HTLVs, which are described later, are the viruses that have been associated with T-cell lymphoma and leukemia.
Sarcoma and acute leukemia viruses: The sarcoma and acuteleukemia viruses cause infection primarily in animals. They are not associated with any human infections. The avian leukosis complex virus includes a group of antigenically related viruses, which induce avian leukosis or sarcoma in fowls.
Leukemia viruses: These are slow oncogenic viruses, whichinduce malignancies after a long latency period of even 30 years. These viruses promote cancerous growth by indirect ways as compared to the oncogene-encoded acute leukemia or sar-coma viruses. These viruses specifically have a taxgene, which is a transcriptional regulator and is capable of activating LTR sequences that enhance expression of cellular growth genes. This leads to uncontrolled cell growth, which may transform the cells neoplastically or promote other genetic changes over a long period of time.
Other viruses: Murine leukosis viruses, which consist of severalstrains of murine leukemia and sarcoma viruses, are associated with infections in mice. Mammary tumor virus of mice is associ-ated with mammary cancer only in certain susceptible strains of mice having a high natural incidence of breast cancer. Leukosis sarcoma viruses of other animals consist of a large number of viruses that have been associated with leukosis and sarcoma in cat, hamster, rat, guinea pig, and monkey.