Recently had a patient pitch up after an afternoon in the garden, she had been gardening when a bug fell down her top and she squished it and carried on gardening. After an hour or so she noticed the area stinging and checked to find a red area. She had a shower and noticed that the stinging was a little less but when the area blistered she came to the acute clinic.
Pt was happy to share her story but as she had squished the bug on her “Décolletage” she wasnt so keen to have photos taken and shared with the word. So here is a nice US Marine with a blistering injury from a bug:
So Blisters from Beetles:
There are a few types of bugs that cause blistering eruptions and/or dermatitis.
The most widely know are the Meloidae family from which comes the Spanish Fly. The Meloidae are known as blister beetles in many parts of the world. They are so named because they cause a painful blistering eruption within 2-3hours of exposure.
A few blister beetles:
Paederus beetles also cause a dermatosis and blistering but this generally occurs 24-72 hours after exposure. These have been having a recent resurgence in research as they are common in Iraq and have caused outbreaks in a number of American Army camps there. These lead to the 2007 report attached.
Depending where you are in the world these beetles have a variety of illnesses named after them. If you are in Africa and squish one and wipe you face you may contract “Nairobi eye or Kenya fly dermatitis” In India Paederus beetles also cause seasonal outbreaks.
In New Zealand Oedemeerida (the false blister beetles) are more common and famously caused an outbreak of blisters in soldiers near Auckland in the 1980s. 74 Soldiers erupted with dermatitis after night exercises. An epidemiologists dream! Investigation lead them to the Thelyphassa lineata (Fabricius) after ruling out a number of other causes. Its ability to produce the reaction was tested on some willing participants (Medical Students)
So how do these little bugs cause such a wonderful bullous eruption and dermatitis. Both Melodiae and Oedemeerida produce Cantharidin which is a potent blistering agent. The male beetles produce all of the cantharidin and gift some to the females after mating. Male beetles secrete cantharidin from their joints so they dont need to be squashed to cause exposure and dermatitis. Wonderfully we dont know the exact biomechanical means of its production within the beetles. I also dont like to tell people where presents for my SO come from. Cantharidin is a very potent toxin with a LD50 of 0.5mg per Kg in humans. The most common animals poisoned by blister beetles are horses as the beetles commonly live in alfalfa and other green feed.
Paederus beetles have a more complex but better understood production of their toxin Pederin. The females in this case have a symbiotic relationship with a Pseudomonas which produces the toxin. This is in turn deposited into the eggs and larvae. Further toxin is ingested when beetles eat the shell of their egg after hatching. Paederus dermatitis takes longer to reveal itself often 24 hours before discolouration which then goes on to blister.
Treatment: The best treatment is prevention, simple things such as removing beetles rather than squashing them. One prevention in Iraq was moving the night guards further from the light towers which attracted the beetles. With Cantharadin patient will usually have washed themselves as the burning is an early symptom. With Paederus they often only present well after the toxin has been spread and absorbed, these patients show classical Kissing signs where skin surfaces have touched eg: elbow flexures. Once the dermatitis is established the best treatment is topical steroids but if the case is severe oral antihistimines and even antibiotics have some benefit.
Blister beetles have been used for centuries and despite their toxicity people took them as an aphrodisiac. In roman times (wake up @eleytherius) Livia Drusilla a great schemer of Rome attempted to poison visitors with cantharidin. Hoping they would act in a manner which they would later regret and allow her to blackmail them. (Its unclear if this was succesful) Cantarella which is the combination of Cantharidin and arsenic was reportedly the poison taken by Juliet to appear dead (We know how succesful that was)
http://www.ncbi.nlm.nih.gov/pubmed/2189910 Oedemerid blister beetle dermatosis: a review. Nicholls DS, Christmas TI, Greig DE.