We chose to use copies/ug DNA like some groups [18, 30] instead of normalizing by copies of β-actin detected like other groups [8, 13, 16, 33], since β-actin can be present in many copies/genome and exists as many pseudogenes unlike single copy genes per haploid genome like the RNase P protein subunit p30 (RPP30) typically used for pVLs in HTLV infection [45]. Here, RPP30 is linked to deltaretrovirus infections.