Abstract: The present invention provides porcine retrovirus (PoEV) polynucleotide fragments, particularly those encoding at least one PoEV expression product, a recombinant vector comprising such a polynucleotide fragment or fragments, use of PoEV polynucleotide fragments in the detection of native PoEV, a host cell containing at least one PoEv polynucleotide fragment or recombinant vector, PoEV polypeptides, antibodies immuno-reactive with PoEV polypeptides, pharmaceutical compositions comprising recombinant PoEV polypeptides for use as prophylactic and/or therapeutic agents and uses of PoEV polynucleotide fragments and/or polypeptides in medicine, including veterinary medicine and in the preparation of medicaments for use in medicine.