Acanthamoeba

Acanthamoeba is a genus of amoebae that are commonly recovered from soil, fresh water, and other habitats.Acanthamoeba has two evolutive forms, the metabolically active trophozoite and a dormant, stress-resistant cyst. Trophozoites are small, usually 15 to 25 μm in length and amoeboid in shape. In nature, Acanthamoeba species are free-living bacterivores, but in certain situations, they can cause infections (acanthamebiasis) in humans and other animals. Acanthamoeba spp. are among the most prevalent protozoa found in the environment. They are distributed worldwide, and have been isolated from soil, air, sewage, seawater, chlorinated swimming pools, domestic tap water, bottled water, dental treatment units, hospitals, air-conditioning units, and contact lens cases. Additionally, they have been isolated from human skin, nasal cavities, throats, and intestines, as well as plants and other mammals. Diseases caused by Acanthamoeba include keratitis and granulomatous amoebic encephalitis (GAE). The latter is often but not always seen in immunosuppressed patients. GAE is caused by the amoebae entering the body through an open wound then spreading to the brain. The combination of host immune response and amoebal proteases causes massive brain swelling resulting in death in about 95% of those infected. GAE is caused by amoebic infection of the central nervous system (CNS). It is characterized by neurological symptoms including headache, seizures, and mental-status abnormalities. These worsen progressively over weeks to months, leading to death in most patients. Infection is generally associated with underlying conditions such as immunodeficiency, diabetes, malignancies, malnutrition, systemic lupus erythematosus, and alcoholism. The parasite enters the body through cuts in the skin or by being inhaled into the upper respiratory tract. The parasite then spreads through the blood into the CNS. Acanthamoeba crosses the blood–brain barrier by means that are not yet understood. Subsequent invasion of the connective tissue and induction of pro-inflammatory responses leads to neuronal damage that can be fatal within days. Pure granulomatous lesions are rare in patients with AIDS and other related immunodeficiency states, as the patients do not have adequate numbers of CD+ve T-cells to mount a granulomatous response to Acanthamoeba infection in CNS and other organs and tissues. A perivascular cuffing with amoebae in necrotic tissue is usual finding in the AIDS and related T-cell immunodeficiency conditions. Brain biopsy normally reveals severe oedema and hemorrhagic necrosis. A patient who has contracted this illness usually displays subacute symptoms, including altered mental status, headaches, fever, neck stiffness, seizures, and focal neurological signs (such as cranial nerve palsies and coma), all leading to death within one week to several months. Due to the rarity of this parasite and a lack of knowledge, no good diagnoses or treatments for Acanthamoeba infection are now known. Acanthamoeba keratitis cases in the past, have resolved from a therapy consisting of atropine and some other drugs with no antimicrobial effects. Recent publications show atropine to interfere with the protist's CHRM1 receptor, causing cell death. Infection usually mimics that of bacterial leptomeningitis, tuberculous meningitis, or viral encephalitis. The misdiagnosis often leads to erroneous, ineffective treatment. In the case that the Acanthamoeba is diagnosed correctly, the current treatments, such as amphotericin B, rifampicin, trimethoprim-sulfamethoxazole, ketoconazole, fluconazole, sulfadiazine, or albendazole, are only tentatively successful. Correct and timely diagnosis, as well as improved treatment methods and an understanding of the parasite, are important factors in improving the outcome of infection by Acanthamoeba. A paper published in 2013 has shown substantial effects of some FDA-approved drugs with an in vitro kill rate above 90%. These results were in vitro effects, but as the drugs are already approved, human infections can be targeted after dose calculations in clinical trials done with these diverse groups of drugs. When present in the eye, Acanthamoeba strains can cause acanthamoebic keratitis, which may lead to corneal ulcers or even blindness. This condition occurs most often among contact lens wearers who do not properly disinfect their lenses, exacerbated by a failure to wash hands prior to handling the lenses. Multipurpose contact lens solutions are largely ineffective against Acanthamoeba, whereas hydrogen peroxide-based solutions have good disinfection characteristics. The first cure of a corneal infection was achieved in 1985 at Moorfields Eye Hospital.