Glochid
Glochids or glochidia (singular "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae. Cactus glochids easily detach from the plant and lodge in the skin, causing irritation upon contact. The tufts of glochids in the areoles nearly cover the stem surfaces of some cactus species, each tuft containing hundreds of glochids; this may be in addition to, or instead of, the larger, more conspicuous cactus spines, which do not readily detach and are not generally barbed. Mechanical irritant dermatitis Reaction to the glochidia Most cacti possess spines, some large enough to cause serious wounds. Glochids however, though smaller, commonly induce more troublesome, more persistent, dermatological manifestations in humans. Though minute, glochids commonly are barbed and once they have penetrated the skin barbed glochids are practically impossible to dislodge without leaving scraps of foreign material in the wound. Implantation of glochidia in the skin does sometimes cause immediate irritation, but not always, as one may deduce from the presentation of patients with granulomatous lesions around glochidia, patients who have no recollection of the penetration that caused the acute injury, even when it is clear that the injury is far from fresh. Distraction or excitement might cause the victim to overlook brushing past a cactus and picking up a few hundred barely visible glochids. In such cases, the irritant reaction may have a delayed onset. Shanon reported that brushing his axillary skin with sabra fruit resulted in no symptoms for a half-hour, followed by hours of "stabbing feelings". Winer reports immediate burning sensation, redness and swelling which remained for one to three days if the spines were removed. Depending on the exposure, widespread areas may be involved, even extending to hard palate, tongue, conjunctiva and cornea. If the glochidia are not removed, a response may ensue that eventuates in granulomatous dermatitis. Within 24 to 72 hours there is the appearance of 2- to 5-mm, asymptomatic, domed, glistening papules, sometimes erythematous, with a central pin-point-sized black dot at the site of the injury. There may be groups of these papules. Vesicles and pustules and even focal ulceration may also occur. In some instances, diagnosis can be made easily by passing the fingers over the affected area and by feeling the embedded glochidia. Left untreated, these lesions may last as long as 9 months. A biopsy of the later lesions reveals granuloma formation with plant material embedded in the dermis. The fragments of the barbed bristles gave strongly positive reactions with PAS. The presence of a cactus granuloma lesion is often followed by post-inflammatory hyperpigmentation. Penetrating injuries can introduce pathogenic microorganisms into the wound. Examples include Clostridium tetani and Staphylococcus aureus (from spines and thorns), Sporothrix schenckii (from rose thorns, grasses, and sphagnum moss), Mycobacterium kansasii (from blackberries), Mycobacterium marinum (from cactus spines), and Mycobacterium ulcerans (from spiky tropical vegetation). Glochids from prickly pears (Opuntia species) can cause an extremely itchy, papular eruption called sabra dermatitis, which can easily be confused with scabies or