This brain-eating amoeba is on the rise—thanks to climate change

A 14-year-old boy who went swimming in a pond in India’s sweltering heat. A 13-year-old girl who bathed in a pool during a school excursion, and a five-year-old girl who took a dip in a river near her home. The three children lived in different parts of the southern Indian state of Kerala. Yet they have something in common ⸺all of them succumbed to a brain infection, Primary Amoebic Meningoencephalitis (PAM), caused by a tiny organism found in warm freshwaters and poorly maintained swimming pools. About a dozen others have been undergoing treatment in India, one of whom, a 27-year-old man, has also succumbed.

“In the past three months, Kerala has reported 15 cases of PAM⸺ as opposed to the previous years, when we saw about one case annually,” says Aravind Reghukumar, who heads the infectious diseases department at Kerala’s Government Medical College, and is a member of the state medical board, which is treating the patients.

Although rare, PAM is a deadly infection with a worldwide occurrence. It is caused by Naegleria fowleri, also known as the "brain-eating amoeba”, as it infects the brain and destroys brain tissue. At least 39 countries have reported such infections so far, and the rate of infections is increasing by 4.5 percent every year. In Pakistan alone, 20 deaths are reported every year due to the disease, and in 2024, infections have been reported in India, Pakistan, and Israel. N. fowleri was also detected at a popular freshwater swimming spot in Western Australia and hot springs in the U.S’s Grand Teton National Park. 

According to the Centers for Disease Control and Prevention (CDC), the majority of global case exposures⸺85 percent⸺have been reported during warm, hot, or summer seasons. Several studies have also observed that changes in temperature and climate may further drive a global increase in PAM incidence. A study published in May last year found that PAM infections are on the rise in the northern U.S. "N. fowleri is expanding northward due to climate change, posing a greater threat to human health in new regions where PAM has not yet been documented," the study noted.

Yun Shen, an assistant professor of chemical and environmental engineering at the University of California, Riverside, says that she considers PAM as “a potential emerging medical threat worldwide”. She explains that while warmer temperatures are likely to facilitate the survival and growth of N. fowleri, the risk of exposure may also increase as people indulge in more water-based recreational activities in hotter weather.

Shen researches pathogens in drinking water and water reuse systems and says, “Climate change may cause the expansion of the habitat range for this amoeba. Therefore, it can survive in warmer freshwater bodies even in regions previously considered too cold.”

Where are brain-eating amoebas found?

N. fowleri is found in warm, untreated freshwater, soil, and dust, says Karen Towne, a clinical associate professor of nursing at the University of Mount Union in Ohio, who co-authored a 2023 study on how the amoeba poses “a new concern for northern climates”. She adds that so far, PAM infections have typically occurred in cases involving swimming, splashing, and submerging one’s head in freshwater lakes, ponds, hot springs, and reservoirs. Meanwhile, less common routes of transmission have included warm hose water, a lawn water slide, splash pad use, and exposure of the nasal membrane to tap water from private well systems.

“Epidemiologically, most cases have occurred in healthy children and young adults⸺more males than females⸺who have had recent contact with untreated fresh water,” Towne told National Geographic in an email interview.

According to Barbara Polivka, an associate dean of research at the University of Kansas School of Nursing, who co-authored the study with Towne, N. fowleri enters the nose via contaminated water, crosses the nasal membrane, and follows the olfactory nerve into the brain, where it incubates for an average of five days. “PAM begins with rapid onset of severe frontal headache, fever, nausea and vomiting, which worsen into stiff neck, altered mental status, hallucinations, coma, and death,” says Polivka.

Once it enters the body, N. fowleri can have “deleterious effects” on the human brain through a host of mechanisms, from directly feeding on brain cells to indirectly secreting harmful substances that can cause cell damage, says Leigha Stahl, a microbiologist at the University of Alabama. “Besides causing direct damage, the presence of N. fowleri in the brain creates an immune response that results in brain swelling that can lead to death,” says Stahl, who authored a study on the effect of temperature on the pathogen.

According to the CDC, PAM has a high fatality rate, and more than 97 percent of people with the disease have died from the infection. In the U.S., only four of the 152 people infected so far have survived. This, say researchers, is because of how difficult it is to detect the disease. Usually, the parasite is detected posthumously, and according to the Indian doctor, Reghukumar, “only around 30 percent of PAM cases are ever diagnosed in India,” while 70 percent remain undetected.

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A 2020 study found that the detection rate also remains low in countries that do not have a surveillance system for PAM or available diagnostic testing. Another major challenge to detecting the infection, says Stahl, is misdiagnoses, as the symptoms of the disease resemble other illnesses such as the flu and bacterial meningitis. “PAM is a relatively rare disease, so it is not likely what people look for first, which can also delay diagnoses,” she says.

Jacob Lorenzo-Morales, a senior lecturer in parasitology and director of Spain’s University Institute of Tropical Diseases and Public Health of the Canary Islands, says PAM is underreported and not well known among clinicians.

“I have been involved [cases] in low-income countries and even in my country. It was very hard, and sometimes, almost impossible, to get miltefosine [known as a ‘miracle drug’ for PAM infections] on time. Sometimes, we had to even limit the doses, waiting for more product to arrive. This is highly worrying,” says Lorenzo-Morales, who also authored a 2019 paper on N. fowleri, finding an increase in the global burden of PAM, and suggesting that climate change is likely increasing the “abundance and range” of the brain-eating amoeba.

The role of climate change

National Geographic spoke to eight researchers, all of whom agree that climate change is fueling the spread of N. fowleri and resultant PAM infections. According to Jimmy Whitworth, an infectious diseases expert at the London School of Hygiene and Tropical Medicine, the presence of N. fowleri, indicated by reported cases, has been moving northwards in the past few years.

Lorenzo-Morales says that N. fowleri thrives in water-related environments with temperatures ranging between 86°F to 114.8°F. The combination of droughts and heavy rainfalls also creates the perfect warm water environment for the amoeba.

“We are seeing an increase in diseases, which were once considered tropical, ‘moving’ to cold regions and countries,” says Lorenzo-Morales, “The future is worrying.”

A Pakistani study published last year notes that worsening heat waves provide suitable temperatures for N. fowleri, which is “already a growing problem for the country”. The South Asian nation has faced several such outbreaks in the recent years, adding to existing healthcare burdens and making proactive measures crucial.

Considering the risk of patient fatality, experts like Towne agree that tackling PAM should be an important clinical and public health priority. She says that to speed up diagnoses, healthcare providers should be educated on climate-related illnesses like PAM.

Expecting an increase in the incidence of PAM cases, Charles Gerba, a professor of virology at the University of Arizona, suggests that children should avoid putting their head underwater or use nose clips when swimming. “Also, with poor quality tap water, avoid splashing the water in your nose or using it for cleaning your sinuses,” he adds.

Although difficult to diagnose and treat, the recent spurt of PAM cases in India has also brought an array of hope. Reghukumar says that in July, a 27-year-old man approached the hospital with PAM symptoms and a history of contact with a mossy, green pond in the city of Thiruvanthapuram. The man had undergone a brain surgery in the past, which increased his chances of infection and death after being exposed to amoeba-infested waters. While he succumbed on July 23, doctors at the hospital went on a search in his locality, looking for active cases of PAM infections. They identified six others, and were able to start their treatment early in the disease course.

“Now, all of them are recovering,” says Reghukumar, “This tells us that although PAM has a high fatality rate, there is a window of opportunity. Early diagnosis and treatment can give the patient a fighting chance to survive.”

Puja Changoiwala is an award-winning journalist and author based in Mumbai. This is her website.