On March 28, 2013, the New York Daily News reported the story of Ashley Hyde, a Florida teen suffering from a parasitic eye infection. Acanthamoeba, the headline screamed, “ATE THROUGH HER EYE.” This conjures up a mental image of something large and voracious; while the parasite is actually microscopic. Unfortunately, however, the headline is relatively accurate.
Various species of Acanthamoeba are widespread in the environment. A current review by Jacob Lorenzo-Morales et al, published in the April 2013 issue of Trends in Parasitology, lists the numerous places where they’ve been found: fresh and salt surface waters, “irrigation water for crops, heating and ventilation systems, soil, bottled water, air, spas, aquariums, plants, marine sediments, sewage sludge, dialysis units, airborne dust, air samples… contact lenses, cases, and solutions, and even in intrauterine devices.” In other words, Acanthamoeba spp. are pretty much everywhere.
When environmental conditions are good, Acanthamoeba feeds and multiplies in its familiar amoeboid stage, engulfing bacteria and other microorganisms. When conditions are harsh, it changes into a tough cyst stage that is resistant to heat and cold, dryness, starvation, chemical disinfectants, and antiparasitic drugs. This cyst stage can wait for years until conditions improve; it’s built for survival and it’s what makes Acanthamoeba so very hard to kill.
Because Acanthamoeba can be present in household plumbing, cleaning contact lenses or cases with tap water, or using tap water to make up contact lens solutions, can expose lenses to these tiny amoebae. Other possible sources of exposure include swimming pools, hot tubs, and even showers, so it’s best not to wear contact lenses in these places. Other types of eye diseases and eye injury can increase the risk as well.
Not all strains of Acanthamoeba cause disease, but as luck would have it, some do well at our normal body temperature, and some are particularly good at attaching to both plastic lenses and the cells of the cornea. Lorenzo-Morales says that once in the eye, “the Acanthamoeba parasite can penetrate the surface of the cornea by secreting a protein that dissolves layers of it. It then finds refuge in the eye and feeds not only on bacteria, but also eye cells.”
This is Acanthamoeba keratitis.
Symptoms of Acanthamoeba Keratitis
The initial symptoms of Acanthamoeba keratitis are much like those seen in other types of keratitis: A painful, red, watery eye, with blurred vision and sensitivity to light. Because these symptoms don’t scream “Acanthamoeba,” doctors may not recognize the infection, which can delay appropriate treatment. In addition, to make things worse, there is no completely effective treatment. Drug combinations are typically used over long periods, and the earlier treatment is begun, the better the outcome is likely to be. Vision loss can be significant and permanent.