Microbiology, parasitology & COVID-19
Parasites-cutaneous / subcutaneous / soft tissue
Myiasis
Last author update: 1 July 2018
Last staff update: 1 June 2023 (update in progress)
Copyright: 2018-2023, PathologyOutlines.com, Inc.
PubMed Search: Myiasis[TI] pathology full text[sb]
See Also: Botfly
Table of Contents
Definition / general | Terminology | Epidemiology | Pathophysiology | Clinical features | Laboratory | Radiology description | Radiology images | Case reports | Treatment | Clinical images | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Videos | Differential diagnosis | Additional referencesCite this page: Asirvatham JR, Jorns J, Pernick N. Myiasis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/parasitologymyiasis.html. Accessed June 5th, 2023.
Definition / general
- Parasitic infestation by fly larvae (maggots) that feed on tissue (Wikipedia: Myiasis [Accessed 2 November 2018])
- Botfly / tumbu fly (Cordylobia anthropophaga and Cordylobia rodhani) and blowfly (Calliphoridae) can create an infestation even on unbroken skin (Wikipedia: Cordylobia anthropophaga [Accessed 1 October 2021])
- Larvae usually occupy skin and subcutis but potentially any organ
Terminology
- Most common: human botfly (Dermatobia hominis)
- Others: Cochliomyia hominovaroxiz, Chrysomya bezziana, Cordylobia anthrophaga
Epidemiology
- Dermatobia hominis (human botfly) is obligate Diptera that needs to feed on a host to complete its development
- Indigenous to Central and South America, occasionally reported in U.S.A. (Radiology 2001;218:517)
- Cordylobia anthropophaga (tumbu fly) is endemic in Nigeria (BMC Surg 2004;4:5)
- Occasional cases of myasis have been reported in North America (Arch Pathol Lab Med 1999;123:829, J Med Entomol 1999;36:831)
Pathophysiology
- Adult flies are usually attracted to host orifices and unattended open wounds where they lay eggs
- Some species infect living tissue (e.g. botfly)
- May lay eggs on soiled clothes, larvae may develop and can penetrate intact skin (e.g. green bottle fly)
- Botfly larvae creates a cavity with an opening (like a long neck bottle) after penetrating the skin and grow into a mature fusiform shape up to 3 cm in diameter
- A firm red subcutaneous nodule / furuncle is formed in 2 - 3 weeks
Clinical features
- May cause fever, local inflammation and bleeding and superimposed bacterial infection
- Cause abscess and rarely granulomatous response to dead larvae
- May be a secondary infection in fungating breast carcinoma
- Can mimic breast carcinoma (East Afr Med J 1999;76:115)
- Often multiple infestations in breast
- Also affects lips of breast fed infants (Int J Dermatol 2006;45:1069)
- Can be misdiagnosed as cellulitis, mosquito bites, herpes etc.
Laboratory
- Genus / species identification: comparing certain morphological structures on the larvae (spiracles, mouthparts, cephalopharyngeal skeleton, cuticular spines)
- Travel history helpful
Radiology description
- May form an ill defined mass with calcification (Radiology 2001;218:517)
- US may show a hyperechoic mass representing the larva surrounded by a hypoechoic halo representing the cavity
- Larval movement may be noted
Radiology images
Images hosted on other servers:
Various images
Case reports
- 26 year old woman with human myiasis caused by the greenbottle fly (Can Med Assoc J 1956;75:839)
- 54 year old woman with myiasis secondary to Sermatobia hominis (human botfly) presenting as a longstanding breast mass (Arch Pathol Lab Med 1999;123:829)
- 61 year old woman with Chrysomya bezziana (Breast J 2007;13:297)
- Middle aged man returned from Tanzania with multiple furuncular lesions (Pritt: Creepy Dreadful Wonderful Parasites Blog - Case of the Week 528 [Accessed 4 October 2019])
- Elderly woman with 10 pruritic burning nodules of the upper arm, face, breast, chest, trunk and legs (Pritt: Creepy Dreadful Wonderful Parasites Blog - Case of the Week 516 [Accessed 2 November 2018])
- Sheep with wound infested with maggots (Pritt: Creepy Dreadful Wonderful Parasites Blog - Case of the Week 501 [Accessed 18 July 2018])
Treatment
- Excision is not necessary but should be removed (Pritt: Creepy Dreadful Wonderful Parasites Blog - Answer to Case 528 [Accessed 4 October 2019])
- The easiest way to remove the larva is to first occlude the opening of the furuncle (through which the larva breathes) with an occlusive substance, such as petroleum jelly or soap paste
- After a short period of time, the larva can be removed by squeezing the lesion
Clinical images
Contributed by Bobbi Pritt, M.D. and Lars Westblade, Ph.D.
Furuncular myiasis
Images hosted on other servers:
Breast lesion with tumbu fly larvae
Sinuses after extraction of the larva
Extracted tumbu fly larvae
One week after extraction
Gross images
Contributed by Bobbi Pritt, M.D.
Cordylobia anthropophaga removed from elderly woman
Posterior end of Cordylobia anthropophaga
Posterior spiracles
with sinuous slits
Sheep with wound infected with blow fly larvae (Phormyia regina or Cochliomyia macellaria)
Images hosted on other servers:
Extracted from dog
Microscopic (histologic) description
- Cordylobia anthropophaga (Pritt: Creepy Dreadful Wonderful Parasites Blog - Answer to Case 516 [Accessed 2 November 2018]):
- Larva is 13 - 15 mm
- Robust form
- Cuticular spines on all body segments
- Spiracular plat; spiracles open through sinuous slits
- Weak or no discernible peritreme (rounded plate that surrounds the spiracles) or ecdysial (casting off the outer cuticle) scar
- Chronic granulomatous response, dead larvae
Microscopic (histologic) images
Contributed by Bobbi Pritt, M.D. and Lars Westblade, Ph.D.
Representative sections of skin biopsy show botfly larva
Videos
Creepy Dreadful Wonderful Parasites Case
Differential diagnosis
- Auchmeromyia (Congo floor maggot):
- Doesn't form furuncles (boil-like lesions with a live dipteran maggot within) but stays on the host only for feeding, similar to a bedbug
- It has 3 spiracular slits per side, straight, lying horizontally
- Cordylobia rodhani (Lund fly):
- Has 3 posterior spiracular slits on each side but its slits are more sinuous than Cordylobia anthropophaga
- Ticks:
- Have legs and mouth and don't burrow deeply into skin
- Tunga penetrans:
- Flea with legs, almost always involves feet, has cuticle > 20 microns, lacks a spine
