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Frequently Asked Questions About
Leeches and Anticlotting Agents

Do I share the clotting cascade with large mouth bass?
I'm not really sure how closely related we are to other vertebrates with respect to the clotting cascade- my guess is that it is pretty close since it is such a fundamental and highly regulated system. With respect to using common mechanisms and similar proteins to inhibit clotting amongst the diverse creatures we're talking about, it is perhaps not so surprising since nature has a way of defining common fundamental principals. For instance, certain proteins or domains of proteins are conserved throughout nature in both prokaryotes and eukaryotes.

What's the nature of the antiseptic in leech saliva or is it an antibiotic?
I'm not aware that leeches have any antibiotic or antiseptic factors in their saliva; I have heard, although I'm not aware of any evidence, that leeches do have an anesthetic factor - this is presumably due to the fact that we can't tell when we've been bitten. (On the other hand, I'm not sure how sensitive our powers of feeling are when swimming in the 'cool' waters of Minnesota!)

Where are leeches found in the US?
I have found leeches in many different locations in Michigan. As a research scientist with the National Park Service who worked on Isle Royale National Park in Lake Superior, I'll never forget the day we were sampling lake sediments from the bottom of Lake Harvey. I scratched the back of my hand on some brush transporting equipment back in to this wilderness location. As we set out to sample the sediments within just a few moments leeches were actually swimming toward our sampling platform looking for the source of fresh blood. At the end of the sampling day, back at camp when I took off my boots I had leeches attached to my feet. They had managed to slither into my boots without my detection. I do not have a great fondness for these strange and unique creatures.

I also have found leeches frozen into ice layers of the Rouge River, the metro Detroit main river system, and when freed they were moving and ready to look for a meal.

I first remember leeches being attached to my legs after swimming in the High Cascade Mountain Lakes (~5000') of Southern Oregon. I was truly surprised because I always had the impression that they were warm water,swamy creatures. The more I look for them, the more I found them. Now days I seem to find them everywhere.

In MN we have a large lake called Leech Lake (guess why). Leeches are a common walleye bait throughout MN. Leeches in Leech Lake can reach several inches. We have a lot of smaller leeches even in little farm ponds. They show up in my natural aquariums too.

Leeches can be found pretty much anywhere there is water. I think they are most abundant in the cool water ponds and streams in the northern U.S. They are also prevalent in polar seas and water holes in the African desert as well as the tropics. Worldwide there are somewhere around 650 different species that have been described.

What would happen if an individual were bitten by a poisonous snake, would a leech attached to the bite help in reducing the effects of the snake venom?
Possibly, although snake venoms contain all kinds of nasty proteins. The leeches might serve to suck out some of these thus reducing the adverse effects. I don't know anyone personally who wants to do the experiment.

Anybody see the episode of Chicago Hope on leech therapy? -
It's one of those medical dramas that was on when I got home the other night. I missed the first part, but apparently one of the doctors lost his finger due to an exploding bullet that was lodged in his patient while he was operating (well, it is TV). Later in the show, they showed another surgeon using a live leech to promote circulation and avoid necrosis after doing reattachment surgery. This is true stuff! I was at a meeting several years ago on leeches in medicine and biotechnology - about 30% of the people there were surgeons who were currently using leeches in their practice when reattaching fingers, toes, ears, etc. ....... and you thought this stuff was just in the history books. Based on the info in the background paper, we now have some pretty good ideas what factors the leech has that carries this out.....

What about heparin?
Someone asked about the pros and cons of heparin, and whether there was an effort on to replace it. The pros are that it is cheap and it does its primary job (preventing reclotting in the arteries) pretty well. The cons I mentioned above, and they can be pretty serious. The most serious potential complication of heparin treatment is internal bleeding. Whereas a shaving cut can be seen and eventually dealt with, internal hemmorhages (particularly in the brain) can be extremly dangerous. For that reason, many companies are looking for safer alternatives to heparin. The question is, how do you get one?

The answer is not clear. But that never stops people from speculating, and in this case the suspicion is that by inhibiting the coagulation cascade somewhere further "up"--heparin indirectly inhibits thrombin, the enzyme at the very bottom of the clotting cascade--one might arrive at a selective anticoagulant, i.e. one that prevents clots in vessels but not those on the skin. There is actually a little data now to support this, but it needs a lot more work.

Among the known alternative strategies include inhibitors of Factors Xa and VIIa. Only time (several years, minimum) will tell if this approach will work."

How is a new protein molecule different in its ultimate effects from heparin? For instance, how does it prevent clots inside vessels and not at the surface?
No one is sure right now how the new protein prevents clots in vessels and not at the skin. The current model is that there are redundant pathways which can cause clotting at the skin, while there may only be one relevant one in vessels. Thus, if the new protein blocks that one, there's still a functioning mechanism remaining to help clots form at the skin. The biochemical details of this are extremely murky right now...

As for aspirin--it acts by inhibiting the ezyme cyclooxegenase. Cyclooxegenase is involved in the biosynthesis of thromboxane A2, which is a potent stimulator of platelets. When stimulated by throboxane A2, platelets become "activated" and initiate a cascade of biochemical events which result in clotting.

The properties of a molecule that make it a good orally active drug include small size (molecular weight less than 500 grams/mole) and what might be called a "medium greasy" nature--i.e., it must be soluble in water (to dissolve in the stomach in the first place) and also somewhat soluble in lipids (to transiently dissolve in, and thus pass through, the lipid membranes which surround cells).

What leeches are found in North America?
Macrobdella decora is commonly called the American medicinal leech because of its use in medicine. It is 5-9 cm in length and has distinctive dorsal red dots. It is dark green with a bright orange underside. It is a northern species and is found from Colorado to Saskatchewan to the Georgian bay to Maine and as far south as Maryland and Kansas. I think these should be relatively easy to get and they are interesting to watch. They are good swimmers - you can buy some and just keep them in a tank of distilled water for months at a time without any care at all except changing the water once in a while.

Placobdella ornata is also abundant in the northern US and Canada - related species are found in the southern states. It is known as the turtle leech and is more distinctive in shape and color but not much of a swimmer. It looks like an almond and has a wide brown dorsal band and is colored brown, cream, and faint green.

Can leeches be used over again for medicinal purposes?Would reuse of leeches spread infectious diseases?
Leeches that are used for medicinal purposes aren't used again. ...it raises some interesting points...For instance, what does the FDA have to say about the use of leeches in clinical practice? Are there regulations in place to protect the public from any potential hazards of using medicinal leeches....perhaps we should ask the surgeon that was highlighted in the Feb 24 issue of the Washington Post on the use of leeches in his practice.

Can the leeches spread the HIV virus?
I asked a student's father who specializes in communicable diseases about the leech, mosquito, HIV thing. He formerly worked at CDC and is considered a pretty good source. No cases of HIV being spread that way have ever been reported. In addition, since the mosquito does not bite again soon after a bite, nor does the leech (didn't we hear that some leeches eat once a year?) the mosquito or leech would have to be able to host the virus for a period of time without either destroying the virus or the host.

How do you get leeches off?
Actually they 'fall' off after they have had their meal - I would guess this is about 5-10 minutes. I don't think it would be difficult to just pull them off, but I haven't had any hands-on experience at this. (Suggestions for safe leech removal contributed by Jim Sangster.)

What about snake venom?
Interestingly, one of the first snake venoms we tested for antiplatelet activity was the Malayan pit viper Agkistrodon Rhodostoma, from which we found the antiplatelet protein which we named 'kistrin'. This venom also contains the protein named Ancrod, which was mentioned as the enzyme that degrades fibrinogen and is now being used clinically. Sounds like this snake has really figured out how to keep us from clotting!!


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