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Introduction
1. Anatomy
2. Microbiology
2.1 General bacteriology
2.2 Introduction to systemic bacteriology
2.3 Gram positive cocci
2.4 Gram negative cocci
2.5 Gram positive bacilli
2.6 Gram negative bacilli
2.7 Other important bacteria
2.8 Virology
2.9 Parasitology
2.9.1 Entamoeba histolytica
2.9.2 Acanthamoeba
2.9.3 Naegleria fowleri
2.9.4 Giardia lamblia
2.9.5 Cryptosporidium parvum
2.9.6 Trichomonas
2.9.7 Plasmodium spp.
2.9.8 Babesia
2.9.9 Toxoplasma gondii
2.9.10 Taenia
2.9.11 Hymenolepis nana
2.9.12 Enterobius vermicularis
2.9.13 Trichuris
2.9.14 Trichinella
2.9.15 Ascaris
2.9.16 Hookworms
2.9.17 Strongyloides
2.9.18 Additional information
2.10 Mycology
3. Physiology
4. Pathology
5. Pharmacology
6. Immunology
7. Biochemistry
8. Cell and molecular biology
9. Biostatistics and epidemiology
10. Genetics
11. Behavioral science
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2.9.3 Naegleria fowleri
Achievable USMLE/1
2. Microbiology
2.9. Parasitology

Naegleria fowleri

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Naegleria fowleri

Commonly called the “brain-eating amoeba.” This free-living amoeba is found in warm freshwater (e.g., lakes, rivers, and hot springs) and in soil.

Transmission and pathogenesis

It typically enters through the nose after swimming or diving in contaminated lakes and rivers. Rarely, it has been associated with neti pot (a small pot used for nasal rinsing) use, because tap water may be contaminated.

After entering the nose, the amoeba migrates to the brain via the olfactory nerve.

Clinical disease

It causes PAM (primary amoebic meningoencephalitis), which presents with:

  • Fever, headache, nausea, vomiting
  • Followed by neck stiffness, seizures, altered consciousness, and coma

Only 5 cases so far have survived the infection in North America.

Laboratory diagnosis

PAM and Naegleria fowleri infection can be diagnosed in the laboratory by:

  • Detecting organisms in cerebrospinal fluid (CSF), biopsy, or tissue specimens
  • Nucleic acid detection in CSF, biopsy, or tissue specimens
  • Detection of antigen in CSF, biopsy, or tissue specimens

Motile amoebae can often be seen moving rapidly under a microscope when examining a fresh CSF sample. The amebae can also be stained with a variety of stains, such as Giemsa-Wright or a modified trichrome stain. Culture can be done as co-culture with E.coli.

Naegleria
Naegleria

IIF of Naegleria fowleri in brain tissue, viewed under UV microscopy.

Naegleria fowleri overview

  • “Brain-eating amoeba,” free-living in warm freshwater and soil
  • Infects humans via nasal entry, often during swimming or diving

Transmission and pathogenesis

  • Enters through nose, migrates to brain via olfactory nerve
  • Rare cases linked to neti pot use with contaminated tap water

Clinical disease (PAM)

  • Causes primary amoebic meningoencephalitis (PAM)
  • Symptoms: fever, headache, nausea, vomiting → neck stiffness, seizures, altered consciousness, coma
  • Extremely high fatality; only 5 survivors in North America

Laboratory diagnosis

  • Detection of organisms, nucleic acids, or antigens in CSF, biopsy, or tissue
  • Motile amoebae visible in fresh CSF under microscope
  • Staining: Giemsa-Wright, modified trichrome
  • Culture: co-culture with E. coli

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Naegleria fowleri

Naegleria fowleri

Commonly called the “brain-eating amoeba.” This free-living amoeba is found in warm freshwater (e.g., lakes, rivers, and hot springs) and in soil.

Transmission and pathogenesis

It typically enters through the nose after swimming or diving in contaminated lakes and rivers. Rarely, it has been associated with neti pot (a small pot used for nasal rinsing) use, because tap water may be contaminated.

After entering the nose, the amoeba migrates to the brain via the olfactory nerve.

Clinical disease

It causes PAM (primary amoebic meningoencephalitis), which presents with:

  • Fever, headache, nausea, vomiting
  • Followed by neck stiffness, seizures, altered consciousness, and coma

Only 5 cases so far have survived the infection in North America.

Laboratory diagnosis

PAM and Naegleria fowleri infection can be diagnosed in the laboratory by:

  • Detecting organisms in cerebrospinal fluid (CSF), biopsy, or tissue specimens
  • Nucleic acid detection in CSF, biopsy, or tissue specimens
  • Detection of antigen in CSF, biopsy, or tissue specimens

Motile amoebae can often be seen moving rapidly under a microscope when examining a fresh CSF sample. The amebae can also be stained with a variety of stains, such as Giemsa-Wright or a modified trichrome stain. Culture can be done as co-culture with E.coli.

IIF of Naegleria fowleri in brain tissue, viewed under UV microscopy.

Key points

Naegleria fowleri overview

  • “Brain-eating amoeba,” free-living in warm freshwater and soil
  • Infects humans via nasal entry, often during swimming or diving

Transmission and pathogenesis

  • Enters through nose, migrates to brain via olfactory nerve
  • Rare cases linked to neti pot use with contaminated tap water

Clinical disease (PAM)

  • Causes primary amoebic meningoencephalitis (PAM)
  • Symptoms: fever, headache, nausea, vomiting → neck stiffness, seizures, altered consciousness, coma
  • Extremely high fatality; only 5 survivors in North America

Laboratory diagnosis

  • Detection of organisms, nucleic acids, or antigens in CSF, biopsy, or tissue
  • Motile amoebae visible in fresh CSF under microscope
  • Staining: Giemsa-Wright, modified trichrome
  • Culture: co-culture with E. coli