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Thursday, 29 December 2016

ACANTHAMOEBA KERATITIS IN CONTACT LENS WEARER

Written by Ana Peña Cabia | Jorge Alfredo Pérez García | Mª José Rodríguez Escudero, Posted in Volumen 4

The image belongs to a 35 year old woman with pain in the left eye. Acanthamoeba spp. cyts can be seen when we examine the contact lenses solution (optical microscope 100x with methylene blue staining). On a slide, a homogenous suspension is made between contact lenses solution and methylene blue. This method allows you to know the protozoa, based on morphological characteristics. It can be seen Acanthamoeba spp. cyst with a double cell wall. The outside wall is called ectocisto, thin and wavy, and inside one is called endocisto, rounded.
figura1Figure 2. Acanthamoeba’s life cycle

This parasite is found on air, land and tap water, and it was identified as a pathogenic eye agent in the 70s. There are three groups based on cysts morphological characteristics and size. The cyst size is between 13-20 μm1.

This parasite exists in two forms: an active, infective trophozoite and a dormant, environmentally hardy cyst. The role of the cyst state is protection against adverse environmental conditions, as lack of food, temperature and pH’s changes. But when conditions change, cysts are broken and the parasite is released to the environment. Acanthamoeba spp. can access in the eye by contaminated water or wearing contact lenses2.

The infection is usually diagnosed seeing the cysts in the contact lenses solution with an optical microscope or in vitro culture with no nutritive agar medium or low nutrients concentrations in the presence of bacteria. Another option could be use of the polymerase chain reaction (PCR)3.

figura2Figura 2. Ciclo biológico de Acanthamoeba spp

In this patient, the diagnosis was delayed because another infection was suspected at the beginning. Physical examination showed corneal ulcer, cellulitis and conjunctivitis. Tobramycin and amoxicilin-clavulanate was prescribed to the patient. Next day, the examination showed “dendritic central ulcer” what is associated with herpes simplex virus infection, so acyclovir was prescribed. A month later, she went to the hospital because she had red eye and pain. In exploration was observed a central corneal edema with “ring-like” infiltrate, typical sign of infection by amoeba. So the treatment was changed to ceftazidime and vancomycin eye drops and chlorhexidine 0,02% eyewash. The first sample sent to the Laboratory was the washing liquid of contact lens Microbiology Laboratory reported cystics forms in this sample, so Acanthamoeba spp. infection was confirmed. Although patient was treated with propamidine isethionate 0,1%, she had a negative evolution, with several bacterial and fungal superinfections. She was requested for a corneal transplantation, with a successful result.

The bacteria are largely responsible for the majority of contact lenses-related infections. A smaller subset of contact lenses-related keratitis is because of fungal or protozoal infections4. Acanthamoeba spp. belong to a protozoal family that is a causative agent of keratitis. Acanthamoeba keratitis is a severe eye infection with a significant risk of vision loss due to corneal ulceration and scarring. Wearing contact lenses is a risk factor, especially if people use homemade saline or tap water5.

Acanthamoeba keratitis is an invalidating and painful disease. It’s important differential diagnosis against herpetic, fungal or mycobacterial keratitis. Before the appearance of optical treatments, it was necessary the eye’s removal in some cases to resolve the infection. Nowadays this practice is infrequent6.

Treatment is usually started with dual agents such as diamidines (propamidine isethionate or hexamidine, that affect the permeability and destroy cytoplasmic enzymes and proteins) and biguanides, because are chemical agents effectives to eliminate Acanthamoeba spp. cysts. However, a long treatment with diamidines could be toxic7.

When acanthamoeba keratitis is suspected or patient has a negative evolution, it’s recommended to order, as soon as possible, analyze the corneal scraping or the washing liquid of contact lenses by Microbiology Laboratory. Early diagnosis is very important to avoid an unfavorably evolution.

References

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