Page 831 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

806 CHAPTER 4

VetBooks.ir common and are found worldwide. G. pecorum may Clinical presentation
Infection is usually inapparent. Adult bot flies may
be involved in Europe, Africa and Asia. T. axei may
also cause gastric parasitism.
while they are flying around horses and depositing
Most adult Gasterophilus flies attach eggs to be of greater significance because of annoyance
the hairs of the legs, shoulders, lips or interman- their eggs.
dibular space of horses during the late summer
and autumn (Fig. 4.132). Eggs are 1–2 mm in Diagnosis
length and creamy-white to orange in appearance. Bot infection can be inferred by the finding of eggs
Eggs around the mouth hatch spontaneously, while deposited on the horse. L3 larvae may be identified
eggs at other sites may hatch in response to warmth in faeces. G. intestinalis larvae are often identified
provided by licking. In contrast, G. pecorum eggs incidentally during gastroscopy (Fig. 4.133). With
are deposited in pasture and ingested during graz- T. axei infection, gastritis may be evident endoscopi-
ing. Larvae enter the mouth, penetrate the tongue cally. The worms are small (<7.0 mm) and may be
or buccal mucosa and reside in these tissues for difficult to identify. T. axei eggs may be identified in
several weeks before entering the stomach via the faecal flotation.
pharynx and oesophagus. G. nasalis larvae tend to
attach to the pylorus and duodenum, G. intestinalis Management
to the non-glandular mucosa around the cardia and Ivermectin (0.2 mg/kg p/o) and moxidectin (0.4 mg/kg
G. haemorrhoidalis to the duodenum and rectum. L3 p/o) are effective against bots. Bot infestation is rarely
larvae are then passed in faeces and pupate in the associated with disease; however, annual boticidal
soil. There is only one generation per year in tem- therapy is usually recommended. In temperate areas,
perate areas. boticidal therapy should be administered in mid-winter
Infective L3 of T. axei are ingested on pasture and once there is no longer ongoing exposure to bot eggs.
tunnel into the gastric wall. Gastritis may result, and Physical removal of eggs that have been deposited on
small erosions can be produced by the congregation the skin can be performed but based on the limited
of large numbers of parasites in a small area. clinical significance and ease of deworming in the

4.132 4.133

Fig. 4.132 Numerous bot eggs are visible on the Fig. 4.133 A Gasterophilus intestinalis (bot) larva is
haircoat over the medial aspect of this limb. present in the stomach of a normal horse.