This blog post today is dedicated to all you visually impaired contact lens wearing folk out there! Before I begin, I just want to say that I truly hope all of you adhere to the instructions your optometrist gives you with regards to using contact lenses (washing hands before and after handing them, taking them out while showering/bathing). If not, I’m afraid you are running the risk of meeting my new acquaintance; Acanthamoeba spp., also known as the cornea guzzling free-living protozoa from hell!
|Acanthamoeba in its two forms: (A) trophozoite, (B) impenetrable cyst|
Image by Jacob Lorenzo-Morales, Naveed A. Khan, and Julia Walochnik, used under CC BY 2.0
The trophozoite is the vegetative form which feeds on organic matter and ranges in size from 10 to 25µm. When the going gets tough, the tough get going... tough being the trophozoite. When conditions become unfavourable, like under extreme heat or lack of nutrients, the trophozoite transforms itself into a double walled cyst which is almost invincible. The cyst remains unscathed by repeated cycles of freeze-thawing, and incredibly high doses of UV and even GAMMA RADIATION. Cue the Terminator and his infamous catchphrase…. “I’ll be back”.
Characteristics of AK include eye pain, redness, itchiness, and a general feeling of something being stuck in your eye. Sounds like most eye infections, right? One extra feature is the presence of a stromal ring-like infiltrate in the eye. Basically, an ulcer forms on the cornea of the infected eye as a result of the hungry Acanthamoeba. It has been discussed that contact lenses serve as vectors for transmitting Acanthamoeba trophozoites, and to make matters worse studies have shown that wearing lenses results in mild corneal trauma which alters the surface of your eye making it even more susceptible to infection!
|Healthy human eye (left) vs infected eye with Acanthamoeba keratitis (right). Arrow indicating stromal ring-like infiltrate.|
From Figure 1 of the paper
Now, before you all go destroying your contact lenses in a panic-stricken state let me inform you that over 30 million Americans wear contact lenses, yet remarkably the incidence of AK in contact lens wearers is less than 33 cases per million. Acanthamoeba species are found in virtually every environmental niche on our planet ranging from thermal springs to solid ice, yet why are AK cases so far and few between? Scientists believe the host’s immune system plays an important role in successful AK infections.
Serological analysis of IgG and tear IgA (both of which are antibodies found in blood) revealed that 50-100% of healthy individuals with no history of AK possessed antibodies against Acanthamoeba antigens. What’s more, the serum IgG and tear IgA levels were significantly lower in patients with AK compared to the cohort of normal individuals with no history of AK, suggesting a prominent role of the mucosal immune system in preventing AK.
In 1939, Winston Churchill referred to Russia as “… a riddle, wrapped in a mystery, inside an enigma” … one might classify Acanthamoeba and the infections it produces in the same way! Although scientists have a clearer understanding of Acanthamoeba keratitis and the parasite which causes it, there is still much to be learned about its cunning and conniving ways.
Neelam S. and Niederkorn J.Y. (2017) Pathobiology and Immunobiology of Acanthamoeba Keratitis: Insights from Animal Models . The Yale Journal of Biology and Medicine. 90:261-268.
This post was written by Sally O'Meara