A recent eye infection suffered by 18-year-old Nottingham University student Jess Greaney is the kind of story that fills us with horror. Greaney had keratitis, an inflammation of the cornea, caused by Acanthamoeba castellanii, a parasite that was living and feasting on her eye.

A. castellanii is a ubiquitous organism, found in many ecosystems worldwide. It is able to survive in harsh environmental circumstances – even in some contact lens solutions – and this is not the first occurrence of A. castellanii appearing in the eye. Acanthamoeba keratitis (AK) is a neglected malady frequently associated with contact lens wear and it is thought Greaney caught the bug after splashing tap water on her contact lenses.

Eye Invader

Acanthamoeba infection of the cornea causes severe inflammation, intense pain and impaired vision, which is blinding if left untreated. Infection begins when the parasite is at its active feeding trophozoite stage and sticks to the corneal tissue before penetrating the lower stromal layer. The resulting opacity leads to less sharp vision and eventually blindness.

Even more worrying is that besides the painful progressive sight-threatening corneal disease, the parasite can cross the blood brain barrier and cause granulomatous amoebic encephalitis, a progressive disease of the central nervous system that often results in death.

Greaney was lucky – if you can put it that way – because she was able to receive treatment. After a week her eye was red, painful and bulged, "it looked like a huge red golf ball," she said. Treatments included clamping her eye open, keeping her awake, scraping off layers of tissue and repeated eye drops.