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Case #459 - January, 2018

A visitor to Hawaii experienced onset of moderate irritation of one eye accompanied by redness and the sensation of a foreign body. The visitor removed a few small, 1-2 millimeter long white-colored motile organisms from the conjunctiva of the affected eye. The organisms were placed on the end of a tube of lip balm for transport to a health care facility for identification. Figures AC are images taken with the camera of a cellular phone via the eyepiece of a microscope and show details of one of the organisms. What is your diagnosis? Based on what criteria?

This case and images were kindly provided by ARUP Laboratories and The University of Utah School of Medicine, Infectious Diseases Division, both in Salt Lake City, Utah.

parasitic image

Figure A

parasitic image

Figure B

parasitic image

Figure C

Case Answer

This was a case of opthalmomyiasis caused by Oestris ovis (the sheep botfly). Morphologic features of what is most likely a 1st instar (stage) included:

  • Spindle/cylindrical shaped body with tapered ends.
  • Visible cephalopharyngeal skeleton including the pair of sharply curved mandibles (mouth-hooks).
  • Body spines arranged in rows that project back towards the posterior end.
  • Terminal hooks arranged in two scallops (only one intact scallop is visible in this specimen).
  • Location in the host.

Adult females of O. ovis are larviparous and deposit their larvae directly into the nasal cavities of the normal host (sheep, goats).  Larvae then move to the frontal sinuses and attach to the mucous membrane.  When mature, they leave the host to form puparia in the soil.  In humans, larvae are often laid directly onto the conjunctiva by female flies.

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Images presented in the monthly case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.

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  • Page last reviewed: March 5, 2018
  • Page last updated: March 5, 2018
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