Liver Flukes in Goats: Parasites With a History
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-by Cheryl K. Smith Liver flukes are parasites that, for centuries, have adversely affected sheep, cattle, and goats throughout the world during wet seasons. According to an account by the U.S. Department of Agriculture (USDA), in the early 1900s, flukes spread rapidly from west to east across the United States, causing disease and death in sheep and cattle. These insidious worms led to not only death but chronic disease that lowered birth rates, slowed growth, and caused unthriftiness. At that time, if livers from slaughtered animals showed fluke infection (also called fascioliasis), the meat was condemned — causing economic loss to farmers.
What is a liver fluke?
The liver fluke (Fasciola hepatica) is a flat, brown, leaf-shaped worm that infects goats and other mammals. (Note: There are other types of liver flukes, but this is the most common in the U.S., and this article is directed to it only.) Liver flukes in goats: The fluke is found in wet pastures and marshy areas because of its life cycle. The parasite lays its eggs in wet areas. The hatching larvae invade the bodies of snails, which are the intermediate hosts in which they develop. After the larvae have developed, they form into cysts that attach to grass or other plants, where they’re eaten by goats. Once in the goat’s digestive tract, the immature flukes emerge and migrate to the liver and bile ducts — where they mature and live for up to four years — causing traumatic hepatitis along their route. They lay eggs in the bile duct, which are then passed out of the goat’s body with feces, and the cycle is repeated.
How do liver flukes infect goats?
Liver flukes only affect goats on pasture that has snails that are the intermediate vector. They can be found in wet, marshy areas or water that is slow-moving and somewhat alkaline. This may be around a fast-moving creek where water has stagnated.
Rainy weather contributes to the problem because it helps wash fluke eggs out of the goat feces and back into the water where the snails can develop. Both cold and dryness can be the enemy of the snails; eggs cannot develop at temperatures under 50℉ and they also need moisture.
Liver flukes typically infect goats between the end of September and the beginning of May. Acute illness occurs 2 to 6 weeks after goats eat the parasites. Signs include weight loss, anemia (often detected by FAMACHA), and bottle jaw.
Once in the goat’s digestive tract, the immature flukes emerge and migrate to the liver and bile ducts — where they mature and live for up to four years — causing traumatic hepatitis along their route.
Besides damage to the liver, flukes can also damage the bile ducts. Goats with a severe or longstanding infection may lose their appetite, decrease milk production, become depressed, and develop ascites (fluid in the abdomen). Kids may fail to gain weight.
How are liver flukes diagnosed?
There are several ways liver fluke can be diagnosed. An ELISA blood test can detect antibodies from 3 to 4 weeks after infection. An ELISA test of feces is not as accurate as a blood test, but can detect mid- to late-stage infection 8 to 10 weeks after infection. There is also an ELISA test for pooled milk, which can be used to monitor herd health status, but it can also show antibodies for 8 months after effective treatment. For a goatkeepers who want to test their own goats, a fecal sample can identify eggs from 10 to 11 weeks after infection. Finally, if a goat or goats have died, a post-mortem exam can definitively identify all stages of infection, letting goat owners know if they have a herd problem.
Treatment for liver flukes began with the land
The first attempts at controlling liver flukes in the U.S. began in the 1920s. At that time, the focus was on destroying snails on land that was infested or keeping goats off that land. This is still a helpful method of control.
Goats can be shut out of infected pastures and fed with cuttings of hay from clean land. Broadcasting an infested pasture with copper sulfate and in and around creeks or swampy areas that contain the snails is another strategy.
Finally, creating drainage ditches, removing vegetation from around creeks, and ensuring adequate drainage of pastures can make them uninviting to the snails that are essential to the life cycle of the liver fluke.
How did they treat them in the animals?
In 1926, carbon tetrachloride was determined to be effective in killing mature liver flukes in sheep. According to an article published that year, “[a] single dose of 1 cc of the drug, given in soft gelatine capsule, destroyed all mature and almost mature flukes infesting sheep.”
Carbon tetrachloride was used to treat liver fluke in sheep and goats for more than 40 years. Besides giving it orally, it was also injected, at least in some studies. Research beginning in the 1950s concluded that either the drug killed liver flukes by damaging the liver rather than by directly affecting the fluke, or damaged the liver, which added to the toxic effect of the drug on the flukes that were destroying the liver.
Past treatments too toxic
carbon tetrachloride dewormer used for goats
until the 1970s, at a farm auction in the early
2000s.
Ultimately, carbon tetrachloride — which was used in old cleaning products, degreasers, aerosol products, and as a fumigant to control insects in grain, among other products — was deemed too toxic to be used in treating liver flukes and is now considered a hazardous waste by the Environmental Protection Agency.
In the 1940s, a chemical called hexachloroethane was mixed with bentonite (a type of clay) and used to treat liver flukes in cattle. This, too, was deemed too toxic, and was also found to be ineffective in treatment.
Current Treatments
The current treatment of choice for goats is the broad-spectrum anthelmintic albendazole. Albendazole was first used as a dewormer in livestock in 1975, and found to be effective against liver flukes in 1977. Albendazole (brand name: Valbazen) is considered to be more than 99% effective. Recommended treatment is 4 ml per 100 lb body weight in goats. (Note that this drug should not be given to goats during the first 30 days of pregnancy or during lactation. It can cause birth defects if given in early pregnancy.)
Owners need to remain vigilant for liver flukes.
Liver flukes can be an ongoing problem in warm, rainy areas throughout the world. Developing safe, effective treatment for animals was a trial-and-error process until the development of albendazole. Goat owners who live in an area at risk for their goats need to be aware of this insidious parasite when using FAMACHA as a method to detect anemia related to potential parasites and not assume that they are dealing with barber pole worms (Haemonchus contortus).
Sources:
Alexander, F, and DC MacDonald. 1959. “The Action of Carbon Tetrachloride on the Sheep’s Liver.” From the Department of Veterinary Pharmacology, Royal (Dick) School of Veterinary Studies, University of Edinburgh. https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/expphysiol.1960.sp001437.
Alicata, JE. 1946. “The Control of the Liver Fluke in Cattle in Hawaii. Circular Number 125. https://scholarspace.manoa.hawaii.edu/server/api/core/bitstreams/305cc500-9d9e-4738-948c-6940edea7907/content.
Ballweber, Lora Rickard. Fasciola hepatica in Ruminants. MSD Veterinary Manual. Updated October 2022.
Fowler, JSL. 1970. “Carbon tetrachloride metabolism in sheep and in Fasciola hepatica.” Br J Pharmac 39: 599-607.
Leathers, CW, et al. 1982. Clinical fascioliasis in domestic goats in Montana. J Am Vet Med Assoc 180(12): 1451–54.
National Agricultural Library. U.S. Department of Agriculture. Liver Flukes.
Sabatini, GA, et al. 2023. “Practical guide to the diagnostics of ruminant gastrointestinal nematodes, liver fluke and lungworm infection: interpretation and usability of results.” Parasites Vectors 16: 58 (2023). doi.org/10.1186/s13071-023-05680-w.
Shaw, JN, and BT Sims. 1930. “Studies in Fascioliasis in Oregon Sheep and Goats.” Station Bulletin 266.
Underwood, Wendy J, and Adam Schoell. 2015. “Biology and Diseases of Ruminants (Sheep, Goats, and Cattle).” In Laboratory Animal Medicine (Third Edition), page 676. https://reader.elsevier.com/reader/sd/pii/B9780124095274000158.
Cheryl K. Smith has raised mini dairy goats in the Coast Range of Oregon since 1998. She is the owner of karmadillo Press, and author of Raising Goats for Dummies, Goat Health Care, and Goat Midwifery. Her first work of fiction, Shed Boy, a cozy mystery set on a goat farm, is due out in June 2023. www.goathealthcare.com
