Skin - nontumor
Infestations
Botfly

Author: Priya Nagarajan, M.D., Ph.D., Liye Suo, M.D. (see Authors page)

Revised: 30 December 2016, last major update December 2016

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PubMed Search: Botfly

Cite this page: Botfly. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/skinnontumorbotfly.html. Accessed October 23rd, 2017.
Definition / general
  • Infestation by larvae of the human botfly (Dermatobia hominis) and tumbu fly (Cordylobia anthropophaga) are common causes of myiasis
  • Skin lesions are due to growth and burrowing of the larva, which feed on the host tissues, liquid body substance or ingested food
  • Other cutaneous locations such as eye, mucosa, breast and gastrointestinal tract can be affected (West Afr J Med 2013;32:149)
Terminology
  • Human botfly, Dermatobia hominis, myiasis
Epidemiology
  • Tropical and subtropical areas with warm and humid climate, such as the Americas, Central and South Africa are most common (CDC)
  • Rarely seen in the continental United States; most commonly seen in travelers
Sites
Etiology
Life cycle:
  • In endemic areas, D. hominis flies typically lay their eggs on mosquitoes, which in turn deposit them on warmblooded mammals such as humans
  • In wound myiasis, an open wound or orifice attracts flies to deposit their eggs
  • The eggs hatch in the skin, stimulated by the heat from the host
  • The larvae mature through 3 stages during which they develop posterior spines, which makes them difficult to dislodge
  • 5 - 10 weeks after deposition, the mature third stage larvae drop from the host and complete the pupal stage in soil
  • Adult botfly emerges from soil after 4 - 11 weeks
Diagrams / tables

Images hosted on other servers:

Life cycle of D. hominis

Clinical features
  • May clinically resemble insect bites, allergic reactions, herpes virus or molluscum contagiosum
  • Furuncular myiasis: A pruritic papule that develops within 24 hours of penetration, enlarging to 1 - 3 cm in diameter
  • These lesions can be painful or tender and may become crusted and purulent
  • In wound myiasis, the larvae are deposited in a suppurating wound or on decomposing flesh
  • Creeping (or migratory) cutaneous myiasis resembles cutaneous larva migrans, but the larvae migrate more slowly, persist for longer (often months) and are larger than helminth larvae
  • Secondary infection by bacteria may be a complication
Diagnosis
  • Thorough physical examination and documentation of relevant exposure history, including travel to warm humid climates
  • Surgical extraction and histologic examination can confirm the presence of larvae
  • In most cases, myiasis is self limited with minimal morbidity
Case reports
Treatment
  • The major reasons for treatment are reduction of pain, cosmesis, psychological relief and to prevent secondary infections
  • Surgical extraction of larvae is the key treatment
  • Systemic medication: broad spectrum antibiotics, oral steroid and ivermectin may also be used (Ocul Immunol Inflamm 2011;19:444)
Clinical images

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Close up, adult and larvae of D. hominis

Fig 1: larvae with anterior end is wider than posterior end;
2: larvae has 2 curved oral hooks on anterior end (for grasping and tearing tissue for feeding);
3: parallel concentric rows of posterior pointing spines on body

Microscopic (histologic) description
  • Histologically, a mixed acute and chronic inflammatory infiltrate composed of varying proportions of neutrophils (early), lymphocytes, plasma cells and histiocytes (late), admixed with eosinophils (J Am Acad Dermatol 2004;50(2 Suppl):S26)
  • Histologically, larvae are characterized by an undulating chitinous exoskeleton and pigmented spines (setae) protruding from exoskeleton
Microscopic (histologic) images

Images hosted on PathOut server:

Courtesy of Priya Nagarajan, M.D., Ph.D.:

2x magnification

10x magnification

Differential diagnosis