Acanthamoeba infection

Acanthamoeba are pathogens of amoebic keratitis (especially in contact lens wearers) and in immunocompromised persons (e.g. HIV-infected persons) they are the trigger of a granulomatous amoebic encephahalitis which often ends fatally. Cutaneous lesions have rarely been observed in HIV-infected persons (chronic granulomas, ulcers). Balamuthia mandrillaris can also infect people without a recognisable immune deficiency.

Acanthamoebae are a genus of ubiquitously occurring protozoa (water, soil, air, upper respiratory tract) and belong to the family Acanthamoebidae. In cystic form they can survive for several years. Under suitable environmental conditions the cyst form of the pathogen changes into its active form (trophozoite) and is then able to penetrate a tissue.

In industrialized countries, infections are mainly caused by direct inoculation with contact lenses that have not been cleaned properly (e.g. contaminated cleaning solution or tap water or saliva). Another route and site of infection is the respiratory tract (inhalation of contaminated dust). Immunocompromised patients are particularly susceptible to active acanthamoeba infections (Tananuvat N et al. 2019).

Clinically significant are:

• Eye infections (acanthamoebic keratitis)
• Respiratory tract infections
• CNS infestation with high lethality (granulomatous amoebic encephalitis); amoebae can enter the brain via the lungs or contaminated wounds, but also directly through the olfactory epithelium Acanthamoeba species and closely related Balamuthia mandrillaris cause granulomatous amoebic encephalitis (GAE).

Microscopic image of the cysts from a smear taken from the cornea with addition of 10% potassium hydroxide. PAS staining is also possible.

Culture: on nutrient-rich agar loaded with killed Escherichia coli

Immunohistochemical: Detection of amoebic antigen by PCR

Confocal in vivo microscopy: Detection in appropriately equipped ophthalmological practices by confocal in vivo microscopy of the cornea.

For immunocompromised persons: targeted optimisation of the immune status.

Acanthamoeba-granulomatous amoebic encephalitis: reports of successful therapy with a combination of pentamidine, sulfadiazine, flucytosine and either fluconazole or itraconazole are available.

Amoebic keratitis: Treatment with local therapeutic agents such as chlorhexidine, neomycin, paromomomycin, azole antifungals, propamidine-isetionate and anti-inflammatory glucocorticoids. Therapy over several months.

1. Bunsuwansakul C et al (2019) Acanthamoeba in Southeast Asia - Overview and Challenges. Korean J Parasitol 57:341-357.
2. Hirabayashi KE et al. (2019) Oral miltefosine for refractory acanthamoeba keratitis. On J Ophthalmol Case Rep 16:100555.
3. Tananuvat N et al. (2019) The First Acanthamoeba keratitis Case of Non-Contact Lens Wearer with HIV infection in Thailand. Korean J Parasitol 57:505-511.