Ascarid Infections in Horses
Key takeaways
Ascariasis is a roundworm infection common in horses, especially foals, young horses, and immunocompromised animals.
- Ascarid eggs pass with feces, and can persist for over a year in a contaminated environment
- Symptoms include poor growth in young horses, a dull hair coat, and a pot-bellied appearance
- Severe infections may lead to intestinal blockage, requiring surgical intervention
- Diagnostics include blood work, and fecal examination
- Ascariasis is treated with dewormer medication or surgery in severe cases
- Prognosis with treatment is good for mild infections, but more guarded if surgery is necessary
- A clean living environment, and vet-directed use of dewormer medication can help control ascarid infections during a horse’s first year where they are most vulnerable
- Mature horses are rarely infected, unless they are immunosuppressed
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A closer look: Ascarid Infections in Horses
Ascarid eggs pass in the fecal matter and contaminate nearby soil, pastures, paddocks, and stalls. These eggs are durable, and may survive more than a year in the environment. Horses living in contaminated spaces consume eggs during foraging, becoming infected.
After ingestion, the eggs hatch in the small intestine. From there, roundworm larvae migrate into a horse’s lungs, into the trachea, and are swallowed, reaching the intestines. Adult roundworms in the intestines lay eggs, continuing the cycle.
Any symptomatic horse requires prompt medical attention.
Risk factors
Ascarid infections are very common in young horses. The immune system of adult horses typically keeps ascarid infections from developing, however immunocompromised adults are still at risk.
Roundworms in the intestines may cause an obstruction, leading to signs of severe colic. In severe cases, the obstruction of the intestine by parasites can result in rupture of the intestinal wall.
Possible causes
Ascariasis is caused by ingestion of ascarid eggs while foraging in feces-contaminated spaces.
Main symptoms
Testing and diagnosis
Diagnostics include:
- Physical examination
- Bloodwork
- Fecal examination
Steps to Recovery
Minor ascariasis is treated by dewormer medication, which forces the adult parasites to pass with feces or kills the adult parasites directly. In severe cases, multiple treatments are necessary to ensure all parasites have passed from a horse’s system.
Follow-up appointments include additional fecal flotation tests to confirm that the treatments were successful.
Intestinal obstructions are more serious, and require surgical intervention to remove the parasites and relieve the obstruction.
Prognosis for minor ascariasis is good with treatment, although an infection may delay a foal’s growth.
Severe cases resulting in colic or intestinal obstructions have a guarded prognosis.
Prevention
It is important to keep broodmares, foals, and weanlings out of contaminated pastures. Frequent removal of manure and cleaning of stalls may reduce contamination. Feeding horses out of containers that prevent fecal contamination of feed can also be beneficial.
Veterinarian-directed deworming medication is recommended to reduce the parasite load in the intestine during a horse’s first year of life, when they are most susceptible to infection.
Deworming broodmares during their last trimester can also help prevent spread of the parasites to the foal. Appropriate dewormer selection must be based on veterinary recommendation.
Is Ascarid Infections in Horses common?
Roundworm infections are very common in young horses. Adult horses typically do not become infected with the parasites, unless they are immunosuppressed.
Typical Treatment
- Deworming medication
- Surgery
