There are several liver flukes that can affect cattle, and although they are not a common parasite in Western Canada, producers and veterinarians should be aware that they can occur.
The most common liver fluke in Western Canada is the giant liver fluke, which is also known as the deer liver fluke. Its scientific name is Fascioloides magna and this parasite is primarily carried by white-tailed deer, mule deer and elk.
Like other flukes, it has a complicated life cycle. The fluke eggs pass through the deer or elk from the liver, through the bile duct into the intestine and feces and hatch in water, infecting a specific species of snail. The snails release thousands of a new stage of the parasite called a cercaria, which then encyst on aquatic vegetation where they are ingested again by a deer or elk and the life cycle continues.
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Occasionally, cattle or sheep can ingest the cercaria stage of the deer liver fluke and become infected as well. Cattle, sheep and moose can all become infected by this liver fluke, but they are “dead end” hosts. They will develop flukes in the liver but because the cysts don’t communicate with the bile duct, they don’t shed eggs in their feces and therefore aren’t able to spread the parasite to other ruminants.
This can make the deer liver fluke difficult to diagnose in cattle and sheep because there are no eggs in the feces. We can sometimes identify the fluke in the liver at postmortem. However, these flukes can migrate through the liver of the dead-end host (cattle, sheep and moose), causing inflammation and extensive damage to the liver.
The most serious consequence of this migration of the fluke through the liver is a disease known as redwater disease or bacillary hemoglobinuria. Redwater is caused by the bacteria Clostridium haemolyticum, which is commonly found in soil and in the rumen and liver of normal cattle and sheep.
However, the damage caused by the migrating liver flukes can allow the spores of this bacteria to germinate and release toxins that can destroy red blood cells in the body.
Cattle affected by redwater disease are often found suddenly dead. If they are identified before death, they may show signs of jaundice and anemia as well as urine that is port-wine in colour due to the presence of hemoglobin from the red blood cells that have been destroyed by the clostridial toxin.
In sheep, another clostridial bacteria can cause a condition known as hepatic necrosis and result in sudden death as well due to the liver damage from migrating flukes.
We do have effective clostridial vaccines that will prevent redwater disease and hepatic necrosis and if your cattle or sheep are in a geographic area where giant liver flukes reside, you should be routinely vaccinating for these clostridial bacteria before releasing your animals to pasture.
A recent paper was published in the Journal of Veterinary Diagnostic Investigation that describes the deer liver fluke in aborted fetuses and neonatal calves that were submitted to the Veterinary Diagnostic laboratory at North Dakota State University.
During the period from 2012 -21, this diagnostic laboratory diagnosed 132 cases of liver flukes in beef and dairy cattle, which were submitted to the lab from Minnesota and North Dakota. About one-third of those cases that had evidence of the deer liver fluke also had evidence of redwater disease.
The study highlighted nine of these cases in which the presumed deer liver fluke was found in either late gestation fetuses or neonatal calves, which suggests that the liver fluke was able to migrate into the fetus during gestation from the dam.
The lab reports suggest that only three of these calves died because of the fluke infestation. However, if calves can become infected as a fetus, this could potentially result in redwater disease occurring in animals at a much younger age than what we would normally see.
Liver flukes are difficult to diagnose, except at postmortem, but we do have treatment options if they are a problem in your area. Your veterinarian can advise you about those options, although some may involve getting an emergency drug release to import specific products.
You should consider including the appropriate clostridial vaccine in your vaccination program to prevent redwater disease if your herd is in an area that is a risk for deer liver fluke.
John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.
