On his VDU's blog, Dr. Ian Mackay conducts some informed speculation on MERS-CoV in the blood.... Excerpt:
The Middle East respiratory syndrome coronavirus (MERS-CoV) is, at its core, a respiratory virus. Well, as far as we know it is anyway. But, like other respiratory viruses (see an earlier post on rhinoviruses), MERS-CoV can be detected in the blood....a so-called "viraemia".
In some cases this is identified in other virus infections in parallel with the viral load being generally high, perhaps indicating that virus is replicating beyond the body's ability to contain and control it at the site of initial replication.
Perhaps, and MERS-CoV may be a good example of this, so-called extra-respiratory spread of a respiratory virus occurs when it has a penchant for blood vessel cells (they present its receptor or have something in their cellular machinery that aids virus replication) or some other ability to specifically get beyond the respiratory tract.
However it occurs, the result is a much wider spread of the virus around the body; blood being something that is widely traveled! We already know that MERS-CoV has a love for growing in kidney cells so extra-respiratory spread may create a perfect storm for delivering this little bomb to a site where it can create even more havoc than in our airways. If those kidneys are already a bit bashed about, say by diabetes, then the blast radius is perhaps increased that much more.