Fasciola hepatica -- the common liver fluke or the sheep fluke -- is a flatworm found in the biliary ducts of the liver and in the gall bladders of some domestic animals. Dogs have them, and they're prevalent in livestock and wild animals. Infected dogs exhibit symptoms related to inflammation of the liver or bile ducts.
The Liver Fluke
Liver flukes are flat, pinkish animals resembling leaves, 25 to 30 millimeters in length. They use two suckers to attach to their host, the amphibious snail. Flukes are most often found in humid regions with mild temperatures; dogs in rural areas are more likely to become infected from drinking water or eating aquatic vegetation contaminated with larvae, or from eating raw liver contaminated with juvenile flukes than dogs in less humid and less temperate areas. Liver flukes cause a disease called Fasciola hepatica, or liver rot.
Harm comes to an infected dog when parasites migrate through liver tissues and cross into the wall of bile ducts -- a process that destroys tissues and causes internal bleeding. Inflammation and fibrosis, or thickening and scarring of connective tissue, cause the liver to increase in size and become impaired, while bile ducts thicken and may become obstructed. Flukes also produce toxins that can be damaging to the liver.
Mildly infected dogs may be asymptomatic, or have no outward symptoms of the disease, or may exhibit generalized weakness or lethargy. In chronic cases, meaning cases in which the infestation has lasted for some time, dogs may be anemic or have edema, digestive problems or loss of appetite or weight. Dogs with severe or acute infestations -- dependent upon how many flukes have been ingested for what length of time -- may become progressively weak, resulting in complete exhaustion, organ failure, coma and eventual death.
Prevention & Treatment
Prevention relies on keeping your dog out of areas where conditions are favorable for flukes and snails to thrive -- streams, ponds, lakes, pools, rivers, marshes, ditches and nearby vegetation. This is not always feasible. If your dog does become infected, seek immediate veterinary care. Treatment usually involves using wormers such as praziquantel. Anti-fluke vaccines are under development, but the results so far been disappointing. Dogs with Fasciola hepatica are not contagious to humans.