The term ‘fluke’ is used to describe short, flat worms, usually of the class Trematode. In contrast to tapeworms which are cestodes, and roundworms which are nematodes. In livestock, ‘fluke’ usually refers to liver fluke. In Australia, we only have one species of liver fluke, Fasciola hepatica. Other flukes present in livestock may include rumen fluke (paramphistomes).
Liver fluke is a truly wonderful parasite, as it will infect nearly all mammal species – and yes, that includes humans. In Australia liver fluke will infect all livestock species (although in pigs it cannot complete its lifecycle) and marsupials. Unlike many of the roundworm parasites, flukes do not have a direct lifecycle, and require a water snail as an intermediate host. Therefore, liver fluke is generally only a problem in areas where livestock graze wet/marshy ground, or where paddocks are irrigated. The correct species of intermediate host snail is also required to be present.
Life Cycle Due to the secondary host, the lifecycle of liver fluke is slightly more complex, however it is in fluke stage within the livestock that is of most concern. Infective cysts are ingested off pasture which develop into immature flukes within the host animal. These immature flukes will migrate from the intestines via the peritoneal cavity and into the liver. This migration causes significant liver damage and blood loss. Once the flukes have matured, adults reside in the bile ducts, where they lay eggs which are passed out via the bile into the intestines, and then out through the manure. Eggs will hatch in the environment, and use the water snail as a intermediate host to continue their development. A reproduction stage occurs inside the snail, where one liver fluke egg and multiply into thousands of infective cysts.
Liver Fluke lifecycle from the CDC: Fasciola hepatica Life Cycle
1. Unembryonated eggs are discharged into the biliary ducts and excreted in feces.
2. Eggs become embryonated in water.
3. Eggs release miracidia, which invade a snail (intermediate host).
4. In the snail, the parasites progress through several developmental stages (sporocysts, rediae, and cercariae).
5. The cercariae are released from the snail and encyst as metacercariae on aquatic vegetation or other surfaces.
6. Fascioliasis is acquired by eating plants, especially watercress, containing metacercariae.
7. After ingestion, the metacercariae excyst in the duodenum.
8. They migrate through the intestinal wall, peritoneal cavity, and liver parenchyma into the biliary ducts, where they develop into adults.
Symptoms The immature flukes cause significant damage and disease to livestock as they migrate through the liver. A sudden infection may lead to acute fasciolosis, leading to anaemia, inflammation of the liver and in some cases, death. More chronic infections with adult fluke result in poor condition, reduced productivity (in livestock), poor weight gain, anaemia and fertility issues. Anaemia may present as bottle jaw (oedema), pale gums/membranes, scouring and weight loss. Chronic infection will lead to calcification of the bile ducts and damage to the liver, from which animals are unlikely to recover fully from. Damage to the liver can also allow the developed of Black Disease – where the liver has a secondary infection with clostridial bacteria, usually in sheep and cattle.
Adult liver fluke in the liver of a sheep. Notice the scaring and calcification of the bile ducts.
Diagnosis The current gold standard for liver fluke diagnosis is through a sedimentation faecal egg count – these are different to normal FECs to detect roundworms due to the size of fluke eggs. Liver fluke FECs are available via WormCheck.. There has been research into using antigen tests (similar to RATs) for diagnosis, as has work into developing PCRs. It is theorised that these can detect infections with immature fluke, however they are not widely commercially available in Australia yet.
Treatment Normal drenches used for treating roundworms are not effective against flukes. Active ingredients such as Triclabendazole and Closantel are required. If you do have a liver fluke problem, it is always best to talk to your local animal-health care professional, as drug resistance is developing, to make sure you use the best drug for your animal and region.
Prevention The best way to prevent infection with liver fluke is to keep animals off marshy/wet ground where water snails are present. Only a small number of water snails can act as the intermediate host for fluke – if you are concerned about your pastures, first off check your waterways for the presence of these snails. If they are not present, you have no need to worry about fluke infection. Information of the identification of liver fluke host snails is available online: DPI NSW have a very good fact sheet (linked in the comments).
Prevalence Liver fluke is not as widespread as other parasites. It is problematic throughout the irrigation district around Maffra is eastern Victoria, and may also be present in throughout Victoria and up the coast into NSW and Qld. South Gippsland (Wonthaggi region) may also be at risk of developing a fluke problem. During my PhD research we found fluke in wildlife on Wilsons Promontory. Western Australia is liver fluke free, and all livestock imported into WA requires a test to ensure they are not infected before being allowed into the state.
Infection in humans Lastly, it is important to note that liver fluke can, and will, infect humans. There has been a case study of a farmer in Victoria who became infected after watering their kitchen garden with farm/irrigation water. Unfortunately, treatment for humans is not as simple as for livestock and in some cases, surgery is required to remove adult fluke.