A Girl Returns From Summer Camp With an Itchy Rash: What’s the Cause?
A mother brought her 8-year-old daughter to the office because of a rash on the girl’s ankle. The rash had first appeared 3 days previously, when the girl returned from summer camp where she had been swimming in a lake. The rash was isolated to her left foot and ankle, and initially it consisted of small, pruritic papules.
The following day, some of the papules had become bullous, and the bullae continued to grow in size, as shown in the photographs. The bullae were not painful or pruritic. The girl had been afebrile and was not on any medications. The rest of the physical examination findings were unremarkable.
What is causing this girl’s rash?
(Answer and Discussion on next page)
Answer: Bullous reaction to chigger bites
Chiggers, commonly known as red bugs or harvest mites, are tiny 6-legged juvenile mites in the Trombiculidae family that bite in the larvae stage.1,2 Chiggers are red in color but are barely visible to the naked eye (Figures 1 and 2). Although they do not burrow into the skin,3 salivary proteins deposited at the site of the bite can induce intensely pruritic, erythematous papules measuring from 1 to 10 mm in diameter (Figure 3).2,3
Adult chigger mite. (Photo by Susan Ellis, Bugwood.org)
Like fleas, bedbugs, and other mites (including scabies), chiggers are small arthropods whose bites can lead to papular urticaria, particularly in young children.2,3 However, a much less common bullous reaction to arthropod bites has been described, which characteristically affects patients who have been previously sensitized to the mite.2,4,5 This reaction, thought to be a delayed-phase response hypersensitivity reaction to insect saliva, can become disseminated in rare cases.4 The eruption must be distinguished from bullous pemphigoid or erythema multiforme.4,6,7
Chigger larvae. (Photo by Hansell F. Cross, Georgia State University, Bugwood.org)
Treatment is supportive. Topical corticosteroids and oral antihistamines are the treatments of choice for associated pruritus.2,3 While the time-honored home remedies of coating chigger bites with nail polish1 or applying household vinegar3 may be effective in relieving the itch, any effectiveness is not related to these measures suffocating the mite, since chiggers do not burrow into the skin.
Three erythematous chigger bites on a patient’s arm approximately 10 days after having been bitten. Note the red welt, or blister-like appearance at each of the three bite sites. Each welt measures approximately 3 to 4 mm in diameter. (Photo by CDC/M. A. Parsons)
Bann Al-Shammaa, MD, is a pediatrician at Inova Cares Clinic for Children in Falls Church, Virginia.
Amy C. Brown, MD, MHS, is an assistant professor of pediatrics in the Division of General Pediatrics at the University of Virginia School of Medicine in Charlottesville, Virginia.
References
1. Stöppler MC. Chiggers. MedicineNet.com. http://www.medicinenet.com/chiggers_bites/article.htm. Updated June 30, 2015. Accessed November 11, 2015.
2. Infestations, bites, and stings. In: Paller AS, Mancini AJ, eds. Hurwitz Clinical Pediatric Dermatology: A Textbook of Skin Disorders of Childhood and Adolescence. 4th ed. Philadelphia, PA: Elsevier Saunders; 2011:416-435.
3. Steen CJ, Carbonaro, PA, Schwartz, RA. Arthropods in dermatology. J Am Acad Dermatol. 2004;50(6):819-842.
4. Leverkus M, Jochim RC, Schäd S, et al. Bullous allergic hypersensitivity to bed bug bites mediated by IgE against salivary nitrophorin. J Invest Dermatol. 2006;126(1):91-96.
5. Doggett SL, Dwyer DE, Peñas PF, Russell RC. Bed bugs: clinical relevance and control options. Clin Microbiol Rev. 2012 Jan;25(1):164-192.
6. Said S, Jay S, Kang J, Liem WH, Jensen JL, Jeffes EW III. Localized bullous scabies: uncommon presentation of scabies. Am J Dermatopathol. 1993;15(6):590-593.
7. Erythema and urticaria. In: James WD, Berger TG, Elston DM, eds. Andrews’ Diseases of the Skin: Clinical Dermatology. 11th ed. Philadelphia, PA: Saunders Elsevier; 2011:138-154.