May
27
Written by:
Surgi-Care Center for Horses
5/27/2011 5:17 PM
Habronema is an infection caused by nematode larvae that is
carried by flies. The adults are found in the stomach of the horse and the
larvae are passed in the horse’s feces. The larvae are ingested by houseflies
or stable flies and then deposited on the horse while the flies are feeding.
The larvae can cause lesions when they are deposited on the mucous membranes,
conjunctiva, abraded skin, or in open wounds. The two most common types of
Habronema infections are cutaneous and ocular lesions.
Habronema larvae tend to be deposited in areas of natural
body moisture. Therefore, lesions are most commonly seen on the lips, prepuce,
urethral process of the penis, medial canthus of the eye, conjunctiva, in the
corner of the lips, and in any area where the skin has been traumatized.
Habronemiasis is characterized by the rapid growth of papules, exuberant
granulation tissue (proud flesh) and failure of a wound to heal. Lesions may be
solitary or multiple. The lesions are typically characterized by ulcerations,
exudate (pus), intermittent bleeding episodes, and pruritis (itching). Lesions
often contain small yellow granules, which are dead or dying larvae.
Habronemiasis is believed to be a hypersensitivity reaction
to the antigen of the dying or dead larvae. Habronemiasis is most frequently
seen during the spring and summer, when fly populations are at their peak. Most
lesions regress during winter. Diagnosis is often made on the basis of history,
location of the lesion, the presence of yellow granules and other clinical
signs that are mentioned in the above paragraph. A definitive diagnosis can and
should be made by taking a biopsy of the lesion.
There have been many treatments of Habronemiasis reported
but no single treatment is consistently successful. Treatment regimens for
Habronemiasis should be made with 4 goals in mind: to reduce the size of the
lesion, to reduce inflammation, elimination of adult Habronema from the
stomach, and reduction of the fly vector populations. The most effective
treatment regimens consist of a combination of local and systemic treatments.
Larger lesions or lesions that do not heal with medical treatment should be
surgically removed. Systemic and local treatments include: Orally administered
Ivermectin; topical, intralesional and systemic corticosteroids;
anti-inflammatory agents; and antimicrobial agents.
Habronema is sporadic but certain individuals are more
susceptible. Prevention of Habronema can be attempted by using fly control: fly
masks, fly sheets, fly spray, and immediate removal of feces from the area.
Regular deworming with ivermection, to eliminate adult Habronema from the
stomach, can also help reduce the incidence of infection and reinfection. It is
also important to wrap existing wounds to prevent reinfection.
Any lesions that fit the description given in the above
paragraphs should be examined by a veterinarian. These lesions need to be
differentiated from squamous cell carcinoma, pythiosis, fungal infections,
bacterial granulomas and exuberant granulation tissue (proud flesh).
Differentiation of these infections can lead to a more cost effective and
clinically effective treatment regimen.
Contact
Surgi-Care Center for Horses at 813-643-7177 or email lkuebelbeck@surgi-carecenter.com
with
any questions regarding this topic