Liver Fluke in Cattle
Liver fluke is an internal parasite that can infect and damage the liver and reduce overall productivity of cattle, sheep, horses, pigs, goats, alpacas and deer; humans can also become infected. With up to six million cattle grazing pastures in fluke endemic areas of south-eastern Australia, it is estimated the parasite causes around $100 million in lost production each year, and around $10 million in treatments.
Liver fluke commonly occurs around shallow, slow moving water courses, marshy areas, irrigation channels and soaks where the parasite's intermediate host snail breeds. These areas are typically found where annual mean rainfall is about 600 millimetres or where irrigation supplements annual rainfall of around 400mm. Importantly, Western Australia proactively manages its fluke-free status.
A complex life-cycle
The liver fluke's lifecycle is dependent on a specific lymnaeid host snail that breeds in waterways.
During the warmer months, when mean temperatures rise above 10 degrees Celsius, liver fluke eggs hatch when separated from faecal material in wet areas. The released larvae invade the snail, where they multiply and develop into tadpole-like forms. Once detached from the host they swim towards vegetation areas and take the form of an infective cyst. Depending on conditions, this process can take between two and three months.
Animals are at most risk of ingesting the infective cyst when grazing around waterways.
A silent path of destruction
Liver fluke is considered a silent assassin as it can erode herd health without affected animals displaying any physical signs. Most damage is caused during the earliest stages of the parasite's development through the animal's liver.
It is important to test stock for liver fluke infection and, in the event of a positive result, a zero tolerance approach to control is recommended because even light burdens cause significant damage, particularly in younger stock which are more vulnerable to the parasite. It is also important to test purchased stock to mitigate the risk of contaminating fluke-free areas.
Dr Boray's five-step strategy for effective control of liver fluke
|Step 1: Understand the fluke life-cycle
||Fluke are dependent on a water-loving snail releasing larvae onto pastures
||>600mm annual rainfall and lower rainfall areas (>400mm) supplemented by irrigation
Tablelands, slopes, coastal and irrigation areas of Qld, NSW, Victoria, SA and Tasmania
|Stages of infection
||Infection is caused when fluke larvae are ingested from pastures enabling early immature and immature fluke to migrate through the liver tissues
Adult fluke live in the bile ducts, sucking blood and laying eggs that re-infect pastures
||Snails and fluke larvae in the snails can survive in the mud for long drought periods
Rain can unearth snails, triggering fluke larvae development and pasture infestation
|Step 2: Regular testing
|ELISA blood / milk test
||Unlike traditional fluke egg counts, the ELISA can detect early fluke infection and is more reliable
|Step 3: Seasonal awareness
||Key time to treat immature and adult flukes following expected high pick up from contaminated pastures during the summer and early autumn
|Late winter/early spring
|Treat infected livestock during this period to remove remaining fluke and stop pasture contamination with fluke eggs contained in faeces
||If animals have a heavy infection, a third treatment is recommended mid-summer, particularly in sheep and young cattle
|Step 4: Treatment
||Flukazole C Plus Selenium is the best fluke drench for early stages (including two week old), as well as adult fluke infection. (Do not use within 21 days before calving in dairy cattle)
||Nitromec injection is effective against triclabendazole-resistant fluke & also against two-week old and adult flukes. Nitromec provides a suitable rotation away from triclabendazole for autumn and summer fluke treatments.(Not for use in lactating dairy cattle)
||Virbamec Plus is recommended for the spring treatment to remove any adult flukes remaining after winter (nil milk witholding period).
|Step 5: Farm management
||Fence off fluke habitats particularly during drier times when stock search for green pick around springs and other waterways. Rain and irrigation can also trigger snail and fluke activity
By Virbac Animal Health - Last updated