Morphologic changes in the nasal cavity associated with sialodacryoadenitis virus infection in the Wistar rat.

A sequential study of lesions of the nasal cavity associated with sialodacryoadenitis virus (SDAV) infection was made in the laboratory rat. Wistar rats were intranasally inoculated with approximately 10(3) TCID50 of the coronavirus SDAV. Transverse sections of four regions of the nasal cavity from inoculated and control animals were examined by light microscopy and immunohistochemistry at 2, 4, 6, 8, 10, and 14 days postinoculation (PI). Lesions were observed in the following regions of the upper respiratory tract: respiratory epithelium, transitional epithelium, olfactory epithelium, nasolacrimal duct, vomeronasal organ, and the submucosal glands of the nasal passages. In general, in structures lined by ciliated epithelial cells, there was focal to segmental necrosis with exfoliation of affected cells and polymorphonuclear cell infiltration during the acute stages, progressing to squamous metaplasia during the reparative stages. Repair in these regions was essentially complete by 14 days PI. In the olfactory epithelium and the vomeronasal organ, there was interstitial edema with necrosis and exfoliation of epithelial cells and minimal to moderate inflammatory cell response during the acute stages. Residual reparative lesions were still evident in the olfactory epithelium, the columnar epithelium and neuroepithelium of the vomeronasal organ, and the nasolacrimal duct at 14 days PI. Viral antigen was demonstrated by immunohistochemistry in all regions during the acute stages of the disease, with the exception of the vomeronasal organ. In view of these findings, infections of the respiratory tract with viruses such as SDAV could have significant effects on functions such as olfaction and chemoreception for > or = 2 weeks postexposure in this species.

Coronavirus infections in the laboratory rat: degree of cross protection following immunization with a heterologous strain.

One hundred and twenty-one specific pathogen-free male Wistar rats eight to ten weeks of age were used to evaluate the efficacy of Parker's rat coronavirus (PRC) in affording cross protection on subsequent challenge with virulent sialodacryoadenitis (SDA) virus. Sixty-two animals were inoculated intranasally on day 0 and 21 days later with approximately 10(2) median tissue culture infective doses (TCID50) of the tenth passage of PRC replicated in L-2 cells. Animals were selected at random postvaccination to evaluate the safety and efficacy of PRC by histopathology, immunohistochemistry and serology. At three and six months postvaccination (PV), vaccinated and seronegative control rats were inoculated intranasally with approximately 10(3) TCID50 doses of virulent SDA virus. Challenged rats were then killed at 6, 10 and 14 days postchallenge and necropsied. Evaluations were based on lesion indices in lacrimal and salivary glands and respiratory tract, the presence of viral antigen by immunohistochemistry, and antibody response. Lesions were observed in rats killed PV, but in general, they were significantly reduced compared with those present in seronegative animals post-exposure to virulent SDA virus (p < or = 0.05). However, they were still considered to be an unacceptable level for a routine vaccination procedure. Potvaccination antibody titers to rat coronavirus were evident in all animals tested at three or six months prior to challenge with SDA virus.(ABSTRACT TRUNCATED AT 250 WORDS)