Microbiology: A Systems Approach 4th Edition by Marjorie Kelly Cowan

Exercise 32

Swim at Your Own Risk
Ah, the dog days of summer. Nothing is more refreshing than diving into the local fishing hole to cool off, but swim at your own risk. Warm weather and rising water temperatures may bring an unwelcome swimming partner: Naegleria fowleri. This eukaryotic amoeba is found in freshwater lakes, swimming pools without adequate chlorination, geothermal pools, and even tap water. Usually, the organism lives in the sediment at the bottom of lakes and in the soil. During the colder times of the year, the organism exists in a cyst form, in which the organism is dormant and covered in a durable coating. In the warmer months of the year, Naegleria enters a trophozoite, or amoebic, phase in which it actively divides and can be infectious.
In August 2010, Kyle Lewis and his family were camping in Glen Rose, Texas, where he swam in several warm lakes and rivers. When he got home, he developed a severe headache, then fever, nausea, and vomiting. His parents didn't know the cause of his symptoms, which continued to worsen. Over the next few days, he developed symptoms of meningitis, began having hallucinations and fevers, and was hospitalized. His condition got progressively worse. Kyle later died.
How is Naegleria fowleri transmitted
How can infections be prevented
N. fowleri gains entry to the body through the nose and mouth, and in Kyle's case, it likely was due to inhalation of water while he was swimming. The organism invades the soft tissues of the olfactory mucosa and penetrates the cribiform plate in the skull. From there, the amoeba is able to access the nerve fibers through the cribriform plate and enter the brain, where it begins to infect brain cells. This causes primary amoebic meningoencephalitis (PAM). N. fowleri is susceptible to the drug amphotericin B in vitro (in the test tube), but there is little evidence that the drug is effective in vivo (in a living organism). Unfortunately, survival rates for PAM are less than 1%.

The Centers for Disease Control and Prevention recommends avoiding swimming in or participating in athletic activities in warm freshwater. If you do choose to swim in warm water, hold your nose or use nose clips, and avoid disturbing the sediment in shallow water. Only 42 cases have been documented in the United States from 2001 to 2010, making it an uncommon phenomenon. However, this "brain-eating" amoeba has caught the attention of the media and scientists alike.
In what other ways can Naegleria fowleri be spread