Control Of Equine Alimentary Parasites

Question 1

1. What are helminths?
2. What are Cestodes?
3. What are nematodes?
4. What are cyathostomes?
5. What are Strongyles?

Answer 1

1. Worms.
2. Tapeworms.
3. Roundworms.
4. Roundworms - small redworms.
5. Roundworms - large redworms.

Question 2

1. What are strongyloides?
2. What are ascarids.
3. What are dictyocailus?
4. What are oxyuris?

Answer 2

1. Roundworms - threadworm.
2. Roundworms - roundworm.
3. Roundworms - lungworm.
4. Roundworm - pinworm.

Question 3

Cyathostomes.

Answer 3

Small redworm.
CAN ENCYST IN LARGE INTESTINAL MUCOSA FOR 2-3 YEARS!
- CAN MASS EMERGE AS HYPOBIOSED LARVAE (early spring), CAUSING A MASSIVE INFLAMMATORY REACTION AND SEVERE DIARRHOEA.
OFTEN FATAL.

Question 4

Strongylus vulgaris.

Answer 4

Cause problems during migration of larvae (direct migratory path).
- causes verminous arteritis.
- travel from GIT to cranial mesenteric artery and back again.
- can cause ischaemic areas of LI
— fatal.
Adults live in LI.
Relatively rare nowadays since use of avermectins.

Question 5

Strongyloides westeri.

Answer 5

Clinically affects foals.
Infects foal through dam milk or via skin penetration.
- Induces diarrhoea ~6m later.

Question 6

Ascarids - Parascaris equorum.

Answer 6

Gain reasonable immunity.
At greatest risk 6 months old, up to 2 years old.
Can cause SI obstruction.
- surgical colic.
— removal of worms.
Greatest risk after using an effective anthelmintic when there is a high burden.

Question 7

Dictyocaulus arnfieldi.

Answer 7

Lungworm cycle NOT completed in horse.
Adult worms do not attain sexual maturity here.
Donkey is the usual host.

Question 8

Oxyuris equi.

Answer 8

Pinworm.
Adults in the colon.
Female worm migrated down GIT
- deposits eggs around anus, cemented to the skin with a sticky substance.
— horse develops severe anal pruritus.

Question 9

Anoplcephala.

Answer 9

Tapeworm.
Incidence of spasmodic colic increases with burden.
Can cause intussusception (ileo-caecal, caeco-caecal).
Thickened SI wall at ileo-caecal junction leads to food (ileal) impaction, leading to a surgical colic.

Question 10

Gasterophilus.

Answer 10

Botflies.
Not proven to cause any problems.
Seen more with advent gastroscopy.
Can remove (some) eggs from hair with a bit knife.

Question 11

1. What was the main focus of the old worming recommendations.
2. Why can the old worming recommendations not be used anymore.

Answer 11

1. Strongyles.
2. Resistance.
   Tapeworm and encysted cyathostome, which are important causes of disease, may be neglected.

Question 12

1. Impact of resistance?
2. Do we need to worry about parasite burdens in horses?

Answer 12

1. Fewer drugs are effective with no new drugs in the horizon.
   Resistance increases the complexity of parasite management programmes.
2. Most horses tolerate even large worm burdens without any effect on health.
   Clinical disease is rare.
   But disease does occur.

Question 13

Define resistance.

Answer 13

The genetically transmitted loss of sensitivity in parasite populations previously sensitive to the same drug.
Due to artificial selection by horse wormers, sensitive worms are killed, leaving only resistant ones to multiply and create new generations of resistant worms.

Question 14

What are refugia?

Answer 14

Parasites in the horse’s environment that are not exposed to an anthelmintic at each dose.
These will include:
- pasture stages — eggs, L1, L2, L3.
- parasites in untreated horses.
- some larval stages in the horse? E.g. encysted.
Increasing refugia is likely to slow down resistance.

Question 15

Measuring resistance.

Answer 15

FECRT = faecal egg count reduction test.
No anthelmintic treatment for at least 8 weeks prior (12 weeks if moxidectin used as longer egg reappearance period).
FEC before treatment.
Administer anthelmintic.
Repeat FEC 2 weeks after treatment.
This testing does not work for tapeworms.

Question 16

Principles parasite control now.

Answer 16

Resistance problems have occurred from blanket / inappropriate anthelmintic usage.
We want a reservoir population of parasites to help reduce resistance.
- do not aim for wipe-out of all parasites.
Now over 50% horse owners use a targeted parasite control programme (though some may be a random).
Needs a co-ordinated vet-led approach.

Question 17

Parasite control principles 2.

Answer 17

Targeted worming - worm those that need it.
Poo pick fields ~weekly.
No overgrazing.
Consider needs of adults, foals and pregnant mares.
Different things at different times of year.
What to do when a new horse arrives at the premises.

Question 18

Challenges of parasite control nowadays.

Answer 18

Owners generally want to give anthelmintics as low effort, cheaper, don’t want horse to have worms, have always given wormers.
Anthelmintics don’t have to be prescribed by a vet.
Worming plans available from drug companies may not be reliable as may be centred around sale of their product.
Owners generally have no clue what drug they are using or what that will treat.

Question 19

Considerations when forming a parasite control plan.

Answer 19

What parasites are you aiming to treat?
- based on horse’s age, time of year, worming history.
Adult or larval stages.
Is the treatment justified?
- likely challenges.
- resistance vs clinical disease.
Which active ingredient has expected efficacy?
- consider original spectrum and known resistance.
Any contraindications.
CANTER risk assessment.

Question 20

Anthelmintics - main groups.

Answer 20

Avermectins - Ivermectin, moxidectin.
Benzimidazole - fenbendazole.
Praziquantel.
Pyrantel.

Moxidectin/Ivermectjn available in combo with praziquantel too.

Question 21

Anthelmintics to treat cyathostomes,

Answer 21

Ivermectin will kill adults but need moxidectin to kill encysted ones.

Could use 5-day course of fenbenbazole but lots of resistance.

If cyathostomiasis, treat with moxidectin and corticosteroids concurrently.

Use once or twice per year during winter (guidance changes!)

Question 22

Anthelmintics to treat Strongyles.

Answer 22

Ivermectin (try to use).
Moxidectin (save for a resistance problem and encysted cyathostome).
Pyrantel - not as effective — resistance.
Fenbendazole - not as effective — resistance.

Question 23

1. What is classed as a low level of Strongyles?
2. How frequently do you need to do a faecal egg count?

Answer 23

1. 200 eggs/gram of faeces on FEC.
   - varies between spp.
2. After egg reappearance period of the anthelmintic that is being used.
   Much more understandable from the client’s perspective to carry out ~every 12 weeks.

Question 24

Anthelmintics to treat ascarids.

Answer 24

Often affecting horses <2yo.
Most sensitive to Pyrantel.
Then avermectins.

Question 25

Anthelmintics to treat Strongyloides westeri.

Answer 25

Ivermectin or fenbendazole.
Can treat the foal.
De-worm the mare a couple of weeks before due-date.

Question 26

1. Anthelmintics to treat dictyocaulus (lungworm)?
2. Anthelmintics to treat gasterophilus (botflies)?
3. Anthelmintics to treat oxyuris (pinworm)?

Answer 26

1. Ivermectin (try to use).
   Moxidectin (save for resistance).
2. Ivermectin (try to use).
   Moxidectin (save for resistance).
3. Ivermectin.
   Pyrantel.
   Fenbendazole.
   If problems with treatment, fenbendazole 3 times at 2-3 week intervals will sort them out.

Question 27

Anthelmintics to treat tapeworm?

Answer 27

Praziquantel (probably best).
Double dose Pyrantel.
Twice yearly - usually spring and autumn but is not seasonal.
Now do tapeworm ELISA (blood or salivary) twice a year to aid decision making.

Question 28

With targeted management, when would you make the decision to treat?

Answer 28

Generally when FEC shows >200 eggs/gram of faeces.
Can be altered based on individual horse.

Question 29

Advantages of targeted dosing?

Answer 29

In theory, are only treating those that need it.
Typically, in each ‘herd’ there are a few individuals who have much higher burdens than the others (80:20 rule).
Cheaper than interval dosing for some.
Can identify very high burdens of e.g. Parascaris so you can treat more carefully.
It is the best strategy to slow onset or possibly avoid resistance.

Question 30

Problems of FEC.

Answer 30

Costs about same as a tube of de-wormer.
Only counts eggs so misses non-producing adults and encysted larvae.
Limitations on detecting individual problems.
Pooled samples may cause treatment of horses that don’t need it.
McMaster rarely detects tapeworm.
Centrifugation better for tapeworm but more expensive and rarely done.
- but can also do a tapeworm blood or saliva ELISA.
- new cyathostome ELISA test.

Question 31

Problems with the tapeworm ELISA.

Answer 31

Blood test:
- looks for antibodies to tapeworm and can tell if an animal has been exposed but antibodies stay high even 6 months after treatment.

Question 32

Problems with cyathostome ELISA.

Answer 32

Very new.
Test antibodies but doesn’t differentiate adults vs encysted although more adults likely to mean greater risk of significant encysted burden at some point.
Can use to guide treatment for encysted cyathostomes in low risk group.
Need to be careful of moxidectin resistance.

Question 33

Pasture management.

Answer 33

Twice weekly manure removal (or more often).
Reduce stocking density.
- increased stocking density, increased helminth pasture burdens.
- what is ideal?
Grazing with ruminants will reduce number of Strongyles, Ascarids and tapeworms on pasture.

Question 34

1. What do CANTER guidelines influence?
2. What does CANTER stand for?

Answer 34

1. Testing and cut-off point for when FEC result means a decision to treat.
2. Clinical history.
   Age profile.
   Number of horses.
   Test results.
   Environment
   Risk profile.

Question 35

Suggested year plan for adult non-gravid horses.

Answer 35

Management advice e.g. poo-picking at least twice weekly, low stocking density, CANTER could affect if stay at 200epg or could allow to go higher.
Feb/March - FEC (Strongyles), de-worm with ivermectin if >200epg.
May - FEC (Strongyles), de-worm with ivermectin if >200epg, tapeworm ELISA, praziquantel if tapeworm, can get ivermectin-praziquantel combined product.
August - FEC (Strongyles), de-worm with ivermectin of >200epg.
November/December - tapeworm ELISA, praziquantel for tapeworm if indicated, cyathostome ELISA in low risk group, otherwise just treat, moxidectin for encysted cyathostomes (no FEC as will treat Strongyles too), can use Praziquantel-Moxidectin combined product.

Question 36

Suggest year plan for pregnant mares.

Answer 36

As for in non-gravid horses but…
Treat with ivermectin a few weeks (before egg reappearance period) before due-date.
Moxidectin now licensed in pregnant mares.

Question 37

Suggested plan for foals.

Answer 37

Need minimum of 4 treatments in their 1st year.
- 1st tx at 2-3 months with fenbendazole.
- 2nd tx at weaning at approx. 6 months — FWEC to assess if Strongyles (treat with moxidectin/praziquantel) or ascarids (treat with Pyrantel).
- 3rd tx at 9 months (primarily Strongyles +/- tapeworm) — treat with moxidectin/praziquantel.
- 4th tx at 12 months (primarily Strongyles +/- tapeworm) — treat with moxidectin/praziquantel.
Only prescribe workers licensed for use in foals.

Question 38

Suggested plan for youngsters (1-4).

Answer 38

Treat as ‘high shedders’ (increase risk on CANTER).
Prioritise manure collection over adults if an either/or situation.
3-4 tx per year.
Include 1 moxidectin/praziquantel late autumn/early winter.
May need a second larvicidal tx 3 months later if:
- grazing over winter.
- High stocking density.
- Inadequate faecal collection.

Question 39

New horse to yard plan.

Answer 39

12-24hr before turnout - moxidectin plus praziquantel.
Keep off pasture for 3 days.