Case #231 – July, 2008

A 25-year-old man, who recently returned from a trip to Brazil, presented to his health care provider with a festering lesion on his forehead. The patient also complained of feeling things moving under his skin. Surgical removal of the outer surface of the lesion revealed several maggot-like organisms (Figure A) beneath the skin. Specimens were sent to the CDC for diagnostic assistance. Figure B shows a close-up of the anterior end of one of the organisms; Figure C shows a close-up of the posterior end. Figures D and E show structures dissected out of the anterior end of one of the organisms. What is your diagnosis? Based on what criteria?

Figure A

Figure B

Figure C

Figure D

Figure E

This was a case of myiasis caused by the New World screwworm fly, Cochliomyia hominovorax. Diagnostic features were:

cuticular spines on every body segment (Figure A).
a fan-shaped anterior spiracle (arrow, Figure B and Figure E) with greater than seven lobes.
posterior spiracles with three spiracular slits (yellow arrow, Figure C) and a weak ecdysial scar (blue arrow, Figure C).
a cephalopharyngeal skeleton consistent with the species (Figure D).

Figure B

Figure C

Cochliomyia hominovorax is the primary screwworm fly in the New World. Larvae are obligate parasites of living flesh in humans and other mammals. Human cases are not common but may be seen in regions where livestock is tended. Females oviposit on or near pre-existing wounds or on mucous membranes just inside the nose or mouth. Larvae feed subdermally and may cause extensive tissue damage. Human deaths have occurred from tissue destruction. Human cases have been drastically reduced in the United States and Mexico by a sterile male release program. Females mate only once, so mating with a sterile male ensures the next generation will not happen.