States where brain-eating amoebas infect people in the United States

  • Every year, a few swimmers in the United States are hospitalized after contracting brain-eating amoebas.
  • Naegleria fowleri can cause a life-threatening brain infection if it enters through the nose.
  • The amoeba lives in warm fresh waters, mainly in the southern states.

When a swimmer recently fell ill after visiting an Iowa lake, health officials were quick to close the beaches with great caution.

The threat wasn’t a shark or a riptide, but a microscopic amoeba that entered through the swimmer’s nose and began to eat away at his brain.

The individual, a Missouri resident, was in intensive care when health authorities announced the case on July 7. According to the state health department, the case was only the second case of Naegleria fowleri infection in a Missouri resident, and the first in 35 years. .

The Centers for Disease Control and Prevention has been tracking infections associated with the amoeba and states where people have been exposed since 1962. Although Naegleria fowleri infections are rare, warming waters may expand the area where the amoeba can to survive.

Why are brain-eating amoebae so deadly?

Naegleria fowleri is known as the brain-eating amoeba because it destroys healthy brain tissue. People can become infected if the amoeba enters through their nose while swimming or diving, not through any other form of exposure to contaminated water.

The amoeba causes a life-threatening infection called primary amoebic meningoencephalitis (PAM). The infection is extremely rare, with 154 cases recorded in almost 60 years of surveillance of the disease, but nearly all of those who contracted it have died.

After initial symptoms like headache, fever, nausea and vomiting, MPA is known to progress rapidly. Later symptoms may include stiff neck, confusion, loss of balance, seizures, and hallucinations. According to CDC data, the infection typically kills an average of five days after the first symptoms appear.

The infection is notoriously difficult to treat and test for, as laboratory tests for PAM are only available in a few locations in the United States. Because the disease is so rare and difficult to detect, about 75% of diagnoses are made after the patient dies, according to the CDC.

They thrive in warm fresh water

The Centers for Disease Control and Prevention has been tracking PAM reports since 1962. A map of case reports through 2021 shows exposures in 20 states, with most reports coming from the South.

The amoeba thrives in warm fresh water, including lakes, rivers, and sometimes contaminated tap water or swimming pools. In 2020, a 6-year-old boy died in Texas after playing in a local wading pool that was not properly chlorinated.

Texas has reported the highest number of Naegleria fowleri infections, with 40 known infections since the CDC began collecting data. Florida has reported 36 infections.

Other states with eight or more infections — the highest range noted on the CDC’s map — include California, Arizona and South Carolina.

Brain-eating amoebas could move north as waters warm

Recent data has not shown an increase in case reports over the past few years. In 2019, 2020, and 2021, three cases were reported to the CDC per year. However, the geographical footprint of Naegleria fowleri could expand, an expert told NBC News.

Julia Haston, a CDC medical epidemiologist, told NBC that one of the MPA cases reported in 2021 came from northern California. The exposure occurred at a similar latitude to the case being investigated in Iowa, suggesting that warming temperatures allowed the amoeba to spread north.

For now, the CDC says people swimming in warm fresh waters — especially in southern states — should assume they have a low risk of contracting the amoeba.


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