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HOUSTON (AP) — A 14-year-old boy is in critical condition in a hospital after coming into contact with a rare amoeba while swimming in a lake north of Houston.

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Relatives say Michael Riley Jr. developed a headache and fever, and later became disoriented, after swimming with friends Aug. 13.

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In online postings, Michael’s family says he has Primary Amebic Meningoencephalitis. The disease usually occurs when the Naegleria fowleri amoeba enters the body through the nose and attacks cells in the brain. The infection causes the brain to swell.

The Centers for Disease Control and Prevention says from 2005 to 2014 the amoeba infected 35 people in the U.S. All but two cases were fatal. A swimmer died of the disease in Oklahoma earlier this month.

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