THE PARASITIC HUMAN botfly is associated with myiasis, the infection of a fly larva (maggot) in human tissue.1 The most common species, Dermatobia hominis (human botfly), is a large, free-roaming fly resembling a bumblebee found in tropical and subtropical areas, particularly Central and South America.1,2 During one stage of its life cycle, its larvae develop in the subcutaneous tissue of a warm-blooded host, most commonly cattle and dogs, causing a raised lesion in the skin that becomes hard and sometimes painful.2
People rarely acquire this parasite in the US, but those who travel to areas where the botfly is endemic are at risk.1 Because myiasis is not spread from person to person, the only way to contract it is through exposure to infested flies, ticks, and mosquitoes.1
How infestation occurs
To reproduce, female botflies lay eggs on blood-sucking arthropods such as mosquitoes or ticks. The infested arthropods deposit larvae from the eggs when they bite a human or other mammal. A botfly larva enters the host's skin through the bite wound or a hair follicle and burrows to subcutaneous tissue.2 It grows there for 6 to 10 weeks, breathing through two posterior spiracles that lie flush with the host's skin. The resulting boil-like lesion, or furuncular myiasis, is commonly misidentified as a methicillin-resistant Staphylococcus aureus (MRSA) infection and treated inappropriately with antibiotics.3
Patients with botfly infestation often describe feeling movement under the skin as the larva feeds and grows, but it does not travel in the body. Once mature, the larva drops to the ground and pupates in soil.
Signs and symptoms include a hard, raised lesion and localized erythema, pain, and edema.2,4 Due to the host's inflammatory response, the lesion may contain purulent exudate.2 Other signs and symptoms include night sweats, nausea, pruritus, and symptoms related to the lesion's location. For example, a lesion near the airway can cause dysphagia and dyspnea.3,4
Treatment options and nursing care
Removing the botfly larva is the only treatment; antibiotics and other medications are ineffective, although corticosteroids may be prescribed to manage pruritus.2,3
Suffocation of the botfly is the most common, least painful form of removal. The larva can be suffocated by covering the openings it uses to breathe with an occlusive dressing or substance such as petroleum jelly.5 Another suffocation method includes placing any type of meat on top of the lesion for 48 hours in hopes that the larva will protrude into the meat and away from the human host.3 After 24 to 48 hours, the larva will begin to emerge and can be extracted by applying pressure to the site or using forceps.3,5
Other removal techniques are likely to be more painful because the larva has spines that anchors it in the wound.2 In a clinical setting, local anesthesia can be used to paralyze the larvae before extracting.2,3 If the late stages of growth include ocular involvement or a pediatric scalp infection, larvae need to be surgically removed by a healthcare provider in an outpatient or clinic setting.
Most reported cases are handled by patients themselves, but the extraction may be extremely painful for those who lack medical knowledge. In addition, patients may succeed in only partially removing the larva, leading to a secondary infection.5
After larva removal, the wound should be cleaned daily with soap and water to prevent a secondary infection.1 Antibiotics may be considered.2 Wounds typically heal without scarring in 1 to 2 weeks.2
Patient teaching
Teach patients traveling to tropical areas where botflies are endemic how to recognize a botfly skin lesion and to seek medical attention if one appears. In addition, advise them to take the following preventive steps.1-3
* Review and follow the CDC's Traveler's Health guidelines for the intended destination, available at http://wwwnc.cdc.gov/travel.
* When spending time outside, cover your skin to limit the area open to bites from flies, mosquitoes, and ticks, and use insect repellent.
* When indoors, protect yourself by using window screens and mosquito nets.
Recognizing suspicious lesions
Because botfly infection is rare, it is often misidentified as a MRSA infection. To prevent inappropriate or delayed treatment, ask about recent travel history when assessing patients with a suspicious lesion. Educating patients to recognize a botfly lesion will also help speed up the treatment process.
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