It is important to emphasize that FIV strains infecting 9 species of the Felidae have been at least partially sequenced and molecularly characterized [3, 10, 11, 25, 34, 38, 42, 43, 66] . Genetic analysis indicates that different felid species are infected by different strains of FIV [8, 11] . Analysis of pol gene sequence of FIV from lions (Panthera leo), pumas (Puma concolor) and domestic cats indicated that each species has a specific strain of FIV and that the strains are related but distinct [7, 43] . Also, strains from African lions (subtype B and E) differ in their abilities to replicate in feline cell lines [59] , their sensitivity to receptor antagonists [71] , and their requirement for ectopic expression of CD134, the primary cellular receptor, for productive infection [41] .