Infectious Diseases Data Verified

Naegleria infection - Symptoms, Diagnosis, and Treatment

Published on Feb 06, 2023 and last reviewed on Feb 28, 2023   -  5 min read


Naegleria is a small, free-living ameba found in freshwater. Read this article to know more about it.


Naegleria fowleri, also known as brain-eating ameba, is a single-celled organism found in fresh or contaminated water. It causes deadly brain infections when it enters the human body. The infection is called primary amebic meningoencephalitis (PAM). A person gets infected only when contaminated water enters the nose, not when drinking or eating contaminated water. This article deals with the infection caused by Naegleria.

Where Is Naegleria Found?

Naegleria can grow in hot water at around 115 degrees Fahrenheit. For example, they can live in

  • Warm lakes and ponds.

  • Mud.

  • Untreated swimming pools.

  • Untreated well water.

  • Aquariums.

  • Soil.

Naegleria cannot live in salt water, adequately treated swimming pools, wells, and municipal water.

What Is the Lifecycle of Naegleria Fowleri?

The lifecycle of Naegleria fowleri has three stages: cystic, trophozoites, and flagellated forms. The trophozoites, which developed from the cystic forms, multiply by pro mitosis, where the nuclear membrane remains intact. The trophozoite form can transform into flagellated form and revert to trophozoites, which infect animals and humans by entering through the nasal cavity, traveling to the brain through the olfactory nerves, and causing primary amebic meningoencephalitis (PAM). The cystic stage of ameba cannot be identified from the brain, but the trophozoites and flagellated forms can be identified in the cerebrospinal fluid (CSF).

How Does Naegleria Infect People?

Naegleria fowleri enters the human body through the nose when individuals swim, dive, or put their hands in fresh or contaminated water. The ameba travels from the nose to the brain and causes a deadly infection. It may happen when individuals use contaminated water to cleanse their faces or sinuses. No scientific studies show the infection through vapor.

What Are the Signs and Symptoms of Naegleria Infection?

Naegleria fowleri causes primary amebic meningoencephalitis, affecting the central nervous system. The infection has symptoms similar to bacterial meningitis, which makes it challenging to identify primary amebic meningoencephalitis at first.

The symptoms include

The symptoms may occur 2 to 12 days after exposure to the organism. As PAM is difficult to diagnose, the infection is diagnosed only after the patient dies.

What Is the Cause of Death From Naegleria Fowleri Infection?

In severe cases, the infection will likely destroy the brain tissue, causing brain swelling and death. The death rate was around 97 % from 1960 to 2021, with which four out of 154 infected individuals survived.

How to Diagnose Naegleria Infection?

  • It is challenging to diagnose Naegleria infection, as it shows symptoms similar to bacterial meningitis. Therefore, almost 75% of cases are diagnosed after death. However, If the physician suspects PAM, specific lab tests can be carried out in cerebrospinal fluid, biopsy, or tissue culture.

  • Lumbar puncture is performed to withdraw cerebrospinal fluid, the primary tool for diagnosing PAM. In contrast, tissue culture can detect granulomatous amebic encephalitis. The findings in the cerebrospinal fluid show leukocytosis (increased leukocyte count), polymorphonuclear leukocyte predominance, increased CSF pressure, hemorrhagic fluid, CSF red blood cells, elevated protein, and hypoglycorrhachia (abnormally low glucose concentration).

  • Motile trophozoites can be observed on centrifuged CSF wet mount preparation. The features of the trophozoites can be well highlighted using Giemsa or trichome stains.

  • A CT (Computed Tomography) scan of the head and MRI (Magnetic Resonance Imaging) should be taken before lumbar puncture if clinical signs of the central nervous system are present. The CT scan can show hydrocephalus (abnormal brain fluid buildup), isolated and multifocal ring lesions, and meningeal thickening. An MRI scan of the brain can show single or multiple ring-enhanced lesions.

  • Most cases are identified after death, and the significant findings noted after death are edema and hemorrhage of the brain.

What Are the Differential Diagnoses of Naegleria Infection?

The differential diagnoses of Naegleria infection (primary amebic meningoencephalitis) are

  • Aseptic meningitis.

  • Bacterial meningitis.

  • Brain abscess.

  • Valley fever.

  • Cysticercus.

  • Encephalitis.

  • Histoplasmosis.

  • Intracranial hemorrhage.

  • Malaria.

  • Meningococcal infections.

  • Mucormycosis.

  • Rabies.

  • Sappinia.

  • Toxoplasmosis.

  • Tuberculosis.

  • Vasculitis.

  • Thrombophlebitis.

How to Treat Naegleria Infection?

Naegleria infection is challenging to treat as its diagnosis is difficult. Intravenous and intrathecal administration of Amphotericin B is recommended for PAM, but a combination of medications was considered due to the severe course of the disease and high fatality rates. The combination of medications includes Amphotericin B, Azithromycin, Rifampin, Dexamethasone, Fluconazole, and Miltefosine, which were found to produce significant results through clinical studies. These drugs are those administered to the surviving individuals, in which Miltefosine, a new drug with amoeba-killing ability, is included in the regime. In addition, it is used to treat Balamuthia and Acanthamoeba infections. Posaconazole is a drug that can replace Fluconazole at times.

How to Prevent Naegleria Infection?

The preventive measures to be followed to prevent Naegleria infection are

Precautions to avoid contact with water:

  • Avoid swimming in warm climates.

  • Use nose clips or shut the nose in water bodies.

  • Avoid swimming in less chlorinated or untreated water bodies.

  • Avoid digging the sediments in shallow water bodies.

Treating water before nasal rinsing:

  • Use water that is boiled and cooled.

  • Filter the water before rinsing.

  • Use chlorine bleach as per guidelines if boiling and filtering are impossible.


Amebic encephalitis is a rare and lethal disease of the central nervous system caused by single-celled organisms. In addition, it is challenging to treat as it is often diagnosed after death. Hence, healthcare professionals must educate patients at a higher risk of infection. For example, people who live near stagnant water bodies where organisms can proliferate must be educated to live with precautions. Furthermore, an interprofessional team of doctors working to identify and treat the organism is required to survive the disease.

Article Resources

Last reviewed at:
28 Feb 2023  -  5 min read




Comprehensive Medical Second Opinion.Submit your Case

Related Questions & Answers

Herpes Meningitis - Symptoms, Complications, and Preventive Strategies

Article Overview: Herpes meningitis is caused by the hidden viruses in the body from a previous herpes infection; they cause inflammation in the meningeal layers of the brain. Read Article

Abhishek Juneja
Abhishek Juneja

What Is Herpes Meningitis? Herpes viruses are very common and quite diverse. Among the eight herpes viruses that infect humans, the herpes simplex virus causes cold sores, chickenpox, and infectious mononucleosis. Rarely they may cause meningitis in an individual. Meningitis is the common term for i...  Read Article

Popular Articles Most Popular Articles

Do you have a question on Meningoencephalitis or Naegleria Fowleri?

Ask a Doctor Online

* guaranteed answer within 4 hours.

Disclaimer: No content published on this website is intended to be a substitute for professional medical diagnosis, advice or treatment by a trained physician. Seek advice from your physician or other qualified healthcare providers with questions you may have regarding your symptoms and medical condition for a complete medical diagnosis. Do not delay or disregard seeking professional medical advice because of something you have read on this website. Read our Editorial Process to know how we create content for health articles and queries.