Range: Cosmopolitan Habitat: Water sources and inside host animals Size: 1.18-3.35in (30-80mm) long; 10-30mm (0.39-1.18in) wide Diet: Nutrients from host livers Threats: Unknown Life span: Up to thirty years

Transcript:

Today on Animal Fact Files we’re discussing liver flukes. Liver flukes are parasites. A parasite is an animal that depends on another organism, the host, for food and shelter. In the case of liver flukes, they are internal parasites and can be found living in the body cavities of other animals. Adult liver flukes are often found on or in the liver of their hosts, hence their common name.

Liver flukes are flatworms. There isn’t a single taxonomic group classified as “the” liver flukes; instead, they make up many groups that don’t share a common ancestor. This means that liver flukes are a polyphyletic group of animals. Liver flukes can be found anywhere their hosts live, so just about anywhere is an option as long as each stage is able to fulfill necessary conditions in order to develop into further life stages. For example, free living liver fluke larvae, meaning the larvae found outside of a host’s body, can’t live without water, so they’re often found near water sources.

Liver flukes begin life as an egg. The eggs are laid by adults and are excreted with the host’s feces. The eggs hatch quickly into larvae, called miracidia, if they come into contact with water. This larval stage is free-living, meaning they can live outside of a host but only for a short time as they require moisture.

The first host will not be the final host and is thus called an intermediate host. The liver fluke will spend time here, but will not develop to adulthood inside this particular organism. An example of an intermediate liver fluke host is a snail. Fish can act as an intermediate host for liver flukes, as well, though! The miracidia will burrow into the intermediate host’s body cavity. Here they will form into a sac-like shape, called a sporocyst, and as this sporocyst grows new larvae will develop inside of it. These are called rediae. These rediae will burrow out of the sporocyst and move to the snail’s digestive tract where they’ll feed and produce more larvae which are called cercariae.

These larvae have long tails and will leave the intermediate host to live in water, using their tails to get around. The cercariae will form into cysts and wait on vegetation to be eaten by a final host. Once in the final host, the cercariae will make their way to the host’s liver and eat the tissue here. Eventually they’ll become adults, attach to a bile duct, and the process will begin anew. Here the adults may live for decades, often going unnoticed by the host.

In total, from egg to adult the process takes about twenty weeks. In the case of humans, liver flukes are often ingested through consumption of raw fish, though even us vegetarians aren’t completely safe because ingestion of raw plants, like raw watercress, as well as contaminated water can also lead to an infection! Other final hosts for liver flukes include sheep, rabbits, deer, including moose, kangaroos, wombats, camels, rats, beavers, boars, and many more.

Like with tapeworms, it’s usually not even apparent to a final host that liver flukes are present, though bad infestations can lead to indigestion, abdominal pain, diarrhea, constipation, and nausea. In human society, liver flukes are treatable, but they’ve caused a lot of problems with livestock. Liver flukes can lead to lower quality meat and milk and they’re difficult to eradicate from an environment once they’ve become established. They may also infect our pets.

Adult liver flukes are usually quite small reaching only 30mm (1.18in) in length and 10mm (0.39in) wide, though the largest liver flukes can reach up to 80mm (3.15in) long and 30mm (1.18in) wide. As flatworms, they appear flat, and they’re also leaf shaped.

For more facts on liver flukes, check out the links in the description. Thank you to Rasmus for today’s request! Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files!