Free-living Amebae

2024 Case Definition

CSTE Position Statement Number: 16-ID-12

1. Naegleria fowleri causing Primary Amebic Meningoencephalitis (PAM)

Clinical Description

An infection presenting as meningoencephalitis or encephalitis. The clinical presentation of PAM is like that of acute meningitis caused by other pathogens and symptoms include headache, nausea, vomiting, anorexia, fever, lethargy, and stiff neck. There are often other symptoms, such as disorientation, mental status changes, seizure activity, loss of consciousness, and ataxia that may occur within hours of initial presentation.

Laboratory Criteria

Confirmatory Laboratory Evidence:

Case Classification

Confirmed case: a case that meets the clinical criteria and confirmatory laboratory criteria for diagnosis

Probable case: a case that meets the clinical criteria and the supportive laboratory criteria for diagnosis

2. Balamuthia mandrillaris Disease

Clinical Description

An infection presenting as meningoencephalitis or encephalitis, disseminated disease (affecting multiple organ systems), or cutaneous disease. Granulomatous amebic encephalitis (GAE) can include general symptoms and signs of encephalitis such as early personality and behavioral changes, depressed mental status, fever, photophobia, seizures, nonspecific cranial nerve dysfunction, and visual loss. 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.

Laboratory Criteria

Confirmatory Laboratory Evidence:

Case Classification

Confirmed case: a case that meets the clinical criteria and confirmatory laboratory criteria for diagnosis

3. Acanthamoeba Disease (excluding keratitis)

Clinical Criteria

An infection presenting as meningoencephalitis or encephalitis, disseminated disease (affecting multiple organ systems), or cutaneous disease. Acanthamoeba spp. GAE presents similarly to B. mandrillaris GAE with early personality and behavioral changes, depressed mental status, fever, photophobia, seizures, nonspecific cranial nerve dysfunction, and visual loss. Skin lesions and sinus disease may also be seen.

Laboratory Criteria

Confirmatory Laboratory Evidence:

Case Classification

Confirmed case: a case that meets the clinical criteria and confirmatory laboratory criteria for diagnosis

Criteria for defining cases of Acanthamoeba Disease (excluding keratitis), Balamuthia mandrillaris Disease, or Naegleria fowleri causing Primary Amebic Meningoencephalitis (PAM).

Criterion Naegleria fowleri
causing PAM,
Probable
Naegeleria fowleri
causing PAM,
Confirmed
Balamuthia mandrillaris
disease,
Confirmed
Acanthamoeba,
spp,

Confirmed
Clinical Evidence
Meningoencephalitis or encephalitis N N
Meningoencephalitis or encephalitis; or disseminated disease; or cutaneous disease; or GAE N N
Laboratory Evidence
Detection of antigen or nucleic acid from a clinical specimen (e.g., immunohistochemistry or PCR) N N N
Visualization of motile amebae in a wet mount of CSF O
Isolation of amebae in culture from a clinical specimen O

Notes:

S = This criterion alone is Sufficient to classify a case.

N = All “N” criteria in the same column are Necessary to classify a case. A number following an “N” indicates that this criterion is only required for a specific disease/condition subtype (see below). If the absence of a criterion (i.e., criterion NOT present) is required for the case to meet the classification criteria, list the Absence of criterion as a Necessary component.

O = At least one of these “O” (One or more) criteria in each category (e.g., clinical evidence and laboratory evidence) in the same column—in conjunction with all “N” criteria in the same column—is required to classify a case. (These “O” criteria are alternatives, which means that a single column will have either no O criteria or multiple O criteria; no column should have only one O.) A number following an “O” indicates that this criterion is only required for a specific disease/condition subtype.

Date Posted: