Case #344 – March, 2013

A 26-year-old female presented at a local hospital with severe pain and bloody discharge from the ear. The symptoms started while on a returning flight from vacation in Central America. The patient explained that while on vacation she visited a local physician to have a fly removed from her ear canal. Tissue was removed and sent to Pathology for testing. Several viable fly larvae were observed in the tissue. The case was diagnosed as aural myiasis and the larvae were allowed to mature to aid in identification. Images of mature (third instar) larvae were captured and sent to the DPDx Team for diagnostic assistance. Figure A shows one of the larvae; Figure B shows a close-up of its posterior spiracles. What is your identification? Based on what criteria?

Figure A

Figure B

This was a case of aural myiasis caused by the primary screwworm fly, Cochliomyia hominovorax. Diagnostic morphologic features included:

an elongate, slightly tapering habitus with cuticular spines on each body segment (Figure A).
posterior spiracles with straight slits, a weakly-sclerotized peritreme with lateral swellings, and an obsolete to absent ecdysial scar (button) (Figure B).

Travel was also supportive, as C. hominovorax is endemic to tropical America. While eggs are usually laid in wounds, C. hominovorax will attack healthy tissue and can be damaging to the host if not removed promptly.