Myiasis (ICD-11: 1G01) - Complete Clinical Coding Guide

1. Introduction

Myiasis is a parasitic infestation caused by the invasion of human tissues by fly larvae of the order Diptera. This condition represents an important public health problem, especially in regions with tropical and subtropical climates, where environmental conditions favor the development and proliferation of these insects. The disease affects millions of people annually, with higher incidence in rural populations, individuals with reduced mobility, people in situations of social vulnerability, and patients with chronic wounds.

Myiasis typically manifests through the development of nodules in affected tissues, accompanied by sensation of movement under the skin, pain, pruritus, and in more severe cases, secondary infection. Transmission occurs through different routes: ingestion of food contaminated with larvae, direct contact with infected flies, or deposition of eggs in open wounds, mucous membranes, or damaged skin. Diagnostic confirmation requires microscopic identification of Diptera larvae in tissue samples.

Correct coding of myiasis in the ICD-11 system is fundamental for adequate epidemiological registration, public health policy planning, resource allocation for prevention and treatment, as well as ensuring appropriate reimbursement for medical services provided. The code 1G01 allows international standardization of records, facilitating comparative studies and the development of more effective control strategies.

2. Correct ICD-11 Code

Code: 1G01

Description: Myiasis

Parent category: Infestations by ectoparasites

Official definition: Myiasis is a disease of the tissues caused by infection with fly larvae of the order Diptera. This condition is characterized by the development of a nodule in the affected tissue, resulting from larval penetration and development. Transmission occurs through three main mechanisms: ingestion of contaminated larvae through food or water, direct contact with infected mosquitoes, ticks, or flies that deposit their eggs, or indirect contact with fly eggs deposited on surfaces that subsequently come into contact with the human host. Diagnostic confirmation is established by unequivocal identification of Diptera larvae in a tissue sample obtained from the patient, whether by direct extraction, biopsy, or analysis of naturally expelled material.

This code belongs to the chapter of infectious diseases and parasitic infestations, specifically in the section of infestations by ectoparasites, which encompasses organisms that live on the surface or superficial layers of the human body.

3. When to Use This Code

Code 1G01 should be used in specific clinical situations where there is confirmation of the presence of fly larvae in the patient's tissues. Below are detailed practical scenarios:

Scenario 1: Furuncular Cutaneous Myiasis Patient presents with single or multiple nodular lesions on the skin, usually in exposed areas such as scalp, face, arms, or legs. The patient reports sensation of movement under the skin, intermittent pain, and pruritus. On physical examination, an erythematous nodule is observed with a central opening through which larval movement or serous fluid drainage is occasionally visualized. Extraction of the larva confirms it to be Diptera. This is the classic scenario for use of code 1G01.

Scenario 2: Myiasis in Chronic Wounds Bedridden patient or one with reduced mobility presents with pressure ulcer, venous ulcer, or traumatic wound that does not heal adequately. During dressing change, healthcare professionals identify the presence of mobile larvae in the wound bed. The patient may present with characteristic foul odor, purulent discharge, and signs of secondary infection. Removal and identification of the larvae as Diptera justifies coding 1G01.

Scenario 3: Nasal Cavitary Myiasis Patient with history of chronic rhinitis, inhalant drug use, or conditions causing nasal lesions presents with unilateral or bilateral nasal obstruction, recurrent epistaxis, facial pain, and foul-smelling nasal discharge. On rhinoscopic examination, larvae are identified in the nasal cavity. Extraction and laboratory confirmation of the larvae establish the diagnosis of nasal myiasis, coded as 1G01.

Scenario 4: Auricular Myiasis Patient with chronic external otitis, tympanic perforation, or history of auricular trauma complains of severe ear pain, sensation of movement, pruritus, and foul-smelling otorrhea. On otoscopy, larvae are visualized in the external auditory canal or tympanic cavity. Careful removal and identification of the larvae confirm the diagnosis, justifying code 1G01.

Scenario 5: Ophthalmic Myiasis Patient presents with acute ocular pain, tearing, sensation of foreign body, photophobia, and conjunctival hyperemia. On ophthalmologic examination with slit lamp, the presence of larvae is identified in the conjunctiva or, in severe cases, with intraocular penetration. This is an ophthalmologic emergency scenario requiring immediate intervention and coding as 1G01.

Scenario 6: Intestinal Myiasis Patient reports ingestion of potentially contaminated food and develops gastrointestinal symptoms such as abdominal pain, nausea, vomiting, and diarrhea. Larvae are identified in stool or vomited material. Laboratory confirmation of Diptera larvae in biological samples establishes the diagnosis of intestinal myiasis, appropriately coded as 1G01.

4. When NOT to Use This Code

It is essential to differentiate myiasis from other parasitic and dermatological conditions that may present with similar clinical manifestations:

Do not use 1G01 for pediculosis: When the patient presents with infestation by lice (Pediculus humanus capitis, corporis or Pthirus pubis), the correct code is 1G00. The main difference lies in the etiological agent: lice are adult hematophagous insects that live on the surface of the skin or hair, whereas myiasis is caused by fly larvae that invade tissues.

Do not use 1G01 for leech infestation: When there is adhesion of leeches (hirudineans) to the skin or mucous membranes, especially after exposure to contaminated water, the appropriate code is 1G02 (External hirudiniasis). Leeches are annelids that attach temporarily for feeding, unlike fly larvae that develop in tissues.

Do not use 1G01 for flea infestation: Fthiriasis or tungiasis, caused by the flea Tunga penetrans, should be coded as 1G03. Although it may cause nodular lesions similar to myiasis, the agent is an adult female flea that penetrates the skin to deposit eggs, not fly larvae.

Do not use 1G01 for bacterial abscesses: Furunculoid lesions caused by bacterial infection (Staphylococcus aureus, for example) may simulate cutaneous myiasis, but in the absence of identifiable larvae, they should be coded as bacterial skin infections.

Do not use 1G01 for sensation of parasitosis: Patients with delusional parasitosis or Ekbom syndrome present with conviction of parasitic infestation without objective evidence. These cases require appropriate psychiatric coding, not 1G01.

5. Coding Step by Step

Step 1: Assess Diagnostic Criteria

The diagnosis of myiasis requires definitive parasitological confirmation. Initial evaluation includes detailed history regarding exposure to environments with fly presence, hygiene conditions, presence of open wounds, and characteristic symptoms. Physical examination should identify lesion location, nodule characteristics, presence of larval breathing holes, and signs of secondary infection.

Mandatory diagnostic confirmation involves larval extraction and microscopic identification. Larvae should be carefully collected, preserved in 70% alcohol or 10% formalin, and sent for laboratory analysis. Identification of the Diptera species assists in therapeutic planning and prognosis, although it is not necessary for basic coding as 1G01.

Diagnostic instruments include dermoscopy for magnified visualization of larvae, ultrasonography to assess depth of tissue invasion, and in cases of cavitary myiasis, endoscopy (nasal, auricular, or gastrointestinal) for larval localization and extraction.

Step 2: Verify Specifiers

Although code 1G01 is used for all types of myiasis, clinical documentation should specify important characteristics:

Anatomical location: Cutaneous, nasal, auricular, ophthalmic, oral, genital, intestinal, or systemic. This information is crucial for therapeutic planning.

Type of myiasis: Primary (when the fly deposits eggs on intact tissue), secondary (when eggs are deposited on wounds or necrotic tissue), or accidental (when larvae are ingested).

Severity: Mild cases with single lesion and no complications, moderate with multiple lesions or involvement of adjacent structures, or severe with extensive tissue destruction, secondary infection, or compromise of vital structures.

Duration: Acute (less than one week), subacute (one to four weeks), or chronic (more than four weeks).

Step 3: Differentiate from Other Codes

Differentiation from 1G00 (Pediculosis): Pediculosis involves infestation by adult lice that remain on the skin or hair surface, causing mainly pruritus from reaction to bites. Myiasis involves larvae that invade deep tissues, causing nodules and tissue destruction. Parasite identification is definitive: adult lice versus fly larvae.

Differentiation from 1G02 (External hirudiniasis): Hirudiniasis occurs when leeches attach to skin or mucous membranes for temporary hematophagous feeding. They are easily visible, removable, and do not cause tissue nodules. Myiasis involves initially microscopic larvae that develop within tissues forming characteristic nodules.

Differentiation from 1G03 (Phthiriasis): Tungiasis or phthiriasis is caused by penetration of the flea Tunga penetrans, usually on the feet, causing a single nodular lesion with central black dot (the flea's abdomen). Myiasis can affect any part of the body, presents identifiable mobile larvae, and does not have the characteristic appearance of tungiasis.

Step 4: Necessary Documentation

Adequate documentation to support code 1G01 should include:

Mandatory checklist:

Date and circumstances of exposure when known
Precise anatomical location of infestation
Detailed description of lesions (size, number, characteristics)
Symptoms presented and duration
Method of diagnostic confirmation (direct visualization, extraction, biopsy)
Identification of larvae as Diptera (preferably with species)
Presence of complications (secondary infection, tissue destruction)
Treatment instituted (mechanical removal, pharmacological)
Response to treatment and follow-up

Photographic documentation: When possible and with patient consent, photographic documentation of lesions and extracted larvae assists in diagnostic confirmation and follow-up.

6. Complete Practical Example

Clinical Case

A 68-year-old male patient, farmer, presents to the emergency department with a complaint of "leg wound that does not heal and has bugs inside." He reports that three weeks ago he suffered minor trauma to his right leg while working in the field, causing superficial abrasion. Initially he treated the lesion with home remedies, but one week ago he noticed that the wound increased in size and began to present yellowish discharge with unpleasant odor. Three days ago he began to notice "something moving inside the wound," accompanied by intense pain that worsens at night.

On physical examination, the patient is in good general condition, afebrile, with normal blood pressure and heart rate. On the lateral aspect of the right leg, middle third region, an ulcer approximately 4 cm in diameter is observed, with irregular borders, perilesional erythema, base with granulation tissue and areas of necrosis. During detailed inspection of the lesion, multiple mobile larvae are identified (approximately 15 to 20 larvae) of whitish coloration, measuring between 8 to 12 mm in length, partially submerged in the tissue. There are no signs of extensive cellulitis or lymphangitis. The patient reports having worked barefoot and wearing clothes that exposed his legs in the days prior to the initial trauma.

Step-by-Step Coding

Criteria Analysis:

Confirmed presence of larvae: Direct visualization of multiple mobile larvae in the wound during physical examination.
Identification as Diptera: The larvae were carefully extracted with forceps, preserved in 70% alcohol and sent for laboratory analysis, which confirmed they were larvae of flies from the Calliphoridae family (blowfly), order Diptera.
Tissue invasion: The larvae were not only on the surface, but partially submerged in the tissue, causing active tissue destruction.
Identified transmission mechanism: Secondary myiasis, with egg deposition in preexisting traumatic wound.
Exclusion of other diagnoses: This is not pediculosis (absence of lice), hirudiniasis (not leeches) or phthiriasis (not Tunga penetrans flea).

Code Chosen: 1G01 - Myiasis

Complete Justification:

The code 1G01 is appropriate because all diagnostic criteria for myiasis were satisfied: parasitological confirmation with identification of Diptera larvae, evidence of tissue invasion with formation of characteristic lesion, history compatible with exposure and identified transmission mechanism. The cutaneous location on the lower limb and the context of secondary myiasis in a traumatic wound are classic presentations of this condition.

Complementary Codes:

Procedure code for removal of larvae and wound debridement
Code for antibiotic therapy if confirmed secondary bacterial infection
Code for the initial traumatic wound (external cause) if relevant for epidemiological recording
Code for guidance on prevention of new infestations

Treatment Instituted:

Mechanical removal of all visible larvae with sterile forceps, thorough wound cleaning with saline solution, debridement of necrotic tissue, application of topical ivermectin, prescription of single-dose oral ivermectin, prophylactic antibiotic therapy, daily dressings and guidance on wound protection. Outpatient follow-up scheduled in 48 hours for reassessment.

7. Related Codes and Differentiation

Within the Same Category

1G00: Pediculosis

Pediculosis refers to infestation by lice of the species Pediculus humanus (capitis or corporis) or Pthirus pubis. Unlike myiasis, lice are adult hematophagous insects that live on the surface of skin or hair, not invading deep tissues.

When to use 1G00 vs. 1G01: Use 1G00 when identifying adult lice or nits (eggs) adhered to hair strands or clothing, with predominant symptoms of pruritus from reaction to bites. Use 1G01 when identifying fly larvae invading tissues, causing nodules or tissue destruction.

Main difference: Etiologic agent (adult lice versus fly larvae) and infestation pattern (superficial versus tissue invasion).

1G02: External Hirudiniasis

External hirudiniasis occurs when leeches (annelids of the class Hirudinea) attach to skin or mucous membranes for blood feeding. It is common after exposure to river waters, lakes, or swampy areas where these organisms inhabit.

When to use 1G02 vs. 1G01: Use 1G02 when the patient presents with visible leeches adhered to skin or mucous membranes (nasal, oral, vaginal), usually after bathing in natural waters. Use 1G01 when there are fly larvae invading tissues, regardless of water exposure.

Main difference: Leeches are segmented organisms visible macroscopically that attach temporarily for feeding, while fly larvae are organisms that develop within tissues over days to weeks.

1G03: Phthiriasis

Phthiriasis or tungiasis is caused by cutaneous penetration of the flea Tunga penetrans, whose females burrow into the skin, usually on the feet, to deposit eggs. It causes a characteristic nodular lesion with a central black dot.

When to use 1G03 vs. 1G01: Use 1G03 when identifying typical nodular lesion on the feet (or occasionally hands) with central black dot, especially after walking barefoot on sandy soil. Use 1G01 when identifying fly larvae in any body location.

Main difference: Tungiasis presents a unique characteristic lesion with the female flea visible at the center, while myiasis presents multiple mobile larvae that cause nodules without the characteristic appearance of tungiasis.

Differential Diagnoses

Bacterial abscesses: Can simulate furunculoid myiasis, but do not present identifiable larvae. Aspiration reveals only sterile purulent material or bacterial growth on culture.

Subcutaneous foreign body: Can cause similar inflammatory nodule, but imaging studies (ultrasonography, radiography) identify non-biological material, and there is no movement or larvae.

Cutaneous leishmaniasis: Causes chronic ulcers that may be confused with myiasis in wounds, but microscopic identification reveals protozoa (Leishmania), not insect larvae.

Sporotrichosis: Fungal infection that causes subcutaneous nodules, but without presence of larvae and with identification of Sporothrix on culture.

8. Differences with ICD-10

In the ICD-10 system, myiasis was coded as B87, with specific subdivisions for different types:

B87.0 - Cutaneous myiasis
B87.1 - Wound myiasis
B87.2 - Ocular myiasis
B87.3 - Nasopharyngeal myiasis
B87.4 - Auricular myiasis
B87.8 - Myiasis of other sites
B87.9 - Myiasis, unspecified

In ICD-11, the code was simplified to 1G01, encompassing all forms of myiasis under a single main code. Anatomical and type specifications are now documented through extensions and additional specifiers, when necessary, or in detailed clinical description.

Main changes:

Simplification of coding with single code
Greater flexibility in documenting specific characteristics
Clearer integration into the category of ectoparasite infestations
Alignment with standardized international terminology

Practical impact: The change simplifies the coding process, reducing selection errors among subcategories. However, it requires more detailed clinical documentation to specify location and type of myiasis, information that was previously implicit in the code. Health information systems needed to adapt to capture these specifications through additional fields or code extensions.

9. Frequently Asked Questions

1. How is a definitive diagnosis of myiasis made?

Definitive diagnosis requires visual identification and laboratory confirmation of fly larvae from the order Diptera in affected tissues. Clinically, the physician may suspect myiasis based on the characteristic presentation of nodules with a central opening, sensation of movement reported by the patient, and history of exposure. Confirmation occurs through extraction of the larvae, which should be preserved in 70% alcohol or 10% formalin and sent for parasitological analysis. The laboratory identifies the morphological characteristics of the larvae, including body segmentation, respiratory spiracles, and oral hooks, confirming they are Diptera and, when possible, identifying the specific species.

2. Is treatment available in public health systems?

Yes, myiasis treatment is widely available in public health systems in most countries. The main treatment consists of mechanical removal of larvae, a procedure that can be performed in basic health units with simple materials (forceps, antiseptic solution). Medications such as oral ivermectin, when necessary, are generally part of the essential medicines lists of many health systems. More complex cases, such as ophthalmic myiasis or with extensive tissue destruction, may require referral to specialized services, but basic treatment is accessible in primary care.

3. How long does treatment last?

The duration of treatment varies according to the severity and location of the infestation. In simple cases of cutaneous myiasis with few larvae, complete mechanical removal may resolve the problem in a single consultation, with follow-up in 48-72 hours to confirm that no residual larvae remain. When oral ivermectin is used, the effect occurs in 24-48 hours, causing death of the larvae, but complete wound healing may take weeks. In cases of myiasis in chronic wounds with secondary infection, treatment may extend for several weeks, including regular dressing changes, antibiotic therapy, and care of the underlying wound. Severe cases with tissue destruction may require months of follow-up, including possible need for reconstructive surgery.

4. Can this code be used in medical certificates?

Yes, code 1G01 can and should be used in medical certificates when myiasis diagnosis is confirmed. Myiasis is a condition that may justify work leave, especially in occupations involving contact with food, public service, or when the location of the infestation interferes with work activities. The duration of leave varies according to severity: mild cases may require only a few days for initial treatment, while severe cases with complications may justify prolonged leave. It is important to adequately document the diagnosis, treatment, and functional limitations resulting from the condition to support the medical certificate.

5. Can myiasis be fatal?

Although rare, myiasis can be fatal in specific situations. Most cases are benign and resolve with appropriate treatment. However, myiasis in critical locations such as the nasal cavity with invasion of paranasal sinuses and intracranial structures, ophthalmic myiasis with ocular perforation, or myiasis in immunosuppressed patients can cause serious complications. Extensive tissue destruction can lead to hemorrhage, serious secondary infections (sepsis), or compromise of vital structures. Debilitated patients, bedridden patients, or those with multiple comorbidities present greater risk of fatal complications, especially when diagnosis is delayed.

6. How can myiasis be prevented?

Prevention of myiasis is based on measures of personal and environmental hygiene. It is recommended to keep wounds clean and properly covered, avoid exposure of open wounds to environments with flies, wear clothing that protects the skin in rural or high-risk areas, maintain good personal hygiene, especially in bedridden patients or those with reduced mobility. In the environment, it is essential to control flies through window screens, judicious use of insecticides, proper management of garbage and organic waste, and control of animals that may attract flies. Patients with chronic wounds should receive regular dressing changes and appropriate supervision. Caregivers of vulnerable patients should be trained to identify early signs of infestation.

7. Can all flies cause myiasis?

No, only flies of certain species from the order Diptera can cause myiasis in humans. The main families involved include Calliphoridae (blowflies), Sarcophagidae (flesh flies), Oestridae (botflies), and Muscidae. Some species are obligate parasites, depositing eggs only on living hosts, while others are facultative parasites, preferring decomposing organic matter but able to infest wounds. The common housefly (Musca domestica), although a disease vector, rarely causes myiasis. Identification of the fly species is important epidemiologically and may influence treatment, although it does not change the ICD-11 code used.

8. Can children develop myiasis?

Yes, children can develop myiasis, and in some regions they represent a significant proportion of cases. Young children are vulnerable due to greater exposure to outdoor environments, lower ability to communicate symptoms early, and in some situations, inadequate hygiene conditions. Myiasis in children can occur on the scalp, ears, nose, and skin. Cases of intestinal myiasis can occur through accidental ingestion of contaminated food. Treatment in children follows the same principles as in adults, with adjustment of medication doses according to weight and age. Prevention in children requires adequate supervision, maintenance of personal hygiene, and protection against exposure to flies in high-risk environments.

Conclusion:

Proper coding of myiasis using ICD-11 code 1G01 is essential for accurate epidemiological recording, public health planning, and appropriate clinical management. This article provided practical guidance for correct case identification, differentiation of similar conditions, and adequate documentation. Myiasis remains an important health problem in many regions, and international standardization through the ICD-11 system facilitates data comparison, development of prevention strategies, and improvement in the quality of care for affected patients.

External References

This article was prepared based on reliable scientific sources:

References verified on 2026-02-03

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