Naegleria fowleri is a free-living thermophilic amoeba found in warm, stagnant freshwater and soil. There are many species of Naegleria which are known to infect fish and mice; however N. fowleri is the only species to be pathogenic in humans. Naegleria fowleri ends its life cycle in humans and cannot infect any other species because it is lethal. In humans, it causes Primary Amebic Meningoencephalitis (PAM), which results in the rapid inflammation of the meninges and the brain. Humans acquire this amoeba while swimming and diving in freshwater ponds and lakes.
The life cycle of N. fowleri can be separated into three (3) stages:
Cysts linger in the water and sediment of lakes and rivers until they encounter the optimal environment. When in the right environment cysts develop into trophozoites (amoebas). Trophozoites can then develop into flagellates or vice versa and then enter the nose and travel up the olfactory nerve and continue to their final destination, the brain. Flagellates are the non-feeding stage, but the most motile, and can be most often found in the cerebral spinal fluid whereas trophozoites are the pathogenic stage and cause the damage in the brain. However trophozoites are the most fragile stage of its life cycle. They are sensitive to environmental changes, even though they can be found at temperatures as high as 115º F/ 46º C. If the environment is unsuitable for trophozoites they can develop back into flagellates or cysts. Cysts can survive in water temperatures as low as 32º F/ 0º C. Once the environment becomes suitable again, the amoeba excyst into trophozoites and they cycle begins again.
Symptoms are often misdiagnosed for another disease, Bacterial Meningitis which is caused by a relative parasite, Fasciola hepatica. Misdiagnosis prevents quick treatment and leads to a most certain death. Fast treatment will not guarentee survival, but is the only thing that will increase your chances. Naegleria fowleri is not an infectious disease nor is it transmitted through drinking contaminated water. The amoeba must enter through the nose to be pathogenic. Death is in result to PAM, a rapid brain infection that leads to the destruction of the brain tissue.
Stage 1 Symptoms: Begin within 1 to 7 days post amebic exposure and include severe headache, fever, nausea and vomiting.
Stage 2 Symptoms: Include stiff neck, confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, death usually occurs within 1 to 12 days of onset of stage 2 symptoms. Final cause of death is brain swelling and deterioration of tissue.
There are five (5) ways in which Naegleria fowleri can be diagnosed. Unfortunately most diagnoses occur postmortem due to the rapid deterioration it has on its host. The fist method of detection is direct visualization of the amoeba. A sample of Cerebral Spinal Fluid (CSF) is obtai
ned by a spinal tap and not only can they be seen moving under a microscope but in some cases the infection is so dense the CSF takes on a cloudy appearance. The second method used is immunohistochemistry. In which an antibody specific to N. fowleri will be used in sync with another antibody that deposits a color or glows under a specific light. Polymerase Chain Reaction (PCR) allows you to amplify the DNA from a CSF or tissue sample to identify which specific amoeba strains are present. In mixed samples Amoeba culture and Environmental detection (water samples) both employ media plates in which cultures are grown in conditions selective and only suitable for N. fowleri.
In a clinical review of Naegleria fowleri by Nancy Barnett et al, they investigated these diagnosis techniques and found out that the optimal ways to determine if N. fowleri is present are direct visualization, to use an Amoeba culture, or Immunofluorescent staining. Gram staining is poor because the amoeba does not stain well. PCR is not ideal because it takes longer than other options and every minute counts in diagnosis. Of the survivors, treatment lasted at least 10 days and included a cocktail of antifungals and antibiotics including, but not limited to, Amphotericin B and Rifampin.
There is no standard treatment for this disease because it progresses so rapidly. If caught early treatment can include Amphotericin B, Miconazole, Fuconazole, Ketoconazole, and/or Rifampin. All of these drugs reduce the amoeba’s activity. However the fatality rate is still over 98% and there have been only 3 recorded survival cases of N. fowleri since 1962 (its first recorded appearance) in the United States. Only 138 cases have been recorded in the U.S. since 1962. N. fowleri does not have a specific age range in which it affects the most. Though of the 107 cases out of the 138 were under the age of 18 probably due to their higher water activity.
Prevention and ControlEdit
Avoiding or not partaking in activities that will put you at risk for infection is the only way to reduce your risk of infection of Naegleria fowleri. Activities that you should be aware of that are associated with the infection are diving or jumping into the water, submerging the head under water or engaging in other water-related activities that will cause water to go up the nose. Limiting the use of neti pots or procedures for nasal irrigation should be monitored. If you will be using these procedures you should clean the water by using a chlorine/bleach solution to disinfect the water.
Barnett, MD, Nancy ,D.P, Allen M Kaplan, MD, Robert J. Hopkin, MD, Michael A. Saubolle, and Mark F. Rudinsky, MD. "Primary amoebic meningoencephalitis with Naegleria fowleri: Clinical review."Pediatric Neurology 15.3 (1996): 230-234. Print
.Fero, Kelly. "Naegleria Fowleri." Naegleria Fowleri. ParaSite, 26 Feb. 2010. Web. 21 Apr. 2014. <http://www.stanford.edu/group/parasites/ParaSites2010/Katherine_Fero/FeroNa egleriafowleri.htm
"General Information." Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 06 Nov. 2013. Web. 21 Apr. 2014. <http://www.cdc.gov/parasites/naegleria/general.html>.
Parija, Subhash C. "Naegleria Infection ." Naegleria Infection. Ed. Burke A. Cunha. Medscape, 27 Aug. 2013. Web. 21 Apr. 2014. <http://emedicine.medscape.com/article/223910-overview#a0199>.