Leech: the parasite physician
"Men's tastes and trades are multifarious,
And so their ends and aims are various
The smith seeks something cracked to mend,
The leech would fain have sick to tend
The priest desires a devotee,
From whom he may extract a fee"
from The Rigveda (Book 9, Hymn 112, translation by John Muir), on the theme of non-attachment, poking fun at desire.
IN A paper by Dr. Andreas Michalsen and colleagues from Essen, Germany, titled "Effectiveness of Leech Therapy in Osteoarthritis of the Knee", published in a recent issue of Annals of Internal Medicine, 24 patients with osteoarthritis, caused by wear and tear of the ageing knee, were given a one-shot leech therapy. Four to six leeches were allowed to attach themselves to each knee and drink blood for about an hour. 27 others with the same ailment were given twice daily doses of the painkiller Diclofenac for a month. Conclusions: leech therapy was better than drug therapy!
The authors are cautious enough about their interpretation, and the editorial commentary by Dr. Marc Hochberg, in the same issue of the journal, is more circumspect. It says: "At the moment, however, on the basis of these data, I am not ready to refer my patients with knee arthritis for leech therapy". Instead, he argues that one should now look for what is in the leech bite — the potential for the discovery of a novel analgesic that could be safely administered without the need for a leech bite. This could benefit not only patients with osteoarthritis, but also those with other causes of pain.
I tend to agree with Dr. Hochberg. What would be exciting is to find the substances of medicinal value in the leech saliva. One could then replace the ikky, yukky leech with a mechanical device that can do the same. Indeed, such a `mechanical leech' has been developed by Drs. Gregory Hartig, Nadine Connor and Michael Conforti of the University of Wisconsin at Madison. Attached to the body, this device delivers an anticoagulant drug, which helps decongest the blood in veins and promotes clot-free circulation.
Is it not interesting how technology learns from nature? Before medicine and surgery went molecular and mechanical, physicians depended on what was available in the surroundings to treat illness. The materials used were minerals, metals and stuff from plants, and some animal products — but seldom whole animals. One outstanding exception has been the use of live adult leeches. Up until a hundred years ago, the physician's bag usually had a few leeches, which were used for blood-letting of patients who had circulation problems. In doing so, the physician was continuing a four millenia- old tradition. Yes, the ancient Egyptians, Greek and Indian medicine men used the leech to help maintain what they supposed to be the humoural balance in the body (the four humours being blood, phlegm, black and yellow bile). They attached the leech to the body for the cure, and detached it by sprinkling some salt water. Ayurvedic vaidyas of yore knew it; read the Rigveda hymn above.
The leech belongs to the class of legless, backboneless animals called annelids or the ringed ones. Of the over 130 species of them, the one used in medicine is called Hirudo medicinalis. This quaint, dark cylinder of 33 body rings has 5 pairs of eyes (to see better?), several pairs of testes (breed better?) and two suckers — both on its front and backside. The head sucker `searches' and penetrates while the tail sucker holds fast to the host. Young hirudo feed on frogs and not mammals, since their jaws are not strong enough to cut through mammalian skin, while adults feed on mammalian blood. The Hirudo is a sparse eater, though. In a full meal lasting 30 minutes, it takes in about 15 ml of blood, bloating up to 10 times its size, and when done, simply drops off. It feeds only once in 6 months, taking all this while to digest the blood. Bacteria that live within the leeches' body help keep the blood from decaying. Sometimes, when blood is not easily available, it may go even longer on a fast, digesting its own tissues!
The bite of the Hirudo is painless. It has an anesthetic that makes the bitten host feel nothing. Biologists are studying this substance in order to understand its chemical nature and mechanism of action. Besides this, the leech saliva has many other molecules of great medicinal interest. One of them is a vasodilator, a histamine that increases the diameter of blood vessels, helping to promote blood flow. Another is an enzyme called hyaluronidase, which breaks down hyaluronic acid, the bonding material of connective tissue, thus fostering the flow of blood and fluids from affected areas.
By far the most interesting substance in leech saliva has been hirudin, a molecule that is the most potent inhibitor of blood clotting known to date. Hirudin in leech guarantees continued blood flow, by breaking off the aggregated fibrin plugs that clot and seal blood leaks. Hirudin also shuts off the mechanism of Factor VIII - mediated blood coagulation. Indeed, even after the leech drops off after feeding, blood is seen to flow for a while from the animal, thanks to hirudin. Genetic engineers in England have been able to clone the gene for hirudin and manufacture it using recombinant DNA technology.
In reality we need to be thankful to the leech for the benefits it has now opened in modern medicine. Had it not been for Hirudo, we would not have hirudin, and its cousins bdellin and eglin.
Neither would we have appreciated the roles of hyaluronidase and the salivary anesthetics. And the poor fellow drinks hardly 15 ml, out of the 3000-5000 ml of blood that we humans have in us. And having drunk, moves on to "chew the cud" for 6 months. It is the slimy feel and the bloodthirstiness that gives it the bad press, and whence the Wisconsin mechanical leech.
D. Balasubramanian
dbala@lvpei.org
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
