When screening tests are used for MuLV class virus(XMRV is a MuLV class virus) investigators search for viral antigens and antibodies.Antigens stimulate the production of antibodies specific to that antigen.
MuLVs, in general are example sof very low titre viruses so the levels of antibodies are miniscule and can be very hard to detect,
While detectable levels of antibodies may be found in a person's blood who has picked up the virus by infection ,from another person for example ,this may not be the case for a person who has inherited the XMRV bound to parental DNA.
These are called horizontal and vertical transfer respectively.
So if looking for inherited dNA the focus will be on detecting antigens.
These are proteins of a particular shape expressed on the coat of the virus
XMRV can be looked at as 6 non identical twins
This means that xmrv antigens can be slightly different to each other and also produce a range of antibodies.
The test has to be able to detect the range of antigens and antibodies produced otherwise there will be a lot of false negatives.
The problems dont stop there these viruses can seroconvert which means that the same XMRV srtain can suddenly express a different antigen and thus slip through the net.
Just to make life even more interesting XMRV is often latent(hidden in our DNA) and not be antigenic at all.Viral DNA does not provoke an antibody response.
MuLVs can also hide in the bone marrow and can hide in brain cells and be completely undetectable
Finally,another possibility is cell-cell transfer.If a cell wall is viewed under an electron microscope it looks like "molecular chicken wire".The "holes are big enough for a virus of this class to get through.These viruses also cling to the"corridors" that link the neucleus to the cell walls.Finding antibodies or antigens for viruses "travelling" like this is dam near impossible.
This will be one hell of a sophisticated test
oh that sounds terrible!