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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Roundworm infestation caused by Parascaris equorum.

Pathophysiology!!navigator!!

  • Direct life cycle—fecal–oral route.
  • Adult horses, especially brood mares, and older foals—main reservoir of infection (eggs).
  • Eggs accumulate in the environment (highly resistant), sticking to different surfaces, including the mare's mammary gland.
  • After ingestion—embryonated eggs hatch in the host's small intestine, larvae migrate through the intestinal wall to the liver and lungs, larvae travel up the bronchial tree, are swallowed, and develop into 10–50 cm long mature adult ascarids in the duodenum and proximal jejunum. Prepatent period, 10–12 weeks.
  • SIO—associated with a large burden of parasites

Systems Affected!!navigator!!

  • Gastrointestinal—colic, enteritis, maldigestion, and malabsorption.
  • Hepatobiliary—migrating larvae resulting in temporary liver damage.
  • Respiratory—tracheobronchitis

Incidence/Prevalence!!navigator!!

  • Prevalence—31–61%.
  • Infection prevalence—up to 100% in tested farms and in 80% of foals.
  • Colic due to SIO—0.5% (25/5134 cases of colic)

Geographic Distribution!!navigator!!

Worldwide

Signalment!!navigator!!

  • Any ages—primarily foals.
  • Adult horses—debilitated and immunocompromised

Signs!!navigator!!

  • Ascarid infestation—lethargy, weakness, decreased weight gain, dull hair coat, and “pot-bellied” appearance.
  • Mild to moderate colic—intestinal phase of the infection.
  • SIO—severe colic, can be complicated with volvulus or intussusception.
  • Peritonitis—perforation of the intestine.
  • Coughing and mucopurulent nasal discharge with or without systemic illness—larval migration through the lungs

Causes!!navigator!!

N/A

Risk Factors!!navigator!!

  • All foals are at risk.
  • Breeding farms—large yearly population of young horses grazing on same pasture.
  • Ascarid impaction and SIO—usually 24 h after anthelmintic therapy (72% of the cases)

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Other causes of delayed growth.
  • SIO—small intestine strangulating lesion

CBC/Biochemistry/Urinalysis!!navigator!!

  • Eosinophilia—during larval migration, 10–40 days post infection.
  • Leukopenia and mild anemia.
  • Hypoproteinemia—severe infestation

Other Laboratory Tests!!navigator!!

N/A

Imaging!!navigator!!

Transabdominal ultrasonography—adult ascarids within the intestinal lumen or in the peritoneal cavity (perforation).

Other Diagnostic Procedures!!navigator!!

  • Fecal flotation.
  • Eosinophils in tracheal wash—verminous lung disease

Pathologic Findings!!navigator!!

Adult forms in the intestinal lumen or free in the abdominal cavity (intestinal perforation).

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

Treatment indicated when fecal egg counts >100 eggs per gram.

Client Education!!navigator!!

Severe parasite burdens suspected—benzimidazoles are recommended. Avoid anthelmintics that result in paralysis of the parasites (e.g. pyrantel pamoate, piperazine, organophosphates, ivermectin).

Surgical Considerations!!navigator!!

For removal of dead parasites and correction of secondary complications (intussusceptions and intestinal volvulus).

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Anthelmintics—do not eliminate migrating larvae. Preventative therapy should be given until 1 year of age.
  • Broodmares—deworm at monthly intervals in the last trimester of pregnancy. Reduce environmental contamination.
  • Fenbendazole—10 mg/kg every 24 h PO for 5 consecutive days (varies in effectiveness against ascarids).
  • Moxidectin—0.4 mg/kg PO and ivermectin 0.2 mg/kg PO. Advocated to be 100% efficient in eliminating ascarid infection in horses. Resistance to these and other macrocyclic lactone anthelmintics has been identified in Europe and North America

Contraindications!!navigator!!

See Client Education.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Fecal floatation—conducted in 10% or more of foals every 4–6 months. If >10% of foals are positive indicates failure of the anthelmintic therapy or of the prevention and control strategies.

Prevention/Avoidance!!navigator!!

  • Contaminated facilities—disinfection with a 5% phenolic compound.
  • Grazing of broodmares, foals, and weanlings on heavily contaminated pastures should be avoided.
  • P. equorum eggs—remain viable in the environment for years.
  • Frequent removal of manure from stalls and pastures

Possible Complications!!navigator!!

Toxicosis—overdose of anthelmintic.

Expected Course and Prognosis!!navigator!!

  • Prognosis—favorable in uncomplicated cases (delay in growth is common).
  • SIO—short-term (discharge from hospital) and long-term (>1 year) survival 64% and 27%, respectively.
  • Formation of adhesions—associated with nonsurvival

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • SIO.
  • Peritonitis

Age-Related Factors!!navigator!!

Primarily in foals.

Zoonotic Potential!!navigator!!

Human infection—extremely rare.

Pregnancy/Fertility/Breeding!!navigator!!

N/A

Synonyms!!navigator!!

N/A

Abbreviations!!navigator!!

SIO = small intestine obstruction

Suggested Reading ⬆ ⬇

Cribb NC, Cote NM, Bouré LP, Peregrine AS. Acute small intestinal obstruction associated with Parascaris equorum infection in young horses: 25 cases (1985-2004). N Z Vet J 2006;54:338–343.

Author(s) ⬆

Author: Diego Gomez-Nieto

Consulting Editors: Henry Stämpfli and Olimpo Oliver-Espinosa

Acknowledgment: The author and editors acknowledge the prior contribution of Carlos Medina-Torres.