TECH NOTES

NAEGLERIA FOWLERI: BRAIN-EATING AMOEBA By the PHTA Recreational Water Quality Committee

NAEGLERIA FOWLERI IS a 99.9% (a 3-log kill) of the amoeba in 9 and migrates along the olfactory nerve microscopic amoeba that grows in minutes (CT=9). to the brain. Once in the brain the warm lakes, ponds, streams and One outbreak in a swimming pool amoeba multiplies and causes PAM. other untreated fresh waters. (It did occur in one conventional pool and Naegleria has been detected in does not grow in salt water.) In rare lasted from 1962 to 1965 in Usti nad swimming pools with less than 1 ppm cases, this amoeba causes serious Labem, Czechoslovakia. During this free chlorine in France and Australia. illness for swimmers, entering the time period 16 deaths occurred due to There are no reported illnesses from brain and causing primary amebic infections from Naegleria. Over several these pools. meningoencephalitis (PAM), which is years it was discovered the pool had usually fatal. Since it was first reported a cracked false wall with a water-filled OCCURRENCE IN NATURE there have been a total of 145 cases in pocket that was not disinfected. The Naegleria fowleri is one of 40 species the U.S. Of these cases, 141 have been pool had been maintained at 80 to 86 of Naegleria but is the only one that fatal. In 2013 a new drug was found to degrees Fahrenheit. As the pool water causes illness in humans. It is one be an effective treatment if given early. level was raised for competitive event of the many microorganisms found it flushed the amoebae and organic in natural waters, particularly warm IS IT A HEALTH THREAT IN matter from behind the cracked wall waters. The amoeba phase is sensitive POOLS AND SPAS? into the pool. Because the free chlorine to changes in the environment. Rapid No. In the time since the CDC first level was maintained at 0.3 ppm the drying kills the amoeba. In less drastic began reporting on RWIs there have concentration was not sufficient to kill situations the amoeba converts to the been no confirmed cases in properly the amoebae. cyst phase. There is no known means chlorinated pools or spas. The most Naegleria fowleri life cycle has three to control Naegleria levels in lakes and recent summary of RWIs in treated phases: 1) the amoeba phase called rivers. venues published by the CDC did a trophozoite, 2) a flagellated phase Naegleria fowleri prefers warm not report any illnesses caused by and 3) an environmentally resistant waters and grows at temperatures up Naegleria in the 2000 to 2014 period. cyst phase. The only phase that causes to 115 degrees Fahrenheit (46 degrees Naegleria is easily killed by chlorine. infection is the amoeba phase. During Celsius). The amoeba may survive at One ppm of free chlorine will kill swimming the amoeba enters the nose even higher temperatures for short

76 JULY 2019 AQUAMAGAZINE.COM WHAT DOES NAEGLERIA FOWLERI DO TO HUMANS? • Causes primary amebic meningoencephalitis (PAM), a normally fatal disease • The amoeba enters the brain through the olfactory nerve canal • The amoeba damages tissue and causes inflammation • Only 4 known survivors out of 145 documented medical cases in the U.S. • These numbers are quite likely a great exaggeration in fatality, as millions of only 34 cases in the US between 2009 the amoeba in 9 minutes (CT=9). This swimmers are exposed but and 2018. The CDC reports that there low CT value verifies that the infective few become ill were 34,000 drowning deaths in the amoeba of this organism will not survive U.S. between 2001 and 2010. in a properly chlorinated swimming • We do not understand why Two recent U.S. cases have pool or spa. The cyst, which is not the some individuals have only heightened awareness of this rare infective form, is more than four times minor reactions and others pathogen. In 2016, an 18-year old died resistant (CT=42). The resistance of the develop the usually fatal after exposure to water at the U.S. cyst is nearly identical to Giardia (CT=45) version (PAM) National Whitewater Center outside of and there are no documented cases of • Infection does not occur in Charlotte, N.C. It is theorized that she Giardia when the pool contained at least properly chlorinated pools was exposed when her raft overturned. 1.0 ppm of free chlorine. At the time of the exposure, the facility The amoeba form is quickly killed by used 200 micron filters on a portion drying. of the water, low-pressure UV and hand fed chlorination when testing PRECAUTIONS AND times but is killed by refrigeration. The revealed coliforms. During a post-event TREATMENTS cysts can survive for weeks to months investigation, the free chlorine in the When in natural warm water, in refrigeration but appear to be killed lower portion of the river was 0.05 swimmers should avoid inhaling water. by freezing. The cysts likely survive ppm and turbidity was 6.7 NTU. The There are no known mechanisms to low temperatures in the sediments of temperature in the lower pool was 86 control Naegleria in natural waters. lakes and rivers and then reemerge degrees Fahrenheit. Because this infection is so rare, as temperatures elevate in the In 2018, a surfer died after exposure the development of effective medical summer months. This may explain the at the BSR surf facility in Waco, Texas. treatment has been a challenge. Prior geographic distribution in the warm A joint investigation of the local health to 2013, only three persons are known Southern and Western states. (See department and the CDC found to have survived infection, two in the map). Recent years have seen several Naegleria in sediment from one of five U.S. and one in Mexico. In that year, incidents in the upper Midwest. park venues but not in the surf resort. the anti-parasitic drug miltefosine was The risk of infection while They also found non-Naegleria amoeba successfully used in two cases. The swimming is very low, even in the in four of five venues. At the time of time between symptom onset and warmer states including those with the investigation the surf resort had treatment appears to be the critical a history of infection. Exposure does no detectable free chlorine and was factor for full recovery. In one case, a not always result in infection. Clinical quite turbid (558 NTU). The health treatment including miltefosine was tests have shown that many people department concluded that the likely used within 48 hours and the patient have developed antibodies. Antibodies exposure occurred at this facility. had a full recovery. In the second case, are developed only after exposure. It is a similar drug treatment was used not clear why some exposures result CONTROL METHODS but not initiated until more than 5 in infection and others do not. Despite The amoeba of Naegleria fowleri is days after symptoms. This person did hundreds of millions of swimmers in sensitive to chlorine. One ppm of free survive but had significant neurologic untreated recreational water, there were chlorine will kill 99.9% (a 3-log kill) of impairment afterward.

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