Liver flukes an emerging threat to district cattle

As if district cattle farmers needed any more problems, it was learned last week there is yet another hazard facing the already-troubled industry.
Dr. Dan Pierroz from the Nor-West Animal Clinic in Fort Frances addressed a group of about two dozen local cattle farmers at the Millennium Hall in Stratton on the status of liver flukes in the district.
The information he offered, although useful, was hardly comforting.
Dr. Pierroz said there are two types of liver flukes that pose a threat to cattle and goats—and each has different characteristics.
Fascioloides magna (F. magna), or the giant liver fluke, has been identified in the district in increasing numbers over the past few years. Fasciola hepatica (F. hepatica), or common liver fluke, has been identified in the United States, but has not been found here yet.
“Magna is the only one we’ve found in Northern Ontario so far, but we’re watching for hepatica, too,” said Dr. Pierroz.
He added both organisms are liver and bile duct parasites, but there are subtle differences in their life cycles.
The natural hosts for both are deer. In this case, the animal ingests the organism from grazing. It then penetrates the gut and migrates through the peritoneal cavity to the liver.
From there, the adult flukes enter the bile duct and shed their eggs into the intestine.
These eggs are shed in the feces and then—under the right conditions—develop into mericidium, which can penetrate a snail. Here they develop into free-living larvae.
The larvae then are passed by the snail and encyst themselves on submerged or damp plant material, where they are ingested by deer to begin the cycle all over again.
When F. magna is ingested by cattle or sheep, however, the cycle is interrupted because the adult parasites become encapsulated in the liver and no eggs can escape through the bile ducts.
This effectively terminates the organism’s life cycle, but in the process, it causes severe damage to the host liver.
These animals are what Dr. Pierroz referred to as “dead-end hosts.” And because there are no traces in the feces, it can be difficult to know liver flukes are present.
In the case of F. hepatica, however, cattle and sheep can pass the eggs and perpetuate the cycle, but as Dr. Pierroz noted, the damage done by the flukes—however serious—is not the main threat to livestock.
Rather, the real threat appears to be from a family of bacteria known as clostridium. There are four types of this bug and the most common form in the region is called clostridium novyii (C. novyii).
However, one confirmed case of C. sordelli was found on a farm south of Devlin this year.
These organisms only can live in an anaerobic, or oxygen-free, environment, so they pose no threat to healthy animals and organs. However, when the liver is damaged by fasciola, tissue dies and becomes prime feeding ground for clostridium.
Dr. Pierroz said it is the toxins released by the bacteria, combined with the already-weakened condition of the liver, that ultimately kills the animal. In the case of sheep, as few as one or two liver flukes can prove fatal.
Part of the problem in diagnosing the condition is that liver fluke and subsequent clostridium infection can mimic other causes, such as anthrax.
“Understandably, when people think anthrax, they don’t want to approach the carcass,” Dr. Pierroz noted. “However, when anthrax hits a herd, it takes them all out quickly.
“When you see only a few animals down, you have to look for something else,” he added.
In fact, it was only because two local farmers took the trouble to take the carcasses to Winnipeg for a thorough autopsy that the cause of death was determined.
Dr. Pierroz said a number of medications have shown some promise in preventing or stopping liver flukes, but the most promising of these—Fasinex—has not yet been approved for general use in Canada.
It can, however, be purchased on an emergency basis.
Another drug—albendazole—has shown to be effective in removing liver flukes from cattle, but only when administered at 2.5 times the recommended dosage.
Furthermore, it cannot be used during early pregnancy.
Dr. Pierroz stressed these drugs must not be administered to milking cows or within a certain period prior to slaughter. In the case of sheep, the clearance time is 28 days; for cattle it is 14 days.
As well, they are expensive and must be administered twice a year in order to be effective.
But the best bet, said Dr. Pierroz, is to try and stop it before it starts. One way to do that is to destroy the habitat of the snails in which the larvae reside.
This involves draining wet pastures or, in some cases, burning them.
Another tactic is to go after the real culprits—the clostridium bacteria.
“Stop the novyii bug instead of the fluke,” he reasoned. “The best bang for your buck from my perspective is to vaccinate against novyii for the foreseeable future.”
So, where did the problem come from and why was it not noticed earlier? Dr. Pierroz has a theory about that.
Two factors that liver flukes need to maintain their life cycle are primary hosts and wetlands. During the springs of 2001-02, there was severe flooding in the district, which resulted in increased areas of wet pasture.
In addition, the deer population has exploded in recent years, providing a vital link in the chain.
“They’ve [liver flukes] probably always been here, but we never noticed it before because the conditions weren’t as good for it as they are now,” he concluded.
This year, there were reports of suspicious deaths from several local farmers.