Lecture 9- Gastrointestinal Nematodes of Horses: Ascarids, Pinworms, Draschia/Habronema

What is the size of Parascaris equorum males and females?

Males: 15-28 cm; Females: up to 50 cm long and 8 mm in diameter.

What is a distinguishing morphological feature of Parascaris equorum?

Anterior opening with three lips.

Where are adult Parascaris equorum parasitic in equines?

In the small intestine.

Is Parascaris equorum sexually dimorphic?

Yes, males and females have distinct size differences.

What type of lifecycle does Parascaris equorum have?

A direct lifecycle.

How do horses become infected with Parascaris equorum?

By ingesting larvated eggs from contaminated pasture.

What type of migration do Parascaris equorum larvae undergo?

Tracheal and somatic migration.

What age group of horses is primarily affected by Parascaris equorum?

Foals

What is the prepatent period for Parascaris equorum?

~12 weeks

What do Parascaris equorum eggs look like on fecal floatation?

Round eggs, ~90μm in diameter

What are common gastrointestinal clinical signs of Parascaris equorum infection?

Diarrhea and enteritis.

What respiratory signs can Parascaris equorum cause?

Nasal discharge and respiratory issues due to larval migration.

How can Parascaris equorum infection affect a foal's appearance?

Dull hair coat and poor growth.

Why can extreme infections of Parascaris equorum be fatal?

Due to a high worm burden, which can outgrow the intestinal tract.

What life-threatening complications can arise from Parascaris equorum infection?

Impaction colic, intestinal perforation, and rupture.

What hygiene measures help prevent Parascaris equorum infection in foals?

Cleaning the mare's udder and teats and providing a clean nursing environment.

How can pasture management help control Parascaris equorum infections?

Grazing foals on dedicated pastures with older animals that have low FECs.

Why should all foals in a herd be on the same anthelmintic regimen?

To prevent reinfection and maintain control over parasite populations.

What is the recommended drug therapy schedule for Parascaris equorum in foals?

Treatments at 2, 4, 6, and 8 months.

Which anthelmintics have shown early indications of effectiveness against Parascaris equorum?

Pyrantel pamoate and Fenbendazole.

Which anthelmintic class has widespread use against Parascaris equorum?

Macrocyclic lactones.

What is the prevalence of Parascaris equorum infections on farms?

High prevalence (>80%) on multiple continents.

How should critically ill foals with Parascaris equorum be treated?

With care using Fenbendazole to gradually kill worms and allow for safe expulsion.

What is the common name for Oxyuris equi?

Equine Pinworm.

What is the size range of Oxyuris equi males and females?

Males: 9-12 mm; Females: 40-150 mm.

What morphological feature characterizes adult Oxyuris equi worms?

A long tail with an acute distal end.

What type of esophagus does Oxyuris equi have?

A muscular "bulb" esophagus.

Where do adult Oxyuris equi worms reside in the horse?

Cecum, small colon, and large colon.

What is the global distribution of Oxyuris equi?

Cosmopolitan (found worldwide).

What age group of horses can be infected with Oxyuris equi?

Horses of all ages.

What type of lifecycle does Oxyuris equi have?

A direct lifecycle.

How do horses become infected with Oxyuris equi?

By ingesting embryonated eggs from contaminated surfaces.

What happens after Oxyuris equi larvae hatch?

They penetrate the colon wall, develop, return to the lumen, and reproduce.

Where do female Oxyuris equi worms deposit their eggs?

In the perianal folds of the horse.

What is the prepatent period of Oxyuris equi?

Approximately 5 months.

How do Oxyuris equi eggs spread in the environment?

They flake off the skin and adhere to surfaces such as buckets, mangers, stalls, and grooming tools.

How long does it take for Oxyuris equi eggs to become infective?

4 to 5 days of development.

What is the main clinical sign of Oxyuris equi infection?

Intense anal pruritus (itching).

How do infected horses behave due to Oxyuris equi irritation?

They rub their hind end on stalls, fence posts, and other surfaces.

What physical signs can indicate Oxyuris equi infection?

Broken tail hair and behavioral issues.

What other conditions must Oxyuris equi be differentiated from?

Mange and other causes of anal pruritus.

What are the characteristics of Oxyuris equi eggs?

Oval, operculated eggs measuring ~90x42 μm.

What is the preferred diagnostic method for Oxyuris equi?

"Scotch tape" test with microscope slide examination.

Can Oxyuris equi eggs be detected in fecal flotation?

Occasionally, but it is not the most reliable method.

What does an Oxyuris equi egg mass in tail hair resemble?

Dried whipped or shaving cream.

Are adult Oxyuris equi worms susceptible to treatment?

Yes, they are highly susceptible to anthelmintic treatment.

What is the efficacy of Pyrantel at 13.2 mg/kg for Oxyuris equi?

91% efficacy (2x the labeled dose).

What is the efficacy of Ivermectin paste at 200 μg/kg for Oxyuris equi?

96% efficacy

How susceptible are L4 larval stages to both Pyrantel and Ivermectin?

>99% susceptibility

Is there confirmed drug resistance in Oxyuris equi?

No, evidence contradicts anecdotal reports of resistance.

Why is hygiene critical in controlling Oxyuris equi?

Thousands of sticky eggs adhere to surfaces and contribute to reinfection

What cleaning method is recommended for affected animals?

Use disposable wipes to remove egg deposits.

What is the common name for Strongyloides westeri?

Equine Threadworm.

Where do adult Strongyloides westeri worms reside in the horse?

In the small intestine.

What is unique about the parasitic females of Strongyloides westeri?

Only females are parasitic; males are not involved in the parasitic stage.

How is the lifecycle of Strongyloides westeri similar to canine species?

The morphology and life cycle biology are similar, including the presence of both homogonic and heterogonic cycles.

What is the prepatent period of Strongyloides westeri?

~7 days of life

How are foals typically infected with Strongyloides westeri?

Through lactogenic transmission, ingestion of L3 larvae, or percutaneous infection

Who is most commonly affected by Strongyloides westeri infection?

Foals, primarily

When do eggs of Strongyloides westeri disappear from feces?

By 24 weeks of age

How does Strongyloides westeri survive in the horse's body?

The larvae are arrested in tissues for life

What clinical signs are associated with Strongyloides westeri infection in foals?

Diarrhea, dehydration, and poor growth.

What is the main treatment strategy for Strongyloides westeri infection?

Removal of adults from the small intestine and supportive care.

What is the common name for Draschia and Habronema?

Equine Stomach Worms

Where do adult Draschia and Habronema worms reside in the horse?

In the stomach

What are the size differences between male and female Draschia and Habronema worms?

Males: 8 to 14 mm; Females: 13 to 22 mm

What type of lifecycle do Draschia and Habronema have?

Obligate indirect lifecycle

How are Draschia and Habronema larvae transmitted to horses?

By fly intermediate hosts, who deposit larvae in cutaneous wounds, warm/moist openings, or wound sites.

What is the prepatent period of Draschia and Habronema?

Approximately 5 months

What is the size of Draschia and Habronema eggs?

~45 x ~12 μm

What disease is associated with Draschia and Habronema larvae deposition?

Cutaneous habronemiasis (also known as "Summer Sore" or "Swamp Cancer")

What type of lesion is associated with cutaneous habronemiasis?

Granulomatous cutaneous lesions that persist through the "Fly Season."

Where do adult Habronema and Draschia worms live within the horse?

Habronema worms live within the mucosal lining of the stomach, while Draschia worms form fibrotic nodules.

What is the global distribution of Draschia and Habronema?

Cosmopolitan distribution, found in the United States, Europe, and the United Arab Emirates.

Why has Draschia and Habronema infection been less common in recent years?

Due to the historical use of Ivermectin for suppressive control.

What is the role of selective deworming in the resurgence of Draschia and Habronema infections?

As selective deworming has increased, these parasites may be making a comeback.

How effective is a single dose of macrocyclic lactone for treating Draschia and Habronema?

A single dose of macrocyclic lactone is usually sufficient.

What other control method is important when treating Draschia and Habronema infections?

Concurrent fly control to limit transmission by the intermediate host.