Actually, we've come quite a bit further than leeches today.  There are
specialized pieces of equipment called needles and syringes, when properly
applied, can extract a relatively precise amount of blood in a short period
of time.
 
Seriously, the use of leeches in surgical therapy is restricted more to
traumatic wounds in which there is interrupted or diminished venous outflow
(such as crushing injuries).  The leech helps in these situations by
removing a portion of the congested venous blood, as well as releasing
natural anticoagulants and anti-inflammatories locally - substances that
are primarily release for its feeding, but also have beneficial effects in
these wounds.
 
P. vera is largely a neoplastic proliferation of the red blood cells.  In
these cases, the blood becomes so thick that it can actually sludge in the
small vessels of the body, resulting in hemorrhage and infarction of these
tissues.  Periodic bleeding is needed simply to keep the level of the RBCs
at a normal level.
 
This is an unusual case, and it will be interesting to monitor over time to
see how effective periodic phlebotomy (still the primary mode of treatment
in humans) works in this ferret.
 
With kindest regards,
Bruce Williams, dVM
 
[Sukie note:  I am not the one with the ferret that has Polycythemia
vera, but I was the one to ask about leeches! :-)  ]
[Posted in FML issue 3470]