It was a bitterly cold spring afternoon as visitors of Yellowstone National Park climb out of their cars, anticipating the pleasures of the warm waters ahead. With an air temperature barely above freezing, tourists walk down a half-mile path from the main road to, undress into their bathing suits and wade through a section of freezing water. Engulfed by steam, visitors approach the area of access, it is almost silent, with only the sounds of flowing water in the distance. Elk scatter the river bank as the sun breaks through the clouds. The scene appears tranquil when suddenly you see a sign: “Many of Yellowstone National Park’s Thermally-influenced waters contain organisms that are known to cause serious skin rashes, infections, and/or primary amoebic meningitis, which can be quickly fatal. Avoid submerging your head and inhalation of thermal steam. If you have any signs or symptoms of irritation or disease, seek medical help immediately. SWIM AT YOUR OWN RISK.”
How the Amoeba Attacks the Brain
Naegleria fowleri is an amoeba present in warm water. Normally this amoeba is free-living, swimming through waterways eating bacteria. When certain conditions present itself, the amoeba finds its way up a mammal’s nose and has the ability to transition from consuming bacteria into consuming flesh. Naegleria fowleri travels up the mucous membrane lining the nasal cavity. As the amoeba migrates it tracks the olfactory nerves up to the victim’s brain and begins to feed on the frontal lobe, devouring tissue with mouthlike feeding structures. Resulting in death usually within 15 days of contraction.
“It actually has to get in your nose and then it crawls up your nose,” said Dr. Sandra Halonen, Professor of Microbiology at Montana State University. “And it migrates along the olfactory nerves. And then it crawls into your brain via the cribriform plate, which is at the base of the nose, and crawls directly into the brain.”
Naegleria Fowleri feeds on the frontal lobe, devouring tissue with mouthlike feeding structures. Once Naegleria fowleri enters the victim’s brain it causes a brain disease known as primary amebic meningoencephalitis, abbreviated as PAM. It takes around ten days for physical symptoms to appear. These symptoms, resembling those of the flu, include fever, stiff neck, headache, nausea, and vomiting. This similarity in symptoms often leads doctors to misdiagnosis patients, only learning the true cause of the disease after the patient has passed away. Naegleria fowleri kills on average within five days after symptoms appear and has been fatal in 95% of reported cases.
"Part of the reason it's so pathogenic is it's direct entry into the brain," Dr. Halonen said.
Early detection is crucial for treatment of PAM. Patients suffering from a Naegleria fowleri infection are currently given miltefosine. This drug is still in its experimental phase but shows potential for treating the brain infection. Other studies are being conducted on various drugs that may be more effective. Although if not detected early it is rare for someone to survive this infection. Education is key; if people are aware of the presence of the amoeba in their area, they are more likely to recognize the signs and seek treatment.
“One way that the infections have occurred is from waterskiing or diving into deep waters, where you dive in and get water up your nose," Dr. Halonen said. "The force of the splash... not just recreational soaking in a hot spring.”
Scientists are unsure currently of the impact this will have on the overall safety of the public. According to data from the Center for Disease Control (CDC), the states with the highest mortality rates from PAM are Florida and Texas with more than 10 reported fatal cases on record from 1962 to 2017. This is not a surprise as these are two of the warmest states in the country.
Scientists fear the range of Naegleria fowleri will expand and the amoeba will become more common in our waterways as global temperatures rise. This has created an environment for the amoeba to begin to spread farther north.
“Generally the temperatures are rising across the United States,” Dr. Halonen said. "Traditionally the infections in the United States have been in the southern United States, Texas and Louisiana. But in 2013, someone in Minnesota got infected. And Minnesota is pretty far north."
Scientists from around the country have been testing monitoring devices to track the presence of the amoeba in hot springs. The USGS has been testing tools developed by the Monterey Bay Aquarium Research Institute to monitor aquatic species in the ocean. This device is known as the Environmental Sample Processor or ESP. The goal of this device is to be able to detect the amoeba in real time.
The ESP used in Yellowstone National Park is a drum-like robotic device which filters water and traps microorganisms like Naegleria fowleri for DNA analysis. These ESP filters were tested alongside traditional analysis completed by the Center for Disease Control or CDC. Scientists hope the information gathered will lead to a clearer understanding of the range, life cycle, and habitat of the amoeba.
“It's important we understand this organism better,” said Dr. Elliott Barnhart, microbiologist of the USGS. “As temperatures warm and the environment may become more suitable for this pathogen, it may become more of a concern.”
Little is known about the range of Naegleria fowleri within the United States. The amoeba appears to be most common in the American South where water temperatures are warmer, although it has been found as far north as Minnesota. The amoeba has been detected not only in rivers but also water parks and municipal water systems. According to CDC data, only one fatal infection has occurred in urban areas from the use of a neti-pot and tap water.
Even though cases of PAM are exceedingly rare, they are usually highly publicized when they occur. Many of the reported cases have been children, which can add to the panic surrounding a death. Some experts believe PAM is under-diagnosed. While only 139 cases have been reported since 1962, all of which were fatal excluding four. This is an average of around 3 victims per year. The CDC believes that due to under-reporting, the actual annual death toll from PAM may be closer to 16.
Thermal Waters of Yellowstone
Municipal water systems that treat and disinfect their water should be sufficient at preventing an outbreak within their towns’ water systems. Soaking in an area where the amoeba’s presence is known poses a far greater risk for contracting the disease. However, this risk does not appear to be stopping visitors from enjoying the warming waters of the Boiling River and other natural hot springs where the amoeba occurs.
Naegleria fowleri thrives in warm freshwater making the geothermal pools of Yellowstone National Park the perfect environment for the amoeba. Temperatures around 115° F are ideal although the amoeba can survive in environments where temperatures reach up to 149°F. This hardy little amoeba can also survive cooler temperatures, entering a dormant state when it encounters cold water environments. The amoeba reawakens when it encounters a warm environment. This adaptability to temperature fluctuation can make the amoeba difficult to trace, allowing survival in a wide range of environments.
The Boiling River is only one of the thousands of sights set up around where the USGS has a streamgage that provides real-time information on water flow and temperature to the public. These streamgages were originally installed to monitor data including temperature and flow rate. The USGS is now working to add additional sensors like MBARI’s ESP that could be used to monitor microbes. If some of these microbes included Naegleria fowleri, public health officials could alert the public to the possibility of an outbreak. These sensors could play an integral part in learning more about the life cycles and feeding habits of the amoeba.
"We are looking at the bacterial communities to try to get an idea of what the amoeba might be feeding on," Rebecca Mueller, Assistant Research Professor at Montana State University said. "We know that they like things like meiothermus, [a bacteria], but whether their able to eat other things, is something that we're trying to understand as well ."
No known cases of Naegleria fowleri have occurred from exposure within Yellowstone National Park, which is remarkable considering the vast number of visitors it receives per year.
In 2017, Yellowstone National Park received 4,257,177 visitors, the majority of which visited in the months of June to September. Since 2008, visitation has increased by 40 percent causing a massive surge in usage of the park's amenities.
Located two miles within park boundaries, from the northern Gardiner entrance, the Boiling River brings thousands of people to the park to soak in the warm waters. Almost all of the other geothermal pools are inaccessible to humans because of the extremely high water temperatures and contain fragile habitats. Tourists have perished from the hot acidic waters after they have slipped and fallen into the pools. The Boiling River is accessible to humans only because the hot water, warmed from geothermal activity, mixes with the cold water of the river creating the perfect soaking environment.
“Infection rates are really really low,” Dr. Halonen said. “42 infections in the last 40 years. We've never had an infection from the Boiling River ever, and a lot of people visit it. To get it, even if it is present, most people have to forcefully splash it up their nose. And most people aren't diving in the Boiling River.”
In the meantime it never hurts to keep your head above water or bring a nose plug, she said.