Liver Flukes Are Problem
Under Specific Conditions

AMARILLO — Liver flukes are usually considered a minor problem, causing about five percent of beef livers to be condemned nationwide.

That's not much economically, says Dr. Jack Malone of Louisiana State University, who has studied liver flukes for more than 20 years, "but it might be the margin between profit and loss."

Fasciola hepatica, the common liver fluke, occurs in the bile ducts of cattle and sheep.

"Most people understand nematodes really well, but flukes are quite a bit different," says Malone. "You have to understand that in order to know how to approach treatment."

There is a difference when flukes present a danger. It can vary with the ranch, the season and the year.

This, Malone says, is a high risk year.

"You'll find the fluke only in specific areas," Malone says. "It's found in alluvial and coastal areas, predominantly. It requires a neutral soil. If you have acid soils, it just doesn't occur because the snail doesn't occur."

Flukes are borne by a mud snail, he explains. That makes moisture a limiting factor. The snails are easily recognized because of their short antennae, and the spiral shell goes right instead of left. Low-lying water, heavy clays and high water tables are all favorable for the snail, and therefore, for the fluke.

"It's not too hard to identify their habitat," he says. "In a feedlot, the habitat has a little standing water six months out of the year or more. In a field, there's a slough or a depression in the field, or a spring."

The life cycle requires the snail. The eggs of the flukes are shed by cattle in their manure, and they have to fall close to the snail habitat.

"If they fall out in the middle of a field, they're not relative," Malone says.

These eggs go into the water, hatch and develop after about 10 days to a month. If the hatchling finds a snail, it penetrates the foot of the snail, goes to the liver and starts multiplying. In good weather, this can take four or five days. In cold weather, it could extend 100 days or more.

"These will release the next stage, a more advanced stage," Malone says. "For every one of these eggs it can go to 100 to 200 infective stages. That's a big difference between flukes and nematodes. With nematodes, one egg goes to one larva, which goes to one worm. With flukes, you've got 50,000 eggs per fluke shed. One egg will go into the water, infect the snail and end up causing 100 or 200."

At this stage, Malone says, it looks like a little tadpole. It swims and is attracted to light, which makes it go to the surface of the water. It's also attracted to green, which makes it go to vegetation. When it reaches vegetation, it drops its tail and attach itself, forming four protective layers.

"That is basically an immature fluke, a little baby fluke inside that wall," he says. "It just sits there and waits to be picked up."

In cold, wet weather, it will remain there for months. If a drouth comes along, it will die within two weeks. That usually ends the season.

As cattle eat the vegetation to which the fluke is attached, they ingest the fluke. After entering the animal's digestive tract, it will work its way to the liver. Once it enters the liver, it will migrate around among the tissues of the liver for about six to eight weeks before settling into a bile duct.

"They'll sit there for a while," Malone says, "then try to bore their way through. When they do that, they're very damaging. That's the most pathogenic time, early in the infection when they're trying to enter the bile ducts in a big way."

Once flukes enter the bile duct, they grow rapidly, reaching an inch in about two to three weeks. Then they start shedding eggs, starting the life cycle over again.

The good news, Malone says, is that most parasite programs will help control flukes, and there are a number of new treatments out on the market.