This map shows which US lakes contain brain-eating amoebas

Texas reported the most cases of the N. fowleri infection.
Deena Theresa
3D illustration of the infectious form of the parasiteDr_Microbe/iStock

A few days ago, a Missouri resident who went swimming in the Lake of Three Fires in Taylor County, Iowa, was hospitalized after a microscopic amoeba entered through their nose and started eating away at their brain.

Better known as Naegleria fowleri, the single-celled organism that thrives in warm freshwater, travels up the nose to the brain where it rapidly multiplies and begins feasting on brain tissue. It can infect people when they are swimming or diving, by entering through their nose.

The state health department reported the case was only the second instance in a Missouri resident and the first in 35 years.

Though the infection is rare, the Centers for Disease Control and Prevention have been tracking infections associated with the amoeba and states where people have been exposed since 1962. 

The CDC has released a map of case reports through 2021 that shows exposures in 20 states, with most reports coming from the South.

While Texas reported the most cases of the N. fowleri infection (40 known infections since the CDC began collecting data), Florida has reported 36 infections. 

Other states with eight or more infections include California, Arizona, and South Carolina. 

The associated brain infection, called primary amebic meningoencephalitis (PAM), has a fatality rate of over 97 percent. Though there have been only 154 confirmed cases of N. fowleri infections in the US from 1962 to 2021, only four survived.

map
The CDC has been tracking Naegleria fowleri infections since 1962. Source: Centers for Disease Control and Prevention

'The worst parasite in the world that we know of'

Dr. Brent Moore, Regional State Public Health Veterinarian for the Texas Department of State Health Services, told CBS19: "The past three years in 2019, 2020, and 2021, we had one case each year, but since 1979, we've had 35 or 36 cases. I know more recently, we've seen it in kids, but it can happen at any age."

A 13-year-old boy who swam in a lake and visited a waterpark in North Florida died from the brain-eating amoeba in 2020. Another six-year-old boy died in Texas after playing at a splash pad that was not properly chlorinated.

One CDC scientist told CBS News that the amoeba is "the worst parasite in the world that we know of" because it is difficult to diagnose and infections progress quickly. People usually die one to 18 days after being infected.

While initial symptoms of PAM include headache, fever, nausea, and vomiting, later symptoms may include stiff neck, confusion, loss of balance, seizures, and hallucinations. As per CDC data, the infection usually kills within an average of five days after the first symptoms.

Now, as laboratory tests for PAM are only available at a few locations in the U.S., the infection is extremely difficult to treat and test for. About 75 percent of diagnoses are made only after the patient has died, according to the CDC.

Climate change could be the culprit

In recent years, the brain-eating amoeba has been spotted in Northern states more often as air and water temperatures rise. According to a CDC study published in 2020, which analyzed U.S. PAM cases from 1978 to 2018, "The rise in cases in the Midwest region after 2010 and increases in maximum and median latitudes of PAM case exposures suggest a northward expansion of N. fowleri exposures."

According to Julia Haston, a medical epidemiologist with the CDC, climate change could be the culprit.

"It’s an amoeba that really likes warm conditions, really likes warm fresh water," she told NBC news. "That’s the concern — that climate change can be contributing to these higher air temperatures."

Avoid jumping, diving, and splashing

Concerned about the N. fowleri exposure, Haston said that precautions can be taken to avoid infection. "When you’re participating in swimming or recreational water activities in lakes or ponds, really avoid getting water in the nose. Avoid jumping, diving, and splashing. If you are going to be swimming, wear a nose clip."

"Any freshwater source, we should assume that it has Naegleria fowleri in it," added Haston.

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