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 Larval Cyathostominosis in Horses Larval cyathostominosis is a clinical syndrome caused by mass emergence of encysted cyathostomin larvae from the large intestinal walls. It is characterized by acute, generalized typhlocolitis... read more 
, 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
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
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
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
Infections rarely occur in horses kept without ruminant contact, but preventive measures have not been specifically recommended for this parasite.
Zoonotic Risk
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 Small Stomach Worm (Trichostrongylus) Numerous parasites can infect the digestive system of horses (see Table: Common Gastrointestinal Parasites of Horses). The most common ones are described in the following text. The stomach worms... read more .
