Tungiasis and myiasis — Viva

Q1: Definition and clinical presentation (2 min)

A returning traveller from Brazil has a painful furuncle-like nodule on the scalp that has not responded to antibiotics, with a central punctum and a sensation of movement. What is the diagnosis, the organism, and its vector? What does the central punctum represent anatomically, and why does it matter for treatment?

Model answer: Furuncular myiasis due to Dermatobia hominis (human botfly). The fly uses phoresy — it glues its eggs to a blood-feeding mosquito, and the larva enters the skin at the mosquito bite. The central punctum is the larva's breathing pore, aligned with its posterior spiracles; it matters because occluding it cuts off the oxygen supply and forces the larva to surface for extraction.

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Q2: Management of furuncular myiasis (3 min)

Walk me through how you would remove the larva. Why must you not simply incise the nodule? What happens if you rupture the larva during extraction?

Model answer: Occlude the punctum with thick petrolatum for several hours; the larva emerges to breathe; grasp it with forceps and extract intact; surgically excise if occlusion fails. Never incise like an abscess — it releases the larva into the wound and leaves the spined larva behind. Never rupture the larva — its cuticular spines anchor it and its contents provoke a severe foreign-body reaction and secondary infection.^[3]

Q3: The differential — distinguishing creeping eruptions (3 min)

The same patient has a serpiginous pruritic track on his foot. How do you distinguish cutaneous larva migrans from larva currens, and from migratory myiasis? What is the first-line treatment for each?

Model answer: CLM (animal hookworm larvae) migrates slowly (millimetres per day), is serpiginous and pruritic, on feet/buttocks after beach exposure; treat with oral albendazole or ivermectin. Larva currens (Strongyloides) is far faster (centimetres per hour), urticarial, often perianal, and recurrent from autoinfection; treat with ivermectin for strongyloidiasis. Migratory myiasis (Gasterophilus/Hypoderma) mimics CLM but the track is longer, less pruritic, with animal (horse/cattle) exposure; treat by extracting the larva or with ivermectin.^[2]

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Q4: Tungiasis and its complications (2 min)

A barefoot child from an endemic community has black-dot nodules on the toes with surrounding erythema and pus. What is the organism, the treatment, and the three complications you must actively prevent or detect?

Model answer: Tunga penetrans gravid female sand flea. Treatment is sterile curette/needle extraction of the flea en bloc (must remove the whole flea and eggs), antiseptic, and tetanus prophylaxis. The three complications are secondary bacterial infection (Streptococcus/Staphylococcus — cellulitis, lymphangitis, abscess, sepsis), tetanus, and (in neglected severe disease) gangrene and autoamputation. Oral ivermectin may reduce the load in heavy infestation.^[1]

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Q5: Special populations and prevention (2 min)

How would your management change if the patient were pregnant? Name one structural prevention measure that actually reduces community transmission of tungiasis.

Model answer: In pregnancy, prefer mechanical extraction of tungiasis and myiasis (safe) and topical thiabendazole for localised CLM; avoid albendazole in the first trimester (teratogenic) and weigh ivermectin's benefit versus risk with obstetric input. The structural measure that reduces community tungiasis is footwear plus concrete floors and sealed cracks in endemic housing; mass ivermectin administration is complementary.^[1]

References3ShowHide

1. [1]Fich F, Del Barrio-Diaz P, Kam S, et al. Tungiasis, an emerging tropical disease in Chile: three imported cases reports Rev Chilena Infectol, 2013.PMID 24522316
2. [2]Caumes E. Treatment of cutaneous larva migrans Clin Infect Dis, 2000.PMID 10816151
3. [3]Calvopina M, Ortiz-Prado E, Castañeda B, et al. Human myiasis in Ecuador PLoS Negl Trop Dis, 2020.PMID 32084134