Natural History of Leeches
The medicinal leech (Hirudo medicinalis) is a segmented worm (Phylum: Annelida).
This phylum includes the Polychaetes, the Oligochaetes (earthworms) and the Hirudinea (leeches).
Leeches have two "suckers," one at each end.
The caudal (back end) suction cup helps the leech to ambulate on dry surfaces, and to attach to its host;
the rostral (front end) suction cup also contains the mouth with three sharp jaws that leave a Y-shaped bite.
The medicinal leech lives in clean waters.
Leeches swim free in the water, with an undulating motion.
When attached to its host for feeding,
the leech remains in place for 30 minutes to 6 hours or more, as it fills with blood.
During feeding, H. medicinalis can suck 5 - 15 mL of blood --- several times its own body weight.
Leech saliva contains several bioactive substances, including anti-cooaggulants, vaso-dilators, and anesthetics.
Hirudin, a potent anticoagulant in leech saliva, inhibits the conversion of fibrinogen to fibrin, preventing blood from clotting.
Indeed, a wound may continue to bleed for many hours after the leech has already detached.
The benefits of leech therapy are due, in large part, to the anti-coaggulant effects,
vasodilatory effects, and anesthetic effects of these biochemicals,
as well as the physical effects of blood letting (phlebotomy).
Like a snake, the leech periodically must shed its skin.
The leech is hermaphtroditic, having both male and female elements.
Fertilization and egg-laying usually occur during the spring, summer, and winter months.
Young leeches feed on the blood of small water animals (frogs, toads or fish).
Leeches may not be ready for medical application until they are several years old.
Clinical Practice of Leech Therapy
The application of leech therapy is simple:
leeches are gently placed in the area needed,
and allowed to attach and engorge for the next 6-12 hours,
after which they will release.
The entire course of treatment may require one to 6 treatments or more,
depending upon the goals and rate of response.
For more details about the specific application procedures, readers are referred to the manufacturer's directions.
A list of manufacturers can be found elsewhere on this site.
Leeches (Hirudo Medicinalis) have been used medically
for more than 1500 years. Originally used to remove “bad blood,”
the leech is now used extensively by reconstructive surgeons needing
to remove stagnant blood from a flap or reattached limb. When the venous
blood does not return to the heart, it pools in the wounded area, increasing
pressure and preventing fresh arterial blood from entering the area with oxygen
and nutrients.
The venous blood must be removed and the pressure must be
reduced in order to save the flap or limb.
The leech is able to do this
exceptionally well, because its saliva contains important biochemicals,
including vasodilators, anticoagulants, and anesthetics.
The leech will withdraw approximately 5 ml (one
teaspoon) of blood.
Further therapeutic benefit of leech therapy comes after the
leech is removed, during which up to 50 mls of blood will continue to ooze,
for up to 48 hours.
More leeches attached to the site mean more blood will be removed.
After 3-7 days, the veins have usually reconnected
themselves such that the blood is no longer pooling in the limb.
Normal color and pressure should return to the area, as arterial
blood circulates easily in the damaged zone.
By that time, the wound will be able to heal, without further phlebotomy (leech
therapy).
The application of leeches to the patient is relatively simple,
but does require care. As few as one, or as many as 6 or more
leeches may be required for a wound, depending upon its size and
its clinical response. The greatest number of leeches should be
applied to the area of maximal venous congestion.
The patient’s skin must be cleaned thoroughly with soap and
water, and then rinsed with distilled, non-chlorinated water. A
gauze barrier around the area intended for the leech will help
prevent the leech from wandering away from the site where
it’s attachment is desired. It can be carried to the site
by hand, or it can be placed within a 5 cc plastic syringe
(plunger removed) and then applied to the wound site, containing
the leech until it is attached.
If the leech is reluctant to bite, it might be necessary to
entice it with a tiny droplet of blood, drawn from the wound site
with a needle prick.
Once the leech is attached, it will likely remain safely in place
until fully distended. The gauze square can be removed and used
elsewhere without disturbing the animal;however, it is important
that the site be checked continuously to insure that the leech
hasn't moved. The leech will let go of the patient (host) when it
is finished (usually within an hour).
