Boy’s mosquito bites develop into ‘impetiginous lesions’ that will not heal
What’s your diagnosis?
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A 5-year-old boy is referred from an Army hospital in Panama in the mid-1980s to Brooke Army Medical Center for evaluation of an unrelated problem when his parent asked about a case of several “impetiginous lesions” that will not heal.
He had taken two courses of oral antibiotics (cefalexin and then clindamycin) without benefit. The lesions all appeared at the same time. At home, he spends a lot of time playing outside, where he is frequently bitten by mosquitos. The mother states that all these lesions started as common mosquito bites, then got infected due to scratching.
A healthy 7-year-old girl is sent to the school nurse by her teacher, who was concerned about the girl scratching her scalp and seeing white material in her hair.
The patient is a healthy child, with immunizations up to date and no other problems related to these skin lesions. His examination is positive for only five discrete skin lesions (Figure 1). One lesion had the crust scraped off (Figure 2).
What’s your diagnosis?
A. Cutaneous myiasis
B. Cutaneous leishmaniasis
C. Impetigo due to MRSA
D. Mycobacterium fortuitum
Answer and discussion
This is a case of cutaneous myiasis, caused by the human bot fly, or Dermatobia hominis (Figure 3).
As illustrated, the fly lays her eggs on the abdomen of a blood-sucking insect, most commonly a mosquito, who carries the eggs until she lands to take a blood meal. At this time, sensing the warmth of the mammal, the eggs hatch and the larvae make their way toward the same hole made by the proboscis of the mosquito. They can also penetrate the skin without an opening, but like humans, they prefer the easy way. In the host, the larvae undergo five stages of development, after which they exit, fall to the ground and pupate into another fly. While these lesions are relatively harmless, most parents do not want to wait for the larvae to exit on their own; they want them out now, and would like to see them punished as well (my personal experience). Removal can be easily accomplished with light sedation and a small incision over the opening through which they breath (Figure 4).
Then simply reach in and pull out the larva with tweezers (Figure 5). Some recommend applying Vaseline or similar occlusion over the opening to suffocate them (this approach falls under the punishment method). However, you are likely to end up with a dead larva under the skin that would come out in pieces and cause an inflammatory response.
This case was initially presented in this column in December 1991. Not much has changed since then. As in the case presented, children with cutaneous myiasis often present with more than one lesion, sometimes in places the parents may not see. A case of a child with multiple lesions on the back (Figure 6) was shown in the March 2020 issue, which was donated by Carly Lyons, MD, and Emily Stewart, MD, of the pediatric and dermatology clinics, respectively, at Baylor Scott & White Health in College Station, Texas.
Cutaneous leishmaniasis (New World type) can certainly be acquired in Central and South America, and even Texas has had cases documented. It typically causes a persistent skin lesion that may develop over weeks to months into a chronic erosion, with raised, erythematous edges and a raw-appearing base (Figure 7). This infection is caused by a protozoon that is transmitted by the bite of the sandfly. New World and Old World leishmaniasis are similar infections but caused by different Leishmania species. I would refer the reader to the CDC’s leishmaniasis site for more information.
Impetigo due to MRSA would typically look like any other impetigo (Figure 8) but may be resistant to initial treatment, thereby explaining the lack of improvement. However, scraping the cap off the myiasis lesion revealed the answer, with the central pore through which the larva breaths (see Figure 2). This feature also makes the diagnosis possible over the phone.
Mycobacterium fortuitum is a nontuberculous mycobacterium species that is occasionally “implanted” by an injury to the skin, resulting in a localized infection. It will slowly (taking weeks) produce a bump with a central dimple that may occasionally drain some clear fluid (Figure 9). Many suggest that an uncomplicated, localized cutaneous infection is best managed by oral therapy and surgical removal. However, M. fortuitum complex contains an inducible erm gene, with possible resistance to macrolides; therefore, the specimen should be sent for culture and sensitivity testing. As such, many experts recommend initial treatment with a combination of IV amikacin and cefoxitin or meropenem pending sensitivity results. If sensitivities are favorable, a variety of oral combinations can then be used (see 2021 Red Book, page 820). Lastly, it is very unlikely that a patient would present with multiple mycobacterial skin lesions.
Columnist comments
Why present an unusual skin problem that has been shown in this column before? This case was shown 31 years ago, and the next was 3½ years ago, and I still get occasional calls and emails about myiasis. I have been to Panama twice — once with the Army on a consultant mission, and once on a cruise through the canal. The cruise reminded me of the enormous popularity of going through the canal and visiting the canal zone as a tourist site. Like any other tropical area, vector control may be “spotty,” and all it takes is a mosquito bite to potentially leave you with a larva in your skin, which may go unnoticed at first. By the time the child or adult seeks care for a persistent skin sore, the vacation may not come to mind. The same could happen with leishmaniasis. This is why it is always important to get a detailed travel history when evaluating a chronic or unusual problem.
As usual, if you have an interesting case you would like to share in this column, please let me know.
References:
American Academy of Pediatrics. Committee on Infectious Diseases. Red Book. Report of the Committee on Infectious Diseases. Academy of Pediatrics; 2021. https://redbook.solutions.aap.org/redbook.aspx. Accessed Nov. 20, 2021.
CDC. Parasites – leishmaniasis. https://www.cdc.gov/parasites/leishmaniasis/index.html. Last reviewed June 1, 2023. Accessed Nov. 15, 2023.
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Brien is a member of the Healio Pediatrics Peer Perspective Board and an adjunct professor of pediatric infectious diseases at McLane Children's Hospital, Baylor Scott & White Health, in Temple, Texas. He can be reached at jhbrien@aol.com.