Weekly Parasite #5: The Eyes Have It

When I was in grad school, I was always a little disappointed that I didn’t need to travel much further than northern Florida. Other students in my graduate cohort were busy going off to do research in interesting and exotic places like Jamaica, New Guinea, Brazil, Peru, or Gabon, and I was driving down to Tallahassee and picking up roadkill.

But sometimes I’m reminded of exactly how much I missed. One of my friends, now a full-fledged professional systematist, came back from one of his field seasons in Africa with a passenger.

                                                   

Loa loa is also known as the African eyeworm. It’s a filarial nematode. Fundamentally, that means it’s a long, thin worm that molts periodically as it grows. There are lots of parasitic nematodes, but Loa loa is the only one where the adults occasionally swim across your eye.

Here’s John:

I thought I had flicked something into my left eye.  There was something in there that was bothersome, but not sharply painful.   So I went to the bathroom mirror and pulled down my lower eyelid.  There I saw (with both my eyes, I suppose) a semi-transparent worm, about 1 cm in length and no thicker than a silk thread, making its way across the white (sclera)  of my eye, below the iris and beneath the conjunctiva…

Of course, by the time that adult was having a swim somewhere visible, John had turned into a worm habitat. Humans are the only known host of adult Loa loa. They typically live in subcutaneous tissue. But they also breed like bunnies, pumping out thousands of tiny threadlike larvae that ride through the bloodstream on a daily basis. At night, they collect inside lung tissue. During the day, they move out to the veins under the skin and wait on the off chance that they’ll get sucked out by their second host – a biting fly.

Once the larvae are inside the fly, they bore through its gut tissue, migrate to its muscles, molt a couple of times, then finally move into the fly’s proboscis. They wait for the fly to bite someone else, and crawl into the wound. New host!

It takes the larvae about 6 months to become adults. But they can live inside human tissues for 15 to 17 years. So it’s not entirely clear when John was infected. He’s been studying fish in central Africa for nearly a decade. He does know that it had been two years since his last research visit, so the worms had him for at least that long.

So, what was it like to have a more-active-than usual adult swimming around?

When it was active, it was quite annoying and my eye teared profusely.  I remember hoping it would just go back to wherever it had come from and leave my eye alone.  It did, eventually.   My eye was a little red where it had broken some of those blood vessels.  It never made a reappearance.

Hey John, I hope that ivermectin works.


Thanks to the CDC and John Sullivan (Academy of Natural Sciences) for the information. Photo from the Filarial Genome Network at Smith College.

Comments

[Becca]

Now I am just completely and totally ooked out.

[DianeAKelly]

What are you ooking at? The worm part, the eye part, or the "this guy lives in the same state as me!" part?

[Thom H.]

I certainly hope that there are none of the fly hosts here in America and that this nematode is host-specific enough not to be able to utilize any or our own biting flies. I'm sure I have quite enough parasites living on me already without having one swimming across my eyeball.

[Chris Higgins]

I have a parsite that is in my eye. Not on the out side but in it. It is transparent and floats around with in my vision parameters. It has a split tail and a tounge that is split about half way. In the center of the parasite is like a knot that makes it look like the two parts of the lower body are connected. The head looks like that of a snake or a dragon. Also there are little dot like substances floating near it and it looks like it's trying to eat them. I would like to know what kind of parasite it is and how to get rid of it?

[Tess]

If you think that being a person with eye worm is gross, try being that person's fiance during that supposed 'romantic' time in your relationship. It was no pleasure trip, let me tell you!

[sally]

wow thats discusting you should shower!

[sally]

wow thats discusting you should shower! you are sick i never herd of such disturbing behavior! its called a shower step in the tub and use some soap.

[DianeAKelly]

Sally, I don't think you've quite grasped what's happening here. If the worm had been on the *outside* of John's eye, I'm sure he would have cleaned it off. But it was on the *inside* of his eye. Fortunately, the deworming medication works great.