As cattle are shipped from one state to another, liver flukes are making the trip, too. “I’m getting calls about flukes from veterinarians who have never seen them in their area before,” shared Christine Navarre, DVM, Extension Veterinarian at Louisiana State University Agricultural Center. “Flukes seem to be spreading, and producers need to be aware and on the lookout.”

Where you find snails, you’ll find flukes

Liver flukes are one of the more complex parasites in beef production. “In order to propagate, liver flukes require an intermediate host,” said Peggy Thompson, DVM, Boehringer Ingelheim. “For a fluke, that is a common fresh-water snail.”

As depicted in Figure 1, the fluke larvae migrate to snails, where they multiply. Once they exit the snail, cattle can ingest them by grazing on infested grass or drinking infested water. Before setting up camp in the bile ducts of the liver, juvenile flukes cause damage in the small intestine and abdominal cavity as they travel, leaving cattle with weakened immune systems and lost growth potential.

Figure 1. The liver fluke's full life cycle typically takes five or more months, making it difficult to detect prior to causing damage in cattle.

Since the host snails are attracted to moist environments, flukes can be found in wet pastures, low-lying areas where water collects, or even water troughs. Dr. Thompson reminds producers that if an environment is good enough for the snail, liver flukes can be around, too.

“Controlling the environment can be really tough,” noted Dr. Navarre. “It might be possible to fence cattle out of those low-lying areas, but that’s not always realistic.” Luckily, there are management steps that can be taken to monitor and deal with liver flukes.

Use diagnostics for sustainable fluke control

Cattle with liver fluke infections may go months without showing clinical symptoms. Depending on the level of infection, cattle can experience loss of appetite, rough hair coat, decreased performance, weight loss and poor reproductive efficiency.¹ Besides monitoring for signs of infection and wet areas for snails, producers can work with their veterinarian to build liver fluke management into a preexisting deworming protocol:

1 . Assess risk with diagnostics

“We need to be doing fecal tests and liver evaluation at slaughter, or at necropsy, when we have the chance,” shared Dr. Navarre. “The goal is to not give fluke treatment when risk is low, but we need to stay aware of when fluke treatment is needed.”

There are several factors to keep in mind when using diagnostic testing for liver fluke assessment:

2 . Manage risk with a qualified product

When treatment is necessary, the type of product used is important. “There are only a few products on the market that control flukes,” said Dr. Thompson. “If you’re looking for fluke control, look for a product with clorsulon, or be sure that flukes are covered on the label.”

Dr. Thompson emphasized the importance of also using other sustainable deworming practices when it comes to fluke control. “The products we do have only eliminate adult flukes, which are much less destructive than juvenile flukes,” she shared. Pasture rotation and refugia, the practice of only deworming high-risk animals, are ways to help control liver fluke and other parasite populations.

3 . Be thoughtful with timing

“When we put together a fluke plan, we have to do that in concert with our gastrointestinal [GI] parasites,” said Dr. Navarre. “The products we use for fluke control will also get those GI parasites. We have to be thoughtful about when we deworm for liver flukes, and only do it when necessary.”

Timing is one of the most important pieces of successful fluke management, and it doesn’t look the same for every producer. “Producers around the Gulf Coast might have a better chance of killing adult flukes in the fall, whereas producers in the Pacific Northwest might have the best opportunity in the springtime,” explained Dr. Thompson. “It’s best to work with your veterinarian to solidify when parasite control is optimal for your region's seasonality.”

Flukes may open the door for other disease

On their own, liver flukes are not likely to cause many fatalities. But without protecting cattle through vaccination, clostridial organisms can find their way into the damaged liver tissues left behind by flukes. “In healthy cattle, pathogens like Clostridium haemolyticum, which causes redwater disease, will have little impact,” stated Dr. Thompson. “But in cattle with liver fluke damage, redwater disease has the potential to take hold and be fatal.”

Dr. Navarre shared the same concern for cattle contracting redwater disease after a bad bout of liver flukes. “Both gastrointestinal parasites and liver flukes can impact cattle immune systems,” she said. “Making sure we control those parasites for general health and vaccine response is essential.”

Droughts don’t stop parasites

“Last year, we had widespread drought, which probably lowered the number of snails,” Dr. Navarre recalled. “But, when we have stressed cattle that might not be getting the nutrition they need, we see an increase in the severity of internal parasites when they do show up, flukes included.”

Most parasites need some level of moisture for their life cycle, but it doesn’t need to be a lot. “We saw some of the highest egg counts toward the end of the drought and we don’t know why,” added Dr. Navarre. “But with good grass quality and hay in short supply, mixed with stressed cattle, those factors together can suddenly magnify a small level of parasites.”

“Testing for internal parasites in general is a great practice to implement,” concluded Dr. Thompson. “Each operation is going to have different risks. Knowing what parasites pose the biggest threat allows for thoughtful control plans and sustainable deworming.”

References:

¹ USDA, National Agricultural Library. Liver Flukes. Accessed May 2, 2024. Available at:  https://www.nal.usda.gov/exhibits/speccoll/exhibits/show/parasitic-diseases-with-econom/parasitic-diseases-with-econom/liver-flukes

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