Animal models for HIV infection and AIDS.

s and Reporfs 215 the virus envelope. These three genes are flanked by sequences repeated on both ends of the genome, known as long terminal repeats (LIR), which contain regulatory elements for transcription. Morphologically, oncoviruses have been subdivided into three groups, referred to as type B, C, and D particles. Type C oncoviruses include, among others, the murine, avian, and feline leukemia/sarcoma viruses. Type B oncoviruses are represented by the mouse mammary tumor virus. The Mason-Pfizer monkey virus is the prototype of type D retroviruses, and more recently other type D viruses (simian retroviruses, SRV) have been identified as the etiologic agents of a fatal AIDS-like disease in rhesus macaques, known as simian AIDS or SAIDS. The two other known human retroviruses (HTLV-I and HTLV-II), as well as bovine leukemia virus (BLV) and the simian T-lymphotropic virus type I (STLV-I), are generally considered as members of the oncovirus subfamily, but perhaps they should be placed into a new subfamily, based on their unique genomic organization that includes the presence of at least two regulatory genes. The spumaviruses (spuma=Latin “foam”) comprise a number of viruses from many animal species, including man, which are not associated with any pathological entity and are frequently recognized by their ability to induce the formation of foamy vacuolated syncytia in tissue culture. Lentiviruses (lenti=Latin “slow”) are non-oncogenic retroviruses that induce chronic debilitating diseases following long-term persistent infections. The Lentivirinae subfamily at present includes viruses from ungulates (maedi-visna virus of sheep, caprine arthritis-encephalitis virus (CAEV) from goats, equine infectious anemia virus (EIAV) from horses, and bovine immunodeficiency virus (BIV) from cattle), felines (feline immunodeficiency 216 PAHO Bulletin 23(1-2), 2989 virus (FIV)), and human and nonhuman primates (HIV simian immunodeficiency viruses (SIV)). The most outstanding characteristic of the genome of the lentivirus subfamily is the presence of a number of accessory genes with regulatory functions. In addition to gag, pd, and env, at least five other genes (tat, rev, vifi ZI~Y, and nef, have been identified. Some of these accessory genes are required for virus infectivity, and they regulate the expression of the viral structural