Virus based vectors of equine infectious anemia (EIAV).

Genome EIAV vector can be packaged and capable of expressing heterologous genes, characterized by comprising a gag truncated gene but retains a packaging signal of gag, in which: (i) the truncation of gag removes more than one nucleotide in sense 3 'nucleotide 350 of the gag coding sequence; and (ii) the packaging signal comprises nucleotides 1-109 of the gag coding sequence.