The liver fluke (Fasciola hepatica) is a parasitic worm that lives in the bile ducts of sheep and cattle. This parasite multiplies so rapidly that it can produce more than 40,000 eggs. The eggs exit the animals body in the feces, where they hatch to form free-swimming larvae. The free swimming larvae enter the freshwater snail (the parasites intermediate host), where the larva will develop into tiny, tailed versions of the adult fluke.
The tiny flukes bore their way out of the snail and make their way up the stems of plants. Sheep and cattle eat the plants and the process starts all over again. When the liver fluke does not have enough food, it actually shrinks in size. It will also digest its own organs. Fortunately for the liver fluke, the missing organs are regenerated.
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To manage parasites in animals, a number of prescription medications are available to either kill or prevent parasites or worms. The most common medications for parasites and worms in animals include Febantel, Fenbendazole, Ivermectin, Milbemycin oxime, Piperazine, and Pyrantel Pamoate. Because medications such as these can cause severe side effects, the type of medication used will depend on the type of parasite, severity of the condition, the animal’s weight, and the animal’s current health. Side effects may include:
- back pain
- dark urine
- extreme lethargy
- loss of appetite
- muscle and joint aches blurred or yellow vision
- pain while urinating
- redness, blistering, peeling, or loosening of the skin
- severe diarrhea
- severe nausea and vomiting
- skin rash
- yellow eyes and skin
In many cases, the risk of side effects are preferred over what can happen to sheep and cattle if infected with a large number of flukes. Flukes can cause damage to the liver, severe diarrhea, weight loss, and jaundice (yellow mucous membranes). They can also destroy red blood cells, damage other organ systems, cause low oxygen tension, decreased reproductive performance, and in some cases, they can even cause death.
According to John Maas, Extension Veterinarian at UC Davis, there are only two drugs available that are effective against liver flukes in cattle – Clorsulon and Albendazole.
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“Both work best against the adult flukes, but there is some effect on the migrating juvenile flukes. Clorsulon is effective only against liver flukes and it is sold alone as Curatrem® or in combination with ivermectin as Ivomec® Plus. Thus, Curatrem® can be used to kill the flukes or Ivomec® Plus can be used to kill the flukes plus the internal parasites (worms) and external parasites (sucking lice). Additionally, albendazole (Valbazen®) has activity against flukes and internal parasites. All the drugs and combinations of drugs have advantages and disadvantages in terms of cost, ease of administration, withdrawal times, and effectiveness. Consult with your veterinarian to be certain which product will work best for your operation. Also, review with your veterinarian the time of year that will be most cost-effective for administration of drugs to kill flukes.”
The Random House Encyclopedia, 3rd Edition
School of Veterinary Medicine University of California, Davis