A couple of years ago, a beef producer from southeast corner of Manitoba showed me a test tube filled with water. It contained a worm that was about three inches long, one inch wide and flat enough to almost see through. He told me that it was a deer liver fluke that the vet had taken it from a dead cow from his 100-cow operation that graze pastures along a strip of swampland.
Until she was found dead and the vet posted her for liver flukes, this producer never associated this particular parasite with several chronic cow herd problems that were tolerated for years. With his vet’s discovery, he has routinely treated his herd with available flukicides and now has the situation under control.
This is a powerful message. Grazing cattle in pastures near muddy or shallow water makes them very susceptible to such infestations of the common liver fluke (fasciola hepatica) or deer liver fluke (fasciola magna). It’s my understanding the deer liver fluke is commonly found in lowland areas of southern Manitoba.
There are no classic symptoms that show grazing cattle are infected with either species. Yet confirmed cases involving liver flukes report it as a typical wasting disease similar to those affecting deer or Johnne’s disease in dairy cattle.
Its symptoms are general in nature and appear as weight loss, reduced body condition and depending upon infestation severity, some cases of chronic diarrhea. Limited university research on spring post-calving cows with liver flukes have reduced milk production and poorer rates of fertility. These conditions usually dovetail into calves with lower weaning weight as well as lowered cow conception rates in the fall.
The accompanying diagram shows the complete liver fluke life cycle from the time the fluke egg is initially shed in the manure of infected cows on pasture until a new generation of eggs are laid. The cycle takes 16 to 24 weeks. There are four major stages from fluke egg to hermaphroditic (contain both sex organs) adult liver flukes, which ultimately reside in the bile duct of cattle:
1. Egg stage — eggs are shed in the manure of the beef cow from adult liver flukes.
2. Miracidium stage — eggs hatches (10 days to several months) into free-swimming, ciliated larvae called the miracidium. Within hours of hatching, the miracidium finds and penetrate snails living on wet pastures.
3. Cercariae stage — Within the snail, one miracidium takes about five to seven weeks to develop into hundreds of cercariae or tadpole-like second larvae stage. After they leave their snail host, attach to grass and becomes encysted metacercaria.
4. Adult stage — The grazing cow ingested the encysted metacercaria-contaminated grass. Once ingested, juvenile liver flukes are released from metacercaria capsules. They penetrate the intestinal wall and burrow their way to and through the liver, which takes up to eight weeks. These fluke larvae enter the bile duct, where they mature into egg-laying adults to repeat the cycle.
Severity of liver fluke parasitism in cattle depends on the degree of infestation. Cattle seldom die from liver flukes, but it can elevate the cow’s susceptibility to a host of secondary problems such as clostridium haemolyticium infections causing Redwater disease. That’s because the migrating juvenile flukes damage the liver and the clostridium bacteria grows inside these damaged areas. Death is a possible in infected animals that are not properly vaccinated.
Once juvenile flukes reach the bile duct, they mature into adults. Their spines cause abrasions along the surface duct lining, which causes internal bleeding. The adult liver flukes feed upon this blood, which leads to common anemia of the cow. Other chronic damage includes liver tissue scarring, hardening of the bile ducts and enlargement of the cattle’s gall bladder.
Treatment of liver flukes in cattle comes down to a few flukicides; albendazole (Valbazen), corsulon (Ivomec Plus), and triclabendazole (Fasinex 240, United Kingdom). The first two flukicides are only effective against mature adult liver flukes. Triclabendazole is the only product effective against very early immature flukes (two weeks old) through adulthood. There is no available flukicide treatment against shed eggs in cow manure.
Producers interested in using triclabendazole require a veterinarian prescription before purchase (which include special instructions for its use). Those people interested in using the other two flukicides should find their protocols are straightforward.
For example, albendazole is to be drenched for its first treatment for confirmed fluke infections in cattle in autumn. This is to remove any buildup of adult flukes that matured over the grazing season. A second treatment is then given again in the following April/May, which reduce the number of egg-shedding adults before letting cattle out on pasture. It is noted that albendazole should not be given to any pregnant cow or replacement heifer during the first 45 days of gestation, otherwise it may cause early embryonic deaths.
Most of the time, flukicides are given to the cow herd after liver flukes are found in a dead cow. I believe this is hardly proactive in controlling a growing problem among beef herds. However, there is hope for a new type of liver fluke diagnosis.
Recently I watched a YouTube video entitled: Science Squad on liver flukes with Tyndall and Teagasc (Dec. 15, 2014). The Tyndall National Institute (Ireland) is developing a simple plus/fail test for the presence of liver flukes in cattle and sheep. These scientists employ microchip technology that detect antibodies in a drop of blood from animals exposed to liver flukes. The chip is linked electronically to a farm-friendly computer reader. The video’s commentators concluded that this new research for early detection of liver flukes may be the key to effective control in the immediate future.