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Preventative Health Care For Elk: Liver Fluke


Robert P Acorn PAg.

About the author: In 1999 Robert Acorn was an agrologist working for the Animal Industry Division of Alberta Agriculture. The article below first appeared as a joint presentation with veterinarian Dr. Carla Lindahl at the 1999 Alberta Elk association Conference in Jasper , Alberta and was then published in The Tracker magazine who have allowed me to include it on this website.

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Introduction

As with many things we do, knowledge is often the key to success. Producers who develop a diverse knowledge and understanding of elk production, requirements for health and related issues, and who work in partnership with their veterinary practitioner and other specialists, will generally be those most successful at elk farming. The following article will help add to the knowledge you now have on keeping elk healthy.

Liver flukes are parasites. Parasites are organisms that live on or in another organism for survival purposes and contribute nothing or harm the organisms they parasitize. Effective control of any parasite requires some knowledge about them, including what they are, where they come from and how they live. The fluke we are concerned about on Canadian elk farms is the Giant Liver Fluke (Fascioloides magna). It is a very large parasitic flat worm which lives as an adult in a thick-walled cyst within the liver of elk and deer. The adult liver fluke averages about 2 inches long and 1 inch wide.

The Giant Liver Fluke normally occurs in wild elk and deer throughout most of the southern half of North America, but has become established as far north as northern Quebec and Labrador in Woodland Caribou. (Editors note: F. magna has been reported in every province in Canada). In Alberta, it is common in wild elk of the foothills, south of the North Saskatchewan river, including the areas of Waterton , Banff and Cyprus Hills parks. Giant Liver Flukes also occur in Elk Island Park. A recent survey conducted by Alberta Agriculture to determine liver fluke presence on elk farms, found 13 of 39 farms sampled had one or more infected animals. Nine of the 13 infected farms had brought the infected elk onto their property from other licensed game farms. Details and results of this study will soon be published in the Canadian Veterinary Journal.
 

Life Cycle

The Giant Liver Fluke is a two host parasite, requiring an elk or deer and aquatic snails to complete its life cycle. Normally, two adult liver flukes are found together within a thick-walled cyst in the liver of an elk or deer. Each cyst intersects bile ducts in the liver. Each pair of liver fluke produce thousands of eggs per day which pass with bile into the intestine and out of the body in feces. If fluke eggs are shed into a slough, ditch or other permanent or semi-permanent water body in warm conditions, they hatch in about 14 days. On hatching, the first-stage larvae must locate and penetrate a water snail within about 24 hours. In the snail, this single larvae encysts and continues to develop, eventually changing into several hundred small larvae which then leave the snail. These larvae attach to vegetation in the water and become the infective stage to animals which eat them while grazing. Warm water temperature quickens development of the liver fluke from the egg to the infective stage. Within about a week of being swallowed, the larvae penetrate the intestine and migrate to the liver. Migrating larvae develop into immature flukes which continue to roam within the liver until they contact another fluke, at which time they encyst and become adults. Immature flukes may migrate indefinitely in the liver until another fluke is encountered. Adult flukes live at least 5 years and possibly as long as the animal they have infected.
 

Clinical signs

Liver flukes cause few reported problems or losses of elk in wild populations. However, under farmed conditions where fluke infection can become more concentrated, problems may occur. Migrating immature flukes can cause extensive liver damage and bleeding. Even minor liver damage can serve as a site for secondary bacterial and viral infection. Blood loss associated with migrating immature flukes, and blood feeding by adult flukes causes anemia. Generally, no obvious clinical signs are evident with liver fluke infection, but growth rate, body weight, conception rates and antler growth can be affected, depending on severity of fluke infection.

Giant Liver Flukes can affect most domestic livestock and moose. In sheep and goats, immature Giant Liver flukes continuously migrate, never encapsulate and usually prove fatal. In cattle and bison, these flukes cause large fibrous capsules in the liver, resulting in condemned livers at slaughter. Fortunately, fluke eggs are unable to escape from encysted adult liver flukes in cattle, bison or moose. One to 1.5 million bovine livers are condemned annually in North America due to liver flukes, at a monetary loss of over 10 million dollars. Total economic losses due to weight loss, effects on digestion and reproduction, and death in livestock is probably more than 30 million dollars. To protect other livestock, do not allow them access to elk pasture containing wet areas infected with liver fluke larvae.

Movement of fluke infected elk to other farms has the potential to establish liver flukes in areas where they normally would not occur. Established fluke infections on elk farms may also put wild elk and deer, and other livestock at risk of fluke infection.
 

Diagnosis

Fluke infestations can be diagnosed by examination of animal feces for the presence of fluke eggs. Infected animals having flukes that are not yet shedding eggs can be missed. Elk must be at least 10 months old. Fluke infection can not be diagnosed by fecal exam in younger animals because it takes at least 7 months from the time an elk ingests a larvae to where adult flukes are shedding eggs. Also, remember that a immature fluke will migrate indefinitely until contact with another fluke occurs, which could be much longer than 7 months. Dissection and examination of the liver for immature and adult flukes is a more definitive method to detect fluke infection.
 

Treatment

To determine if your elk already have flukes, obtain fecal sample examinations for elk 10 months or older. Hopefully, results are negative. However, since fecal testing may miss infection, you should perform annual random testing of a percentage of your elk herd. If any elk test positive for flukes and you do not have suitable snail habitat, seek veterinary treatment of infected animals. If your farm has suitable snail habitat, immediately isolate all elk onto dry pasture to prevent further exposure to infective fluke larvae and the contamination of wet areas by infected elk. Consider the histories of the infected animals. When did they arrived at the farm? Were they born on the farm? Have they had access to wet areas since they arrived? Infected animals born on the farm indicates that a cycle of liver flukes is now established on your farm and water sources are affected. If infected acquired animals have had access to snail infested wet areas, you must assume those areas now contain infective liver fluke larvae until proven otherwise.

If you have an established liver fluke infection:

  • Treat all elk with a flukicide as prescribed by a veterinarian to destroy all adult and immature flukes. If possible, keep treated elk on dry pasture for at least 3 weeks, since fluke eggs contained within encapsulated cysts in the liver will continue to be shed in feces even after adult flukes are killed. One or more repeat treatments may be required, especially for younger stock. Immature flukes seem to be more difficult to control than adult flukes. Monitor control results with fecal testing. Conduct chemical treatments in colder months. The goal is to destroy all liver fluke infection in each member of the herd prior to next spring, to prevent continued shedding of liver fluke eggs.  
  • If possible, fence out wet areas of your pasture or keep elk isolated on pastures away from fluke infected wet areas for at least one grazing season. Encapsulated fluke larvae on vegetation have been reported to survive up to 14 months. Fence dugouts and pump water from them to a trough for stock watering.  
  • If practical, ditch and fill wet areas to destroy snail habitat. Treating blue-green algae in dugouts with copper sulfate will also control snails. Follow use procedures and precautions on product labeling. Monitor dugouts for snail presence.  
  • Burn grass and bull rushes in wet areas in the spring to destroy fluke larvae.  
  • Conduct a rigorous herd monitoring and treatment regime each fall until the farm liver fluke infection is controlled.
     
Prevention

The answer to most parasite problems is to prevent or break the life cycle of the parasite. For liver flukes, water is essential for it's on-farm establishment. Water is required for hatching of fluke eggs, for movement of fluke larvae and for the presence of the snail intermediate host.

Elk farms on dry land that use well water will not have the right conditions for snails or fluke establishment. However, elk farms that have dugouts, ditches, sloughs and other low land containing water throughout most of the summer, are prime sites for establishing a liver fluke problem.

To prevent the arrival of liver flukes on your farm:

  • When purchasing elk, ask the owner if he has tested or treated for liver fluke and if so, the details. (How long has he had flukes? When did he test/treat the elk? What were elk treated with?) Whatever the circumstances and if possible, keep new arrivals, including calves until they are 1 year old, on dry ground until treated or tested free of liver flukes.  
  • Do not allow farmed elk to share sloughs, ditches, etc. with wild elk or deer on a perimeter farm fence, especially in locations of province where wild elk and deer are known to be infected with liver fluke.  
  • Use well water or treated dugouts as the only water source on your farm.
  • Conduct occasional fecal tests for the presence of liver fluke.