They’re hard to diagnose but flukes are a concern

Unexplained weight loss is one sign that this parasite may be affecting your herd

I hear of the diagnosis of liver flukes here and there, a condition that can be hard to diagnose and has rather limited treatments.

One of the first clinical signs is non-specific weight loss, which can be confused with many things. As well, having liver flukes predisposes cattle to a susceptibility to a clostridial disease (clostridium hemolyticum) better known as Redwater disease.

Producers and veterinarians need to be vigilant on watching for them. The initial diagnosis is usually made on a post-mortem exam when closely examining the liver. That is where you find the adult flukes or the characteristic necrotic areas we get with Redwater. The liver may appear to have lumps and bumps, and on cut surface we find the flukes themselves and the inflammatory response around them.

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The liver is pretty resilient but if there are lots of flukes, there is considerable damage and a poorly functioning liver. On an initial post-mortem the internal organs are checked and often the standard procedure is to make several slices through the liver. We also look for any discolouration indicating things like copper deficiency or abscesses (indicating a prior grain overload). We may even pick the flukes up in the liver on slaughter, in which case the liver is condemned but the animal may or may not have shown any clinical signs to that point. At least this alerts us to varying levels of infection that may be present with the rest of the herd.

The animal may not be showing signs of liver failure but if adult flukes are found we know they are at least a major part of the problem. There are two types of flukes in the livestock population: the common fluke and the giant fluke. They have a more complicated life cycle involving aquatic snails so are seen in wet, boggy pastures primarily. Wildlife such as the deer species can be a common source of the giant fluke and that could either be wildlife or game-farmed animals.

I hear of more cases of the giant fluke. The issue in domestic species such as cattle, bison, sheep or goats is they are a dead-end host — meaning the life cycle doesn’t perpetuate itself and so the adult flukes do not pass eggs in this species. Fecals then would not pick up any eggs and so the primary diagnosis is the post-mortem.

If you have had a problem in the past, your herd vet may go on the assumption that a fluke diagnosis is likely. In pastures identified as having flukes in the past, a management scheme would be to treat in the fall with a flukicide. Again, there is a dilemma. The albendazole dewormer has treatment for the common fluke (fasciola hepatica) listed on the label. To my knowledge though, it is pretty ineffective against the giant fluke (fasciola magna) and a product called fasinex (trichlabendazole) needs to be brought in from the U.S. as an emergency drug release as the product is not licensed in Canada.

Keep in mind wildlife are going to be the source of magna, but cattle or bison don’t spread the eggs. All these reasons are why it is critical to determine if the infection is from the giant fluke or common fluke.

When we get flukes of any kind we must always make sure the herd is vaccinated for clostridium hemolyticum. It is in some of the eight-way clostridial vaccines, but not all of them, so make sure it is on the label.

For cattle going to pasture, it is wise to clostridial vaccinate routinely. Immunity to Redwater only lasts about six months, so make sure to vaccinate on the way out to pasture. As well, keeping cattle, sheep, and goats out of boggy, wet areas will break the life cycle. That is easier said than done, and in wetter years we see an increased incidence.

Any time we find flukes it could be a serious herd problem, so treat and monitor, and keep in mind that with a product like Fasinex there is a very long meat withdrawal period. We need to always keep that in mind whenever treating with any parasiticide — they are like antibiotics, residues remain, so a withdrawal or holding period is necessary.

In countries where it is approved, slaughter withdrawal is in excess of two months. Check with local regulators to see what is recommended in Canada as again, product must be brought in under an EDR (emergency drug release).

The good news is there is a way to treat and monitor for flukes. In other countries such as Britain, which is much wetter, cattle and especially sheep may need to be treated a few times a year with oral fluke products. Convenience with these oral products combined with good chutes are making accurate, quick oral administration easier and easier to achieve.

We can control flukes, but you first need to know they are there and then get proper treatment and put whatever preventive measures in place that you can. It is another parasite to keep our eyes on in Western Canada and can affect most species on the farm.

About the author

Contributor

Roy Lewis practised large-animal veterinary medicine for more than 30 years and now works part time as a technical services veterinarian for Merck Animal Health.

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