Deadly "brain-eating amoeba" infections have historically occurred in the Southern United States. But cases have been appearing farther north in recent years, likely because of climate change, a new study finds.

The study researchers, from the Centers for Disease Control and Prevention (CDC), examined cases of this brain-eating amoeba, known as Naegleria fowleri, over a four-decade period in the US.

They found that, although the number of cases that occur each year has remained about the same, the geographic range of these cases has been shifting northward, with more cases popping up in Midwestern states than before.

N. fowleri is a single-celled organism that's naturally found in warm freshwater, such as lakes and rivers, according to the CDC. It causes a devastating brain infection known as primary amebic meningoencephalitis (PAM), which is almost universally fatal.

Infections occur when contaminated water goes up a person's nose, allowing the organism to enter the brain through the olfactory nerves (responsible for your sense of smell) and destroy brain tissue. Swallowing contaminated water will not cause an infection, the CDC says.

Because N. fowleri thrives in warm waters, up to 113 degrees Fahrenheit (45 degrees Celsius), it's possible that warming global temperatures may affect the organisms' geographic range, the authors said.

In the new study, published Wednesday (Dec. 16) in the journal Emerging Infectious Diseases, the researchers analyzed US cases of N. fowleri linked to recreational water exposure – such as swimming in lakes, ponds, rivers or reservoirs – from 1978 to 2018.

They identified a total of 85 cases of N. fowleri that met their criteria for the study (i.e. cases that were tied to recreational water exposure and included location data).

During this time, the number of yearly reported cases was fairly constant, ranging from zero to six per year.

The vast majority of cases, 74, occurred in southern states; but six were reported in the Midwest, including Minnesota, Kansas and Indiana. Of these six cases, five occurred after 2010, the report said.

map of n fowleri cases across the u s (CDC, Emerging Infectious Diseases, 2021)

Above: Cases of N. fowleri infections tied to recreational water, from 1978 to 2018.

What's more, when the team used a model to examine trends in the maximum latitude of cases per year, they found that the maximum latitude had shifted about 8.2 miles (13.3 kilometers) northward per year during the study period.

Finally, the researchers analyzed weather data from around the date each case occurred, and found that on average, daily temperatures in the two weeks leading up to each case were higher than the historical average for each location.

"It is possible that rising temperatures and consequent increases in recreational water use, such as swimming and water sports, could contribute to the changing epidemiology of PAM," the authors wrote.

Efforts to characterize PAM cases, such as knowing when and where these cases occur, and being aware of changes in their geographic range, could help predict when it's riskiest to visit natural swimming holes, the authors said.

Since there is no rapid test for N. fowleri in water, the only sure way to prevent these infections is to avoid swimming in warm freshwater, the CDC says.

If you choose to go swimming in warm freshwater, you can try to avoid having water go up your nose by holding your nose closed, using nose clips or keeping your head above water.

This article was originally published by Live Science. Read the original article here.