The name “hirudotherapy” comes from the Latin name for leech – HIRUDO. This therapy primarily uses leeches belonging to the species Hirudo medicinalis, which includes:
- The pharmacy medicinal leech (Hirudo medicinalis officinalis), with two orange-colored lines on the bottom of its dorsal side, featuring evenly repeating expansions. The ventral side of this leech is olive-green with black stripes on the sides.
- The therapeutic medicinal leech (Hirudo medicinalis medicinalis), with four pairs of lines on its dorsal side, containing repeating expansions filled with black, drop-shaped points.
- The oriental medicinal leech (Hirudo medicinalis orientalis), dark green in color, with four orange lines covered uniformly with black quadrangular points. The belly of this leech is black (dark) and evenly covered with green dots. This leech does not occur naturally in Poland.
Worldwide, another leech species used in leech therapy is the giant Amazon leech Haementeria ghilianii, which belongs to the so-called proboscis leeches and lacks developed jaws and teeth. It has an average body length of 45 cm.
The medicinal leech, Hirudo medicinalis, inhabits peat bogs, oxbow lakes, river backwaters, overgrown lakes, and other freshwater reservoirs in many countries around the world. It reaches an average size of 120 mm with a diameter of 10 mm, and its body can contract and elongate. In breeding, with intensive feeding, a specimen of 44 cm in length was obtained within 1.5 years. The body of the medicinal leech is flattened dorsoventrally, smooth, and without bristles. The dorsal side is convex, while the ventral side is flat. The coloration varies from yellow through green to dark brown.
In natural habitats, the medicinal leech alternately feeds on the blood of frogs and mammals using the watering hole. Adult individuals consume 10-15 ml of blood at a time and can starve for up to 2 years. The leech is very agile and actively responds to any stimuli that may come from a potential host. Its entire body is divided by circular grooves into regular rings. However, the external metamerism does not correspond to the internal one. One internal segment corresponds to five external rings.
The boundaries of the actual body segments can be distinguished by color. On the ventral side, the internal segments are marked by small excretory openings, of which there are only 17 pairs, while the leech’s body consists of 27 segments. The blood of the medicinal leech is colored red.
At the front end of the body, there is an anterior sucker, at the bottom of which lies the mouth opening. The mouth opening leads to the oral cavity, which contains three radially placed jaws. Each jaw is equipped with 80-90 tiny, chitinous teeth that the leech uses to bite (saw) through the skin to a depth of about 1.5 mm. The wounds left by the leech have the shape of three diverging rays.
Behind the oral cavity is a heavily muscled pharynx running along the 4th-8th rings. The pharynx acts as a sucking apparatus and is surrounded by unicellular glands, whose secretions (about 100 identified hirudocompounds) are transported with the leech’s saliva into the host’s (patient’s) bloodstream and into the tissues of its body within a radius of about 2.5 to 3 cm from the site of its attachment (feeding).
The pharynx connects to a thin-walled crop running along the 8th-18th rings. The crop is a reservoir that stores a supply of sucked blood and does not perform digestive functions. These functions are performed by the next section of the digestive tract, called the stomach. Blood passes from the crop into the stomach very slowly, and digestion of the entire contents of the crop can take up to two years.
The stomach passes into the small intestine, which expands into a short rectum (R), exiting through the anal opening (A) located on the dorsal side, above the second sucker located at the rear end of the body.
On the dorsal surface of the anterior part of the body, on segments 2 to 6, there are 5 pairs of eyes in the form of spots. They react to the slightest changes in light (illumination of the background) in the 450-650 nm band.
The medicinal leech also reacts to temperature, smell, magnetic field, sounds, water or air movement, chemical content, gravity, and electric field. The sensory organs also include mechanoreceptors scattered throughout the skin.
The medicinal leech is a hermaphroditic animal, but fertilization can only occur crosswise with another individual. In nature, it matures in the third year of life and reproduces only once a year, in the summer period. Under laboratory conditions, with the maintenance of specific breeding conditions, Hirudo medicinalis can reproduce several times a year.
Cocoons measuring 20 x 14 mm, containing 8 to 20 eggs each, are laid above the water surface level, sometimes at a greater distance from the shore, from which young leeches hatch after an appropriate incubation period.
In the present era, the medicinal leech is considered a living, miniature pharmacological laboratory. Unfortunately, most of the hirudocompounds it produces have not yet been identified and scientifically studied. Their structure is a proverbial Tower of Babel, waiting to be deciphered by modern science.
The use of medicinal leeches in therapy has a long and fascinating history, dating back to ancient times. The unique properties of these creatures have been harnessed to treat a wide range of ailments, from blood disorders to skin conditions. The secret lies in the complex mixture of compounds found in the leech’s saliva, which contains anticoagulants, anti-inflammatory agents, and other bioactive substances.
As our understanding of these compounds grows, so too does the potential for their application in modern medicine. Researchers are working to isolate and characterize the individual components of leech saliva, with the aim of developing new drugs and therapies based on these natural products.
One of the most promising areas of research involves the use of hirudin, a potent anticoagulant found in leech saliva, as a template for the development of new blood-thinning medications. Synthetic versions of hirudin have already been developed and are being used to treat a variety of cardiovascular conditions, including deep vein thrombosis and pulmonary embolism.
Other compounds found in leech saliva, such as eglin and bdellin, have shown promise as anti-inflammatory agents and may one day be used to treat conditions such as arthritis and inflammatory bowel disease. The potential applications of these compounds are vast, and researchers are only beginning to scratch the surface of their therapeutic potential.
Despite the many advances in our understanding of medicinal leeches and their saliva, much remains to be discovered. The complex interplay of the various compounds found in leech saliva is still not fully understood, and there are likely many more bioactive substances waiting to be identified.
As research in this field continues, it is clear that the humble medicinal leech will play an increasingly important role in the development of new therapies and treatments. From ancient times to the present day, these remarkable creatures have proven themselves to be invaluable allies in the fight against disease, and their secrets are only beginning to be revealed.
