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

• Creeping Myiasis

What is Migratory Myiasis? (Definition/Background Information)

• Myiasis is primarily a skin disease caused by several species of parasitic fly larva (of taxonomic order Diptera). The fly larvae (maggots) cause disease in humans and other vertebrate animals by feeding on the tissues. The infection is usually characterized by a painful, itchy, boil-like skin lesion that contains the parasite within it
• Migratory Myiasis or Creeping Myiasis is a form of cutaneous myiasis that develops when the maggots buried beneath the skin, start to move randomly through skin burrows, leaving behind a visible trail of wavy or zigzag pattern skin lesions. In nearly all cases, the causative parasites are larvae of the horse bot fly (Gasterophilus sp.) and cattle bot fly (Hypoderma sp.)
• Migratory Myiasis can cause severe and extensive tissue destruction and serious complications depending on the body systems affected. The preferred treatment is a surgical excision to remove the larva; however, this may be challenging if the larva is buried deep within the body. Even though the infestation may be self-limiting, severe cases can result in fatalities

Who gets Migratory Myiasis? (Age and Sex Distribution)

• Migratory Myiasis may be observed in individuals of any age group (children and adults are affected)
• Both males and females are affected, and no gender preference is noted
• Worldwide, individuals of all racial and ethnic groups may be affected

The horse bot fly is found across the world, and the cattle bot fly is more commonly found in Asia (specifically China) and parts of Europe.

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

The following are the risk factors for Migratory Myiasis:

• Living in or traveling to the endemic regions
• Handling horses and other animals that are infected by bot flies
• Handling infected cattle, such as by farmers and farmhands, children who interact with farm animals

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 Migratory Myiasis? (Etiology)

Migratory Myiasis is a parasitic infection caused predominantly (almost always) by the following two species of insect larvae:

• Horse bot fly (Gasterophilus sp.): Eggs on skin produce larva that produces a superficial skin lesion (like a furuncular lesion); the larva then buries itself into the subcutaneous layers and starts to migrate. Most infections arise from handling animals such as horses
• Cattle bot fly (Hypoderma sp.): People who handle cattle (including yaks), such as on farms, are at risk. Most cases are seen in the colder months. The fly lays eggs on human hair, or when larva from animal fur moves to humans via contact with bare hands. After deep (subcutaneous) penetration, a furuncular lesion forms

It is important to note that humans are accidental hosts for the horse and cattle bot flies. Also, in human skin, these parasitic larvae cannot complete their lifecycle.

What are the Signs and Symptoms of Migratory Myiasis?

The signs and symptoms of Migratory Myiasis may vary from one individual to another and is based on the type of larva species causing the infection.

Horse bot fly larva signs and symptoms:

• After invasion into the subcutaneous layers, the larva causes a very itchy inflammatory skin lesion with raised borders
• Path of migration: The lesion increases in length in a curvy manner depending on how the larva moves under the skin. The trailing end of the lesion gradually deflates and fades
• The rate of migration per day may be between 1 cm to 30 cm, and the larva may live for many months
• The path of migration may present redness, swelling, and pus-filled blisters and nodules
• The maggot infestation may end suddenly and spontaneously, with the lesion discharging large amounts of pus (in many cases)
• Rarely, the larva may move to the lungs and form a nodule in the lung tissue

Cattle bot fly larva signs and symptoms:

• Following invasion into skin, the lesion develops to a large painful red boil when the larva starts to move randomly. The redness may be noted for many days
• The lesions formed, as the larva migrates, are tender with poorly-defined boundaries and between 1 to 5 cm in size. A pricking and sometimes burning itchy sensation may be noted
• Along the path of travel, numerous itchy red papules may form. Some individuals may present nodules on the neck or chest. Once the larva moves from a site, it turns into a yellowish skin patch
• The rate of migration per day is 2-30 cm when the larva is in the subcutaneous tissues; if superficially located, the speed may be even 2.5 to 3 m per day
• Following this, the larva may move into the upper skin layers forming a tender red lesion that progressively increases in size. From the center of this lesion, discharge of fluids, blood, and pus may occur. The lesion is very itchy, but pain is generally absent
• The movement of the larva may be felt; the larva grows in size, and finally rupturing the skin, breaks out to complete its lifecycle. The point of exit may be the head and neck region, including face and scalp, or the arms or legs
• In a majority of cases, the larva may die inside the body

Hypoderma larva (cattle bot fly) migration paths are more linear than Gasterophilus larva (horse bot fly) migration paths, which are often very random and wavy.

Additionally, systemic signs and symptoms, such as high-grade fever, muscle and joint pain, and limb paralysis that may be temporary may be noted.

How is Migratory Myiasis Diagnosed?

Migratory Myiasis is diagnosed on the basis of the following information. The diagnostic techniques used may vary based on the specific type of causative parasite.

• Complete physical examination and a thorough medical history evaluation, with emphasis on recent travel and/or handling of animals which may be infected
• Assessment of signs and symptoms, including a visual examination of the lesion (usually mineral oil may be used on the lesion to visualize the larva)
• Laboratory tests: Blood tests, such as complete blood count and peripheral blood smear
• Polymerase chain reaction (PCR) test
• Imaging studies, as necessary: Ultrasound scan of the affected region to localize the larva and extent of involvement. This can help enable the surgeon to remove the larva without damaging the surrounding tissues

A differential diagnosis to eliminate other similar skin conditions may be needed before arriving at a definitive diagnosis. These include:

• Cutaneous larva migrans
• Gnathostomiasis
• Sparganosis

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 Migratory Myiasis?

The complications of Migratory Myiasis may be significant, and often unpredictable, due to migration of the parasitic larvae across the human body. The condition may affect the eye, ear, lung, nervous system, or any other body systems presenting associated complications.

The complications may include:

• Severe emotional stress
• Severe pain and discomfort
• Secondary infection of the abscess; rupture of the abscess
• Cellulitis: Skin infection that involves the deeper skin tissues
• Ascites (fluid in the abdomen)
• Pleuropericardium and hemopericardium
• Scrotal edema in males
• Meningitis and intracerebral invasion
• Hypereosinophilia
• Paralysis
• Severe inflammatory response to dead larvae or parts of larvae, especially during its removal
• Sepsis, which can be life-threatening

How is Migratory Myiasis Treated?

The treatment for Migratory Myiasis may involve the following measures:

• Surgical extraction of the larva from affected skin region:
  • Surgical incision and removal after precisely locating the larva is almost always undertaken
  • However, if the larva buries deep into tissues, surgery may be challenging
  • Care must be taken to excise the complete larva from the abscess; breaking or rupturing the larva while extracting it, can result in severe inflammatory reactions
• Dressing and wound care, as required
• A course of prescription oral medications (albendazole or ivermectin) may be prescribed, if surgery is not feasible

Examination and identification of the larva following removal from skin tissues may be undertaken.

How can Migratory Myiasis be Prevented?

Migratory Myiasis may be prevented by considering the following measures:

• Maintaining basic personal and community hygiene and proper sanitation is highly important, particularly in the endemic zones
• Washing hands after handling farm animals, especially horses and cattle
• Extra care should be taken while travelling to the endemic regions
• Try to cover all portions of the skin using long-sleeved shirts, full trousers, and socks to protect the body and skin from insect bites
• Use insect repellents to prevent the insects from entering residences
• Seek medical attention for any changes in skin; especially, after visiting known endemic regions
• The growth of adult flies must be effectively controlled and methods for eradication followed on a regular basis

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

The prognosis of Migratory Myiasis is good, if the larva or larvae can be located and removed completely from the body.

• In many individuals, the condition may be self-limited, although it can cause severe complications as the larva migrates, which may even be fatal
• In some individuals, rupture of an abscess containing the larva may lead to a severe inflammatory response
• Additionally, life-threatening sepsis may occur due to secondary infections

Additional and Relevant Useful Information for Migratory Myiasis:

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

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