Myiasis

 Infestation of a live Vertebrate (human or animal)  by the larvae of flies, characterized as cutaneous (subdermal tissue), gastrointestinal, nasopharyngeal, ocular or urinary symptoms depending on the region invaded. Often caused by two-winged (dipterous) flies.

Oral Myiasis

This condition was first observed by Ambroise Paré, the chief surgeon to King Charles IX and King Henry III, who said that maggots often infested open wounds, but the term "Myiasis" was coined by Reverend Frederick William Hope in 1840 to refer to diseases resulting from dipterous larvae which differs from those caused by other insect larvae(scholechiasis).

The name Myiasis comes from the Greek word "myia" which means "fly"

Epidemiological data on human myiasis are scant as registration of cases is not usually obligatory
Myiasis is not prevalent in any particular race & has no sex or age predilection.

Risk Factors.
The following risk factors for developing myiasis;
Traveling to endemic areas.
Tropical and subtropical countries (climatic conditions)
Children are particularly prone to the infestation ( thinner skin and lesser immunity),
elderly, psychiatric patients, alcoholics, and other helpless patients,
homeless,
Poor hygiene,
Poor socioeconomic circumstances,
presence of an open wound (preexisting suppurative lesions)
population Hits, (e.g sitting or lying on the ground and some religious rites).
Dermatologic Conditions (e.g Neuropathic ulcers,cutaneous B lymphoma, leprosy etc.)

Pathophysiology

Dermatobia hominis/human bot fly (South and Central America);  the female egg-bearing Bot fly catches a blood-sucking arthropod (e.g a mosquito), and attaches her eggs to its abdomen (means of transportation known as phoresy). When the mosquito takes a blood meal from human, the local heat induces the eggs to hatch and drop to the skin of the host and enter painlessly through the bite of the carrier or some other small trauma.This gives rise to  Furuncular myiasis.

Cordylobia anthropophaga/tumbu fly (Sub-Saharan Africa); The Tumbu fly is attracted by the odor of urine and feces. The females lay their eggs on dry, sandy soil or on damp clothing hung out to dry. The eggs hatch in 1-3 days and can survive near the soil surface or on clothes for up to 15 days waiting for contact with a suitable host. Activated by heat, such as the body heat of the potential host, they are capable of penetrating the unbroken skin with sharp mandibles resulting in  Furuncular myiasis.

Cochliomyia hominivorax/blow fly (South and Central America) The adult Female Blow flies deposit the eggs near poorly managed wounds and the larvae feed on necrotic tissue resulting in Wound Myiasis. Flies may be dispersed by prevailing winds, and infection is often acquired while resting outside during the day or may result from trauma.

Cuterebra sp (North America)
Wohlfahrtia sp (Europe, North America, and Pakistan)

Signs & Symptoms

• History of an insect bite which precedes the lesion
• In human beings, the most common site is the eye
• severe eye irritation, pain, redness,swelling of the eyelids, foreign body sensation & lacrimation are common symptoms of patients with ophthalmomyiasis.
• epistaxis, foul smell, passage of worms, facial pain, nasal obstruction, nasal discharge, headache, dysphagia, and sensation of foreign body in the nose can be seen in Nasal Myiasis.
• Myiasis is very painful, with sudden paroxysmal episodes of lancinating pain
• intense itching (Pruritus)
• at first, It looks like an ordinary large boil,often ooze (serosanguineous drainage or purulent fluid),
• a small aperture is seen covered by a crust at the apex ( central punctum ), on removal of this crust, the posterior end of the larva can be seen.
• Crawling sensation,
• Fever.

If the condition is left to itself, in due course the larva dilates the opening by means of its posterior end and eventually escapes, and crawls away and becomes a pupa.

Classification of Myiasis
a)Ecological Classification of myiasis;

• 1)Specific/obligatory Parasite dependent on host for part of its life cycle
• 2)Semispecific/facultative ;  Primary; The fly-larva is the true cause of the condition (Free living and initiates myiasis). Secondary; The fly-larvais a secondary invader (Free living and unable to initiate myiasis).  Tertiary; Free living and unable to initiate myiasis; may be involved when host is near death.
• 3)Accidental/pseudomyiasis;  Free-living larva & not able to complete its life cycle; causes pathological reaction when accidentally in contact with the host

b)Anatomical classification of myiasis
Classification by Zumpt      Classification by Bishopp               Classification by James
Sanguinivorous                     Bloodsucking                                  Bloodsucking

Dermal/subdermal                Tissue-destroying                            Furuncular
                                              Subdermal migratory                      Creeping
                                                                                                      Traumatic/wound
                                                                                                      Anal/vaginal

Nasopharyngeal                  Infestation of the head passages        Nose, mouth, sinuses
                                                                                                       Aural
                                                                                                       Ocular

Intestinal                             Intestinal/urogenital                           Enteric
                                                                                                       Anal/vaginal

Urogenital                          Intestinal/urogenital                            Bladder, urinary passages
                                                                                                       Anal/vaginal


Diagnosis
This is solely clinical;
Patients gives history of traveling to an endemic area or insect bite.
elevated immunoglobulin E, marked Eosinophilia and leukocytosis can be seen on Laboratory investigation
Dermoscopy; identifies the posterior parts of the maggot within a lesion. The examination reveals a central opening surrounded by dilated blood vessels and a yellowish structure with black barblike spines in Furuncular Myiasis.
Rhinoscopy Can be used to diagnose Nasal Myiasis.
Ultrasound confirms cases of furuncular myiasis and helps in the complete removal of the larva. A definitive diagnosis of myiasis can be achieved if larval movement is detected during the ultrasound. Color Doppler sonography has proven to be useful for the detection of the larvae when ultrasound is not able to detect it.


Differential Diagnosis
Furunculosis, Insect bite, Abscess,Cellulitis, Pyoderma, Inflamed cyst, Tungiasis, Delusional Parasitosis,
Labial cases may be confused with labial cellulitis.
Breast myiasis may be confused with periductal mastitis, benign mass with microcalcification, and inflammatory carcinoma.
Clinical and radiologic confusion with arteriovenous (AV) malformation and hemangioma occurred in one case of preauricular myiasis.
herpes simplex, helminthic cutaneous larva migrans, gnathostomiasis, sparganosis.
Hypereosinophilic syndrome,
Exaggerated arthropod reaction,
Foreign body reaction,
Lymphadenopathy,
Onchocerciasis (River Blindness)

Treatment
The following methods can be used in the treatment of Myiasis;
1)Occlusion/suffocation approaches- This method prevents the larva from having access to atmospheric Oxygen, thus forcing it to migrate to the surface. To achieve this, place petroleum jelly, liquid paraffin, beeswax, heavy oil, or bacon strips over the central punctum.

2)Systemic/topical ivermectin; An alternative treatment for all types of myiasis is oral ivermectin or topical ivermectin (1% solution), proven especially helpful with oral and orbital myiasis.

3)Surgical removal with local anesthesia; This is an invassive proceedure, anasthetize locally  with lidocaine. After removal of the larvae, antiseptic dressings, thorough cleansing, and debridement are indicated.

4)Wound Debridement for Wound myiasis; irrigate wound to eliminate the larvae from the wound or surgical removal. Application of chloroform, chloroform in light vegetable oil, or ether, with removal of the larvae under local anesthesia, has been advocated for wound myiasis.

Complications
Secondary bacterial Infection
Cellulities
Local enlarged lymph nodes (lymphoadenopathy)
fistula formation.
Cerebral infestation
Death

Oral Myiasis (Picture Credit; Reddit)

NOTES
1) Aydin E, Uysal S, Akkuzu B, et al. Nasal myiasis by fruit fly larvae: a case report. Eur Arch Otorhinolaryngol. Dec 2006;263(12):1142-3.

2) Dorland's Medical Dictionary for Health Consumers. © 2007 by Saunders, an imprint of Elsevier, Inc

3) Fabio Francesconia and Omar Lupi. Myiasis Clin Microbiol Rev. 2012 Jan; 25(1): 79–105. 

4) Hope FW. 1840. On insects and their larvae occasionally found in the human body. Trans. R. Entomol. Soc. Lond. 1840: 256–271

5) James MT. 1947. The flies that cause myiasis in man, p 1–175 U.S. Department of Agriculture miscellaneous publication no. 631. USDA, Washington, DC

6) James, WD, Berger, TG, Elston, DM. Myiasis. In: Andrews' Diseases of the Skin. 11th ed. Elsevier; 2011:438

7) Masoodi M, Hosseini K. External ophthalmomyiasis caused by sheepbotfly (Oestrus Ovis) larva: a report of 8 cases. Arch Iran Med. 2004;7:136-139.

8) Sharma H, Dayal D, Agrawal SP. Nasal myiasis: review of 10 years experience. J Laryngol Otol. May 1989;103(5):489-91.