Liver Fluke Infection

by Susan Frazer

Several producers in Manitoba have encountered problems with liver flukes. Since fluke infection needs an intermediate host (water snails), which in turn need a wet poorly drained enviornment, these infections have been a direct consequence of the high rainfall and favourable temperatures of last summer.

Fluke infection diagnosed on several Manitoba farms in 2005 was due to Fasciola hepatica, which is 18 to 32 mm in length and 7 to 14 mm wide. The adult flukes reside in the bile tract of hosts such as goats, sheep, deer, etc and lay eggs that are passed via the bile duct to the feces. The eggs hatch within 10 to 12 days and invade the intermediate host snails. The eggs hatch optimally at 26oC and it must be at least 10oC for further development. Several stages of development take place within the snail and in 5 to 8 weeks cercariae are released into the enviornment, and swim to a nearby plant, attach to the herbage, encyst, and wait to be ingested by the goats. The ingested metacercariae penetrate the intestinal wall and migrate through the abdominal cavity to the liver. They penetrate the liver capsule and wander around, growing, and destroying tissue. Finally the immature fluke enters a bile duct, matures, and begins to produce eggs - all about 8 weeks after infection.

Symptoms of liver fluke infection can be acute or chronic. If massive numbers of the parasite are ingested over a short time then there is tremendous injury to the liver. The symptoms are sudden (distended painfull abdomem, anemia, anorexia) and death can occur in a short time. The chronic disease is more common with signs such as anemia, unthriftiness, submandibular edema, and reduced milk production.
 
Diagnoses can be confirmed by finding fluke eggs in the feces (fecal sedimentation method), or by the liver damage at post mortem. Adult flukes can be easily seen in the bile ducts, and black tracts (hemorrhagic) observed within the liver.

Always consult with your veterinarian for diagnosis and treatment if you suspect liver fluke infection. In the cases seen in Manitoba the producers are treating with Valbazen (Albendazole). Given orally at 15 mg/kg it is reported to be 95.9% effective against adult flukes and has a wide safety margin. However caution is advised if using Valbazen during the first 3 weeks of gestation. Retreatment will be necessary to eliminate the maturing larvae.

To help control future fluke infections it is best to limit the goats access to low lying wet areas of their pasture. As well using an anthelmintic that kills immature and mature flukes should be considered periodically during the grazing season.