An Infant With Furuncular Myiasis: Human Botfly Infestation
During our recent medical mission trip to a small village in the Orange Walk District of Belize, an 8-month-old girl, accompanied by her mother, presented to us with a history of a rash on her trunk and left arm for more than a month.
The mother stated that the rash originally had looked like 3 separate mosquito bites that grew and started to appear infected. The mother had squeezed the 1.5-cm lesion on her daughter’s forearm, resulting in a thick yellowish-white discharge mixed with a small amount of blood. The infant had been scratching at the lesions and had not been sleeping well at night. There were no symptoms such as fever, swollen lymph nodes, or loss of appetite. The girl is otherwise healthy and is up-to-date on immunizations.
On physical examination, 2 erythematous lesions with excoriation were noted, each with a central punctum, a 1-cm lesion on her left upper trunk and a 2-cm lesion on her left forearm (Figure 1). There also was a 1-cm erythematous nodule on her left lower trunk (Figure 2). The mother gently squeezed a small amount of serosanguineous fluid from the lesion on the baby’s forearm during the examination.
Figure 1. An 8-month-old Belizean girl presented this 2-cm lesion on her left forearm.
The infant received a diagnosis of furuncular myiasis, a cutaneous infestation of humans and vertebrate animals by the developing larvae (maggots) of certain species of two-winged flies. The larvae feed on the living or dead tissue of its host.1-3 Furuncular myiasis is seen most commonly in tropical regions of the world, including Central and South America and sub-Saharan Africa.
Botfly Infestation
The human botfly (Dermatobia hominis) is responsible for furuncular myiasis in Central and South America. These flies (Figure 3) do not lay eggs directly on the host; rather, they lay their eggs on mosquitoes, ticks, or other blood-sucking insects, which in turn bite a warm-blooded host.1 About one week after the blood-sucking insect bites an animal, the warmth of the host’s body triggers the eggs to hatch. Within 20 days of hatching, the larvae drop onto an animal or human, where they enter the skin, usually painlessly.
Figure 2. A 1-cm erythematous nodule was present on the infant’s left lower trunk.
Symptoms typically develop within 2 days and include an initial raised erythematous papule, which continues to evolve into a larger boil-like nodule, often with serous or serosanguineous discharge from a central punctum.3 Sometimes the respiratory spiracle located on the posterior aspect of the larva may be seen protruding from the center of the lesion. Each lesion contains only one human botfly larva.3 Many patients report nocturnal pruritus, pain, and a sense of movement at the site of infestation, which can lead to insomnia. If left untreated, the larva stays with the host until it matures into its next stage, then emerges and drops to the ground to pupate in the soil. The larva may take 5 to 10 weeks or longer to mature before spontaneously exiting from its host.3 Most patients are not willing to wait for the larva to emerge on its own without treatment.
Treatment
The goal of treatment is to remove the larva while keeping it completely intact. There generally are 3 ways to remove larvae: surgical removal (during which care must be taken, because the larvae have spines and hooks that make simple extraction difficult); local application of a toxic substance to larvae, such as 1% ivermectin; and localized hypoxia using materials such as mineral oil, petroleum jelly, glue, nail polish, chewing gum, or pork fat. In the latter method, the larva is asphyxiated and forced to reposition, usually allowing it to be visualized and manually extracted with forceps.2,3
When using toxic substances and asphyxiation methods, it is possible for the larva to die and become trapped in the skin.3 If other methods of larval extraction are contraindicated due to, for example, the presence of cellulitis, a venom extractor reportedly has been used successfully to remove a larva from a patient’s leg lesion.2
Lesions typically heal well after larvae have been successfully removed. However, if any part of the larva remains inside the body, inflammation and foreign-body reaction will occur, along with a possible secondary bacterial infection. Appropriate oral antibiotics are indicated if a bacterial infection is present.3
Figure 3. The larva of the human botfly, Dermatobia hominis, and the female adult botfly. (Larva: public domain photo by Capt. R. Goodman, U.S. Air Force. Adult: public domain photo by Jonathan M. Eibl, Systematic Entomology Laboratory, U.S. Department of Agriculture)
Prevention
Persons who live in or travel to rural botfly-endemic areas should wear insect repellent, hats, and garments that cover the arms and legs to protect their skin. The use of mosquito nets during sleep is recommended. Proper sanitation and hygiene practices also are recommended.
Although furuncular myiasis is not commonly seen in the United States, increased ecotourism to Central and South America likely will lead to more cases in returning U.S. travelers. Physicians and other health care providers should keep furuncular myiasis in the differential diagnosis of a boil-like lesion in a patient returning from an endemic area.
It is important to accurately diagnose and treat cases of furuncular myiasis to avoid secondary complications in affected patients and to prevent widespread invasion of myiasis-causing flies.
References:
1.Bhandari R, Janos DP, Sinnis P. Furuncular myiasis caused by Dermatobia hominis in a returning traveler. Am J Trop Med Hyg. 2007; 76(3):598-599.
2.Boggild AK, Keystone JS, Kain KC. Furuncular myiasis: a simple and rapid method for extraction of intact Dermatobia hominis larvae. Clin Infect Dis. 2002;35(3):336-338.
3.Francesconi F, Lupi O. Myiasis. Clin Microbiol Rev. 2012;25(1):79-105.
Dr Peter, Mr Philip, and Ms Swan are affiliated with Crestview Pediatrics and Adolescent Center in Crestview, Florida.