Acanthamoebiasis: causes, symptoms, diagnosis, treatment

Acanthamoebiasis is a protozoan disease caused by various species of free-living amoebas, which manifests itself in lesions of the eyes, skin and central nervous system.

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Epidemiology of acanthamoebiasis

Acanthamoeba are usually free-living animals that, when they enter the human body, are capable of becoming parasitic and completing their development cycle in the host's body, forming cysts.

The source of the invasion is the external environment (water, soil, etc. contaminated with amoebas). A person becomes infected with acanthamoebiasis by contact, water, and food. The incidence is sporadic, infection is possible in all seasons of the year. The pathogens are widespread. Most often, cases of the disease are registered in countries with tropical and subtropical climates.

What causes acanthamoebiasis?

Several species of amoebas belonging to the genus Acanthamoeba are pathogenic for humans.

The life cycle of Acanthamoeba includes two stages: trophozoite and cyst. The trophozoite has an oval, triangular or irregular shape, 10-45 μm in size, one nucleus with a large endosome, and also has an extranuclear centrosphere. Trophozoites form narrow, filiform or awl-shaped pseudopodia. The size of the cysts is from 7 to 25 μm. Cysts are mononuclear, with a multilayer membrane.

Biology of Acanthamoebiasis

Amoebas of the genus Acanthamoeba are aerobes that live in soil and warm freshwater bodies of water, mainly in the bottom layer. They are especially numerous in reservoirs formed by discharges from power plants and polluted by wastewater. The presence of a large amount of organic matter and high water temperature (+28 °C and above) in these reservoirs contribute to a sharp increase in the population of amoebas. When the water temperature drops, the pH changes, or the substrate dries out, the acanthamoebas encyst.

Cysts are resistant to drying, cooling and the action of many antiseptics in standard concentrations; due to their small size, they can be spread by airborne transmission; they are isolated from the tissues and excrement of many species of fish, birds and mammals.

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Symptoms of Acanthamoebiasis

Acanthamoebas are found in nasopharyngeal smears and in the feces of healthy people. Most often, acanthamoeba keratitis and skin lesions develop. If amoebas are carried to the brain by the hematogenous route from primary lesions in the cornea or in the respiratory tract, granulomatous acanthamoeba encephalitis develops. The incubation period of acanthamoebiasis usually lasts from several weeks to several months. In the initial period, the symptoms of acanthamoebiasis are latent. Headaches, drowsiness, convulsions, and mental disorders appear.

Acanthamoebiasis disease gradually progresses, a comatose state develops, which leads to death. Pathological examination reveals edema of the cerebral hemispheres, softening foci with exudate on the surface of the cortex and thickening of the soft membranes. In sections, in most areas of the brain, multiple softening foci with hemorrhagic necrosis ranging in size from 1.5 to 6.5 cm are found. Trophozoites and cysts of Acanthamoeba are found in necrotic masses.

Complications of acanthamoebiasis

If the eyes are affected, corneal perforation may develop. Amebic abscesses of internal organs may form when pathogens disseminate from the primary lesion.

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Diagnosis of Acanthamoebiasis

Acanthamoeba keratitis is diagnosed based on the results of microscopic examination for the presence of vegetative and cystic forms of amoebae in lacrimal-meibomian fluid, washes and scrapings from ulcerative lesions of the cornea and sclera. Native preparations are examined under a conventional microscope with low light or using phase contrast. Permanent preparations stained using the Romanovsky-Giemsa method are first microscopically examined at low and medium magnifications and then examined in more detail under an immersion lens. Sometimes they resort to culturing acanthamoeba on Robinson's medium, etc. In some cases, a bioassay is used for diagnosis by infecting laboratory animals.

The diagnosis of acanthamoeba skin lesions is established based on the detection of amoebae and their cysts in native and stained preparations prepared from the substrate of infiltrates and biopsies of affected tissues.

The most effective method for diagnosing amoebic encephalitis is the study of native preparations of cerebrospinal fluid, in which mobile trophozoites are determined. For more accurate identification, permanent preparations from the cerebrospinal fluid sediment, stained with Giemsa-Wright, are studied. Trophozoites and cysts are stained purple. Cultural diagnostics of acanthamoebiasis with seeding of cerebrospinal fluid on Culberston medium is also used.

Differential diagnostics for acanthamoeba lesions of the eyes, brain and skin are carried out with keratitis, encephalitis and dermatoses of other etiologies.

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Treatment of acanthamoebiasis

In case of acanthamoeba keratitis, a mandatory condition of treatment is to stop wearing contact lenses. Maxitrol or Sofradex is prescribed locally in the form of drops 6-12 times a day or in the form of an ointment 3-4 times a day. In combination with drops, the ointment is used once at night. Drops of solutions of gentamicin (0.3%), tobramycin (0.3%), paromomycin (0.5%), tetracycline (1%) or other eye ointments containing these drugs are used. It is also possible to use instillations of solutions of neomycin, polymyxin B up to 6 times a day. In rare cases, despite drug treatment of acanthamoebiasis, it is necessary to resort to keratoplasty.

Treatment of acanthamoebiasis and skin lesions is carried out with antibiotics of the aminoglycoside group (gentamicin, paromomycin). Neomycin, polymyxin, etc. are used locally.

Treatment of amoebic encephalitis is effective only if it is diagnosed early, which is extremely rare. Only three cases of recovery from granulomatous acanthamoeba encephalitis are known.

Acanthamoebiasis has a favorable prognosis when the skin and eyes are affected, but when the central nervous system is affected, the prognosis is usually unfavorable.

How to prevent acanthamoebiasis?

Acanthamoebiasis can be prevented by following proper contact lens hygiene. Lenses should not be stored in tap water or homemade saline solutions. They should only be stored in sterile solutions specially prepared in ophthalmological institutions. These solutions should be changed according to the contact lens instructions.

Prevention of acanthamoeba skin lesions and encephalitis involves following personal hygiene rules and limiting contact with areas where acanthamoeba live.