Spleen Focus-Forming Virus

**Semantic type:** Virus

**Definition:** Defective virus found in certain strains of Friend virus, detected by its ability to form foci in spleens of mice and believed to be responsible in those strains for the production of a leukemia associated with polycythaemia rather than anemia. (DictionaryBarn.com)

**Synonyms:** - Friend Spleen Focus-Forming Virus