Disease Information Sheets

Myiasis (fly strike)
Introduction

Myiasis (fly strike) is a condition in which the body is invaded by the larvae (maggots) of one of several species of fly. Female flies may lay eggs or larvae directly onto the skin, and larvae may then penetrate the skin or invade wounds or natural orifices such as the nose, ear or eye. Some flies attach their eggs to mosquitoes - the eggs travel under the skin when the mosquito feeds. Tropical and subtropical regions worldwide are affected, and it is more common in poorer communities. Worldwide, the most common flies that causing myiasis are the human botfly and the tumbu fly.

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How common is it?

Many people with myiasis will never seek formal healthcare, so it is difficult to know how common it is. Surveys estimate that most people living in the tropical and subtropical regions at highest risk will contract myiasis at some point in their lives. Among travellers, myiasis is usually among the five most common skin conditions, representing approximately 10% of skin cases presenting at travel clinics. People with pre-existing wounds or open skin sores are most at risk.

Are travellers and/or expat workers at risk?

Yes. People travelling to tropical and subtropical regions who are staying in rural or poor areas are at risk. 

 

What happens?

In both botfly and tumbu fly myiasis you experience a boil-like lesion 1-3 cm in diameter and up to 1 cm in height. Whereas myiasis from the tumbu fly occurs on the trunk, thigh, and buttocks, botfly lesions are on the exposed areas of the body, including the scalp, face, forearms, and legs. The “boil” has a central hole that may weep fluid, and through which the tip of the larva may be visible. It can be painful and itchy, and you may have the sense of something moving under the skin. Sometimes it causes fever, swollen glands, or swollen hands or feet. 

 

How is it treated?

Often, the preferred treatment is surgical removal of the affected area of skin under local anaesthetic. You should not:

  • Pull the larva out through the central hole – it has rows of spines which will prevent this and cause damage

  • Damage the larva or cause it to burst – parts of the larva will remain in the skin and cause a foreign body reaction

 

Alternatively, if advised to do so by a doctor, a suffocation method may be effective. This involves something like petroleum jelly, liquid paraffin, beeswax or bacon being placed over the central hole to coax the larva to emerge spontaneously over the course of several (maybe 24) hours. Once emerged sufficiently far, a pair of tweezers can be used to help with final removal. These approaches take advantage of the larva’s oxygen requirements and encourage it to exit on its own. The covering should not be occlusive (e.g. nail polish) because this may asphyxiate the larva without giving it enough time to migrate out of the skin - if the larva dies and remains in the skin it will cause a foreign body-type reaction. Alternatively or in addition, a doctor may give anthelminthic tablets or lotion. Secondary infection may need antibiotics, but antibiotics are not effective against the larvae themselves. Once the larva has exited or been removed the skin lesions usually heal rapidly.

 

How can it be prevented?
  • Wear long-sleeved clothing, trousers, a hat and proper shoes - some eggs will attach to bare skin from soil

  • Insect repellent and sleeping under a bed net are protective

  • Wash clothing in hot water and, if dried on an outside line, iron them (hot) afterwards to remove any residual eggs

  • Clean and irrigate wounds at regular intervals and keep them covered with a proper clean dressing

  • If you have a skin wound it is preferable not to sleep outside or in unscreened accommodation