Difference Between a Fluke & a Leech

Hundreds of species of flukes exist worldwide. Classified as termatodes, all are parasites that go through a similar and rather complex life cycle. The large American liver fluke, for example, begins life as an egg deposited in the feces of its host, mainly deer, elk, cattle, sheep and llama. After 25 days, the eggs hatch into miracidia and enter the bodies of passing snails where they spend four days developing into cercaria. The cercaria then leaves the snail as a larva known as a metacercaria and resides on plant material until eaten by a host. Once ingested, the larval fluke burrows through the intestinal wall and travels to the liver where it reaches maturity after three months and begins to lay its own eggs.

Leeches lay their eggs in cocoons and the young hatch into tiny versions of their adult selves, changing little in appearance other than to grow larger as they mature. Despite their reputation, only a few of the 700 to 1,000 species of leeches are actually bloodsuckers, according to Northern Arizona University. Some leeches swallow their prey whole. Others use a proboscis, a tube-like structure with a sharp point that they extend from their mouth to stab their victims. They then use the proboscis like a straw to consume all the fluids from the body. Those that are bloodsuckers use teeth to attach themselves to the skin of a host for a liquid meal but detach and leave the host alive once full.

Leeches may inhabit freshwater ponds or rivers, oceans or the moist earth underneath a rock. Their prey includes insects, birds, frogs, worms, fish and mammals. Some marine leeches attach themselves to the soft bellies of sharks while their freshwater cousins prefer the juice of pond snails for dinner. Even crocodiles and alligators play hosts to leeches. Humans fall prey as well but might serve as willing victims of a leech attack. These leeches have histamines and anticoagulants in their saliva that prevent blood from clotting. Surgeons sometimes apply bloodsucking leeches, including the Hirudu medicinalis, after a limb reattachment, vein reconstruction or other procedure to promote blood flow to the damaged tissue and speed healing.

Flukes can invade the organs of fish, birds and mammals, including people. A host’s reaction to these parasites varies. Sheep are particularly vulnerable to the American liver fluke and the Michigan Department of Natural Resources notes an infestation is typically fatal. However, deer don’t seem particularly bothered by infestations of the same liver fluke. Humans in central and Southeast Asia are at risk for consuming larva of the giant intestinal fluke by ingesting infected water chestnuts, according to the North Carolina School of Medicine. These flukes attach to intestinal walls and cause ulcerations, inflammation, pain and diarrhea. Lung flukes most commonly affect humans in Asia, Africa and South America through ingestion of undercooked freshwater crab.