What’s Eating You? Blister Beetles Revisited
Blister beetles are a group of insects that include the Meloidae, Oedemeridae, and Staphylinidae families. The most well-known family, Meloidae, has more than 200 species known for causing a blistering dermatitis in humans by emitting the substance cantharidin, which has been pharmacologically used as a vesicant and can cause deleterious effects if ingested. Most recently, blister beetles have been studied for their anticancer properties.
Practice Points
- Exposure to cantharidin presents initially with burning and tingling before progressing to bullae formation, sometimes in a linear fashion. Rupture of bullae and crust formation can occur.
- Washing of the exposed skin with soap and water may prevent development of blistering dermatitis.
- Clinical use of cantharidin is favorable in treating pediatric patients with common warts and molluscum contagiosum due to tolerability and painlessness of application.
If blister beetles are ingested, they can cause poisoning characterized by abdominal pain and hematuria.1,3,9,10 In fact, blister beetle ingestion by animals consuming baled hay is an important agricultural and economical implication. Several cases of fatal farm animal ingestion resulting in gastrointestinal erosion have been reported.4,6
Medicinal Properties
Medicinal use of cantharidin has been recorded as early as the 19th century and is believed to have been part of ancient medicinal practices in China, Spain, South Africa, and pre-Columbian America for its vesicant, abortifacient, and supposed aphrodisiac properties.2,4,8
Toxicity from internal ingestion has been well documented.1,3,9,10 The Mylabris and Epicauta genera of the family Meloidae, most commonly the Spanish fly, are used for modern extraction of cantharidin. Up to 5% of the dry weight of a blister beetle can be constituted by cantharidin.4
,Although its use has diminished due to limited availability, cantharidin is still used for treatment of common warts, periungual warts, and molluscum contagiosum. It is a favorable choice for treating pediatric patients because of the tolerability and painlessness of application. Due to its acantholytic properties, warts generally slough with the cantharidin-induced blister.11
In recent years, cantharidin has been studied for its anticancer properties. It has been shown to weaken cancer cell antioxidant properties by interfering with glutathione-related enzymes, thus inducing oxidative damage. Additionally, cantharidin is associated with decreased mitochondrial cytochrome C and increased cytosolic cytochrome C, an important signal for apoptosis.12 Furthermore, cantharidin recently was shown to increase expression of proapoptotic proteins and decrease expression of antiapoptotic proteins causing cell death in nasopharyngeal carcinoma, making it a potential anticancer treatment.13
Conclusion
Blister beetles, long known for their production of vesicant agents, are both a cause of as well as a potential treatment of dermatologic disease. The blistering associated with exposure to a disturbed beetle generally is mild and heals without scarring if vital areas such as the eyelids are not affected.
