The original title of Dr Siddall's lecture was Resolution and Independence, but changed the title upon finding that Wordsworth fans were underrepresented in the crowd... Dr Siddall began the lecture with a quick disclaimer, something along the lines of "if you're not grossed out, I'm DOING IT RONG!!!". He followed that up by asking if any of us had had a close encounter with a leech. Yeah, I have, I even brought a leech from Maine back to New York to give to a crazy friend of mine. I'm cool with the leeches.
Leeches belong to the phylum Annelida, the segmented or "ringed" worms (ringworm, as Matt Groening observed, is neither a ring nor a worm- it is a fungus. The annelids are divided into three sub-groups, according to their "hairiness". Polychaetes (sadly, most likely a paraphyletic group) have many chitinous bristles, Oligochaetes have few bristles, and the Hirudinea (the leeches, baby!) have no bristles. The Hirudinea and the Oligochates belong to the class Clitellata (no laughing!), they have a clitellum (I said no laughing!)- a "collar" which forms a protective egg sac. The Branchiobdellidans, which parasitize crayfish are thought to be the closest living relatives to the Hirudinea. Dr Siddall confessed to not being that interested in Oligochaetes, with some notable exceptions.
Leeches, like earthworms, are hermaphrodites, they possess both female and male reproductive organs. Leech sex is often rough, involving traumatic insemination in many species. Basically, sperm packets are "injected" directly into another leech's "skin", with fertilization of the ova taking place later. Oddly enough, those other beloved sanguivores, bedbugs, also rely on traumatic insemination. Yeah, they're even creepier than you think they are. It is thought that leeches have a terrestrial (as opposed to marine, sillies) origin- many aquatic leeches leave the water to deposit their egg sacs. Many leeches also exhibit parental care.
Many leeches have three-"toothed" jaws which produce a "Y" shaped bite (Dr Siddall joked, "if you get a leech bite, you'll be sporting a little "Benz" logo). Other leeches have a long proboscis which they insert into their hosts- many of these leeches feed on crocodilians, which have bony scutes which would hinder a "three toothed" leech. Not all leeches are sanguivores, some feed on other invetebrates or the eggs of fish and amphibians.
Leeches have been used medicinally for millennia. The height of leech "therapy" (often used to "balance" the "humours" of the body, was the early-to-mid nineteenth century (oddly enough). Leech collection proceeded at such a brisk pace that conservation measures had to be put in place. Leeches have re-entered the pharmacopeia- they produce anticoagulents which prevent the blood they ingest from clotting. German physician Georg Haasused ground-up leeches as an anticoagulent while researching dialysis- ultimately, a purified form of the anticoagulent hirudin was available to Haas, who employed it in dialysis. Hirudin has largely been supplanded by heparin, which is easier to "dose". Leeches have recently proved to be invaluable in extremity reattachment surgery- while arteries have thick walls and can be reattached fairly easily, stitching veins together is more difficult... Dr Siddall likened it to "sewing two wet soda crackers together". The leeches prevent blood from coagulating and maintain a positive blood flow into a severed extremity. Of course, leeches don't purify the blood, they just remove it and ensure that it doesn't coagulate. Leeches are one of two invertebrate groups approved for use as medical devices in the U.S. (maggots being the other). A lot of terrestrial leeches move like "inchworms"
Dr Siddall then regaled us with tales of his globe-trotting, leech-hunting adventures. Well, "leech-hunting" is a misnomer, because leeches hunt you. The key to finding leeches is to do everything you are typically told not to do- you take off your shoes and socks, roll up your pants legs, and hike through the jungle/wade through the swamp. Eventually, the leeches will find you... leaping leeches, some of them move quickly! Aquatic leeches tend to swim in a "sine wave". Here is an excerpt from NOVA Science Now in which the two hunkiest scientists in the world, besides those supersexy "Riddled" boys, go on a leech-finding expedition:
I am proud to say that I have met both of them, and they are both awesome guys.
One of the Dr Siddall's most memorable leech-finding (insert leechfinder general joke) expeditions involved trying to collect a leech which lives exclusively in hippo asses. On this particular trek, Dr Siddall was accompanied by a guide with a rifle. Hippos are dangerous, so Dr Siddall asked the guide, "If a hippo charges, would you shoot it with the rifle?" The guide's answer was terse, "No, this rifle is too small to stop a hippo. If you get bitten by a hippo, the rifle is to shoot you." As a trivia bonus, courtesy of the good doctor, hippos are an invasive species in Colombia, some having escaped from a menagerie belonging to druglord Pablo Escobar. Dr Siddall eventually found his hippo ass leeches when a dangerous hippo (it had been subdued while invading a village, then was tagged and released, but ended up back in a village, thereby demonstrating that it wasn't afraid of humans) was put down. Dr Siddall had pictures of the leech in its natural environment... I'll refrain from finding a picture to link. Another leech which was profiled in this part of the lecture was the giant Amazon leech, which is one of those "proboscis possessing leeches". The lecture also touched upon the recently discovered T. rex leech, a monster with a single jaw with really gnarly teeth, which lodges itself in the nasopharyngeal region to feed. Dr Siddall showed an arthroscopic video of a leech being plucked out from someone's nose (they can't be washed out, because they could be aspirated). He also showed a picture of a leech resting on someone's eye, than told the audience, "If you think this is gross, I can change the picture." His next "slide" was the same image flipped- well, played, doctor!
Perhaps the funniest moment of the night was when Dr Siddall (who periodically punctuated his lecture with exhortations to the crowd to buy drinks and to tip the bartenders generously) related a leech-hunting trip to the upper Midwest. The good doctor needs to feed the leeches he finds, so he stopped at an abbatoir to obtain a liter of fresh blood (since he was getting it straight from the source, he got a couple of additional liters on his arms). The leeches need to "feed" through a natural membrane, so Dr Siddall, accompanied by two female associates, went to the local pharmacy to buy three boxes of "sheepskin" condoms, afterward asking the ladies, "Do you think these will be enough?" PURE HILARITY...
I'm going to stop here, because I forgot to bring my lickle notepad to work. I will update the post to include the information about the different anticoagulents that leeches produce, and about the correct identification of medicinal leeches. There will be
Ya know, I may as well plow through the parts that I recall... I'll post the addendum, mainly about anticoagulents, when I get my notes.
Dr Siddall then touched upon the (mis)identification of medicinal leeches. The classic medicinal leech is Hirudo medicinalis (Dr Siddall touched upon the handsome colors that some leeches sport- it's possible that some leeches mimic the toxic spotted newt in order to deter predators- though Dr Siddall recounted an incident he witnessed in which spotted turtles ate leeches which had attached themselves to a large snapping turtle... turtles playing plover, who knew?).
Anyway, leeches typically have bacterial symbionts in their gut, probably to "crowd out" dangerous bacteria. The best known bacterial symbiont of the medicinal leech is genus Aeromonas. Different species of Hirudo leeches have different species of Aeromonas associated with them- Hirudo medicinalisis associated with Aeromonas hydrophila while Hirudo verbana is associated with Aeromonas veronii. In the U.S., many of the leeches sold as H. medicinalis are actually H.verbana (Dr Siddall related to us a call he received from customs officials who had found 750 leeches in a package which was being smuggled into the country from Turkey). It is critical to determine what species a particular "medicinal" leech is in order to determine which Aeromonas bacteria it harbors in order to determine what antibiotic prophylaxis needs to be performed.
I'll post an addendum about the anticoagulents when I get my little steno book... needless to say, there are three basic ones, each acting on the "clotting cascade" in different ways. There are some indications that leech saliva can have an anti-metastasis effect (hmmm... maybe I can just link to Dr Siddall's blog and blow off the update...). Some bastard in the audience asked Dr Siddall about the similarities between the anticoagulates produced by arthropods such as mosquitoes and those produced by leeches, and he wrote down the answer somewhere... I'll just say now that some of the chemicals involved are also related to toxins employed by certain snakes. After the lecture, said bastard asked about a study (which may be a piss-take) which seemed to suggest that garlic can kill leeches. Dr Siddall indicated that he may try to replicate said study.
All told, the subject matter of the lecture was certainly sucky, but the lecture was a grand slam. Truly, this lecture was one of my favorites... I'm a sucker for biological topics anyway, and Dr Siddall was not only the go-to guy about the subject, but he was used to playing to an audience. Once again, the Secret Science Club delivered the goods in spectacular fashion... Christmas came early, and it was bloody good!
Now, check out this NOVA FAQ for additional reading... it actually lists the anticoagulents produced by leeches, and the different mechanisms in which they work (whether they act on thrombin or platelets). It also mentions the chemoreceptors that leeches use to find that tasty, tasty blood. If I can't find my notepad, no big loss!