Acanthamoebiasis: causes, symptoms, diagnosis, treatment

Acanthamoebiasis is a protozoal disease caused by various kinds of free-living amoeba, manifested by the damage of the eyes, skin and CNS.

[1], [2], [3]

The epidemiology of acantammebiasis

Akantameby - usually free living animals, which, getting into the human body, are able to pass to parasitism and end in the host organism its development cycle, forming cysts.

The source of infestation is the external environment (water, soil contaminated with amoeba, etc.). A person becomes infected with acanthamoebiasis by contact-household, water and food routes. Incidence sporadic, infection is possible in all seasons of the year. Pathogens are ubiquitous. Most cases of the disease are recorded in countries with a tropical and subtropical climate.

What causes acanthamoebiasis?

For humans, several species of amoebas belonging to the genus Acanthamoeba are pathogenic.

The life cycle of acanthamoeb includes two stages: trophozoite and cyst. Trophozoite has an oval, triangular or irregular shape with a size of 10-45 μm, one core with a large endosome, and there is an extra-nuclear centroscope. Trophozoites form narrow, threadlike or styloid pseudopodia. The size of cysts is from 7 to 25 μm. Cysts are single-core, multilayered.

Biology of Acanthamoebiasis

Amoeba of the genus Acanthamoeba - aerobes, inhabit the soil and warm freshwater reservoirs, mainly in the bottom layer. Especially a lot of them in the reservoirs formed by discharges of power plants and contaminated with sewage. The presence of a large amount of organic substances and a high water temperature (+28 ° C and above) in these reservoirs contribute to a sharp increase in the populations of amoebae. With decreasing water temperature, changing the pH or drying the substrate, acanthamoebas are encysted.

Cysts are resistant to drying, cooling and the action of many antiseptics at standard concentrations, due to their small size they can spread aerogenically; are excreted from the tissues and excrement of many species of fish, birds and mammals.

[4], [5], [6], [7]

Symptoms of acantammebiasis

Acanthamoebas are found in smears from the nasopharynx and in the feces of healthy people. Most often develop acanthamoebic keratitis and skin lesions. In the case of skidding of amoebas in the brain by hematogenous way from the primary lesions in the cornea of the eye or in the respiratory tract, granulomatous acanthamoebic encephalitis develops. The incubation period of acantammebiasis usually lasts from several weeks to several months. In the initial period, the symptoms of acanthamoebiasis appear in an erased form. There are headaches, drowsiness, convulsions, mental disorders are noted.

The disease of acantamoebiasis gradually progresses, the comatose state develops, which leads to a fatal outcome. In pathological anatomical studies, edema of the cerebral hemispheres, foci of softening with exudate on the surface of the cortex and thickening of the soft membranes are noted. On the sections in the majority of the brain areas, multiple foci of softening with hemorrhagic necrosis of 1.5 to 6.5 cm are found. In the necrotic masses, trophozoites and acanthamoeb cysts are found

Complications of Acanthamoebiasis

If the eyes are affected, corneal perforation may develop. It is possible to form amoebic abscesses of internal organs during dissemination of pathogens from the primary lesion.

[8], [9]

Acanthamoebiasis Diagnosis

Diagnosis of acanthamoebic keratitis is based on the results of a microscopic examination for the presence of vegetative and cystic forms of amoebas in the tear-meibomian fluid, washings and scrapings of ulcerative lesions of the cornea and sclera. Native drugs are examined in a conventional microscope under low light or with phase contrast. Constant preparations, stained using the Romanovsky-Giemsa method, conduct microscopy first with small and medium magnifications, and then examine in more detail under the immersion lens. Sometimes resort to the cultivation of acanthamoeb on Robinson's medium, etc. In some cases, a bioassay is used for diagnosis by infecting laboratory animals.

The diagnosis of acanthamoebic skin lesions is established on the basis of the detection of amoebas and their cysts in native and colored preparations prepared from the substrate of infiltrates and biopsies of the affected tissues.

The most effective method of diagnosing amoebic encephalitis is the study of native preparations of the cerebrospinal fluid, in which mobile trophozoites are determined. To more accurately identify them, constant preparations from the cerebrospinal fluid sediment, colored according to Gimza-Wright, are studied. Trophozoites and cysts are dyed purple. Also, cultural diagnostics of acanthamoebiasis with culture of cerebrospinal fluid on the Coulberston medium is used.

Differential diagnostics with acanthamoebic lesions of the eyes, brain and skin are carried out with keratitis, encephalitis and dermatoses of another etiology.

[10], [11], [12], [13]

Treatment of Acanthamoebiasis

With acanthamoeic keratitis, a mandatory condition for treatment is the refusal to wear contact lenses. Locally appoint Maxitrol or SofraDex in the form of drops 6-12 times a day or in the form of ointment 3-4 times a day. In combination with drops, the ointment is used once for the night. Gentamicin solutions (0.3%), tobramycin (0.3%), paromomycin (0.5%), tetracycline (1%) or other ophthalmic ointments containing these drugs are used. You can also use instillations of solutions of neomycin, polymyxin B up to 6 times a day. In rare cases, in spite of the drug treatment of acanthamoebiasis, one must resort to keratoplasty.

Acanthamoebiasis and skin lesions are treated with antibiotics of the aminoglycoside group (gentamicin, paromomycin). Locally used neomycin, polymyxin, etc.

Treatment of amoebic encephalitis is effective only if it is diagnosed early, which is extremely rare. There are only three cases of cure for granulomatous acanthamoebic encephalitis.

Acanthamoebiasis has a favorable prognosis for skin and eye lesions, with CNS lesion, as a rule, unfavorable.

How to prevent acantammebiasis?

Acantamoebiasis can be prevented if the rules of hygiene of contact lenses are observed. Do not store lenses in tap water or saline solutions at home. They should be stored only in sterile solutions, specially prepared in ophthalmic institutions. These solutions must be changed according to the instructions for using contact lenses.

Prevention of acanthamoebic damage to the skin and encephalitis is to observe the rules of personal hygiene and limit contact with habitats of acanthamoebas.