The pathogens lurking in our pools and lakes: What you need to know

Some have been called "flesh-eating," others "brain-eating."

Certain strains of very rare, dangerous microbes made headlines this summer after people contracted infections, fell ill and in some cases, died.

A New Jersey man lost all his limbs after contracting an infection from the Vibrio vulnificus bacteria while crabbing on the beach. The ‘brain-eating’ amoeba Naegleria fowleri was behind the death of a North Carolina man who contracted the infection after swimming in a man-made lake.

Here’s what you need to know about these menacing microbes.

What are the pathogens?

The bacteria Vibrio vulnificus is called a ‘flesh-eater’ because it causes necrotizing fasciitis: a skin condition in which the body’s soft tissue is rapidly and progressively broken down.

“Most Vibrio vulnificus infections cause a mild gastroenteritis,” Dr. Todd Ellerin, director of infectious disease at South Shore Health in South Weymouth, Massachusetts, told ABC News, referring to a condition in which the intestines become inflamed. “On the severe end, you can get sepsis – a bloodstream infection – and necrotizing fasciitis.”

“The vast majority of people with severe Vibrio infection have another underlying problem – particularly liver disease,” he said.

The ‘brain-eating’ Naegleria folweri sounds like it comes straight from a horror film. It’s a parasite that typically infects people swimming in lakes and rivers, travelling through the nose and into the brain.

“Naegleria likes fresh water – lakes and ponds. Infection is even rarer than Vibrio, but the stakes are even higher,” Dr. Ellerin told ABC News.

“It travels up the nose and through the cribriform plate – a little sieve separating the nasal cavity and the brain,” Dr. Ellerin said. “When it reaches the brain, it causes Primary Amoebic Meningoencephalitis, or PAM for short, with seizures, headaches, personality changes and confusion. Most people with PAM have died – and unfortunately two-thirds of the cases are in otherwise healthy children.”

Where are these types of pathogens found?

“What’s really important is that both Vibrio and Naegleria are thermophilic – this means they like warmer waters,” Dr. Ellerin told ABC News. “For example, when temperatures reach greater than 20oC in the Chesapeake Bay, almost 100% of oyster beds have Vibrio.”

Vibrio vulnificus lives in salt water, or brackish water where fresh and salt water mix. “Entering brackish water with a cut puts you at risk of Vibrio infection,” Dr. Ellerin said.

Naegleria, by contrast, lives in freshwater such as lakes, rivers and hot springs.

What precautions can you take?

There are steps you can take to reduce the risk of waterborne illness, according to the Centers for Disease Control and Prevention

First, don’t swim in any kind of water if you have an open wound. Give the cut time to heal by waiting for it to scab over.

Second, shower after getting out of the water. Showering afterwards, especially with soap, can prevent infections. Parents should also check their children to make sure they haven’t developed new cuts or scratches.

Third, people who are immunocompromised or have liver disease are at higher risk of Vibrio infections, and need to be extra cautious.

“These people should be extremely careful when swimming, and not go into water with open wounds,” Dr. Ellerin said.

If you are unlucky enough to get scratched, rinse the wound thoroughly – irrigation is key – and apply some antibiotic ointment. If you fall ill and develop diarrhea after swimming, you should seek medical attention right away.

What should you look out for in the water?

Both recreational and drinking water can be contaminated with pathogens and cause illness, according to the CDC.

Bodies of water can be the hosts of a menagerie of microorganisms capable of causing serious trouble.

When you go for a swim, it’s good to always presume that there is a low-level risk so that you take the right precautions. Dirty, murky waters are red-flags.

If you are going to swim in a pool, check if you can see the drain – the water should be crystal clear, and drain covers should be secured and in good repair.

The CDC also recommend using pool testing strips. Check that the pH of the water is between 7.2-7.8, and the free chlorine concentration is at least 1 ppm in pools and 3 ppm in hot tubs or other types of spas. You can also check if your local pool has passed its health inspection at the Water Quality and Health Council’s website.

Why are we hearing about water-borne pathogens now?

Climate change is expected to affect fresh and marine water in a way that will increase peoples’ exposure to water-related illness, according to the U.S. Global Change Research Program – a federal program looking at the impacts of a changing global environment.

“Global warming is important for both of these pathogens,” Dr. Ellerin told ABC News. “We see more of these, not less, as water temperatures rise.”

“There may also be an increased prevalence of risk factors – more underlying liver disease, more people with weakened immune systems, and increased use of immunosuppressant medications,” he said.

The bottom line

“My message to swimmers and parents: recognize that both these infections are rare, and severe infection is even rarer,” said Dr. Ellerin. “But take sensible precautions to reduce your risk.”

Dr. Laith Alexander is an MB/PhD student at the University of Cambridge, U.K., working with ABC News Medical Unit.