Leeches also still play a role in medical treatments, from Wikipedia:

Medicinal leech therapy (also referred to as Hirudotherapy or Hirudin therapy) made an international comeback in the 1970s in microsurgery,[16][17][18] used to stimulate circulation in tissues threatened by postoperative venous congestion,[16][19] particularly in finger reattachment and reconstructive surgery of the ear, nose, lip, and eyelid.[17][20] Other clinical applications of medicinal leech therapy include varicose veins, muscle cramps, thrombophlebitis, and osteoarthritis, among many varied conditions.[21] The therapeutic effect is not from the small amount of blood taken in the meal, but from the continued and steady bleeding from the wound left after the leech has detached, as well as the anesthetizing, anti-inflammatory, and vasodilating properties of the secreted leech saliva.[5] The most common complication from leech treatment is prolonged bleeding, which can easily be treated, but more serious allergic reactions and bacterial infections may also occur.[5] Leech therapy was classified by the US Food and Drug Administration as a medical device in 2004.[22]

Because of the minuscule amounts of hirudinpresent in leeches, it is impractical to harvest the substance for widespread medical use. Hirudin (and related substances) are synthesized using recombinant techniques. Devices called "mechanical leeches" that dispense heparin and perform the same function as medicinal leeches have been developed, but they are not yet commercially available.[23][24][25][26]