Skin inflammatory (nontumor)
Infestations
Botfly


Topic Completed: 1 December 2016

Revised: 2 April 2019

Copyright: (c) 2002-2019, PathologyOutlines.com, Inc.

PubMed Search: Botfly[TI]

Priya Nagarajan, M.D., Ph.D.
Liye Suo, M.D.
Page views in 2018: 517
Page views in 2019 to date: 410
Cite this page: Nagarajan P, Suo L. Botfly. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/skinnontumorbotfly.html. Accessed July 17th, 2019.
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: Parasites - Myiasis [Accessed 10 October 2018])
  • 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
  • In most cases, myiasis is self limited with minimal morbidity
  • 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
  • Supportive travel history
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

Images hosted on other servers:

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

Gross description
Gross images

Contributed by Bobbi Pritt, M.D.

Dermatobia hominis, the human botfly

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:S26)
  • Histologically, larvae are characterized by an undulating chitinous exoskeleton and pigmented spines (setae) protruding from exoskeleton
Microscopic (histologic) images

Contributed by Priya Nagarajan, M.D., Ph.D.

2x magnification

10x magnification

Videos

Differential diagnosis
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