[viruses]
   Order Ortervirales
     Family Retroviridae
       Subfamily Orthoretrovirinae
         Genus Gammaretrovirus
           01 Chick syncytial virus
           02 Feline leukemia virus
           03 Finkel-Biskis-Jinkins murine sarcoma virus
           04 Gardner-Arnstein feline sarcoma virus
           05 Gibbon ape leukemia virus
           06 Guinea pig type-C oncovirus
           07 Hardy-Zuckerman feline sarcoma virus
           08 Harvey murine sarcoma virus
           09 Kirsten murine sarcoma virus
           10 Koala retrovirus
           11 Moloney murine sarcoma virus
           12 Murine leukemia virusᵀ
           13 Porcine type-C oncovirus
           14 Reticuloendotheliosis virus
           15 Snyder-Theilen feline sarcoma virus
           16 Trager duck spleen necrosis virus
           17 Viper retrovirus
           18 Woolly monkey sarcoma virus