PARASITOLOGY - Ruminant Trematodes

Question 1

What is the most significant trematode that affects ruminants?

Answer 1

Fasciola hepatica (‘Liver fluke’)

Remember liver fluke can be transmitted between cattle and sheep

https://www.youtube.com/watch?v=n7xVlcZPLtQ

Question 2

(T/F) Ruminants develop immunity to fasciola hepatica

Answer 2

FALSE. Ruminants don’t develop protective immunity against fasciola hepatica

Question 3

What is the lifecycle of fasciola hepatica?

Answer 3

1. Fluke eggs are shed in the faeces of the final host (10 - 12 weeks after initial infection) onto pasture
2. Fluke eggs require moisture and over 10°C in order the undergo embryonisation into miracidia
3. After 2 - 4 weeks, the miracidia hatch from the eggs and migrate in thin films of moisture to actively seek a galba truncatula intermediate host
4. Over 6 - 8 weeks, the miracidium develop into cercariae within the galba truncatula
5. The cercariae emerge from the galba truncatula under the correct environmental conditions (moisture and over 10°C)
6. Cercariae migrate onto wet herbage and shed their tails, encysting as metacercariae, the infective stage of fasciola hepatica
7. Metacercariae are ingested by the final host when grazing
8. Metacercariae are excysted within the small intestine, releasing juvenile fluke
9. Over 1 - 8 weeks, the juvenile fluke migrate through the intestinal wall, along the inner surface of the abdominal wall to the diaphragm against which lies the ventral lobe of the liver. The juvenile fluke penetrate the diaphragmatic surface of the liver and migrate through the liver parenchyma to the bile ducts
10. Between 8 - 12 weeks of infection, the juvenile fluke develop into adult fluke and feed off blood at the biliary mucosa. At 10 - 12 weeks, the adult fluke begin to produce eggs

Question 4

What is the prepatent period of fasciola hepatica?

Answer 4

10 - 12 weeks

Question 5

What is the ideal environment for galba truncatula?

Answer 5

Galba truncatula live in muddy/areas with slow moving water

Question 6

Describe the epidemiology of fasciola hepatica (liver fluke)

Answer 6

The pasture contamination is determined by the overwintered metecercariae on the pasture, the presence of galba truncatula on the pasture (which can go into suspended animation and carry infection over the winter) which will shed metecercariae onto the pasture, and untreated ruminants that have carried infection over the winter and are put out to pasture where they shed eggs. Because of this, the infective challenge can rise in the spring. The snails are most prevelant in the summer and become infected. There is peak pasture challenge in the autumn as the ruminants shed more eggs and the snails shed more metecercariae. Because of this, acute fascioliasis is more prevalent in the autumn because of the build up of infective metecercariae on the pasture resulting in high larval challenge and clinical disease. Chronic fascioliasis is more prevelant on the winter/early spring as the fluke need time to develop into adults and manifest as chronic disease

Question 7

When is liver fluke challenge at its peak?

Answer 7

Liver fluke pasture challenge peaks in the autumn

Question 8

What is acute fascioliasis?

Answer 8

Acute fascioliasis is acute disease as a result of the mass migration of juvenile fluke through the liver parenchyma to reach the bile ducts, which results in extensive parenchymal damage, haemorrhage, severe abdominal pain and sudden death

Seen 1 - 8 weeks into the PPP as this is when the juveniles migrate

Question 9

(T/F) Acute fascioliasis is only typically seen in sheep

Answer 9

TRUE.

Question 10

When is acute fascioliasis most prevalent?

Answer 10

Acute fascioliasis is more prevalent in the autumn

Question 11

What is chronic fascioliasis?

Answer 11

Chronic fascioliasis is a chronic disease as a result of adult fluke in the bile ducts, resulting in anaemia, submandibular oedema, ascites (due to hypoalbuminaemia), anorexia, immunomodulation and weight loss/ill thrift. Immunmodulation increases the risk of secondary bacterial co-infection, especially clostridial disease

Seen 10 - 12 weeks after initial infection

Question 12

When is chronic fascioliasis most prevelant?

Answer 12

Chronic fascioliasis is most prevelant in late winter/early spring

Question 13

Which factors influence the epidemiology of fasciola hepatica?

Answer 13

Local environmental conditions
Presence of galba truncatula
Farming management

Question 14

What is the economic impact of fasciola hepatica in dairy cattle?

Answer 14

Reduced milk yield and quality
Poor calving to conception rates

Question 15

What is the economic impact of fasciola hepatica in beef cattle?

Answer 15

Reduced growth rates
Poor fertility
Poor calf weaning weight
Poor feed conversion ratio
Liver condemnation at the abattoir

Question 16

What is the economic impact of fasciola hepatica in sheep?

Answer 16

Poor growth rates
Poor fertility
Mortality
Liver condemnation at the abattoir

Question 17

What can be used to monitor and diagnose fasciola hepatica?

Answer 17

Fluke egg detection
Coproantigen ELISA
Serology
Post mortem (PM)
Abattoir feedback

Question 18

What is indicated by the detection of fluke eggs on a faecal sample?

Answer 18

Detection of fluke eggs on a faecal sample detects liver fluke when egg-laying adults are present, so should be used later in the autumn/winter, when the flukes have had 10-12 weeks to develop into adults

Question 19

What are the benefits of fluke egg detection?

Answer 19

Fluke egg detection can be undertaken on individual faecal samples or pooled samples, which can reduce costs. Fluke egg detection can be used to both detect infection with adult fluke and to assess treatment efficacy and indicate resistance if used like a FECRT

Question 20

Why is it so important to be able to differentiate between liver fluke and rumen fluke eggs on fluke egg detection?

Answer 20

Both liver and rumen fluke use the same intermediate host, so both are likely to be present where galba truncatula habitats exist. Correctly identifying these eggs is essential given that adult rumen fluke are not thought to cause any significant health impacts, whereas liver fluke do and require treatment

Question 21

What is the coproantigen ELISA?

Answer 21

The coproantigen ELISA detects a secretory antigen produced by feeding adult fluke in the bile ducts

Question 22

What are the limitations of the coproantigen ELISA for diagnosis of fasciola hepatica?

Answer 22

Coproantigen ELISA has limited sensitivity and specificity for diagnosis of fasciola hepatica

Question 23

What is the main benefit of coproantigen testing for fasciola hepatica?

Answer 23

Coproantigen testing can be used to assess treatment efficacy for fasciola hepatica and indicate resistance if used like a reduction test

Question 24

How can you do serology testing for fasciola hepatica?

Answer 24

Serology can be done using an ELISA on individual blood or milk (individual or bulk tank) samples to detect antibodies produced following exposure to fasciola hepatica. This usually has to be sent to a lab for results however there is now a pen-side lateral flow test available to detect antibodies in cattle and sheep using a drop of blood from an ear prick

Be aware the antibodies produce DO NOT provide protective immunity

Question 25

What are the benefits and limitations of serology to test for fasciola hepatica?

Answer 25

Serology testing is useful as the ELISA can detect antibody levels from two weeks after exposure to fasciola hepatica, and thus is the most reliable indicator of fluke. However, the antibody levels will remain high even after successful treatment and in previously exposed older animals, so this test is best used to demonstrate if the animals have been exposed to fasciola hepatica. Monitoring first season grazing animals through regular serology testing can be used to roughly determine when the fluke challenge starts on that particular farm. Once there is evidence of exposure, using fluke egg detection (and maybe coproantigen ELISA) will give more information on the age of fluke present and the likely level of infection. Using the first season grazing animals as 'sentinel' animals can guide both the need and the timing of treatments, providing an early warning system before other tests can be utilised.

Question 26

What is an ideal way to utilise the serology ELISA for fasciola hepatica?

Answer 26

It is useful to take monthly, representative samples from approximately 10 first season, sentinel grazing animals beginning mid-summer to guide both the need and the timing of treatments, providing an early warning system before other tests can be utilised

Question 27

What are the control methods for fasciola hepatica?

Answer 27

Grazing management Flukicide drugs

Question 28

What grazing management can be used to try and control fasciola hepatica infections?

Answer 28

Avoid grazing on high risk pasture (however this can be very challenging as on some farms every pasture can be high risk). Drainage techniques can be suggested but they are often impractical ## Footnote High risk pasture is pasture that is an ideal environment for galba truncatula

Question 29

What is strategic flukicide treatment?

Answer 29

Strategic flukicide treatment is the treatment of groups of animals at particular times to limit pasture contamination with eggs and hence reduce the risk of parasitism

Question 30

What is therapeutic flukicide treatment?

Answer 30

Therapeutic flukicide treatment is treating animals with flukicides when they exhibit clinical signs

Question 31

Which flukicides are available in the UK?

Answer 31

Triclabendazole Nitroxynil Closantel Clorsulon Oxyclozanide Albendazole ## Footnote It is important not to always use the same flukicide and to be aware overuse of any individual flukicide will speed up the development of resistance

Question 32

Which flukicide have fasciola hepatica started to develop resistance to?

Answer 32

Triclabendazole | Try to avoid if necessary due to developing resistance

Question 33

What is the spectrum of activity for triclabendazole?

Answer 33

Triclabendazole targets all stages of the fasciola hepatic lifecycle in an infected animal

Question 34

What is the only flukicide licensed in dairy cattle?

Answer 34

Triclabendazole

Question 35

What should you be aware of when using triclabendazole to treat dairy cattle?

Answer 35

Triclabendazole cannot be used to treat dairy cattle when they are contributing to the milk tank, and thus you are limited to being only able to treat dairy cattle for fluke during the dry off periods

Question 36

What are the benefits of nitroxynil as an alternative flukicide to triclabendazole?

Answer 36

Though nitroxynil doesn't target the early stages of fasciola hepatica, it does target some of the immature stages and targets the adults. Furthermore, nitroxynil has an injectable form which is a more practical route of administration | Oral admin - esp. for beef cattle - can be very challenging ## Footnote However needs to be imported

Question 37

Which flukicides are used commonly in sheep?

Answer 37

Triclabendazole as it targets all stages which can cause sudden death in sheep, and closantel which doesn't target the early stages but is used commonly in sheep | Remember closantel also targets haemonchus contortus

Question 38

Which flukicide is sold in combination with ivermectin?

Answer 38

Clorsulon is often sold in combination with ivermectin | Remember closrulon is only licensed in cattle

Question 39

Why are combined fluke and worming products discouraged?

Answer 39

Combination fluke and worming products are discouraged due to the unlikelihood of animals needing to be treated for fluke and nematodes at the same time of year, risking speeding up the development of anthelmintic resistance

Question 40

Which flukicide has efficacy agaisnt rumen fluke as well as liver fluke?

Answer 40

Oxyclozanide | Remember rumen fluke doesn't really have a clinical effect

Question 41

What should you be aware of if using albendazole as a flukicide?

Answer 41

Albendazole is a benzimidazole but at double dose has a flukicide effect on fasciola hepatica. Be aware you will also be treating for nematodes when using this product

Question 42

Why is it so important to monitor and do diagnostic tests prior to treating with flukicides?

Answer 42

The threat of fasciola hepatica varies from year to year, from farm to farm, and even from field to field so it is important to risk assess and test for fluke prior to treatment to determine if treatment is necessary and appropriate, especially as treatment options vary depending on the maturity of the fluke present. Overuse of flukicides speeds up the development of resistance

Question 43

How can you use diagnostics to determine appropriate flukicide treatment during the grazing season?

Answer 43

Can do penside serology on 10 sentinel animals *(animals which haven't had a previous grazing season)* every month to determine exposure for fasciola hepatica for that specific farm, or you can use pooled faecal egg counts and treat when you detect exposure - and make sure to treat the entire flock/herd ## Footnote Especially useful for sheep flocks where acute fluke can cause death

Question 44

What strategic treatments could you do at grazing?

Answer 44

You could treat mid-summer with anthelminitcs to reduce pasture contamination to remove adult fluke ## Footnote However don't advocate for this, it is better to test before you treat to determine if necessary

Question 45

What anthelmintic treatments could you do at winter housing in cattle?

Answer 45

Can blood sample sentinel animals for serology to determine exposure for fasciola hepatica (can also send for pepsinogen for oestertagiosis in cows). Can also monitor using pooled fluke egg counts. If evidence of exposure, can treat with flukicides at housing and retreat 8 weeks later, or can just delay flukicide treatment 8 weeks into housing ## Footnote Don't use triclabendazole as acute fluke doesn't affect cattle and most will be adult at this point of the year anyway

Question 46

What can you do to detemine flukicide efficacy?

Answer 46

You can use FECRT or coproantigens after treating with flukicides to determine if treatment has been effective