The genus Acanthamoeba includes several species of opportunistic free-living amebae that might invade the brain through the blood, probably from a primary infection in the skin (from ulcers or dermatitis) or sinuses. Once in the brain, the amebae cause granulomatous amebic encephalitis (GAE). Acanthamoeba GAE has a slow and insidious onset and develops into a subacute or chronic disease lasting several weeks to months. Acanthamoeba GAE affects both immunocompetent persons and persons who are immunosuppressed from a variety of causes (e.g., HIV/AIDS, organ transplantation). Initial symptoms of Acanthamoeba GAE might include headache, photophobia, and stiff neck accompanied by positive Kernig’s and Brudzinski’s signs. Other symptoms might include nausea, vomiting, low-grade fever, muscle aches, weight loss, mental-state abnormalities, lethargy, dizziness, loss of balance, cranial nerve palsies, other visual disturbances, hemiparesis, seizures, and coma. Once the disease progresses to neurologic infection, it is generally fatal within weeks or months. However, a few patients have survived this infection.
Laboratory Criteria for Diagnosis
Laboratory-confirmed Acanthamoeba spp. infections (excluding keratitis) are defined as the detection of Acanthamoeba spp.
- Organisms in CSF, biopsy, or tissue specimens, OR
- Nucleic acid (e.g., polymerase chain reaction) in CSF, biopsy, or tissue specimens, OR
- Antigen (e.g., direct fluorescent antibody) in CSF, biopsy, or tissue specimens.
A clinically compatible illness that is laboratory confirmed.*
Acanthamoeba and B. mandrillaris can cause clinically similar illnesses and might be difficult to differentiate using commonly available laboratory procedures. Definitive diagnosis by a reference laboratory might be required. Several species of Acanthamoeba are associated with infection (i.e., A. castellanii, A. culbertsoni, A. hatchetti, A. healyi, A. polyphaga, A. rhysodes, A. astonyxis, A. lenticulata and A. divionensis). A negative test on CSF does not rule out Acanthamoeba infection because the organism is not commonly present in the CSF.