Over the past few days, there have been numerous scary news stories about a “brain-eating” amoeba that has killed six boys and young men this year (three in Florida, two in Texas and one in Arizona, the most recent case being that of 14-year-old Aaron Evans, who died on September 17th).
The amoeba in question is Naegleria folweri, a thermophilic (heat-loving) free-living organism that is commonly found in rivers, fresh water lakes and soil all over the world.
N. fowleri infects humans very rarely, but infection is usually fatal. It normally occurs during water-related activities such as swimming or diving. The amoeba enters the body through the nose and travels to the brain via the olfactory bulb. Infection causes a disease called primary amoebic meningoencephalitis (inflammation of the brain) which destroys nervous tissue.
The images on the right come from a case study of a 9-year-old boy who was admitted to a hospital in Este, a small town in the Veneto region of northern Italy in July 2003. The boy’s parents reported that he had suffered with a fever and persistent headache for one day prior to being admitted, and told the doctors that he had been playing in a swimming hole at the Po River 10 days before his symptoms began.
Upon his admission, the boy was lethargic, and a few hours later, became unresponsive to painful stimuli. The next day, a CT scan was performed; this showed a small lesion in the right frontal lobe, and swelling in the left hemisphere (indicated by an arrow) that had caused the midline to shift towards the right.
About 1 hour after the CT scan, the boy developed severe aniscoria (a difference in the size of the pupils), and then mydriasis (excessive dilation of the pupils); 6 days after the onset of these symptoms, he was pronounced dead. Upon post-mortem, a sample of brain tissue showed large numbers of the amoeba, which were present in three large clusters.
Because N. folweri is thermophilic, infection is most common during the summer, when the surface temparature of water in lakes and rivers increases. The case study mentioned above, for example, occurred during a particularly hot summer, and was the first such infection reported in Italy. But the increases in global temperatures that are likely to occur in the future could increase infection rates slightly.
To date, however, there have only been about 200 reported cases of N. fowleri infection worldwide. And, according to the Centers for Disease Control, there were just 23 documented infections in the U.S. between 1995 and 2004. So, despite the scary “brain-eating amoeba” headlines, there’s really no need to panic.