In a turn of unfortunate events, a life threatening amoeba takes the life of a promising athlete in a matter of days.

14-year-old Michael John Riley Jr had been just days away from starting his freshman year of high school, but it all came to an end due to a fatal brain-eating amoeba.

The Houston star teen, who qualified for the Junior Olympics three times in track, was swimming with his cross-country team on August 13 at Sam Houston State Park, Reports CNN.

That's when Michael encountered the Naegleria fowleri amoeba. Within days, the teen's bad headache turned into a total loss of brain function. He died Sunday.

Dr Umair Shah said the Harris County, Texas, health department, which he heads, learned of Micheal's case a few days earlier on August 22. His agency soon became one of many -- including the hospital, the state and US Centers for Disease Control and Prevention -- involved in the case, trying to pin down the source of his illness and get the word out to the public and health professionals.

Naegleria fowleri are rare, Shah points out. But they can be found waters, especially those that are warm and still.

"It's such a sad undertaking," the doctor said of Michael's story. "(The idea that) someone who had such a fantastic future would get such an amoeba and would be primary amebic meningoencephalitis and it's unfortunately not a good outcome."

Here's what to know about the brain-eating parasite:

What is it?

Naegleria fowleri is a single-celled organism that can cause a brain infection called primary amebic meningoencephalitis, or PAM, the Centers for Disease Control and Prevention said.

It's typically found in warm fresh water such as lakes, rivers and hot springs.

"These disease-causing organisms are naturally present in most lakes, ponds, and rivers but multiply rapidly in very warm and stagnant water," the Oklahoma State Department of Heath said.

How do you get it?

People can get infected by swimming or diving into infected, warm bodies of water, the CDC said. The amoeba enters the nose and travels to the brain.

In extremely rare cases, swimmers can get infected from pools that are not adequately chlorinated.

But it's impossible to get infected by drinking water contaminated with the amoeba. And infections are not contagious.

How often does it strike?

Very rarely. In the past 53 years, 133 cases have been documented, according to the CDC.

Most of those cases happened in Texas, Florida, Arkansas, Arizona and California.

How often is it fatal?

Very often. Of those 133 cases, only three people survived.

Who else has gotten infected recently?

Earlier this month, an Oklahoman died after swimming in Lake Murray in Ardmore,  CNN affiliate KFOR said.

Last summer, 9-year-old Hally Yust of Kansas died after swimming in several bodies of fresh water.

"Our precious daughter, Hally, loved life and part of her great joy was spending time playing in the water," her family said in a statement.

"Her life was taken by a rare amoeba organism that grows in many different fresh water settings. We want you to know this tragic event is very, very rare, and this is not something to become fearful about."

In 2013, 12-year-old Zachary Reyna of Florida became infected after he went knee-boarding in fresh water near his home. He later died.

That same summer, Kali Hardig of Arkansas went for a swim and was infected by the parasite.

Despite the incredible odds against her, Kali survived.

How can you prevent it?

The extreme rarity and randomness of such infections can make it difficult to predict where they might occur.

"It is unknown why certain persons become infected with (Naegleria fowleri) while millions of others exposed to warm recreational fresh waters do not, including those who were swimming with people who became infected," the CDC said.

The Kansas health department advises swimmers to use nose plugs when swimming in fresh water.

It also suggests not stirring up the sediment at the bottom of shallow freshwater areas and keeping your head above the water in hot springs.

The Oklahoma health department also said people shouldn't swim in stagnant water, water that is cloudy and green, or water that has a foul odor.

It also said signs that say "no swimming" should be taken seriously.