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Myiasis

Last updated Dec. 1, 2018

Approved by: Maulik P. Purohit MD, MPH

CDC

The most common flies that cause Myiasis in human beings are Dermatobia hominis (human botfly).


What are the other Names for this Condition? (Also known as/Synonyms)

  • Blow fly Strike
  • Fly-Blown
  • Maggot Infestation

What is Myiasis? (Definition/Background Information)

  • Myiasis is primarily a skin disease caused by the fly larva (maggots). The fly larvae cause disease in humans and other vertebrate animals by feeding on the tissues. The infection is characterised by a painful, itchy boil-like skin lesions that contains the organisms within it
  • The most common flies that cause Myiasis in human beings are Dermatobia hominis (human botfly) and Cordtlobia anthropophagi fly (tumbu fly). The condition is most commonly found in tropical and subtropical areas
  • The main risk factors for Myiasis are poor hygiene and sanitary conditions, advanced age, psychiatric illness, children with mental retardation, and those travelling to the tropical and sub-tropical regions
  • The signs and symptoms of the infection depend upon the specific body part involved. A diagnosis is typically made by identifying the fly larvae and maggots in the affected body parts
  • Removal of the larva is required to treat Myiasis in most of the cases. The condition is easily curable once the larvae are removed from the wound/body
  • Individuals should adopt preventive methods when travelling to high-risk regions; especially those having untreated and open wounds

Based on the place of infection, Myiasis is classified into the following types:

  • Cutaneous Myiasis:
    • Wound Myiasi
    • Furuncular Myiasis (follicular): The larva remains at a single spot causing a boil-like lesion     
    • Creeping Myiasis, where the larvae burrows into the skin
  • Nasopharyngeal Myiasis - the nose, sinuses, and pharynx are infected
  • Opthalmomyiasis: The eyes, orbits, and periorbital tissues are involved
  • Intestinal, gastric, and rectal Myiasis, where the parts of the digestive system are infected
  • Urogenital Myiasis: It involves the urogenital system (urinary and the genital system)
  • Auricular Myiasis, when the ears are infected
  • Hematophagus Myiasis: This is a very rare disease commonly found in infants younger than 9 months who are living in rural and endemic areas, where the furuncular lesions occurs on the face

Classification of Myiasis based on the relationship between host and the parasites:

  • Obligatory: The parasite cannot complete its life-cycle without a parasitic phase. It may be further classified into the following types:
    • Specific
    • Semi-specific
    • Opportunistic
  • Facultative, Incidental, and Accidental Myiasis: It is also known as Pseudomyiasis in which a free living larva accidentally enters the host, like by swallowing eggs or larvae with food 

Who gets Myiasis? (Age and Sex Distribution)

  • Myiasis can affect any individual irrespective of their age, race, community, or gender
  • It is more common amongst people living in the tropical and subtropical parts of the world
  • Hematophagous Myiasis is largely found in infants who are less than 9 months old, living in rural and endemic areas

What are the Risk Factors for Myiasis? (Predisposing Factors)

Following are the risk Factors associated with Myiasis:

  • Advanced age
  • Poor hygienic conditions
  • Psychiatric illness
  • Alcoholism
  • Diabetes
  • Vascular diseases causing obstruction in blood flow
  • Travelling to tropical and subtropical areas that include Central America, South America, Africa, and the Caribbean islands
  • Season: Myiasis attack is very common during spring and summer season
  • Low socioeconomic status: Individuals belonging to this group are the most common victims of Myiasis, because of the poor sanitation and hygiene status
  • Children living near or swimming in stagnant water are prone to Aural Myiasis
  • Farmers and shepherds, who are in close contact with goat, sheep, and cattle, are more susceptible to this disease, because they (domestic animals) are the main carriers of Myiasis
  • Children with mental retardation who cannot take care of themselves
  • Those with open and untreated wounds are at high risk for developing Myiasis

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider. 

What are the Causes of Myiasis? (Etiology)

Typically, Myiasis is a skin infection caused by fly larva (maggots) that affects human beings and other vertebrate animals. The most common flies that cause the infection in human beings include:

  • Dermatobia hominis (human botfly)
  • Cordtlobia anthropophagi fly (tumbu fly)

The various methods by which the larvae can enter the human body include:

  • The eggs of the fly gets attached to the underside of a female mosquito, and penetrates the unbroken skin while the mosquito feeds
  • The eggs may also get attached with the clothing or towel left out in the open to dry and then enter the human skin
  • The larva can enter the body through open wounds and lesions, or even through unbroken skin
  • Some enter the human body through the nose and ears
  • Larvae can reach the stomach and intestine when they are accidently swallowed with food; this leads to Gastric or Intestinal Myiasis

A boil-like lesion then develops rapidly at the infected site, which is red in color and tender to touch. This is accompanied by shooting pains caused by the movement of the organisms inside the wound.

What are the Signs and Symptoms of Myiasis?

The signs and symptoms of Myiasis differ as per the location of the infection and include the following:

  • Cutaneous Myiasis:
    • Painful and slow developing ulcers
    • Sores and boils that lasts for a prolonged period
  • Nasal Myiasis:
    • Nose congestion
    • Nose blockages
    • Nose irritation     
    • Fever
    • Facial edema (swelling of the face)
  • Aural Myiasis:
    • Crawling sensation in the region
    • Buzzing noises
    • Hearing disturbances  
    • Rarely, it may be accompanied by smelly discharge
  • Opthalmomyiasis:
    • Severe irritation in the eye
    • Redness of the eye  
    • Swelling of the eyes

The general signs and symptoms of Myiasis may include:


  • Boils
  • Vision abnormalities
  • Diarrhea
  • Vomiting

How is Myiasis Diagnosed?

The diagnosis of Myiasis involves the following tests and exams:

  • A complete evaluation of medical history and a thorough physical exam
  • During the patient's evaluation, the emphasize may be on:
    • Details of any recent visits to the tropical and sub-tropical areas
    • Patient's socioeconomic and hygiene status
  • The following tests are usually done:
    • Blood tests, such as complete blood count, which may show increased white blood cells
    • Ultrasound of the affected region to localize the larva and extent of involvement. This can help enable the surgeon to remove the larva without damaging other important parts like the facial nerve
    • MRI scan in case of brain, face, and orbit Myiasis    
    • Biopsy of the wound may be performed: A small sample of the tissue is removed and sent to a lab for examination under the microscope 

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis. 

What are the possible Complications of Myiasis?

The following are the complications associated with Myiasis:

  • The patient can develop allergies, if the larvae is not removed completely
  • Secondary pyogenic (pus) infection
  • Pneumocephalus: The presence of air or gas in the cranial cavity
  • Extensive erosion of the nose, face, and eyes can occur because the larvae feeds on the mucous membranes in these areas
  • Meningitis: An inflammation of the protective coverings of the brain
  • Pin-site Myiasis: It is a very rare complication that can occur when an individual with spinal fracture is fixed with a pin to stabilize the fracture. In such cases, proper norms of sterilization must be followed to avoid infection

Death may also occur when Myiasis is left unattended and untreated.

How is Myiasis Treated?

The treatment of Myiasis includes the following procedures:

  • Removal of the larvae is recommended in most cases of Myiasis, either by surgery or using other techniques (such as suffocation and occlusive techniques)
  • In suffocation and occlusive techniques, a material such as petroleum jelly and liquid paraffin is applied over the punctum where larvae are present. Larva that is deprived of oxygen will exit from the body on their own
  • Proper and hygienic cleaning methods should be strictly followed for wound cleaning, after removal of the larva
  • Sometimes, medications are also prescribed, depending on the type of Myiasis. This includes the use of the drug ivermectin for oral and orbital Myiasis

However, typically the fly larvae are removed only through surgery and no medications are specifically available for treatment of the infection. 

How can Myiasis be Prevented?

The following precautionary measures need to be followed to prevent or reduce the incidence of Myiasis:

  • Extra care should be taken while travelling to tropical and sub-tropical areas
  • Try to cover all portions of the skin using long-sleeved shirts, full trousers, and socks to protect your body and skin from fly bites
  • Use insect repellents to prevent the insects from entering the residence areas
  • Insecticides containing organophosphorus can be sprayed around the area
  • Window screens and mosquito nets can used to prevent insects and flies from entering one’s home
  • Iron or heat press the clothes (that are dried in open air) before wearing them, because any insect or fly attached to the clothes will be destroyed
  • Wounds should always be covered to protect from superimposed infections
  • Follow personal hygiene habits such as:
    • Washing hands before and after every meal
    • Proper sanitation methods
    • Washing clothes regularly       
    • Drying the clothes under direct hot sun and in open spaces
  • The growth of adult flies must be effectively controlled and methods for eradication followed on a regular basis

What is the Prognosis of Myiasis? (Outcomes/Resolutions)

  • Myiasis is not a fatal condition, however the prognosis depends upon the region of infection
  • The infection is generally curable after the larvae is removed from the wound

Additional and Relevant Useful Information for Myiasis:

The following DoveMed website link is a useful resource for additional information:

https://www.dovemed.com/healthy-living/skin-disorders/

What are some Useful Resources for Additional Information?


References and Information Sources used for the Article:


Helpful Peer-Reviewed Medical Articles:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 4, 2015
Last updated: Dec. 1, 2018