There can be nothing more satisfying or refreshing than diving into a glistening lake or river to cool off, but in certain, exceedingly rare circumstances, this can prove to be a fatal mistake, thanks to a freshwater-dwelling amoeba. This has already been demonstrated once this summer, and saddeningly perhaps twice, as two cases of infection with this “brain-eating” parasite have already been reported in the U.S.
The organism blamed in both of these situations is a free-living, single-celled amoeba called Naegleria fowleri. It’s ubiquitous in the environment, meaning it’s found pretty much everywhere, but it’s heat-loving (thermophilic) and often found in warm freshwater, like lakes or hot springs. People are therefore often exposed to this organism and nothing comes of it, but in rare circumstances it can cause a serious brain infection called primary amoebic meningoencephalitis (PAM).
This usually only happens when the organism is forced up the nose, for example during recreational activities such as swimming or diving, which gives it an opportunity to breach the nasal cavity and subsequently make its way up the olfactory nerve – needed for smell perception – and into the brain.
From here, it feeds on nervous tissue using sucker-like structures, triggering an inflammatory immune response that causes a severe increase in pressure in the skull, ultimately killing the infected individual about 97% of the time.
The latest cases experienced in the U.S. have both been reported in the last month. The first was a 21-year-old woman from Central California, whose infection was confirmed by the Centers for Disease Control and Prevention (CDC), CBS News reports. After waking up on June 16 with nausea that had not resolved itself a day later, the victim was admitted to Northern Inyo Hospital where she was diagnosed with meningitis, which presents itself similarly. Her condition worsened and she later died after being transferred to a different hospital in Nevada.
It’s extremely difficult to ascertain where she contracted the amoeba, but according to CBS News, officials said it’s likely that she became infected on a private property that is inaccessible to the public. But even if it were an area commonly used by the public, panic would not be warranted as PAM is very rare.
The second case, however, is even more out of the ordinary. As reported by the Minnesota Department of Health, an ongoing investigation is taking place for a suspected case of PAM in a 14-year-old boy who is currently critically ill. Officials in the department established that he became infected in Lake Minnewaska, Pope County, marking the third infection to be witnessed in Minnesota in the past five years.
These three cases are interesting because the majority of U.S. infections have occurred in warmer southern states like Florida and Texas, and before 2010 it had never been reported above Missouri. This indicates that the organism is spreading northward, which could possibly be attributable to climate change given N. fowleri’s preference for warmer waters. But this doesn’t necessarily indicate a future rise in cases; between 2002 and 2011 only 32 infections were reported in the U.S., so they're still extremely rare.