Published Sept 11 2018
To the Editor
I enjoyed your article on swimmer’s itch and perhaps you would be interested in some more information.
In 1971 while in graduate school studying parasitology in Toronto my supervisor was called to Toronto General Hospital (TGH). A 35-year-old lady from Belleville was having “black outs” in one eye. It was described as a curtain being pulled across the eye. It would disappear and later reappear. There was no pain.
TGH took a very large photograph of a “question mark” type of inclusion in the eye and brought it back for parasitologists to view. He said it looked like a cercaria which is a larval stage of a trematode the parasite that causes swimmer’s itch. He saw a sucker at the front of the larva and a bifurcated tail.
He called TGH and the lady was not a swimmer but she did gather frogs in the fall. Frog legs are a delicacy. That was the discovery.
The larva is found in snails and is released into the water looking for a frog or waterfowl to attach. The sucker attaches to the “prey” and enzymes are released allowing it to penetrate the animal; thus the red itchiness of swimmer’s itch.
It appears that the lady transferred a larva from the frog to her hands and probably wiped her face. The larva penetrated the eye and started to wander around looking for a correct environment to continue its development briefly blocking the retina. For many years tracts were seen in many cases with no explanation. After a while the larva dies and becomes a small cyst causing no further problems.
TGH said they were going to use a cryoscope with liquid nitrogen to attach and pull out the larva after it left the area of the retina. But it was later learned that a laser was used to kill the larva and it was left in the eye. An early use of a laser.
Best to tell children about this story. A good introduction to parasitology.