Influence of viral infections on body weight, survival, and tumor prevalence in Fischer 344/NCr rats on two-year studies.

Sendai virus (SV), pneumonia virus of mice (PVM), and rat coronavirus/sialodacryoadenitis virus (RCV/SDAV) were common viral infections of rats in the National Cancer Institute-National Toxicology Program (NCI-NTP) studies from 1977 to 1983. Influence of these viral infections on body weight, survival, and prevalences of spontaneous tumors in the F344/NCr rats of 28 diet control groups at five different laboratories were evaluated. Tumor prevalences evaluated in this investigation included the following: leukemia and tumors of the anterior pituitary, lungs, salivary glands and Harderian glands in both sexes; adrenal pheochromocytomas in male rats; and mammary tumors in female rats. SV and PVM but not RCV/SDAV infections were associated with significant (P less than 0.05) decreases in body weights of male and female rats. Male rat groups with PVM infection had a lower prevalence of leukemia and male rat groups with RCV/SDAV infection had a higher prevalence of anterior pituitary tumors than the corresponding uninfected groups. Female rat groups with SV infection had greater survival and a higher prevalence of lung tumors than groups without SV infection. However, none of the tumor prevalence and survival differences were statistically significant when interlaboratory variability and time-related effects were taken into account.