7.1.4: Equine GI parasites Flashcards
1
Small strongyles (a.k.a. cyathostominosis)
2
Large strongyles (S. vulgaris, S. endentatus, S. equinus)
3
Roundworms (Parascaris equorum)
4
Pinworm (Oxyuris equi)
5
Tapeworm (Anaplocephala magnum, Anaplocephala perfoliata)
Habronemiasis
* Mainly associated with skin sores and occasionally conjunctivitis
* Transmitted by flies
* Adult worms live and reproduce in the stomach
* Those who are deposited in the conjunctiva/in wounds can’t migrate so cause disease locally
Which horses are predisposed to this and when?
Habronemiasis
* Affects all ages of horse
* Typically seen in June-September (‘Summer sores’)
What disease do these worms cause in the stomach? How are they diagnosed?
Habronemiasis
* Adults in the stomach usually cause no disease
* Occasionally horses mount a response against the worms causing nodules of granulation tissue which also contains eosinophils
* Hard to diagnose on faecal analysis as eggs are very fragile and rupture
* Identify gastric lesions using gastroscopy
Prevention of habronemiasis
- Good fly control and muck heap management
- Frequent replacement of bedding
- Collection/removal of droppings in paddocks
- Cover wounds and treat ocular diseases causing ocular discharge
- Habronemus spp. will be killed when the horse is wormed for other parasites.
What is this and which horses does it typically cause disease in?
Parascaris equorum
* Usually causes disease in horses less than 2 years old
* Immune response is more developed in older animals
Life cycle including reservoirs
Parascaris equorum
* Life cycle involves migration through the liver, vena cava, bronchi, trachea
* Eggs are coughed up and swallowed
* Reservoirs = adult horses. They carry small numbers but shed enough eggs to infect foals/youngstock
* Foals are NOT infected in-utero or via milk
* Disease is typically seen in horses <2 years old; older horses develop protective immunity
Clinical signs of Parascaris equorum
- Some of the clinical signs are due to hypersensitivity reactions to the worm
- Coughing and nasal discharge - may see as an outbreak
- Poor coat
- Weight gain
- Dull
- Anorexic
- Occasionally colic inc bowel obstruction
- Disorders of bone and tendons as the parasites consume lots of Ca, P, Zn, Cu
Treatment of Parascaris equorum
- There is emerging multi-drug resistance to Parascaris equorum
- Do not rotate drugs - this does NOT prevent resistance, it selects for MDR parasites. Stick to the drugs that work.
- Use pyrantel
- Be warned that we may see colic is we treat lots of adult worms with paralytic drugs e.g. avermectins, pyrantel
Anoplocephala perfoliate/magna
* Equine tapeworm (cestode)
* Usually affects young horses but can be any age
* These parasites have large suckers that attach to the intestinal mucosa
Clinical signs of Anoplocephala perfoliate/magna
Colic
* Ileal impaction - often very painful
* Intusseceptions
* Caecal impactions and motility disorders
* Spasmodic colic
* Diarrhoea
* Functional and physical blockages
Life cycle of Anoplocephala perfoliate/magna including prepatent period
- Egg shedding is irregular; sometimes released from segments in L1 and sometimes after excreted frm horses
- The eggs released are infective to oribatid mites
- Mites live on the ground eating plant debris and lichens -> overwinter in the soil
- Horses infected in spring when they eat grass and therefore mites
- Prepatent period = 6-10 weeks -> can then shed large numbers of eggs
Diagnosis of Anocephala perfoliate
- ELISA: semi-quantitative serological test. Good for populations but not individuals as lots of false positives.
- Can be done on blood or saliva.
Treatment of Anocephala perfoliate
Drug options
* High dose pyrantel (double the dose required for other worms)
* Praziquantel (treat in autumn/winter)
Other measures:
* Stable horses for 48hrs after worming to prevent increased pasture contamination
* Can’t kill the mites (they are nature’s dustman)
Clinical signs of Strongylus vulgaris
- In adults: protein losing enteropathy and anaemia
- Colic
- Diarrhoea
- Ischaemia -> gut is dying off, requires surgery
- Can form thrombi at aorto-iliac junction -> this can lead to lameness and poor performance
- Occasionally can migrate aberrantly and end up in brain, kidneys, lungs, liver, and form granulomas
Which worm causes verminous arteritis?
Strongylus vulgaris
Verminous arteritis: an inflammatory process that occurs in the mesenteric artery due to large strongyle larval migration
Which wormers is Strongylus vulgaris sensitive to?
- Benzimidazoles and avermectins kill both larvae and adults
- Pyrantel kills adults only
- Otherwise, avoid overgrazing (eggs are often on the ground) and pick up faeces regularly
True/false: it is best to use worm egg counts to guide worming protocols, including for large strongyles such as Strongylus vulgaris
False
* Strongylus vulgaris causes prepatent disease - the disease is caused by migration of larval stage
* There is no correlation between strongyle eggs and luminal worm counts
* It is not appropriate to wait for egg counts and use them to assess disease
Which animals are the reservoir for Strongylus vulgaris?
- Asymptomatic horses that shed large numbers of eggs
What is the prepatent period for S. endetatus and what are clinical signs of infection?
PPP = 11 months
* Causes colic due to liver disease/peritonitis
* This is a hepatoperitoneal strongyle
What is the prepatient period for S. equinus and what are the clinical signs of infection?
PPP = 9 months
* Mild colic; some association with pancreatic disease and primary diabetes mellitus (both these conditions are v rare in horses)
* S. equinus is a hepatopancreatic strongyle
S. endentatus/S.equinus
What is the prevalence and clinical relevance of cyathostominosis?
- 80% prevalence
- Currently the most important equine parasitic disease in terms of prevalence and severity of clinical signs seen
- Cyathostominosis = small strongyles. There are 50 equine species.
Encysted hypobiotic larvae of small strongyles are hard to kill. What can we use?
- Moxidectin
- But kill rates are poor 20-60% and yet this is still the best we have
Describe the life cycle of small strongyles (cyathostominosis)
- Larvae emerge in spring, often many at once
- PPP = 6-14 weeks if no hypobiosis
- Most larvae are on the pasture in autumn
True/false: horses form immunity to cyathostominosis.
True
but forming immunity takes a long time and is never complete
Describe the two clinical syndromes seen with cyathostominosis
Acute larval cyathostominosis
* First syndrome
* Seen in spring
* Due to mucosal damage caused by the emergence of the late L3
* Clinical signs: colic, weight loss, diarrhoea (both acute and chronic), wasting and death (either acute or chronic)
Autumn syndrome
* See when larvae are entering the intestinal wall
* Less common than syndrome in spring
* Clinical signs: colic, diarrhoea due to inflammation
Diagnosis of cyathostominosis
- Very difficult as PPP disease
- Based on history and clinical signs: young animals with poor worming history, recent change
- May see larvae in faeces/on glove after rectal in acute larval cyathostominosis
- In future, hope to have ELISA against the larvae; currently we have have an ELISA for IgG antibodies against specific cyathostomin antigens (this can assess the probabilities of total worm burdens but not likelihood of disease)
Which horses are predominantly affected by Oxyuris equi ?
- Affects horses of any age
- This is a disease of stabled horses; eggs don’t survive well outdoors
- Reservoirs are other infected horses and the immediate environment
Clinical signs of Oxyuris equi
- Anal pruritus
- Skin excoriation
- ± Myiasis
- Eggs in the perianal region on exam
Diagnosis of Oxyuris equi
- Sellotape test around tail -> put on slide and examine under microscope
Oxyuris equi
Treatment and prevention of Oxyuris equi
- All anthelmintics should be effective; there is some resistance sometimes
- Anal paste can be applied
- Can use topical/systemic anti-inflammatories to decrease pruritus and keep area clean with disposable material
- Good stable hygiene: water troughs, mangers
What is our main aim in parasite management?
- Prevent the development of resistance to anthelmintics where possible
- Maintain parasites low enough to mitigate clinical signs -> achieve this through strategic use of anthelmintics and pasture management
True/false: rotating different anthelmintic products is a good idea.
False
It is a bad idea! Do not do this and avoid resources >10 years old that tell you to do this.
What should you use to treat larval cyathostominosis?
Moxidectin
What should you use to treat a horse who has recurrent colic due to high Parascaris equorum burden?
Pyrantel
What should you use to treat a horse who has colic and a high ELISA for Anapolcephala ?
Praziquantel
OR
Double the standard dose of pyrantel
Describe how you could manage pasture to prevent parasitic disease
- Appropriate stocking
- Faecal collection - minimum 2x weekly - remember that larvae do not stay in faeces or recognise electric fencing
- Keep dung heaps separate to grazing area
- Rotate pastures - esp in hot dry conditions as larvae overwinter in mild winters
- Grazing with ruminants
What is the principle of an in refugia population?
- It would be ideal to only treat horses with high parasite burdens (if only we knew)
- This would minimise shedding and parasite contamination (10-20% of horses produce 80% of eggs)
- Not treating all horses would mean a large percentage of parasites were not exposed to the anthelmintic
What are some recommendations for how to select which horses to treat and when to do this?
- Must have yard-wide approach
- Treat if clinical signs
- FWEC every 8-12 weeks in grazing season; treat if >250epg (give ivermectin or pyrantel)
- Perform a faecal egg count reduction test ater 14 days to assess efficacy of treatment
- Treat new arrivals at yard and hold away from turnout for a minimum of 3 days (or ideally until FWEC reduction)
- For young horses, FWEC required more frequently
1
Low risk
2
Moderate risk
3
High risk
Describe which horses to treat and how over the course of a given year, with reference to risk
Low risk horses:
* No autumn treatment
Moderate/high risk horses:
* Moxidectin/ivermectin in autumn
Tapeworm
* Do ELISA in spring and autumn
* Treat if high antibody titre
* Treat with pyrantel (2x dose) or praziquantel
