Parasites

    Cards (55)

    • fill in the blanks
      A) 5
      B) 15
      C) 15
      D) 5
      E) youngstock
      F) resistance
    • Parasites in the horse include…
      • Strongylus vulgaris
      • Strongylus equinus
      • Strongylus edentatus
      • Small strongyles – Cyathostominosis (most clinical relevance for disease in adult horses)
      • Previously called cyathastomosis
      • Oxyuris equi
      • Gasterophilus spp. or ‘bots’
      • Habronema spp.
      • Parascaris equorum
      • Strongyloides westeri
      • Anoplocephala perfoliate/magna
      • Dictyocaulus arnfieldi
    • name the parasite
      A) strongyles
      B) strongyles
      C) parascaris
      D) pinworm
      E) tapeworm
    • Treat all animals with clinical signs of disease in accordance to the parasite found…
      • Larval cyathostominosis = moxidectin
      • Colic due to high Parascaris burden = pyrantel
      • Recurrent colic and high ELISA for Anoplocephala = praziquantel or double the standard dose of pyrantel
    • there are some anthelmintic drug resistance (ADR) to be aware of…
      A) cyathostomes
      B) large strongyles
      C) ascarids
    • for the creation of refugia, you need to…
      • Treat those with high parasite burdens (if only we knew)
      • This can be guessed but can never really be known. In general the younger the horse is the higher the burden but the horse has to be old enough to be eating grass and hence possibly ingesting the larvae.
      • Minimize pasture contamination
      • 10-20% of horses produce 80% of the eggs
      • Create a large percentage of parasites not exposed to anthelmintics
    • The decision on which horses to treat needs to be a yard wide approach. Ideally, treat if faecal WEC exceeds 250epg (Based on testing every 8-12 weeks throughout the grazing season) with ivermectin or pyrantel. Then perform a faecal egg count reduction test after 14 days of treatment to assess efficacy. Also treat new arrivals at yard and hold away from turn out for a minimum of 3 days (or ideally until FWEC reduction) is assessed
      • For young horses FWEC are required more frequently
    • Low risk horses require no Autumn treatment but those that are moderate-high risk should be given Moxidectin (or ivermectin although this may make things worse but can be better for moderate risk horses) in Autumn. Tapeworm ELISA in spring and Autumn and treat if high Ab titre with pyrantel/praziquantel
      • Other GI parasites should be controlled with the measures instigated for control of small cyathostomins.
    • habronemiasis is mainly associated with skin sores (‘Summer sores’) and occasionally conjunctivitis. Adult worms live and reproduce in the stomach (where they do not cause disease) but those deposited in the conjunctiva or in wounds can’t migrate so cause disease locally. This is seen in all age of horses during June to September
      • Some horses prone to re-infection
    • The adults of habronemiasis live in in stomach and this is asymptomatic. Occasionally horses mount a response against the worms causing nodules of granulation tissue which also contain eosinophils
      • Often hard to diagnose on faecal analysis as eggs are very fragile and rupture
      • Identify gastric lesions using gastroscopy and biopsy
    • Prevention of habronemiasis involves…
      • 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
      This parasite will be killed in the horse with worming for other parasites (Avermectins/Benzimidazoles to a lesser extent)
    • what is the causative parasite of this lesion?
      habronemiasis
    • parascaris equorum  fits into the ascarids group and usually causes disease in horses less than 2 years old as a protective immune response is more developed in older animals
      • Life cycle involves migration through the liver, vena cava, alveoli, bronchi, trachea so eggs are coughed up and swallowed
    • Parascaris equorum is an equine specific parasite that is quite common (prevalence of 10-50%). They are the largest worms of horses as they can be up to 10cm in length and are cream and round. Adult horses act as reservoirs, containing small numbers of these parasites but shed enough eggs to infect foals/young stock.
      • Foals are not infected in utero or via milk
    • Clinical signs of a Parascaris equorum infection are…
      • Coughing and nasal discharge (when the parasites are in the lungs)
      • Often ‘mini-outbreaks’ on farms
      • Some of this is hypersensitivity to the worm
      • Poor coat and weight gain (more common presentation)
      • Dull
      • Anorexic
      • Occasionally the horse may be colicking which can be due to a (SI) bowel obstruction
      • This presentation can sometimes be fatal and also causes systemic inflammation
    • Disorders of bone and tendons may be seen as the parascaris equorum consumes lots of Ca, P, Zn, Cu. Diagnosis can be difficult but there are very distinct eggs when present. Treatment is done with pyrantel but there is a lot of anthelmintic resistance
      • Can see colic if treated lots of adult worms are with paralytic drugs e.g., avermectins and pyrantel
    • There is significant resistance to moxidectin and avermectins by parascaris equorum. This is the only ascarid with moxidectin drug resistance (MDR), there is none in pigs, dogs and people this likely relates to the treatment regimens we have and use.
      • Drug rotation DOES NOT prevent resistance, it selects for MDR parasites so stick to drugs that work
    • Equine tapeworm – a cestode with an indirect lifecycle = anoplocephala perfoliata
    • A. perfoliata causes colic due to…
      • Ileal impaction due to reduced motility –often very painful
      • Intussusceptions
      • Caecal impactions and motility disorders
      • Spasmodic (gas) colic
      • (Diarrhoea)
      • Functional and physical blockages
    • Tapeworm disease is seen frequently in infected horses (most common Oct/Nov), this is usually young horses, but can be any age. These parasites have no hooks, but very large suckers that attach to the intestinal mucosa
      • Prevalence is around 60%
    • with tapeworms, egg shedding is irregular and sometimes released from segments in LI and sometimes after excreted from the horse. The eggs released are infective to oribatid mites, which live on the ground eating plant debris and lichens which can then overwinter in the soil. The horses ingest these mites when they are turned out and eat the grass in spring. There is a PPP of 6 to 10 weeks, after this, they can then shed large numbers of eggs.
      • It can overwinter to an extent in horses, but overwintering in Oribatid mites plays an equal or more important role.
    • The immune response due to tapeworm within the intestine is more pronounced in older horses and hence, they are more likely to clear the infection. This is the basis of a semi-quantitative serological test based on antibodies. ELISA can be done for diagnosis in the population (NOT individual diagnosis as there are lots of false positives). Other options are…
      • A blood test (approx. £30) which numerous labs run
      • Saliva test (approx. £18) which can be taken by owners
    • Currently, less than 25% of horses tested require treatment for tapeworm. This treatment has two effective drugs…
      • High dose pyrantel (double dose required to kill tapeworm in comparison to other worms)
      • Praziquantel –treat in Autumn/Winter
    • Prevention of tapeworm involves stabling horses for 48 hours after worming to prevent increased pasture contamination.
      • Can’t kill the mites
    • The most clinically important is large strongyle as it causes ‘verminous arteritis’, this is due to the immune response from the blood vessels due to parasite dissemination through them. It was a very important cause of surgical colic that was frequently fatal.
      • It is mainly the larvae that cause disease hence it is a pre-patent disease
    • After infection with strongyles, horses get some immunity but never complete to stop re-infection. The disease is often most severe in those young/unexposed animals (weanlings and yearlings) but it can be seen in all ages. The reservoirs are the asymptomatic horses that shed large numbers of eggs onto the pasture. There is a high burden on pasture in Spring/Summer and then the parasites are often in the arteries in Autumn/Winter and hence this is when disease is seen.
    • Clinical signs of a large strongyles infection include…
      • Protein-losing enteropathy and anaemia (adults)
      • Colic
      • Diarrhoea
      • Anorexia
      • Ischaemic, dying gut=sick
      • Colicking, dying horse
      • Need surgery for resection if possible
      • Lameness (often associated with exercise) and poor performance (as they can form thrombi at aorto-iliac junction)
    • Occasionally large strongyles migrate aberrantly and end up in the brain, kidneys, lungs, and liver and can form granulomas. Diagnosis is difficult as this is a pre-patent disease (the disease caused by the larval stage)but you may be able to feel thrombi when performing rectal examination. Faecal analysis is not always useful and you can’t tell S. vulgaris from other Strongyle eggs.
      • No correlations between Strongyle egg counts and luminal worm counts!
    • increased egg counts with s. vulgaris do not mean large worm burdens. What we also don’t know is whether the worm burden (which we can’t easily measure) correlates with disease.
    • pre-patent disease = disease caused by larval stage
    • All drug groups are okay for use with strongyles as there is little anthelmintic resistance…
      • Benzimidazoles (fenbendazole) and avermectins (ivermectin and moxidectin) kill the larvae and adults
      • Pyrantel only kills the adults
    • For prevention of strongyles, avoid overgrazing (eggs often on the ground) and pick up faeces regularly.
    • strongylus edentatus and S. equinus are less significant than S. vulgaris but are still important in some forms of clinical disease. Their prevalence is now similar to S. vulgaris for the same reasons. Diagnosis is the same as S. vulgaris (adult eggs in the faeces but this is difficult as it is the larvae that cause the disease).
    • is S. vulgaris a large or small strongyle?
      large
    • fill in the blanks
      A) peritoneal
      B) 11
      C) colic
      D) pancreatic
      E) 9
      F) rare
    • Cyathostomins are also known as small strongyles
    • cyathostominosis is currently the most important equine parasitic disease in terms of prevalence (80%) and severity of clinical signs seen. Management is also difficult without promoting anthelmintic drug resistance. It causes severe acute diarrhoea and colic or chronic diarrhoea.
      • 50 different species of equine small strongyle
    • the encysted (factors on what makes them encyst in the colon is unknown), hypobiotic Cyathostomin larvae are largely unaffected by any anthelmintic, this is not due to resistance but rather the encysting physiology. The hypobiotic population makes up 50% of the larval population, which is 90% of the total population (10% adults). For various reasons, larvae emerge in Spring, often many at once (one is a reduction of adults in the lumen). This disease has a PPP of 6-14 weeks if there is no hypobiosis. Most larvae are on the pasture in Autumn.
    • It is possible for a horse to gain immunity to cyathostominosis, but this takes a long time and is never complete. Younger horses are more likely to have higher burdens.
    • As cyathostominosis is a prepatent disease, diagnosis is difficult, what can be used to get a diagnosis include…
      • History and clinical signs e.g., young animals, poor worming history or change
      • With the changes of climate, these syndromes may not truly relate to the seasons but it present in spring and autumn
      • May see larvae in faeces or on gloves after rectal examination in animals with acute larval cyathostominosis
      • These horses have projectile diarrhoea and sometimes the larvae can be seen stuck to the paint on the walls