The rising threat of amoebae

 Dangerous amoebas spread globally and urgent action is required to be taken

Scientists are warning that a little-known group of microbes called free-living amoebae may pose a growing global health threat. Amoebae, single-celled protists capable of altering their shape and moving via pseudopodia, represent a growing public health threat worldwide. Free-living species such as Naegleria fowleri and Acanthamoeba spp. are of particular concern. Found in soil and water, some species can survive extreme heat, chlorine and even modern water systems, conditions which kill most germs. One infamous example, the “brain-eating amoeba,” can cause deadly infections after contaminated water enters the nose. Even more concerning, these amoebae can act as hiding places for dangerous bacteria and viruses, helping them evade disinfection and spread. Although often overlooked in conventional biosecurity research, these protozoa can survive extreme environmental conditions, including high pH, elevated temperatures and high chlorine concentrations, making them resistant to standard water treatment approaches. Their widespread presence in both natural and engineered environments poses significant exposure risks through contaminated water sources, recreational water activities and drinking water systems. While conventional disinfection methods show limited efficacy, emerging technologies and materials, such as novel chemical systems and piezo-catalytic composites, offer promising avenues for reducing amoeba viability. Nevertheless, a significant gap persists in the early detection and monitoring of these pathogens. Future research should prioritize the development of integrated strategies under the One Health framework, linking human health with environmental and ecological dimensions, while advancing innovative vector control measures to limit transmission. Given the rising global incidence of amoeba-related diseases, there is an urgent need for more proactive public health surveillance and intervention efforts.

A microscopic survivor hiding in our water could be the next public health threat, and climate change is giving it an edge. Environmental and public health researchers are drawing attention to a little-known group of pathogens which may pose a rising global danger: free living amoebae. In a new perspective, the team explains that these microscopic organisms are gaining ground worldwide, driven by climate change, deteriorating water systems and limited monitoring and detection efforts. Amoebae are single celled organisms which naturally occur in soil and water. Most are harmless, but certain species can cause severe and sometimes fatal disease. One of the best-known examples is Naegleria fowleri (often referred to as the brain eating amoeba), which can cause a rare but almost always deadly brain infection. Infection can occur when contaminated water enters the nose during activities like swimming. In recent years, cases of primary amebic meningoencephalitis (PAM), a fatal infection caused by the 'brain-eating amoeba' Balamuthia mandrillaris, gained significant attention on Chinese social media following reports of multiple infections among children in several provinces, predominantly linked to water-based recreational activities. In 2025, an outbreak of another 'brain-eating amoeba', Naegleria fowleri, was reported in Kerala, India, resulting in 69 confirmed cases and 19 fatalities, which heightened public concern in the region. As of now, more than 33 countries worldwide have reported approximately 500 cases. While the majority of cases have been reported in the US, Mexico, Australia and India, infections have also been documented across Asia, Africa, Europe and Oceania.

Another pathogenic amoeba, Naegleria fowleri, commonly known as the 'brain-eating amoeba', causes primary amebic meningoencephalitis, which has a case fatality rate exceeding 98%. Due to their significant public health impact, these amoebae have recently been designated by the World Health Organization (WHO) as priority pathogens for research and control. The pathogens involved are amoebae, free-living protists which are mostly harmless, while a subset can be lethal. Amoebae are single-celled protists capable of changing shape and moving via pseudopodia, allowing them to inhabit diverse environments such as water and soil. While most amoebae are harmless, some species can cause severe human diseases. For instance, Entamoeba histolytica is a parasitic amoeba responsible for amoebic dysentery, which can lead to severe intestinal and hepatic conditions. This infection remains a significant global health burden, particularly in regions with poor sanitation and limited access to safe drinking water. Scientists urge a coordinated One Health strategy which brings together public health, environmental research and water management. They emphasize the need for better surveillance, faster and more accurate diagnostic tools, and advanced water treatment technologies to reduce risks before infections occur. Amoebae are not just a medical issue or an environmental issue. They sit at the intersection of both, and addressing them requires integrated solutions that protect public health at its source. "What makes these organisms particularly dangerous is their ability to survive conditions that kill many other microbes," said corresponding author Longfei Shu of Sun Yat sen University. "They can tolerate high temperatures, strong disinfectants like chlorine and even live inside water distribution systems that people assume are safe."

Amoebae not only thrive in natural water bodies such as lakes, rivers and ponds, but also in human-made systems like drinking water distribution networks, swimming pools, sewage systems and hot springs. This broad environmental presence increases the risk of human exposure, potentially facilitating disease transmission. Studies have frequently detected amoebae, including pathogenic species, such as Acanthamoeba spp. and N. fowleri, in treated drinking water supplies and recreational waters. Consequently, common activities like swimming are exposure routes. The risks may be further amplified in some regions by specific religious and cultural practices, where rituals such as ceremonial bathing and the use of neti pots for nasal irrigation can serve as significant additional pathways for infection. N. fowleri, which typically inhabits warm freshwater or polluted environments, invades the central nervous system by ascending from the nasal mucosa via the olfactory nerve, ultimately causing the severe inflammation characteristic of primary amoebic meningoencephalitis. Similarly, A. castellanii and B. mandrillaris can cause granulomatous amebic encephalitis (GAE) and Balamuthia amoebic encephalitis (BAE), respectively. A. castellanii and B. mandrillaris can invade the human body through breaches in the skin or nasal passages and may subsequently disseminate to the brain, causing severe infections. A. castellanii can infect the cornea and cause amoebic keratitis, a sight-threatening infection primarily associated with contaminated contact lenses which can result in blindness in severe cases. The accurate scale of human exposure to amoebae is likely substantially underestimated. Amoebic infections are prone to clinical misdiagnosis as other diseases, as amoebae in traditional microscopy are easily confused with yeast, macrophages or other artifacts, thereby eliminating the impetus for molecular testing and substantially elevating misdiagnosis rates. Given the ubiquity of amoebae across diverse environments, the actual exposure level is likely far greater than currently recognized. Together with historical diagnostic limitations, these factors indicate a significant burden of undiagnosed and underreported infections, highlighting a considerable underestimation of this public health threat.

The researchers also point out that amoebae can act as protective hosts for other disease-causing microbes. Bacteria and viruses can survive inside amoebae, shielded from disinfection processes which would normally eliminate them. This so called Trojan horse effect allows harmful pathogens to persist and spread through drinking water systems and may also play a role in the rise of antibiotic resistance. In addition to being pathogens themselves, amoebae can significantly influence the fate of other biocontaminants. As one of the oldest microbial predators in nature, amoebae feed on bacteria, fungi and viruses through phagocytosis. While most ingested microbes are eliminated within phagosomes via acidification, oxidation and nutrient deprivation, certain bacteria, which are known as amoeba-resisting bacteria (ARB), can evade or resist these killing mechanisms. These ARBs can survive and replicate within amoebic trophozoites and cysts, eventually being released back into the environment. Notably, ARBs include not only nonpathogenic bacteria but also human pathogens such as Legionella pneumophila, Chlamydia, and Mycobacteria. Mycobacterium tuberculosis and L. pneumophila can not only survive within amoebae but also benefit from enhanced pathogenicity, as amoebae provide protection against disinfection treatments and facilitate their prolonged environmental persistence. Beyond safeguarding fungi such as Cryptococcus neoformans through predation, amoebae also act as hosts for enteric viruses such as coxsackieviruses, human norovirus, and adenovirus, significantly enhancing their environmental persistence. This ability turns amoebae into a 'Trojan horse', facilitating the survival, dissemination, and even the spread of antimicrobial resistance among pathogens in aquatic and soil ecosystems.

In addition, recent studies indicate that amoebae can serve as unexpected reservoirs of biocontaminants, including antibiotic resistance genes (ARGs), underscoring their potential role in the dissemination of antimicrobial resistance. For instance, an investigation revealed that Dictyostelium discoideum amoebae collected from the topsoil of a forest park carried substantial levels of both ARGs, encompassing β-lactam, multidrug and aminoglycoside among others, and metal resistance genes (MRGs), including those for elements such as Cu, As, Zn, and Hg. Rising global temperatures are expected to make the problem worse by allowing heat loving amoebae to spread into regions where they were once uncommon. Several recent outbreaks linked to recreational water exposure have already increased public concern in multiple countries. The control of amoebae-related health risks presents significant challenges due to the remarkable resilience of these pathogens, particularly in their cyst forms. Furthermore, evidence suggests that exposure to sublethal chlorine doses may even enhance the virulence of some amoebae, such as A. castellanii, by upregulating the expression of their virulence genes. Besides chemical disinfection, physical barriers such as membrane filtration can be compromised, as amoebae can use ultrafiltration membranes as growth interfaces, thereby contributing to biofouling. In contrast, ultraviolet (UV) disinfection at conventional germicidal wavelengths (e.g., 254 nm) also shows limited effect against resistant cysts.

Given the limitations of traditional methods, advanced oxidation strategies show promising potential for effective inactivation. For instance, the FeP/persulfate system can achieve a 1-log reduction in amoebic spore viability and a more substantial 4-log reduction in the viability of intracellular bacteria housed within the spores. Similarly, a MoS2/rGO composite utilizing piezocatalysis achieved a 4.18-log reduction in amoebic spores and a 5.02-log reduction in intracellular bacteria within 180 min[64]. Another innovative approach, a two-electron water oxidation strategy using BiSbO4 as an anode material, effectively inactivated amoeba spores and their intracellular bacteria, achieving inactivation rates of 99.9% and 99.999%, respectively. Beyond end-point disinfection, source control is also an essential measure. Amoebae are predominantly found in biofilms within distribution pipe networks and point-of-use filters. Therefore, physical removal through pipeline flow velocity adjustment and regular flushing, or chemical intervention, can be employed to address biofilm in distribution networks. The threat posed by amoebae is compounded by environmental changes, particularly climate warming, which is anticipated to expand the geographical distribution of thermophilic species like N. fowleri, potentially increasing incidence in previously unaffected regions. This growing risk is underscored by the increase in fatal cases of primary amebic meningoencephalitis globally. In response, the World Health Organization (WHO) issued guidelines specifically for controlling N. fowleri in drinking-water systems, signaling increased international attention to amoeba-related public health risks and marking a critical step toward a coordinated global response. Ultimately, mitigating the risks from amoebae requires a multi-faceted approach which combines robust water safety plans, encompassing system assessment, operational monitoring and management, with the adoption of advanced inactivation technologies and continued vigilance in the face of environmental change.

Effective mitigation requires comprehensive strategies combining enhanced surveillance, rapid diagnostics and targeted environmental interventions. Key priorities include understanding how global changes, such as climate shift and biodiversity loss, influence the geographic distribution and transmission dynamics of pathogenic amoebae. Genomic tools are critical for pathogen detection and for deciphering mechanisms of environmental adaptation and virulence evolution. Additionally, developing highly sensitive, rapid and quantitative detection methods is essential to establish reliable early warning systems. Despite growing awareness, critical knowledge gaps impede effective risk management and outbreak prevention through following measures:-

While amoebae are known for their general resilience, the effectiveness of disinfection strategies (e.g., chlorine, UV) can vary dramatically between different amoeba species and their life stages (trophozoites vs cysts). There is a significant lack of quantitative, species-specific data on inactivation rates for many pathogenic amoebae. This gap makes it challenging to establish science-based regulatory standards for water treatment which are guaranteed to be effective against all threatening species.

Accelerate genomic studies to uncover virulence factors and ecological drivers of pathogens like N. fowleri, using whole-genome sequencing to track strains and identify targets for interventions. Clarify pathogenic mechanisms, including how amoebae invade the brain via the olfactory nerve and evade immune responses, and explore host-pathogen interactions to pinpoint host factors which increase susceptibility. Integrate environmental and clinical data to guide public health strategies.

For many amoebic infections, especially those affecting the central nervous system, current diagnostic methods are often slow, inaccessible in low-resource settings, and can have high error rates. Furthermore, the prognosis for infections like primary amebic meningoencephalitis and granulomatous amebic encephalitis remains poor, with mortality rates exceeding 97%. There is an urgent need to develop affordable, rapid point-of-care diagnostics and more effective, accessible therapeutic protocols.

Promote interdisciplinary cooperation under the One Health framework by systematically linking environmental microbiology, clinical medicine and public health policy. This integrated approach will bridge preventive control, diagnosis and treatment, forming a closed-loop management system.

The role of amoebae as reservoirs and training grounds for other pathogens is a critical aspect of their public health threat. However, the full spectrum of these interactions across diverse environmental microbiomes and their contribution to the spread of antibiotic resistance genes remains poorly quantified. More research is needed to understand how these 'Trojan horse' dynamics impact the effectiveness of water safety plans and public health outcomes.

The precise ecological and environmental factors which facilitate the emergence and spread of pathogenic amoebae are poorly understood. Research is needed to elucidate how factors like climate change, land-use changes, and shifts in microbial communities affect the abundance and pathogenicity of amoebae in the environment.

Launch targeted public awareness campaigns focusing on high-risk periods like summer and high-risk activities (swimming, diving in warm freshwater lakes, rivers and poorly maintained pools). Key messages should emphasize practical precautions: using nose clips to prevent water from entering, avoiding submersion of the head, and refraining from disturbing sediment in shallow areas. Engaging high-risk groups and healthcare providers can enhance early recognition and reduce exposure.

Establish a coordinated surveillance and data-sharing system which integrates clinical diagnostics, environmental monitoring and wastewater management. This will create an end-to-end monitoring framework covering prevention, detection, diagnosis and source tracing around the world.