Chronic Infections of C-Type RNA Viruses

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Oncornaviruses comprise a large group of structurally similar viruses, some of which are known to cause malignant disease in their hosts. They are morphologically classified into B-type virus particles, characteristic of the murine mammary carcinoma virus, and C-type viruses, characteristic of widespread infections of numerous species. While not all C-type virus strains are known to be pathogenic, they are frequently associated with lymphoma, leukemia and other mesenchymal tumors. The viral etiology of these kinds of tumor in the domestic fowl was first noted nearly 70 years ago when Ellerman and Bang in 1908 demonstrated the infectious transmission of leukosis by cell-free filtrates and Rous in 1911 made similar observations with sarcomas. Nevertheless, 40 years elapsed before Gross was able to prove that thymic lymphoma in the AKR mouse was similarly caused by a filterable virus, and only in recent years has it become evident that C-type viruses are also a major cause of hemopoietic neoplasms in other rodents and in cats, cattle and possibly gibbons too. C-type viruses have now been isolated from numerous species of mammals, birds and at least one reptile (the viper). We expect that many more species of virus remain to be discovered, and that the spectrum of disease with which they are associated will not be confined to neoplasia. The association of a murine C-type virus with the “autoimmune” hemolytic anemia and glomerulonephritis in New Zealand mice (15), and the presence of C-type virus genetic information in latent or partially expressed states in so many vertebrate species, suggests that C-type viruses might be implicated in some chronic inflammatory diseases.