via the blood to other organs within 7 days. The serum immunofluorescence antibody titer peaked by day 21. None of these mice died, although focal peribronchial interstitial pneumontitis was found in infected animals. Mice give .gtoreq. 104 PFU of MCMV developed a severe diffuse interstitial pneumontitis closely resembling that seen in immunocompromised patients and in newborn infants; 20% of the animals died. Normal pulmonary architecture was obliterated by sheets of histiocytes, many containing MCMV intranuclear inclusions, and by accumulation of proteinaceous fluid in the interstitial and alveolar spaces. MCMV as a sole pathogen can cause severe interstitial pneumonitis in normal mice and subclinical systemic infection results from respiratory inoculation of small amounts of virus.