POLYOMA VIRUS

minute infectious agent normally present in extremely small amounts in wild mice and causing no obvious ill effects. There is evidence that the virus may induce malignant tumours if grown in tissue culture and injected in sizable quantities into newborn mice or young hamsters, guinea pigs, and rabbits. The virus is highly antigenic; i.e., all animals bearing its tumours also have virus-neutralizing antibodies in their blood. The virus is also capable of clumping red blood cells and affecting deoxyribonucleic acid (DNA) synthesis. Polyoma virus is one of the infectious oncogenic (tumour-forming) viruses and belongs to the papova group of viruses. Another oncogenic virus of the same group is simian virus 40 (SV-40). Great care has to be taken to make sure that vaccine viruses grown on monkey (simian) kidney cells are not contaminated with SV-40.