Cutaneous Habronemiasis

• Grossly:
  • Single or multiple tomorous masses that proliferate and ulcerate
  • Red to brown, on section have small gritty yellow to white foci
• Microscopically:
  • Nodular dermatitis
  • Eosinophils, epithelioid macrophages, multinucleated giant cells
  • Larvae and necrotic tissue
  • Granulation tissue with neutrophils along ulcerated surface

Description

Cutaneous Habronemiasis is a hypersensitivity reaction to the larvae of the nematode species Habronema and Draschia. The adult nematode lives in the stomach of the horse and produces eggs which are then passed in the faeces as larvae. The larvae are ingested by the house fly (Musca domestica) or stable fly (Stomoxys calcitrans) in their larval phase, and deposited on equine skin when they feed as adult flies. The condition is characterised by ulcerative, granulomatous skin lesions which do not heal.

Signalment

The condition occurs most commonly in warm wet climates such as the tropics and sub tropics but is also a common skin condition in the UK. It affects moist regions of the body and open wounds; it typically has a seasonal distribution with partial or full resolution during the winter.

Diagnosis

Clinical signs

Single or multiple nodular lesions Excessive granulation tissue Pruritus lesions most commonly occur on the legs, ventral abdomen, around the eyes, urethral process and prepuce and at the site of pre-existing wounds.

Treatment

Systemic glucocorticoids decrease the inflammatory response of the the hypersensitivity reaction, oral prednisolone is effective at a dose of 1mg/kg SID or BID for 14days and then tapered. Organophosphate pastes and anti-inflammatory pastes can be applied to the wound until it has healed, or thye wound should be bandaged to prevent reinfestation. Excessive granulation tissue should be removed surgically. Ivermectin or appropriate anthelmintics should be used to limit nematode infestation, fly control will also reduce exposure to the larvae.

Prognosis

Recurrence is common. Fly control, meticulus wound management and regular anthelmintic use is needed to prevent or limit the condition.

References

• Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool
• Rose, R. J. and Hodgson, D. R. (2000) Manual of Equine Practice (Second Edition) Sauders.

Also known as:

Summer sores Granular dermatitis Bursautee