Case Report: Re-Emergence of Cochliomyia hominivorax in Costa Rica: Report of a Human Myiasis Case 23 Years after Elimination.

The New World screwworm, Cochliomyia hominivorax Coquerel (Diptera: Calliphoridae), was officially eliminated from Costa Rica in 2000, but it was reintroduced in 2023. A myiasis by C. hominivorax in a 71-year-old man with a 4-month history of foot hyperkeratosis and interdigital ulcers is reported. The myiasis was detected before sampling for bacterial culture. Approximately 160 first- and second-instar larvae were recovered and identified as C. hominivorax. Morphological identification was based mainly on characteristics of the cephalopharyngeal skeleton, spiracles, and pigmented dorsal tracheal trunks. Sequencing of a cytochrome c oxidase subunit I gene fragment confirmed the identity. The ulcers healed after extraction of the larvae and ciprofloxacin treatment of a concurrent Staphylococcus aureus and Pseudomonas aeruginosa infection. Given the reintroduction of C. hominivorax in Costa Rica and the risk of northward expansion, this report highlights its impact on public health and calls for awareness among clinicians and healthcare practitioners.