Internal parasites in horses Flashcards
Name the 4 most important horse parasites.
Parascaris spp. (SI but have lung stages)
Anoplocephala perfoliata
Small strongyles so Cyathostomin spp.
Large strongyles so Strongylus vulgaris, S.equinus, S.edentatus
Less important include Oxyuris equi, Strongyloides westeri and liver Fasciola hepatica.
Horse lung worm?
Dictyocaulus arnfieldi
Parascaris spp. live in SI but have lung stages.
bot fly larvae spp. in horses
Gasterophilus spp.
Main 5 anthelminthics used in horses.
ivermectin
moxidectin
fenbendazole
pyrantel
praziquantel
Basically only these used in horses actually which is why we need to be so careful about resistance.
We mostly deworm horses for what parasite specifically out of all of them?
small strongyles like Cyathostomins spp.
This group is referred to as the “small redworms”.
Name 3 spp. of Large strongyles.
Strongylus vulgaris (migratory phase into blood vessel walls)
S.equinus (liver migratory phase)
S.edentatus (liver migratory phase)
hairworm of horses is called?
Trichostrongylus axei
Main tapeworm spp. to affect horses?
Anoplocephala perfoliata
What is cyathostominosis?
Clinical disease caused by mass release of large numbers of encysted larvae.
Usually affects young horses 1-4 years old in winter and early spring.
Small strongyles, Cyathostomins, can become encysted in intestinal mucosa. The danger lies in them emerging in large quantities at the same time causing cystostaminosis.
Mucosal damage
Inflammation
And toxin release
Lots of weight loss, dehydration, hypoalbuminemia (causing peripheral edemas).
Moxidectin is the only help for these before they encyst preferably.
Deworming will not help at this point. Prognosis is very poor even with intensive treatment.
Horse roundworm spp.
Parascaris equorum
Horse threadworm spp.
Strongyloides westeri
Horse pinworm spp.
Oxyuris equi
Main 2 endoparasite spp. to affect foals.
Parascaris equorum = roundworms
Strongyloides westeri = threadworms
Describe Fenbendazole.
1970s: Fenbendazole
Inhibits the parasite’s ability to produce energy, paralyzing the parasite until death.
Fenbendazole is effective against equine endoparasites such as
large strongyles (Strongylus spp.),
small strongyles (cyathostomins),
ascarids (Parascaris equorum),
pinworms (Oxyuris equi), and
some lungworms (Dictyocaulus arnfieldi).
Describe Pyrantel.
1970s: Pyrantel embonate is the same as pyrantel pamoate.
Causes spasmodic muscle paralysis in parasites.
Pyrantel is effective against
large strongyles (Strongylus spp.),
small strongyles (cyathostomins),
ascarids (Parascaris equorum), and
pinworms (Oxyuris equi) in horses.
Describe Macrocyclic lactones:
1980s: Ivermectin
1990s: Moxidectin
Increase the permeability of the cell membrane to chloride ions and results in hyperpolarization of the cell, leading to paralysis and death of the parasite.
Macrocyclic lactones (ivermectin and moxidectin) are effective against
large strongyles (Strongylus spp.),
small strongyles (cyathostomins, including some encysted stages with moxidectin),
ascarids (Parascaris equorum),
pinworms (Oxyuris equi),
stomach bots (Gasterophilus spp.),
lungworms (Dictyocaulus arnfieldi), and some external parasites like lice and mites in horses.
What additional risk do donkeys pose toward horses in regard to endoparasites?
Donkeys can act as reservoirs for Dictyocaulus arnfieldi (lungworms), often carrying the parasite without showing clinical signs.
When housed with horses, donkeys can shed lungworm larvae in their feces, leading to infections in horses, which may develop significant respiratory disease, including chronic coughing and bronchitis.
Tx ivermectin and moxidectin.
Describe Large strongyles.
Are Migratory strongylids.
Strongylus vulgaris = bloodworm, migrates into blood vessel walls
Strongylus endentatus & Strongylus equinus migrate into the liver and Damage to the intestinal blood supply.
Are clinically the most important due to high pathogenicity.
Clinical signs of Strongylus vulgaris in horses.
Very pathogenic.
Adult worms cause diarrhea, weakness, weight loss, anemia.
Migrating larvae cause thromboembolic colic, non-strangulating infarctions in large intestines.
Mild/recurrent colic, fever, peritonitis
Peritonitis can be the only sign too.
Without surgery, intestinal rupture due to the necrosis and then, death.
Large strongyle infection is Rare nowadays (regular use of MLs).
No reports of resistance.
Treatment 1-2x year with MLs provides sufficient control.
Describe Small Strongyles (Cyathostomins).
Are Non-migratory strongylids. More than 50 species but only About 10 comprise >98% of all of them.
Reside in the Cecum and colon and are Present almost in 100% of horses.
Number of parasites often very high.
Adult worms rarely pathogenic.
Accumulation of parasites towards the end of grazing season. Larvae become encysted in the intestinal mucosa.
Larval cyathostominosis: diagnosis
Fecal sample?
- Large number of larvae in feces
Suspicious, but is not actually diagnostic.
- This parasite’s burden Does not correlate with FEC (immature parasites).
Signalment and anamnesis:
- Herdmates often unaffected
- Particularly at risk: horses 1-4 y old
- More in winter and early spring
- Treatment with a drug without efficacy against encysted larvae (cause if they all die at the same time, the horse can die).
Removal on luminal cyathostomin burdens appears to trigger re-emergence of encysted larvae.
Larval cyathostominosis: clinical signs 10+
Diarrhea
Dramatic weight loss
Severe dehydration
Circulatory shock
Colic signs
Fever
Numerous larval cyathostomins in the feces
Leukocytosis
Hypoproteinemia and hypoalbuminemia → ventral edema
Larval cyathostominosis: treatment
Supportive treatment for diarrhea:
- Intensive fluid therapy +/- plasma transfusion
- Binding agents for toxinx (e.g. BioSponge)
- NSAIDs
- Dexamethasone to descrease inflammatory reaction
(0,04 mg/kg IV/IM SID for 3 days)
Consider Antihelmintic treatment too
- Moxidectin 0,4mg/kg
- Fenbendazole 10mg/kg PO SID for 5 days
but not if Resistance, or real bad intestinal inflammation.
Larval cyathostominosis: prognosis
Treatment can be unrewarding due to severe intestinal damage.
Deworming does not help if clinical disease is radically developed.
High mortality rate despite intensive treatment, thus Poor prognosis.
Describe Parascaris spp.
Parascaris univalens (most prevalent) and P.equorum which Cannot be distinguished by appearance.
Primarily affect horses less than 2 years old.
Most common under 1 year of age.
Adults develop an immunity.
Largest nematode parasite of equids.
4 mm in diameter and 25 cm long!
Eggs stay in the environment for a very long time (months, years) even in Dry and freezing conditions.
The Eggs are sticky so they can adhere to perineum, udder and to objects.
Describe Parascaris spp. disease.
Severe infestation causes severe damage:
- Coughing, nasal discharge during migration through the lungs.
- Damage to the intestine, and colic (small intestinal blockage, rupture).
Describe Parascaris spp. - small intestinal impaction.
Affects Foals with large burdens of Parascaris equorum. Median age of 5 months.
Usually occurs when Foals have often received anthelmintic treatment within 24 h (Ivermectin, pyrantel.
Dead worms mechanically obstruct the small intestine.
Presents with gastric reflux and shock.
Nasogastric tubing is needed for alimentary decompression. Deworming is contraindicated!
Give Supportive therapy. + Often need surgical intervention.
Guarded prognosis!
Describe Parascaris spp. – disease prevention.
In order to prevent parascaris disease, Regular anthelmintic treatment of horses from 2 months of age onwards is needed.
Benzimidazoles are preferred (so fenbendazole 10 mg/kg PO). Is safer than ivermectin, pyranthel and Less resistance.
Fenben. May also lessen the risk of a post-treatment impaction.
Definitely favor fenbendazole if:
- No prior history of deworming
- Very high P. equorum egg counts
- Abdominal enlargement
Describe Parascaris spp. - disease prevention.
The key is Management.
Anthelmintic treatment for foals 60-70 days of age.
Thereafter should be repeated at the greatest interval that minimizes environmental contamination with ascarid eggs.
So, Three-month interval (approx. every 90 days).
More frequent intervals intensify selection for resistance.
Monitor the efficacy of all drug classes against P. equorum populations on each farm! to avoid using an ineffective drug on a resistant population
Describe the life cycle of Anoplocephala perfoliata.
Horse tapeworm
Require intermediate host (mites)!
Horses ingest infective mites while grazing,
Adult cestodes develop 2 to 4 months after infection.
Attach to the cecal mucosa near the ileocecal valve.
Segments pass distally with the ingesta, break apart and eggs are released into feces.
These are only a problem of grazing horses.
Increased infection risk at the end of grazing season.
Describe the prevalence of Anoplocephala perfoliata.
Horse tapeworm
Endemic in many herds.
A.perfoliata (most common); found in cecum (ileocecal junction).
A.magna and Anaplocephaloides (uncommon): found in SI.
Less than 50% prevalence in adult horses in UK.
In Finland (2022): 7% of horses infected; previously found in 1/3 of horses in post-mortem. More in young horses.
Serum or saliva antibody testing or treatment 1x year (autumn) if endemic!
Describe the effects of Anoplocephala perfoliata on the internal organs.
Ulceration of the cecal mucosa, local inflammation and development of fibrous connective tissue.
Small numbers are not pathogenic though.
Large numbers increase the risk for colic.
Ileal impaction
Spasmodic colic
Ileocecal intussusceptions
Cecal rupture
Anoplocephala perfoliata: treatment.
Ideally, tx in autumn.
Use either:
Praziquantel 1 mg/kg PO
Pyrantel embonate 13.2 mg/kg PO (double the “normal” dose)
Both are very effective but Praziquantel preferred.
No resistance reported.
Activity of both compounds is fairly rapid,
24-48 h. Colic has been reported after tx.
Serum or saliva antibody testing or treatment 1x year (autumn) if endemic!
Describe Gasterophilus spp. life cycle.
Female bot flies lay eggs onto the hair of a horse.
Initial parasitic stages (L1 and L2) develop in oral cavity before they migrate to the stomach.
2nd and 3rd -stage larvae of Gasterophilus intestinalis are found attached to the nonglandular mucosa of the horse stomach. G. intestinalis often form very large dense mats.
Larvae of G. nasalis occupy the duodenal ampulla.
In one layer, luminal compromise is minimal.
Bot infections are highly prevalent.
Describe the prevalence of Gasterophilus spp.
In some herds very prevalent. Often occur in more than 90% of herd members during the autumn and winter months.
Probably not pathogenic at all but Some exceptions.
Ivermectin (and moxidectin) are effective.
Initial parasitic stages (L1, L2) develop in oral cavity then migrate to the stomach, then L2, L3 attach to the epithelial part of the stomach or the duodenal ampulla.
Descibe Oxyuris equi.
Horse pinworm
Ingestion of larvated eggs from the environment.
Low pathogenity.
Adults live in the large intestine.
After mating: males die, females migrate to the end of rectum to Lay eggs on the peri-anal skin causing Perineal pruritus and tail rubbing.
Younger horses used to be more susceptible but now
Increasing affect among all age groups.
Diagnosis of Oxyuris equi.
horse pinworms
Tail-rubbing behavior, brokwn tail hair, and FEC are not diagnostic alone.
Also do a Tape-test + microscopy.
Adult female parasites occasionally seen around the anus.
Oxyuris equi: treatment
Anthelmintic use for treatment is actually questionable.
Ivermectin/moxidectin, fenbendazole, pyrantel all work but there’s a Resistance question. Definitely don’t do repeated use of different drugs as they wont
Likely be effective for long.
Decontamination of the environment is important.
Perineal region cleaned 1-2 times a day to remove eggs – break the life cycle. Apply Vaseline so new eggs won’t stick.
Describe Strongyloides westeri.
Horse threadworm
Reside in the Duodenum and jejunum and Affect foals up Until 6 months old.
Larvae come in via the dam’s milk or from the environment through the skin.
Easily diagnosed by fecal flotation.
Eggs easily distinguishable from Strongylid eggs.
May cause local mucosal damage, Diarrhea, lethargy, reduced weight gain. Deaths are reported with severe infections
Clinical signs more common if >2000 epg.
Presence of S.westeri in a foal with diarrhea is not diagnostic. Treatment only reserved for cases of enteritis. Usually ivermectin or Fenbendazole.
Describe horse Lungworm: Dictyocaulus arnfieldi.
Not a very common problem in horses but prevalent among donkeys (4% vs 35%).
Risk group: horses grazed with donkeys
Not detected with regular FEC, needs the Baermann method. Strong eosinophilia in blood and BAL.
The adult lungworm lives in the lung and releases larvae into the lung tissue which Causes cough, then are swallowed and pooped out.
Describe Liver fluke: Fasciola hepatica.
Uncommon problem of horses, prelevance unknown.
Horses are more resistant than ruminants.
Consider liver flukes if wet soil (cause snails are intermediate hosts) and/or if the horses are grazed with ruminants.
No good testing method:
- Fecal samples unreliable
- Increased liver enzymes can help
Treatment: ticlalbendazole 12mg/kg which is
Not licensed, but is efficient and safe. Some others used in cattle are toxic to horses.
