Free-living Amebae Infections
2012 Case Definition

Clinical Description

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.

Confirmed

A clinically compatible illness that is laboratory confirmed.*

Comments

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.

Clinical Description

Acanthamoeba keratitis is a local infection of the cornea (outer layer of the visual pathway of the eye) caused by a microscopic, free-living ameba belonging to the genus Acanthamoeba. Symptoms include foreign body sensation, photophobia, decreased visual acuity, tearing, pain, and redness of the eye. It occurs most typically among healthy, contact lens users, but can occur in anyone. Although treatable with topical medications, affected individuals are at risk for permanent visual impairment or blindness. Acanthamoeba organisms are ubiquitous in nature and can be found in bodies of water (e.g., lakes and oceans), soil, and air.

Laboratory Criteria For Diagnosis

Laboratory-confirmed Acanthamoeba spp. keratitis infections are defined as the detection of Acanthamoeba spp.

• Organisms in corneal scraping, or biopsy specimens, OR
• Nucleic acid (e.g., polymerase chain reaction) in corneal scraping, or biopsy specimens, OR
• Antigen (e.g., direct fluorescent antibody) in corneal scraping, or biopsy specimens.

Probable

A clinically compatible illness with positive identification of Acanthamoeba trophozoites or cysts using confocal microscopy.

Confirmed

A clinically compatible illness that is laboratory confirmed.*

Clinical Description

B. mandrillaris is an opportunistic free-living ameba that can invade the brain through the blood, probably from a primary infection in the skin (from ulcers or dermatitis), sinuses, or via organ transplantation. The incubation period is not well-characterized but has been observed to range from 2 weeks to months or possibly years. Once in the brain, the amebae can cause meningoencephalitis and/or granulomatous amebic encephalitis (GAE). B. mandrillaris GAE often has a slow, insidious onset and develops into a subacute or chronic disease lasting several weeks to months; however, B. mandrillaris infections associated with organ transplantation have an especially rapid clinical course. B. mandrillaris GAE affects both immunocompetent persons and persons who are immunosuppressed from a variety of causes (e.g., HIV/AIDS, organ transplantation). Initial symptoms of B. mandrillaris 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. Painless skin lesions appearing as plaques a few millimeters thick and one to several centimeters wide have been observed in some patients, especially patients outside the U.S., preceding the onset of neurologic symptoms by 1 month to approximately 2 years. 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 B. mandrillaris infection is defined as the detection of B. mandrillaris

• 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.

Confirmed

A clinically compatible illness that is laboratory confirmed.*

Comments

B. mandrillaris and Acanthamoeba spp. 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. A negative test on CSF does not rule out B. mandrillaris infection because the organism is not commonly present in the CSF.

Clinical Description

N. fowleri is a free-living ameboflagellate that invades the brain and meninges via the nasal mucosa and olfactory nerve to cause acute, fulminant hemorrhagic meningoencephalitis (primary amebic meningoencephalitis – PAM), primarily in healthy children and young adults with a recent history of exposure to warm fresh water. Initial signs and symptoms of PAM begin 1 to 14 days after infection and include sudden onset of headache, fever, nausea, vomiting, and stiff neck accompanied by positive Kernig’s and Brudzinski’s signs. In some cases, abnormalities in taste or smell, nasal obstruction and nasal discharge might be seen. Other symptoms might include photophobia, mental-state abnormalities, lethargy, dizziness, loss of balance, other visual disturbances, hallucinations, delirium, seizures, and coma. After the onset of symptoms, the disease progresses rapidly and usually results in death within 3 to 7 days. Although a variety of treatments have been shown to be active against amebae in vitro and have been used to treat infected persons, most infections have still been fatal.

Laboratory Criteria For Diagnosis

Laboratory-confirmed N. fowleri infection is defined as the detection of N. fowleri

• 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.

Confirmed

A clinically compatible illness that is laboratory confirmed.*

Comments

N. fowleri might cause clinically similar illness to bacterial meningitis, particularly in its early stages. Definitive diagnosis by a reference laboratory might be required. Unlike Balamuthia mandrillaris and Acanthamoeba spp., Naegleria fowleri is commonly found in CSF.