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Photo courtesy of: Patrick Ma, M.D. Used with permission. Not to be reproduced.

A 7-year-old boy presents with decreased vision in the left eye over the past few weeks. On examination you see a posterior pole granuloma, and a dense vitritis in the left eye and a normal fundus examination of the right eye.  He was recently given a puppy and plays frequently with the dog outside.  You suspect Toxocariasis.

Which diagnostic tests should you first order and perform?

a -- ELISA for T. canis and eosinophil count Toxocariasis This disorder is caused by a canine ascarid (roundworm), Toxocara canis.  Human infestation is caused by the accidental ingestion of soil or food contaminated with ova shed in dogs' feces. After infection of the human intestine, the ova develop into larvae which penetrate the intestinal wall and travel to various organs, including the eyes.  When the larvae die, they cause an inflammatory reaction followed by granulation. This can cause leukocoria, strabismus, and/or unilateral visual loss.