Liver Fluke
Liver Fluke- Fasciola hepatica
Liver fluke is a common parasite found in grazing cattle and sheep in the UK where it can have a devastating impact, and ultimately lead to death of infected animals. It is thought to cost UK agriculture up to £300 million per annum.
The impact of liver fluke in equines is somewhat less well understood although indications suggest a much greater level of resistance and that infection does not result in such problemtatic outcomes in horses comapred to other grazing animals.
More details below…..
Ask us what treatment we recommend for your horse
The Parasite:
The liver flukes latin name is Fasciola hepatica, and it is a flat, leaf-like parasite which is found in the liver of infected grazing animals. Adult flukes are brown in colour and usually some 2 – 3cm (20 – 30mm) in length and have tiny, sharp spines. The adult has an oral sucker which it uses to attach to the host. The fluke is a trematode (~flatworm)
Liver fluke infection is not particularly associated with a high risk in horses and most animals will be asymptomatic i.e. do not exhibit any clincal signs. The primary clinical signs can be generic in nature, but include:
- Weight loss
- Jaundice, often mild
- Poor performance and growth rate
- Lethargy
- Anaemia- fluke feeding pattern
- Diarrhoea
- Raised liver enzymes, inc GGT
In the most severe cases, due to the damage to the liver, clincal signs consisent with damage to this organ will become apparent. You should consult with your experienced equine vet to get an definitive diagnosis, but often present is oedema, signifcnat weight loss and persistent or chronic diarrhoea. The severity of disease is broadly correlated with the infective burden i.e. number of infective cysts.
There are a number of other diseases, infections and situations that can result in similar clincal signs to liker fluke infection so this does not aid a rapid diagnosis.
Details and Treatment
Are liver flukes associated with other worm burdens ?
No; there does not appear any relationship between loiver fluke infections and concurrent nematode infections in horses.
Are there any products licensed to treat fluke in horses?
There are no licensed veterinary medicinal products indicated for treating liver fluke in horses. If your vet diagnoses and recommends treatment then it will be an “off-label” usage which your vet will prescribe under the cascade system.
Do not use a product without qualified veterinarian advice as many are potentially toxic to equines
Testing for Liver fluke
Due to improvements in methodology, and understansinding of the life-cycle (see below), it is possible to test for fluke using a modified faecal test.
Both cows and sheep reliably and routinely excrete fluke eggs in their faeces. However this is not the case in horses as the fluke is often not able to complete its life-cycle within the equine host. To run the faecal test separate samples of poo are needed to be collected over a consectuive 3-day period which are then analysed in the laboratory. Testing is best conducted during February to May.
There is also an ELISA-based test for fluke, which requires a blood sample, that has been developed by the University of Liverpool. The ELISA test detects antibodies againt the liver fluke. The test can be accessed here but you will need your vet to assist- University of Liverpool- Test A Pet
Is Co-grazing my horse with cows or sheep a risk for fluke infection ?
There is a significant benefit in co-grazing horses with other species in terms of intestinal worm control as these other species act as biological dead-ends.
However, sheep and cows are the preferred definitive host for liver flukes (the fluke species is common) and research has shown that the flukes isolated from horse are from the same population as those found in sheep and cattle. The University of Liverpool have some great information on liver fluke disease in UK horses.
So yes, co-grazing horses with ruminants including cattle and sheep is a strong risk factor for infection of horses on the same pasture. Studies report that the majority of liver fluke infected horses have a history of grazing on land previously used by ruminants.
Remember infection does not require direct contact between animals.
Environmental conditions which play a factor in liver fluke risk:
- Warm and wet condtions
- Marshy, waterlogged or boggy fields
- Shared grazing with sheep and/or cattle
Treating Lungworm
Firstly, you will need a positive clinical diagnosis from your vet. This will likely be based on blood tests as noted above (ELISA) but also potentiallly liver and liver enzyme function.
Ther are no licensed veterinary medicines indicated for the treatment of fluke in horses so your vet will prescribe an off label treatment. The most likely treatment will be with a member of the benzimidazole family which is widely used in ruminants.
Liver Fluke Life-cycle
The fluke has a particularly interesting life-cycle and one which hinders our ability to detect an infection.
- Liver flukes mature within the horse and lay eggs in the gallbladder. This routinely occurs during February to May.
- Some 8 – 12 weeks after initial infection eggs can begin to appear in the faeces.
- At suitable environmental temperatures (> 10oC), and with adequate dampness, the excreted eggs hatch to form a larva known as the miracidium.
- The miracidium migrates within thin films of moisture, where it actiavely seeks out its mud snail host- Galba (Lymnaea) truncatula.
- The larval stage (miracidia) can only survive for a few hours outside of the snail.
- Once within the snail the larva undegoes two further developmental stages, including multiplication, eventually becoming infective cercariae. The cercariae emerge from the snail when the temperature and mositure levels around them are suitable. Development within the snail takes some 5 – 7 weeks.
- The infective cercariae migrate onto wet grass and then form an encysted stage as a metacercariae- this is the highly resilient and infective stage of the liver fluke.
- The metacercariae are then ingested by the horse during normal grazing.
- Once ingested the metacercariae move out of the intestinal tract to the liver where they mature and start the life-cycle again.
Can humans be infected with fluke?
Yes, people can be infected by Fasciola hepatica…But, you cannot catch fluke by direct contact with animals. The source of infection will be ingestion, and most likely to be from eating raw vegetables or eating grass (!?) from infected areas where the secondary host (snail) is located