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Cutaneous habronemiasis is caused by the migration of larvae
through tissues. When the larvae are deposited in wounds, or
more commonly, near the mucocutaneous junction of the eyes, the
larvae migrate through the tissues causing a granulomatous reaction.
Ocular lesions at the medial canthus are the most common location,
but granulomatous lesions can happen anywhere that the larvae
are deposited. Any open wound is susceptible. Raised proliferative
granulomatous non-healing lesions are commonly described
manifestations of cutaneous habronemiasis. ese lesions are
typically extremely pruritic, and usually result in self trauma due to
itching.
ere is some evidence that lesions can occur in the same location
year aer year. is reoccurrence in some individual horses (at
the site of a previous lesion) suggests that the larvae may be able to
remain dormant in these lesions. ere have been suggestions that
perhaps these dormant larvae are evading the immune system of the
individual host, but these theories have not been proven. ere is no
doubt, however, that there are individual horses who develop lesions
year aer year at the same location of previous lesions. ese lesions
can reoccur with no initial break in the skin, leading to further
speculation that the larvae are remaining dormant while evading
host immune measures.
Figure 3: Extremely pruretic
facial habronema lesion (with self
trauma)
Figure 4: Lesion aer debridement
(following day)
Figure 5: Lesion 1 year later
Above, Figure 6: Embedded 'sulfur' granule
Below, Figure 7: Sulfur granule aer removal
Caution: Care should be taken to
ensure that there are no corneal lesions
before starting topical steroids for the
medial canthus lesions.
