NAME: Naegleria fowleri
CHARACTERISTICS: The ameboid form of Naegleria fowler is elongated, 15-30 μm, and feeds on Gram-negative bacteria (4, 5). The cytoplasm is granular, has a single nucleus with a prominent and contains vacuoles (6). Blunt lobular pseudopodia are formed at the widest point. The flagellated form is smaller, with a pear shape and two flagellae at the broad end. N. fowleri cysts are round, 7-15 μm in diameter and have a thick smooth double wall (4, 5). N. fowleri is thermophilic, preferring water temperatures between 35 and 46ºC (7).
PATHOGENICITY/TOXICITY: N. fowleri is the causative agent of primary amoebic meningoencephilitis (PAM) (4, 5, 8-10). PAM is an acute, fulminating, rapidly fatal disease that is often observed after exposure to fresh water, with symptoms such as sore throat, blocked nasal passages, fever, vomiting, stiff neck, confusion, and abnormal behaviour (4-6, 11, 12). Three to four days after the onset of the initial symptoms, mental confusion and coma occur. Death usually occurs 3-4 days after coma. Time from infection to death is 7-10 days (9). Mortality rate is estimated at greater than 95% (7).
EPIDEMIOLOGY: Worldwide (4). The most commonly infected are children, young adult and immunocompetent patients. Between 1996 and 2003 there were 179 cases reported in humans.
INFECTIOUS DOSE: Unknown.
MODE OF TRANSMISSION: N. fowleri enters the nasal passage, carried in contaminated water, while the individual is swimming or diving in freshwater, then penetrates through the mucosal layer and travels along the olfactory nerve to the brain (5). Once it has reached the brain, N. fowleri will consume erythrocytes and nerve cells, causing damages and inflammation (9). Ingestion of contaminated water does not lead to PAM (5).
DRUG SUSCEPTIBILITY: N. fowleri is susceptible to amphotericin B, which is often used in combination with rifampin, orindazol, miconazol, sulisoxazole, or chloramphenicol (13). Miltefosine and voriconazole has also been found to be effective against infection (6).
DRUG RESISTANCE: Resistance of Naegleria spp. has been shown against fluconazole and itraconazole (14). This area remains a growing concern when repeated doses are administered, especially in endemic regions.
SUSCEPTIBILITY TO DISINFECTANTS: N. fowleri is susceptible to NaCl at concentrations greater then 1%, w/v (15). N. fowleri is susceptible to chlorine at concentrations of 0.5 and 1.0 mg/L, ozone, and Deciquam 222 (16).
PHYSICAL INACTIVATION: Heating water to 50ºC for 5 minutes will kill all forms of the amoebae (17). Both amoeba and cysts can tolerate temperature of 65ºC for 1-3 minutes and temperatures below 20ºC inhibit reproduction (15). Degradation occurs when temperatures reach below 10ºC. Dehydration is lethal to N. fowleri.
SURVIVAL OUTSIDE HOST: N. fowleri can survive in water at temperature up to 45ºC and at pH 4.6 - 9.5(5).
SURVEILLANCE: Monitor for symptoms. Identification is done by microscopic examination of CSF for presence of amoebic organism (2, 4, 8). Molecular biology techniques such as PCR and real-time PCR have been recently developed for detecting N. fowleri (18).
Note: All diagnostic methods are not necessarily available in all countries.
FIRST AID/TREATMENT: Treatment of PAM is rarely successful and depends on prompt diagnosis and administration of medication (9). The usual course of treatment involves amphotericin B administered in combination with rifampin and other antifungals (13).
PROPHYLAXIS: None. Recreational waters should maintain effective levels of chlorine to protect against harbouring N. fowleri amoebas (12).
LABORATORY-ACQUIRED INFECTIONS: None reported (10).
PRIMARY HAZARDS: Inhalation of aerosols during manipulation of infectious samples or cultures is the primary hazard associated with N. fowleri (19).
SPECIAL HAZARDS: None.
RISK GROUP CLASSIFICATION: Risk group 3.
CONTAINMENT REQUIREMENTS: Containment Level 3 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, or cultures.
PROTECTIVE CLOTHING: Personnel entering the laboratory should remove street clothing and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes (21).
OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) or other appropriate primary containment device in combination with personal protective equipment. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animals or large scale activities (21).
SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply an appropriate disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (21).
DISPOSAL: Decontaminate all wastes that contain or have come in contact with the infectious organism before disposing by autoclave, chemical disinfection, gamma irradiation, or incineration (21).
STORAGE: The infectious agent should be stored in leak-proof containers that are appropriately labelled (21).
REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.
UPDATED: September 2011
PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.
Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.
Public Health Agency of Canada, 2011