Features and Occasionals

Facts About Flukes

By Diane Olson

Flukes, also called trematodes, are a type of parasitic flatworm that infests everything from ants to elephants. Ranging in size from 0.2 to 4 inches, they resemble leaves or pieces of ribbon with big, leech-like suckers; have no respiratory or sense organs; and excrete through their mouths. There are between 8,000 and 24,000 species worldwide; fortunately, a mere 35 of them inhabit humans and none of those typically live in North America. Fluke infections are, however, a huge health problem in Asian, Africa, South America and the Middle East.

Flukes and snails and puppy dog tails

Flukes have strange and complex lifecycles, and they always revolve around snails. Starting out as an egg expelled from its host, the fluke first embryonates in water and then infests a snail. Next, it waits inside the snail for the snail to be eaten, or busts out to either find another intermediary host; bore into its final host; or position itself to be eaten by the final host. Once inside the final destination, it migrates to the liver, lungs, intestines or circulatory system and develops into an adult. Most are hermaphrodites, so they don’t need a partner to reproduce, though blood flukes apparently enjoy long-term, passionate, monogamous relationships while clinging to the wall of their host’s abdominal veins.

The Flukeman cometh

A particularly gross episode of the 1990s TV series X-Files centered around the Flukeman, a large, sewer-dwelling humanoid with a sucker-like orifice, who injected his victims with flukes. That’s not typically how people become infected. When it comes to liver, lung and intestinal flukes, un- or under-cooked fish, crab or crayfish is usually the culprit, though you can also get them from eating watercress, water chestnuts, or anything else contaminated with fluke-infected water. Blood flukes are generally contracted from swimming or walking through water in areas with poor sanitation or where human waste is used as fertilizer. Some

species of North American blood flukes do try to infest humans, but only succeed in causing “swimmer’s itch” as they attempt to bore through the skin.

Getting flukes is no fluke

Symptoms from fluke infection range from none to death—and everything in between. The tropical disease schistoso­ia­sis, caused by blood flukes, is second only to malaria, affecting approximately 200 million people. Untreated, it can wreak havoc on organs and impair cognitive development. Millions of people also have liver flukes—particularly in parts of the world where people regularly dine on raw, smoked, pickled or dried fish—but only about a quarter of those infested develop health problems (which may include vomiting, diarrhea, jaundice, enlarged liver, liver stones and abdominal pain). While no human-infecting flukes dwell in North America, you can still acquire them, thanks to international trade in fish and seafood—and, of course, travel. Thing is, though, unless they are long-term, fluke infections rarely cause lasting damage, and can be treated with anti-parasitic drugs (such as Flagyl). American doctors, however, may not think to check for flukes, since they’re not endemic here. If you’re ailing with a seemingly undiagnosable malaise, and flukes are a possibility, ask to get tested for them.

Of flukes and zombie ants

You know how some flukes have a second intermediary host? In the case of the lancet blood fluke, it’s ants. So, the final host excretes the eggs in water; the eggs hatch; the hatchlings invade a snail. The snail then leaves behind a trail of infected slime, and that slime is full of flukes. Along comes an ant, which collects the slime and takes it back to the colony for everyone to eat. The flukes from the slime then burrow into the ants’ brains, turning them into suicidal zombies bent on getting themselves eaten by a creature with a warm liver. When there’s no potential host around, the ants act normal, but when a grazing mammal approaches, they clamber to the top of a plant, where they can be easily eaten. Should an accommodating deer or cow consume them, the flukes burrow out of the animal’s stomach and into its liver.

This article was originally published on May 29, 2013.