Farms that practise grazing or feed fresh grass may sooner or later be confronted with liver fluke. Liver fluke is steadily gaining ground in Western Europe. Mortality due to liver fluke is rare in cattle – but does that make the disease less significant? Certainly not.
Liver fluke
Liver fluke infection, or distomatosis, is a parasitic disease of ruminants caused by trematodes or flatworms. The common liver fluke found in our region is Fasciola hepatica. Worldwide, this disease causes major economic losses, mainly due to reduced milk production, weight loss, and condemned livers at slaughter. Additionally, liver fluke infection can reinforce or reduce the effects of other pathogens or interfere with their diagnosis. What is sometimes forgotten is that this parasite can also cause problems in other grass‑eating species and even humans.
Liver fluke – prevalence and risk factors
Whereas liver fluke infections used to occur mainly in more southern regions, in recent years we have seen an increasing number of infestations in Western Europe. Changing climatic conditions (milder winters, higher temperatures, and increased rainfall) have improved the conditions for development of the parasite. Moreover, these altered weather patterns mean the period of infection risk begins earlier in the grazing season.
Other factors also contribute to the spread of liver fluke within a herd. A Danish study showed that heifers and dry cows grazing on wet pastures are significant risk factors for maintaining infection on a farm. Buying in infected animals, insufficient or poor treatment of infected youngstock, and too little monitoring for resistance also contribute. Resistance to triclabendazole can allow liver fluke infections to spread steadily.
Liver fluke – life cycle
Liver fluke has an indirect life cycle in which the mud snail Galba truncatula acts as an essential intermediate host. Its presence is necessary to complete the parasite’s development.
In the liver, adult flukes lay eggs, which are excreted with the bile into the faeces. A single adult fluke can produce 4,000–7,000 eggs per day. In the environment, the eggs hatch into ciliated larvae (miracidia). These must find a mud snail within 24 hours to survive. Inside the snail, they develop further into cercariae, which leave the snail and encyst on pasture as infective metacercariae. Cattle become infected by ingesting these cysts. Once ingested, the juvenile flukes migrate through the gut wall, across the abdominal cavity, and into the liver and bile ducts.
In cattle, the lifespan of a liver fluke ranges from six months to two years.
Figure 1 The liver fluke life cycle in cattle with intermediate host Galba truncatula
In cattle, infection is usually subclinical and therefore insidious, with economic consequences. In sheep it can cause acute death, especially in young animals.
Liver fluke – diagnosis
Diagnosis can be made in several ways. Not every method is suitable at every stage of infection.
Fecal examination
Sedimentation–flotation can detect eggs produced by adult worms. Fresh feces (preferably taken rectally) can easily be examined using the Micron Kit, a tool based on advanced AI technology. Dopharma is distributor of the Micron Kit in certain countries.
Egg detection alone is not conclusive and cannot be always carried out during infection. In the prepatent period, immature flukes do not yet produce eggs. Moreover, the number of eggs does not always correlate with the number of adult parasites. After ingestion of metacercariae, it takes on average 10–12 weeks before flukes reach maturity. The best time for fecal testing is three months after the end of the grazing season. Due to intermittent shedding, sampling multiple animals is recommended.
Antibody detection in blood
A liver fluke infection triggers antibody production. These can be detected from four weeks after infection using ELISA. Antibodies persist for up to 180 days, meaning a positive result may reflect an infection acquired the previous autumn. Therefore, this test cannot be used to demonstrate infection. Liver enzyme levels (GGT and GLDH) can also be measured to assess liver damage.
Antibody detection in milk
Bulk‑tank milk testing measures the Optical Density Ratio (ODR) of antibodies against Fasciola hepatica. This test can be used year‑round but is preferably performed before the end of the grazing season. This test can help the farmer to get an idea about level of contamination on his farm. ODR less than 0.30 is considered negative; 0.30–0.50 indicates infection without major production losses; an ODR more than 0.50 indicates significant infection with possible negative effects on yield and fertility.
Antigen detection in feces
A highly sensitive ELISA that detects fluke antigens in feces can determine whether an animal is heavily infected.
Post‑mortem examination
Lesions in the liver can be assessed by post-mortem examination in deceased animals.
Liver fluke – prevention and treatment
Control relies on two pillars.
Prevention
A good pasture management plan and the judicious release of animals can go a long way in controlling liver fluke. Adapted pasture management can significantly reduce contact between the definitive host and the infectious liver fluke stages.
Treatment
Several flukicides are on the market in the Netherlands. Not every product is effective against all stages of liver fluke. Triclabendazole, formerly widely used because it targets all life stages, is increasingly affected by resistance. Moreover, it cannot be used in lactating dairy cattle.
Products containing oxyclozanide can be used in dairy cattle during lactation and the entire dry period and are effective against adult flukes. Dopharma offers Distocur® 34 mg/ml, containing oxyclozanide, for the treatment of liver fluke infection in dairy cattle.
References
- A.A. Rana et al, Fascioliasis in cattle – A review. The Journal of Animal &Plant Sciences, 24(3):2014, Pages:668-675
- J. Beesley et al, Fasciola and Fasciolosis in ruminants in Europe: Identifying research needs. Transboundary and Emerging Diseases, 65 (Suppl. 1):2018, Pages: 199-216
- J.L. Williams, Liver fluke – an overview for practitioners. http://www.cattleparasites.org.uk/
- Takeuchi-Storm et al, Patterns of Fasciola hepatica infection in Danish dairy cattle: implications for on-farm control of the parasite based on different diagnostic methods. Parasites & Vectors, 2018, 11:674
- Focus op Leverbot, Praktische handleiding. DGZ – Ugent
- Moreau and Alain Chauvin, Immunity against Helminths: Interactions with the Host and het incurrent infections. Journal of Biomedicine and Biotechnology, Volume 2010, Article ID 428593, 9 pages
- J. Flynn et al, Experimental Fasciola hepatica infection alters responses to tests used for diagnosis of bovine tuberculosis. Infection and immunity, Mar. 2007, Pages 1373-1381
- M. Aitken et al, Effects of experimental Salmonella dublin infection in cattle given Fasciola hepatica thirteen weeks previously. Journal of Comparative Pathology Volume 88, Issue 1, January 1978, Pages: 75-84
- K. Howell et al, Co-infection with Fasciola hepatica may increase the risk of Escherichia coli O157 shedding in Britisch cattle destined for the food chain. Prevetmed, 2017
More information
For more information on liver fluke and Dopharma’s solutions, please contact our Technical Support team at [email protected].
Chris Cornelis
Technical Support Veterinarian Ruminants
