Health Alerts Following Naegleria Discovery
The detection of Naegleria amoebae in six artificial lakes across Mérida, Yucatán, has raised public health alarms following the tragic death of a 34-year-old man in September due to an infection caused by Naegleria fowleri, often referred to as the “brain-eating amoeba.” This microorganism can lead to a devastating disease that damages brain tissue, with a mortality rate exceeding 97%. Despite this, human infections remain exceedingly rare. What does this finding mean for public safety, and who is at risk?
On October 14, Yucatán’s health services reported that six out of nine tested artificial lakes in Mérida were positive for Naegleria amoebae. Among these was the lake at Plaza La Isla, where the deceased man was known to engage in water activities, as well as two lakes from the Cabo Norte complex and those located at the Centenario Zoo, Gran Parque La Plancha, and Parque Ecológico del Poniente. In response, authorities have restricted water contact and initiated cleaning operations, although parks and zoos remain open to the public.
Testing was expanded after the Epidemiological Diagnosis and Reference Institute confirmed that the death was linked to Naegleria fowleri. The amoeba was also found in samples from Plaza La Isla, believed to be the site of infection. However, officials have not confirmed whether the amoebae detected in the other five lakes belong to the same species.
Mauricio Rodríguez Álvarez, a professor at the Faculty of Medicine and spokesperson for the University Programme for Epidemiological Risk Research at the National Autonomous University of Mexico (UNAM), emphasises the importance of distinguishing the severity of a disease from the likelihood of contracting it. “It’s one thing for the disease to be very serious and another for the risk to the population to be high,” he explained in an interview.
Understanding Naegleria fowleri and Its Transmission
Naegleria fowleri is a single-celled amoeba found naturally in warm freshwater environments such as lakes, ponds, rivers, and hot springs. Rodríguez Álvarez elaborates that these microorganisms differ from bacteria, as they belong to the eukaryotic group, characterised by cells with a defined nucleus and a more complex structure. They can take on various forms throughout their life cycle and are often found in sediment of natural water bodies or, under certain conditions, in pools and artificial lakes.
Factors such as warmth, stagnant water, and organic matter—which can promote the growth of the bacteria that the amoeba feeds on—create favourable conditions for its proliferation. The US Centers for Disease Control and Prevention (CDC) have also documented its presence in poorly maintained recreational facilities.
The infection occurs when water containing the amoeba enters the body through the nose, which can happen during swimming, diving, or engaging in water sports. From there, the microorganism can reach the brain via the olfactory nerve pathway, which is responsible for the sense of smell.
Rodríguez Álvarez explains that there is a very small gap at the top of the nasal cavity between the nasal mucosa—the tissue lining the interior—and the brain. In this area, a thin bone with small holes allows the nerve fibres to pass through. “It can enter there, infect the cells, and reach the brain almost directly without having to circulate through the blood or pass through the meninges,” he clarified.
Once it reaches the brain, the amoeba can cause primary amoebic meningoencephalitis (PAME), leading to inflammation of the membranes surrounding the brain, known as meninges, and damaging brain tissue. Initial symptoms typically include fever, severe headache, nausea, and vomiting. As the disease progresses, symptoms may include neck stiffness, confusion, seizures, and loss of consciousness.
According to the CDC, death usually occurs between one and 18 days after symptoms appear, typically around the fifth day. The disease cannot be contracted by drinking contaminated water, nor does it spread from person to person. Consequently, merely being near a lake where the microorganism has been detected does not inherently pose an infection risk.
Rare but Challenging Infections
PAME is among the deadliest brain infections known. A study published in 2021 in Clinical Infectious Diseases compiled 381 cases reported up to 2018 across 33 countries. Out of the 380 patients with known outcomes, 348 died while 32 survived. The study included confirmed, probable, and suspected cases; among the 182 confirmed cases, only seven individuals survived. Another review in 2025 identified 488 reported cases globally since 1962.
The CDC notes that children and adolescent males are more frequently represented among cases, possibly due to their higher participation in activities that allow water to enter the nose. However, the reasons for this discrepancy are not yet fully understood.
Mexico has also reported cases of PAME. An examination of epidemiological bulletins from the Health Secretariat identified 16 cases reported between 2015 and 2025. This count includes retrospective records—cases from previous years incorporated in later bulletins—as well as probable cases that may not have been definitively confirmed. The highest incidence was recorded in Guerrero, with five cases in 2020. In 2026, Yucatán reported the first confirmed case of the year.
Rodríguez Álvarez attributes the high mortality rate to several factors. The rarity of the disease often leads physicians to overlook it when presented with patients exhibiting meningitis symptoms. Moreover, initial symptoms closely resemble those of other infections, while a patient’s health can deteriorate rapidly within days. This timeframe can be crucial. Although laboratory tests exist to identify the amoeba, and some patients have received combinations of medications alongside intensive care, treating the infection remains complex. The infrequency of cases further complicates research and the development of new treatments.
Assessing the Risks of Naegleria in Yucatán’s Lakes
Amoebae are integral to aquatic ecosystems, and various species do not cause human disease. Therefore, Rodríguez Álvarez cautions that the mere presence of Naegleria microorganisms in Mérida’s artificial lakes does not automatically indicate the level of danger associated with each location. “To assess any risk, we may need to know exactly which species were found, in what quantities, and in which locations, as well as the sampling methods and temperature,” he explained.
In light of these findings, the Yucatán government has ordered restrictions on water contact at the six lakes and implemented barriers and warning signs. The managers of these facilities have begun cleaning efforts alongside specialists from the Autonomous University of Yucatán and the Centre for Research and Advanced Studies. Authorities have also announced plans to establish new regulations to monitor the conditions of the state’s artificial lakes.
Rodríguez Álvarez advocates for regular assessments of water quality in these spaces, including analyses to identify present microorganisms and temperature measurements. Additionally, maintaining water circulation can help alter conditions that favour amoeba growth. “Simply moving the water changes the distribution of nutrients, oxygen, predators, and microbes residing there,” he noted. In artificial lakes, systems can even be installed to enhance water circulation and oxygenation.
In the case of Plaza La Isla, the Yucatán government fined the company responsible for water activities in the lake 2.1 million pesos for sanitary irregularities. Authorities discovered deficiencies in cleaning, circulation, and water filtration, as well as a lack of residual chlorine at the sampled points.
In addition to improving the maintenance of these areas, Rodríguez Álvarez considers it beneficial to conduct specific tests for Naegleria fowleri in locations where infections have already been reported. Molecular tests, such as PCR, can detect the microorganism’s genetic material.
For Rodríguez Álvarez, the events in Yucatán highlight the necessity of clear communication regarding health risks. The term “brain-eating amoeba” might lead to the impression that anyone near a lake hosting the amoeba is in danger, despite the fact that infection requires specific conditions. He stresses that information about these cases should include details about where the infection occurred, the exposure conditions, and preventive measures that can be taken. “Rather than simply reassuring or alarming people, it is essential to provide information that allows individuals to understand the real risk involved,” he concludes.