California Association
for
Medical Laboratory Technology

Distance Learning Program

PRIMARY AMEBIC MENINGOENCEPHALITIS (PAM)
Course # 056-930

by

Harris S. Goodman, M.D., Pathologist
Valley Care Health System Clinical Laboratory
Pleasanton, CA

Level of Instruction: Intermediate

Approved for 1.0 CE/Contact Hours

CAMLT is approved by the California Department of Health Services as a CA CLS Accrediting Agency (#0021)
and this course is approved by ASCLS for the P.A.C.E.® Program (#519)

1895 Mowry Ave, Suite 112
Fremont, CA 94538-1700
Phone: 510-792-4441
FAX:  510-792-3045

Notification of Distance Learning Deadline

December 31 at 11:59 PM is the deadline for submission of distance Learning materials for CE credit for the calendar year. This deadline means that must have submitted your materials and passed the test questions. Individuals who wait until December 31 to submit their answer sheet, and fail the test, will have no further recourse. CE units cannot be awarded. Don't risk losing your license! Allow yourself enough time to retake the test should you fail on your first attempt.

Links to:

Review Questions at the end of this Course
Printable Answer Sheet/Registration Form
Other Distance Learning Courses

Course Objectives:

  1. Recognize the appearance of the etiologic agent of primary amebic meningoencephalitis (PAM).
  2. List the sources of infection of PAM.
  3. Explain the route by which Naegleria fowleri gains access to the central nervous system.
  4. Describe the clinical course of PAM.
  5. State a different diagnosis for amebic infections of the central nervous system.

Case Presentation:

A 20-year-old Norwegian male nurse, previously healthy, who traveled extensively and worked with Mother Teresa, presented to his physician complaining of fever, headache, photophobia, blurry vision, nausea, vomiting, dizziness, purulent nasal discharge and feeling "cold." The patient was admitted to U.C.S.F Medical Center on October 21st for observation. He appeared a well-developed, well-nourished white male with projectile vomiting.

Travel History:

January

Departs Norway

January - October Visits India (and Mother Teresa), Nepal, Thailand, Vietnam, Australia, New Zealand, Malaysia, Indonesia, Fiji and the Cook Islands

October 10th

Arrives in Los Angeles, continues on to San Francisco, CA

October 11th Departs San Francisco on a 9-day Green Tortoise® bus tour of the Western United States
October 12th Swims in Deep Creek Hot Springs, San Bernardino National Forest, CA
October 13th - 15th Visits the Grand Canyon, Painted Desert, and Canyon de Chelley, AZ
October 16th Swims in the San Juan River between AZ and UT
October 18th

Swims in Lake Powell and Pah Tempe Hot Springs, UT

October 19th Visits Zion National Park, UT
October 20th Visits Las Vegas, NV and returns to San Francisco, complains of feeling "cold"

Laboratory Studies:

WBC: 16.2 k/µL with 93% neutrophils

Hemoglobin: 14.0 g/dL

Hematocrit: 39.5%

Platelets: 230 k/µL

Glucose: 223 mg/dL

Electrolytes: Normal

Liver function tests: Normal

Chest x-ray: Normal

EKG: Normal

HIV antibody: Negative

Malaria blood smear: Negative


Lumbar Puncture:

Appearance: cloudy
WBC: 6.2 k/µL with 70% neutrophils
RBC: 1.4 k/µL
Protein: 296 mg/dL
Glucose: 79 mg/dL (Serum glucose: 223 mg/dL)
VDRL and Cryptococcus antigen studies negative

Hospitalization:

Day 1 (Oct. 22):The patient was diagnosed with acute bacterial meningitis and treated with ampicillin, nafcillin and cefotaxine.
Day 2 (Oct. 23):The patient no longer responded to verbal commands and began to suffer intermittent disconjugate gaze and decreased deep tendon reflexes. A CT scan of the brain suggested mild edema, but no loss of definition of the gray-white junction or focal lesions observed. The onset of generalized tonic-clonic seizures required dilantin, lorazepam and dexamethasone administration.
Day 3 (Oct. 24):The Clinical Laboratories Department identified amebic trophozoites consistent with either Naegleria or Acanthamoeba in CSF obtained at admission. The patient was taken to surgery where an Ommaya reservoir was placed into the right ventricle and intrathecal Amphotericin B and hydrocortisone was administered. Post-operatively, the patient became comatose and required ventilatory support.
Day 4 (Oct. 25):Patient’s pupils became fixed and dilated and no longer responded to cold calorics or deep pain.
Day 5 (Oct. 26):A repeat CT scan revealed worsening diffuse cerebral edema with interval development of mild hydrocephalus.
Day 6 (Oct. 27):Life support was withdrawn and the patient expired.

Discussion:

Naegleria fowleri is the etiologic agent of the rapidly fatal disease known as primary amoebic meningoencephalitis (PAM). Human disease caused by free-living amoeba was first reported by Fowler and Carter in 1965, who studied four patients with PAM in Australia. The following year, several cases of PAM acquired in the United States were reported by Butt in Florida, who coined the term "primary amoebic meningoencephalitis, "to distinguish infection of the central nervous system by free-living amoeba such as N. fowleri from the rare invasions of the brain by the intestinal amoeba Entamoeba histolytica (1).

Acanthamoeba spp are a rare cause of amebic encephalitis. This disease associated with Acanthamoeba is mostly subacute or chronic granulomatous amebic encephalitis with symptoms of headache, altered mental states, and focal neurologic deficit which progresses over several weeks to months to death. Acanthamoeba can also cause skin lesions as well as keratitis and corneal ulcers following corneal injury or in association with contact lenses.


Figure 1 Differentiating between N. fowleri and Acanthamoeba.

N. fowleri trophozoites are small amoeba which move by producing smooth hemispherical bulges. Cysts are usually spherical, measuring 7-15mm. Acanthamoeba trophozoites are slightly larger and move by fine, tapering hyaline projections called acanthopodia. It produces a double walled cyst measuring 10-25mm with an outer wrinkled wall. Both Naegleria and Acanthamoeba are uninucleate and the nucleus has a large, dark staining, centrally located karyosome. Naegleria has a flagellated stage whereas Acanthamoeba does not.

PAM generally occurs in previously healthy children and young adults with a recent history of swimming in warm fresh water lakes, ponds, or hot springs. Infection results from the introduction of water containing amoeba into the nasal cavity and up against the olfactory neuroepithelium. Sustentacular cells of the olfactory neuroepithelium are capable of active phagocytosis, which appears to be the means by which the Naegleria penetrate the central nervous system (2). From the olfactory neuroepithelium, the amoeba migrate along the mesaxonal spaces of the unmyelinated olfactory nerves. The olfactory nerves terminate in the olfactory bulbs, located in a subarachnoid space bathed by CSF. Once the amoeba reach these bulbs, they are free to disseminate throughout the CNS. Extremely rare cases of infection resulting from the inhalation of N. fowleri cysts, as occurs during dust storms, has also been reported as a means of infection (1).

Following an incubation period of 2-15 days, there is a relatively abrupt onset of severe meningeal symptoms. Symptoms begin with fever and headache, and are rapidly followed by photophobia, nausea, projectile vomiting, nuchal rigidity, and in many cases disturbances to taste (ageusia) and smell (parosmia). Generalized seizures may also be present. Rapid progression from lethargy to coma occurs, followed by transtentorial and/or cerebellar herniation secondary to massive cerebral edema. The vast majority of cases end in death 3-7 days after the onset of symptoms (2).

At autopsy, the cerebral hemispheres are usually severely edematous. Uncal and cerebellar tonsillar herniation may be present. The meninges typically are hyperemic and exhibit a purulent exudate. The olfactory bulbs may display marked involvement with hemorrhage and necrosis. Microscopically, the leptomeninges display a fibrinopurulent exudates with numerous polymorphonuclear leukocytes, eosinophils, a few monocytes, and some lymphocytes. Amoebic trophozoites are also seen within the exudates, resembling macrophages, but are characterized by a prominent karyosome. The cortical gray matter is also involved in all cases. Encephalitis ranges from slight amoebic invasion and inflammation to massive invasion with purulent hemorrhagic necrosis, as was seen in this case. As the amoeba travel throughout the ventricular system, an acute ependymitis may also result. Myocarditis has also been associated with PAM; it has been suggested that a circulating myotoxin produced and released by the amoeba may be the etiologic agent. However, no evidence of myocarditis was found in this case (1).

Diagnosis of PAM is difficult. Clinically, PAM resembles fulminating bacterial meningitis, with its acute onset of meningeal symptoms and the finding of a purulent or sanguinopurulent CSF with a predominantly neutrophil leukocyte count. Diagnosis is made when stained amoeba are seen in Wright or Giemsa preparations of CSF; motile amoebic trophozoites are readily seen in simple wet mount preparations of CSF observed at room temperature (3).

Table 1 (Part A). Cerebrospinal Fluid (CSF) Findings in Primary Amebic Meningoencephalitis

CSF Findings

Acute
Amebic Meningoencephalitis

Granulomatous
Amebic Encephalitis

Opening pressure

elevated (often markedly)

elevated

Protein

moderately elevated (75-970 mg/100ml)

slightly elevated

Glucose

low (often markedly)

normal to low normal

White blood cell count

300-24,000

usually <500

Differential

90-95% neutrophils

>50% neutrophils, but round cells may predominate

Red blood cell count

few to 25,000

not usually present

Ameba

usually Naegleria present (highly motile)

Acanthamoeba spp. not usually present


Table 1 (Part B). Differential Factors of Primary Amebic Meningoencephalitis

Factors

Acute
Amebic Meningoencephalitis

Granulomatous
Amebic Encephalitis

Disease

Acute, fulminant pyogenic meningitis

Chronic or subacute encephalitis with reactive meningitis

Responsible ameba

Principally N. fowleri

Principally Acanthamoeba spp.

Age

Child or young adult

Any age

Sex

Males 3:2

Males 5:1

Prior Health

Excellent

Often underlying diseases present (e.g. cirrhosis, immunosuppressed host)

Epidemiology

Prior intimate contact with fresh water (e.g., swimming); seasonal (hot, summer months)

Unknown

Incubation period

3-8 days

Unknown; may be >10 days

 

 

 

Portal of entry

Nose, via olfactory mucosa and neuroepithelium

Skin, eye, lung, ear, prostate, uterus, urinary tract, nose

Invasion route to CNS

Direct via fila olfactoria (amyelinic nervous plexus)

Usually hematogenous; on occasion directly via fila olfactoria

Course

Acute, rapidly fatal 2-3 days

Usually subacute or chronic; fatal

 

Clinical presentation

Resembles acute bacterial meningitis

Resembles brain abscess(es); occasionally subacute bacterial meningitis

Diagnostic tests

Direct visualization of amebae in CSF; serum and CSF indirect immunofluorescense; N. fowleri agglutination titers; precipitin gel diffusion test; direct fluorescent or immunoperoxidase staining of involved brain tissue

Serum and CSF indirect immunofluorescence; amebic immobilization test; direct fluorescent or immunoperoxidase staining of brain tissue

Pathology

Hemorrhagic, necrotizing meningoencephalitis primarily involving grey matter (olfactory, frontal, temporal lobes, cerebellum)

Granulmatous encephalitis with multiple lesions primarily involving white matter (midline structures); with more acute disease can be necrotizing

Histopathology

Predominantly neutrophilic response

Predominantly round cell response with giant cells and neutrophils

Protozoology

Trophozoites seen in and isolated from CSF and brain tissue

Trophozoites and cysts seen in and isolated from brain tissue but organism rarely found in CSF

Differential diagnosis

Acute bacterial or viral meningitis

Tuberculosis or fungal meningitis, brain abscess or brain tumor

Treatment

Amphotericin B; may add rifampin tetracycline or minocycline

No chemotherapy available; early surgery may be important

 

Treatment:

Treatment of PAM is generally unsuccessful. By 1998 there were 344 cases reported, only 4 patients had survived the infection (4). The most recent survivor received intrathecal and intravenous amphotericin-B, intrathecal and intravenous miconazole, and oral rifampin. In addition, dexamethasone and phenytoin were administered for increased intracranial pressure and seizure activity, respectively. The patient was discharged one month after admission with residual decrease in pain sensation in her left leg, and was asymptomatic two months later. The clinicians felt that survival was related especially to the early diagnosis, prompt intervention, and intensive supportive care the patients received (3).

The risk of infection from water containing Naegleria fowleri is unknown but probably small, since thousands of people swim in lakes, ponds and hot springs known to contain these organisms, and yet cases of PAM are extremely rare (5).

References:

  1. John D: Primary amebic meningoencephalitis and the biology of Naegleria fowleri. Ann Review Microbiology 36: 101-123, 1982
  2. Ma P, et al: Naegleria and Acanthamoeba infections: Review. Rev Infec Dis 12: 490-513, 1990.
  3. Seidel J, et al: Successful treatment of primary amebic meningoencephalitis. NEJM 306: 490-513, 1982
  4. USFDA Center for Food Safety and Applied Nutrition, Foodborne Pathogenic Microorganisms and Natural Toxins Handbook ("Bad Bug Book") http://vm.cfsan.fda.gov/~mow/chap29.html
  5. Centers for Disease Control. Primary Amebic Meningoencephalitis - - California, Florida, New York. Morbidity and Mortality Weekly Rpt 37: 343-344, 1978.
  6. Marciano-Cabral, F: Biology of Naegleria Spp. Microbiol Rev 52: 114-133, 1988.

More information can be obtained by looking up Primary Amebic Meningoencephalitis on the internet.


Questions: - Go here to get a printable answer/registration form

(Please select the one best answer)

  1. The organism which causes primary amebic meningoencephalitis (PAM) is a:
    1. bacteria
    2. fungus
    3. protozoa
    4. virus

  2. All of the following are sources of the infectious agent of PAM except:
    1. warm water lakes
    2. natural hot springs
    3. fresh water ponds
    4. steam baths and saunas

  3. Amoeba that have been reported to infect the CNS include all but one of the following:
    1. Acanthamoeba
    2. Naegleria fowleri
    3. Entamoeba coli
    4. Entamoeba histolytica

  4. The etiologic agent of primary amebic meningoencephalitis gains access to the central nervous system by way of:
    1. oral ingestion, followed by absorption within the intestinal tract and hematogenous spread to the brain.
    2. nasal inhalation, followed by absorption in the lungs and hematogenous spread to the brain.
    3. nasal inhalation, followed by absorption through the nasal mucosa directly along the olfactory nerve and into the olfactory bulb of the brain.
    4. direct penetration of the skin, followed by hematogenous spread to the brain.

  5. The incubation period for Naegleria is:
    1. 2 to 3 weeks
    2. 1 to 5 days
    3. one year
    4. 2 to 15 days

  6. Symptoms of PAM begin with:
    1. diarrhea and vomiting
    2. fever and headache
    3. chest pain and shortness of breath
    4. nasal congestion and sore throat

  7. Clinically, PAM resembles:
    1. fulminating bacterial meningitis
    2. viral meningitis
    3. influenza
    4. malaria

  8. In laboratory findings, the CSF is purulent or sanguinopurulent combined with:
    1. elevated WBC count, elevated glucose, and decreased protein, positive gram stain.
    2. decreased WBC count, decreased glucose, decreased protein, negative gram stain.
    3. low to high WBC count, decreased glucose, increased protein, negative gram stain.
    4. low to high WBC count, increased glucose, increased protein, negative gram stain.

  9. The diagnosis of PAM is made by:
    1. finding cysts in fecal specimens
    2. thick and thin blood smears
    3. bacterial gram stain
    4. microscope identification of living or stained amoebae in CSF

  10. Treatment of PAM caused by N. fowleriis usually ineffective, with death usually occurring:
    1. in 3-6 weeks after onset of symptoms
    2. in 10-15 days after onset of symptoms
    3. in less than a week after the onset of symptoms
    4. in 2-3 months prior to the onset of symptoms.