Deer liver flukes in particular are becoming a more common problem in cattle herds, and treatments can prove tricky for producers
Liver flukes start their life cycle in tiny freshwater snails but end up in the livers of grazing animals, where they mature and pass their eggs.
Feces containing fluke eggs must land in water for transmission to snails. If the animals’ feces lands on dry ground, the eggs die.
Cattle generally get two types of liver flukes: the cattle fluke, Fasciola hepatica; and the giant deer fluke, Fascioloides magna.
Certain areas of the United States and Canada with habitat for snails have a problem with flukes in cattle. Some have greater problems with deer flukes because these parasites are endemic in deer, moose and elk. Deer flukes in cattle can be more difficult to control.
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Dr. Anne Rogers of the Edson Veterinary Clinic in Edson, Alta., has seen a growing number of deer fluke cases crossing from elk into cattle.
“We used to see this problem primarily in cattle grazing pastures that had previously been used by farmed elk, but now these parasites are also in the wildlife population in our region. We are seeing this problem increasingly spreading west over our practice area,” she says.
“We tend to see flukes most commonly in cattle grazing low-lying areas that have water, since the snail is the intermediate host. These flukes damage the liver, and we’ve seen everything from cattle just not doing well to cattle that actually die of liver failure if the damage is severe.”
These cattle can also die from redwater disease caused by Clostridium hemolyticum. Liver damage opens the way for this infection, which is acute and deadly.
“If we find flukes in the area where a rancher is grazing cattle, we recommend vaccinating annually with an eight-way clostridial vaccine that contains protection against redwater,” says Rogers.
In some areas ranchers should vaccinate twice a year to be safe.
It’s helpful to know the cause of death in any animal that dies.
“We are lucky here because we have the BSE surveillance program that will pay to have a veterinarian come to your ranch and do a post-mortem on animals found dead,” Rogers notes.
In the case of cattle flukes, feces can be checked for eggs. This isn’t a good test for deer flukes because cattle internally wall off the flukes and do not pass the eggs. That is why the problem is generally not diagnosed until the animal dies or is slaughtered and the liver is checked.
Some animals with deer flukes will lose weight but others appear healthy.
“We’ve found deer flukes in 4-H steers that were fat and healthy otherwise,” says Rogers.
“In our experience, we see everything from nothing obviously wrong … to poor-doing animals, to animals suddenly dead from redwater disease.”
If a damaged liver is discovered at slaughter and the animal is otherwise healthy, the liver would be discarded but the rest of the meat is fine to eat.
The typical treatment for cattle flukes is albendazole (Valbazen), which kills mature flukes in the liver. However, it doesn’t work as well for deer flukes.
“If we find a herd that has an issue with deer flukes, we use albendazole in higher dosage. At necropsy in treated animals, we’ll find dead flukes in the liver, so it does seem to kill them. There is no drug specifically labeled for deer flukes, however, so your veterinarian would have to recommend and prescribe the higher dose.”
Rogers said veterinarians also battle the problem in farmed elk. Typically, they are treated once or twice a year, but there is no on-label use in elk. A European product called Fasinex has shown efficacy but its use in Canada would require an emergency drug release.
To effectively treat either type of fluke, producers should consult their veterinarian on products, dosage and timing.
“The flukes need to be at a certain level of maturity before they are susceptible to the drug. There are also some cautions about using albendazole during the first trimester of pregnancy,” Rogers says.
“In some herds, if we’ve only found one animal with flukes and haven’t seen any issues, we may not treat the entire herd for flukes. We may just monitor.”
Annual vaccination for redwater is recommended.
“In many regions in Canada, ranchers used to simply vaccinate young cattle for blackleg and maybe revaccinate every few years and got by. I’ve been trying to educate producers and let them know they need to vaccinate every year with the eight-way vaccine that contains protection against redwater. This is a very inexpensive and effective vaccine. There is no excuse for not using this one.”
Deer fluke prevalence is difficult to determine but “with veterinarians, ranchers and butchers working together, we get a picture of what’s going on,” says Rogers.
“I’ve talked with other veterinarians and deer flukes seem to also be an issue in southern Manitoba and some of the northern U.S. states.”
The cattle fluke is more common. Redwater is also becoming more common and producers in some areas now must vaccinate for it.
“Twenty years ago, we didn’t have redwater in our practice area,” says Rogers, “but it’s been steadily increasing in incidence and moving across this region. Parasites move around, with their hosts, and so do various diseases.”
