Page 1281 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

1256 CHAPTER 12

VetBooks.ir megastoma and H. majus commonly cause ulcerative failure to heal; and caseous sulphur-like granules in
sores, especially in the medial canthus. Some sores
cutaneous granulomas in horses. Larval worms are
capable of penetrating intact skin. Recurrence of
areas can be affected. Infection of the urethral pro-
infection can occur on a yearly basis. It is associated show a stringy serosanguineous exudate. Multiple
with an increased fly population, poor manure col- cess can lead to bleeding during covering by stallions,
lection or disposal and moist patches of long grass. and may reduce fertility and produce blood-stained
A predilection has been shown in light-coloured urine. Rubbing of eyes, very mild pruritus and biting
horses. at lesions also occur (Fig. 12.51).

Aetiology/pathophysiology Differential diagnosis
Habronemiasis is caused by the combined pres- Exuberant granulation tissue; SCC; phycomycosis;
ence of Habronema spp. stomach worms, house and/ pythiosis; fibroblastic sarcoid; botryomycosis lesions.
or stable flies and poor hygiene. It is most prevalent
in summer and autumn. Cutaneous habronemiasis Diagnosis
is part hypersensitivity reaction and part seasonal, Diagnosis is based on history, clinical signs, presence
with spontaneous regression in the winter months of sulphur granules and cytological and histopatho-
because larvae do not overwinter in the tissues. It logical identification of larva(e). Histopathological
is a sporadic disease, with only individual horses findings typically include granulation tissue with
in a herd affected on a recurring annual basis. The focal to diffuse infiltration of eosinophils and areas
prevalence of habronemiasis varies considerably with coagulation necrosis surrounding a centrally
throughout the world and, in great part, may have located larva. The eggs are not usually identified
been decreased by the regular use of de-worming in faeces because they have thin walls which read-
agents. However, with the recent shift to limit use of ily collapse. There may be haemorrhage from an
de-wormers to only high-shedding individuals based enlarged urethral process.
on faecal evaluation, a resurgence of habronemiasis
and onchocerciasis may be imminent. Management
Ivermectin (0.2–0.3 mg/kg) has been shown to be
Clinical presentation effective and is considered the treatment of choice
Affected animals have rapidly granulating sores at to address the larvae. Occasionally a second dose is
the medial canthus, prepuce and urethra, or else- required 3–4 weeks after the initial dose. Eye lesions
where; rapid growth of granulating wounds, with may also require a local application of cortisone drops
plus a 50% mixture of ivermectin and artificial tears
solution. Given the hypersensitivity reaction that
12.51 accompanies the infection, anti- inflammatory sys-
temic oral (prednisolone 1 mg/kg q24 h for 14 days
and then tapered), intralesional (3–5 mg of triamcino-
lone per lesion; maximum dose of 20 mg to avoid ste-
roid-induced laminitis) and/or topical corticosteroids
are prescribed. In severe cases, surgical removal or
debulking of the lesion should be considered. Strict
attention to fly control and wound management will
minimise recurrence of the lesions. The average
recovery time reported was approximately 23 days.

Prognosis
The prognosis is good, but all aspects of control as
Fig. 12.51 Habronemiasis lesion in a tear duct. well as treatment must be followed.