Acanthamoeba is a microscopic, single-celled organism commonly found in natural environments around the globe. It thrives in soil, dust, and various bodies of water, from oceans and lakes to tap water. While generally harmless, this amoeba can enter a dormant state by forming a cyst. This cyst is a highly protected version of the organism, created to survive harsh conditions, and it is this resilient form that is implicated in human infections.
The Two Stages of Acanthamoeba
The Acanthamoeba life cycle consists of two distinct phases. The first is the active, feeding stage known as the trophozoite, where the organism is mobile, consumes bacteria for nourishment, and reproduces. This is the infectious form of the amoeba that allows it to establish itself within a host.
When conditions become unfavorable, such as a lack of food or extreme temperatures, the trophozoite transforms into a dormant cyst. This cyst has a protective, double-walled structure that makes it exceptionally resistant to freezing, heating, and chemical treatments like chlorine, which explains why infections are difficult to treat.
Acanthamoeba Keratitis and Other Infections
The most common disease caused by this organism is Acanthamoeba keratitis, a severe infection of the cornea, the clear front part of the eye. Symptoms often include intense eye pain that can seem disproportionate to the visible signs of infection, along with redness and blurred vision. Individuals may also experience sensitivity to light and a persistent sensation that something is in the eye. If not diagnosed and treated promptly, Acanthamoeba keratitis can lead to permanent visual impairment or even blindness.
While keratitis is the most frequent infection, Acanthamoeba can cause other serious diseases, although they are much rarer. Granulomatous Amebic Encephalitis (GAE) is an infection of the brain and central nervous system that is often fatal. In individuals with compromised immune systems, the amoeba can cause disseminated infections that spread throughout the body, leading to skin lesions or lung infections.
How Infection Occurs and Prevention
Infection with Acanthamoeba occurs when the amoeba comes into contact with the cornea, especially when there is minor damage to the eye’s surface. Contact lens wearers represent the highest-risk group, accounting for an estimated 85% of keratitis cases. Unsafe hygiene practices are a major contributing factor, such as rinsing or storing lenses in tap water or showering while wearing them.
Preventing infection requires diligent hygiene and careful handling of contact lenses.
- Always wash hands thoroughly with soap and water before touching lenses.
- Use only sterile, commercially prepared solutions to clean, disinfect, and store them; never use tap water.
- Regularly clean and replace the contact lens case to avoid contamination.
- Remove lenses before any activity involving water, such as swimming in pools, hot tubs, or natural bodies of water.
Medical Diagnosis and Treatment
Diagnosing an Acanthamoeba infection begins with clinical suspicion, especially in a contact lens wearer who presents with eye pain. A definitive diagnosis is often made by taking a small sample from the cornea, a corneal scrape, and examining it under a microscope to identify the amoebic cysts or trophozoites. Advanced imaging like confocal microscopy can also be used to view the organisms directly within the cornea.
Treating Acanthamoeba keratitis is a challenging and lengthy process, primarily because the cyst form is so resilient. The treatment involves an intensive course of prescription antiseptic eye drops, which may need to be administered for six months to a year. Therapy must be continued long enough to eradicate all forms of the amoeba. Early and accurate diagnosis is directly linked to a better outcome and is important for preventing severe vision loss.