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Trichostrongylus axei Infection in Horses

By

Martin K. Nielsen

, DVM, PhD, DACVM, University of Kentucky

Last full review/revision Dec 2019 | Content last modified Dec 2019

The small stomach worm, Trichostrongylus axei, is the only nematode species that occurs in humans, ruminants, and horses. Infection is rarely diagnosed in horses maintained without ruminant contact, but infections have been described in horses co- or mixed-grazed with ruminants. Weight loss has been described in T axei infections, but the parasite is not considered a major parasitic pathogen of horses. Treatment with ivermectin or benzimidazole products is reported to be effective.

Trichostrongylus axei, the stomach hair worm, is a trichostrongylid parasite infecting a variety of hosts, including sheep, goats, cattle, and horses. Human infections have been described as well. The environmental life cycle is similar to cyathostomins, with the third stage larva being the infective stage. Once ingested, the larvae penetrate the gastric mucosa and develop into adult worms and emerge into the gastric lumen. Egg production begins 3–4 weeks after infection.

The parasite is seldom encountered in domestic horses and is not considered a primary parasitic pathogen.

Clinical Signs of Trichostrongylus axei Infection in Horses

Infection has been reported to cause a catarrhal gastritis with small lesions that may coalesce to form larger erosions and ulcers. Clinical signs have not been well described, but it has been implicated as a cause of weight loss in horses.

Diagnosis of Trichostrongylus axei Infection in Horses

The eggs are morphologically indistinguishable from strongylid eggs of horses and ruminants. Third stage larvae can be morphologically identified under the microscope, so the parasite can be diagnosed via coproculture.

Treatment of Trichostrongylus axei Infection in Horses

Although no recent anthelmintic efficacy studies exist, T axei is expected to be susceptible to macrocyclic lactone (ivermectin or moxidectin) or benzimidazole (fenbendazole or oxibendazole) treatment. Benzimidazole resistance has been reported in T axei infecting sheep, so this could also occur in horses.

Prevention of Trichostrongylus axei Infection in Horses

Infections rarely occur in horses kept without ruminant contact, but preventive measures have not been specifically recommended for this parasite.

Zoonotic Risk of Trichostrongylus axei Infections

Human infections have been described. Infection occurs by ingestion of infective larvae present on contaminated lettuce, cabbage, etc.

Key Points

  • Trichostrongylus axei infection is rare in domestic horses.

  • Infection can occur if horses are co- or mixed-grazed with ruminants.

  • Antemortem diagnosis is by coproculture.

  • Macrocyclic lactones and benzimidazoles are believed to be effective treatments.

For More Information

Also see pet health content regarding small stomach worms in horses.

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