Liver fluke prevention
Keep animals from grazing wet areas.
Control snail population by fencing off marshy, or wet areas.
Keep deer, elk, moose out of pastures and away from water supplies by keeping a guardian dog with the flock;
Use a strategic control program, such as early-spring drenching with Ivomec Plus to prevent pasture contamination. A Fasinex drench in summer or early fall may be used to kill immature flukes.
Make sure new entries are fluke free by quarantining and medicating them in a separate pen for at least two weeks before letting them join the flock.
Alternate dewormers to avoid resistance.
“If the animals have picked up a lot of them in the infective stage, we should be seeing acute cases, dead animals and sudden deaths on the farm in the month of October.”
– MAMOON RASHID
Sheep producers should keep their eyes open for signs of liver fluke infestations in their flocks as the parasite is becoming more common in Manitoba.
Because the internal parasite – which resembles a small, round leech about the size of a thumbprint in its adult stage – needs a particular kind of snail to complete its life cycle, producers in areas with wet, low-lying pastures or sloughs need to be especially vigilant, according to MAFRI sheep and goat specialist Mamoon Rashid.
Sheep, cattle and goats can carry liver flukes, as well as wild ruminants such as deer, elk and moose, which are passed on through eggs in feces.
If sheep are put on pasture May 1, within as little as 20 days the eggs could be picked up by snails, the intermediate host. From there, they spend two months inside the snail, and are then deposited as eggs on pasture grasses as early as July 1.
“By then, we don’t see any animals sick or dying, but the cycle is running,” said Rashid, at the Manitoba Sheep Association AGM in Portage la Prairie March 6.
“If the animals have picked up a lot of them in the infective stage, we should be seeing acute cases, dead animals and sudden deaths on the farm in the month of October,” he said.
Animals with a low load of flukes may not show adverse signs until December, or after the immature flukes have travelled around the bloodstream. In their search for their final destination, the liver, they leave telltale signs of blackened tissues in the rumen and other organs which can be clearly seen in a post-mortem exam.
There are three types of liver fluke infestation: acute, subacute and chronic. Acute cases may occur in the form of an outbreak when pasture grasses are massively contaminated with the flukes in the larval stage. Sudden deaths due to liver hemorrhages without prior symptoms such as anemia are common in such cases.
Subacute cases mani fest symptoms of anemia due to severe internal blood loss caused by extensive liver damage.
Chronic infections are the most common type seen in Manitoba, according to Rashid.
Animals show clear signs of jaundice, or pale mucous membranes on the gums or eyelids, and death occurs after a slow loss of overall body condition which may include edema or bottle jaw.
In chronic cases, the liver flukes have reached the adult stage, and kill the animal by slowly draining its blood at a rate of up to two cc per day or clogging up the bile ducts in the liver. Infected animals in this stage can shed untold tens of thousands of liver fluke eggs.
Anemic, non-weight gaining animals are a dead giveaway for parasite infections, said Rashid, and the cause could be liver flukes or barberpole worms. Fecal egg counts can pinpoint chronic cases in both, he added.
Serological testing can be used to screen a flock, but it may not catch individuals. Slaughterhouse reports of condemned organs are another indicator.
Animals with liver flukes are at risk of a secondary infection – Black disease caused by clostridium novyi, which attacks dead tissues damaged by liver flukes. So vaccination is key.
Broad-spectrum medicines that can kill liver flukes at all life cycle stages such as Fasinex are not available in Canada or the U. S. They can only be imported from overseas via an emergency drug release (EDR) appl icat ion with Health Canada filed by a veterinarian.
Valbazen and Ivomec Plus kill only mature liver flukes, so timing is critical when using both drugs.
Ivomec Plus has a downside, however. Even if the flukes are killed by the dewormer, it doesn’t repair the damage they caused. That means the sheep themselves may have sustained severe, permanent organ damage and may not recover.
Liver flukes do not pose a food safety issue. But the production and economic losses in the form of reduced weight gains, lower lambing percentages, increased replacement costs, vet bills and condemned carcasses could push a sheep operation over the edge, said Rashid. [email protected]