Gasterophilus

Gasterophilus



Basic Information image



Definition


The most common, although rarely clinically significant, gastric endoparasite in adult horses and foals



Synonym(s)




• “Bots,” the bot fly larvae, are the stage found in the equine stomach.


• Gasterophilus intestinalis and Gasterophilus nasalis are most commonly found in horses; other less frequently identified species include Gasterophilus haemorrhoidalis and Gasterophilus pecorum.



Epidemiology



Geography and Seasonality




• Found worldwide.


• Adult bot flies are present during the summer months and lay their eggs on the hairs of the horse’s face and legs in the fall. The larvae overwinter in the equine stomach, are passed in the feces in the spring, and then pupate and mature into adult bot flies.



Clinical Presentation



History, Chief Complaint


Associated clinical signs are rare but may include signs similar to gastric ulceration (see “Gastric Ulceration” in this section) if large numbers are present in the stomach or signs consistent with gastric outflow obstruction (see “Gastric Impaction” in this section) if large numbers obstruct the duodenum.



Physical Exam Findings




• Usually within normal limits.


• In the fall, small, yellow bot fly eggs may be visible stuck to the hairs of the face and forelimbs.



Etiology and Pathophysiology


Direct life cycle:



• The adult bot fly lays eggs on the horse’s hair coat (legs or head) during warm months. The eggs hatch on the hair coat, releasing first-stage larvae, which then enter the oral cavity by crawling there or are ingested by the horse during grooming behavior.


• First- and second-stage larvae develop in the oral cavity in the gingival tissue (G. nasalis) or tongue (G. intestinalis).


• Late second-stage larvae are swallowed and mature to third-stage larvae in the stomach. The third-stage larvae then attach to the gastric (G. intestinalis) or proximal duodenal (G. nasalis) mucosa, where they overwinter.


• Third-stage larvae detach from the gastric mucosa in the spring and are passed in the feces and pupate. Adult bot flies emerge during the summer and repeat the cycle.


• In general, Gasterophilus organisms are nonpathogenic, and related clinical disease is uncommon unless large numbers of larvae are present in the stomach, resulting in gastric mucosal pain or inflammation or in the duodenum, resulting in gastric outflow obstruction.

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Gasterophilus

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