General Health

Leeches are annelids comprising the subclass Hirudinea. The medicinal leech, Hirudo medicinalis, which is native to Europe, and its congeners have been used for clinical bloodletting for thousands of years.

The leech has long been used in medicine, although today its use is mainly limited to limb reattachment procedures instead of the wide-ranging medical use in the past. They have proven highly effective at preventing venous congestion after the surgical re-attachment of fingers, toes, ears and other parts of the body.

Externally, medicinal leeches tend to have a brown and red striped design on an olive colored background. These organisms have two suckers, one at each end, called the anterior and posterior sucker. The posterior is mainly used for leverage while the anterior sucker, consisting of the jaw and teeth, is where the feeding takes place. Medicinal leeches have three jaws—tripartite– that look like little saws, and on them are about 100 sharp teeth used to incise the host. The incision leaves a mark which is an inverted Y inside of a circle.

Leeches’ bodies are composed of 34 segments. They all have an anterior (oral) sucker formed from the first six segments of their body, which is used to connect to a host for feeding, and can also release an anesthetic to prevent the host from noticing the leech. They use a combination of mucus and suction (caused by concentric muscles in those six segments) to stay attached and secrete an anti-clotting enzyme into the host’s blood stream.

Leech saliva contains a number of compounds which assist in its feeding. An anaesthetic limits the sensations felt by the host (and thus reduces the chance of the host trying to detach the leech). Lastly, the leech saliva contains a peptide called hirudin, which is a highly effective anticoagulant. The leech needs this to prevent blood clots (which would block its feeding) from forming in the wound created by its mouthparts. These properties are difficult to achieve using other medical techniques, and it is for this reason that leeches have come back into clinical practice in the last 25 years.

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