Nature: Host factors, inflammatory markers, and clinical outcomes of Naegleria fowleri meningoencephalitis

B3 Avian Flu Diary (Mike Coston) — zoonotic outbreak commentary · 2026-06-10 · United States · SNV

#19,197 Nearly every year I end up blogging about a rare , mostly fatal brain infection caused by free living amoebas ( Naegleria fowleri ) that inhabit warm, fresh water (see A Reminder About Naegleria Season - 2019 ). Dubbed the ` brain eating amoeba ' by the press - this infection is called PAM ( Primary amebic meningoencephalitis ) - and occurs when the amoeba enters the brain through the nasal passages, usually due to the forceful aspiration of contaminated water into the nose. Not every PAM case is due to Naegleria , as Balamuthia mandrillaris and Acanthamoeba - and other non-Naegleria amoebic infections - can cause similar pathologies. As a thermophilic ( heat-loving ), free-living amoeba, it is hardly surprising that Naegleria is mainly reported during the summer - and that Florida and Texas lead the nation in cases over the past three decades - although infections have occurred as far north as Minnesota . Last year the CDC's MMWR carried a report on a fatal 2024 case from Texas, which involved a previously health 71-year old woman who used unsterilized water to perform nasal irrigation. This is a common way that people around the world have become infected (see 2011's Neti Pots & Naegleria Fowleri ). The CDC and state health departments have long warned on the dangers of using tap water to perform nasal irrigation, and offer advice on safer alternatives. For a more detailed look as PAM risks from nasal irrigation, you may with to revisit EID Journal: (Mis)perception and Use of Unsterile Water in Home Medical Devices . Other routes of infection include swimming in stagnant, warm fresh water ponds, attending water parks , and even in a child playing with a water hose in their own yard. Only 3 or 4 cases are reported in the United States each summer, but in 2017 a research letter written by epidemiologists at the CDC (se e EID Journal: Estimation of Undiagnosed Naegleria fowleri (PAM), United States) estimated the yearly number PAM cases in the United States probably averages closer to 16 (8 males, 8 females). Meaning that 70%-80% likely go unrecognized. Every year Pakistan reports a dozen or more infections from this `killer amoeba’, as chlorination of their water supplies is often inadequate, and for many, nasal ablutions are part of their daily ritual. But in 2025 Kerala, India saw an unprecedented outbreak (see The outbreak of amoebic meningoencephalitis in Kerala: A wake-up call ) `with with reports indicating a total of 129 cases and 26 deaths as of October 18, 202 5 1 . ' Even more remarkable than the sharp rise in cases was the unusually low fatality rate - which normally exceeds 90% - even with treatment. Since it was published 2 weeks after the Hantavirus outbreak aboard the m/v Hondius and 4 days after the announcement of a large Bundibugyo virus outbreak in Africa, the following study - published in Nature - probably didn't garner as much attention as it should. In short, this study looked at a cohort of roughly 200 PAM patients from Kerala, India treated between January and November 2025 using a standardized amphotericin B/miltefosine protocol . Roughly of 1/3rd of cases were unresolved at the time of the cut off, and were not included in the analysis - but of the 134 who were - 61 died , while 73 recovered , giving a case fatality rate of 45.5%. Given this remarkable success rate, and the increasing risk of PAM due to climate change, the following report should be of particular interest to clinicians. Host factors, inflammatory markers, and clinical outcomes of Naegleria fowleri meningoencephalitis Vijeesh Kadukkatti , Brijil K. Mathew & Peter Mac Asaga Communications Medicine volume 6, Article number: 290 (2026) Abstract Background Primary amoebic meningoencephalitis (PAM) caused by Naegleria fowleri carries historical case fatality rates (CFR) exceeding 97%. The 2025 Kerala outbreak, the largest documented globally, provided an unprecedented opportunity to identify host factors and inflammatory correlates influencing survival under standardised management. Methods We conducted a prospective observational study of 200 laboratory-confirmed PAM cases across six districts of Kerala, India (January–November 2025). All patients received protocolised amphotericin B ± miltefosine. Demographic, clinical, and laboratory data were collected, including inflammatory biomarkers (IL-6, TNF-α, IL-1β, neutrophil-to-lymphocyte ratio), pathogen burden (qPCR), and treatment timing. Multivariable logistic regression identified mortality predictors; bootstrap resampling and E-value sensitivity analyses assessed robustness. Results Here we show that among 200 patients (median age 41 years; 50% male), 134 with resolved outcomes yield a CFR of 45·5% (95% CI 37·3–54·5%; 61 deaths, 73 recoveries). Diabetes mellitus is the only statistically significant predictor of mortality in the adjusted model (adjusted OR 2·59; 95% CI 1·01–6·66; p = 0·048), though the proximity of the lower confidence bound to unity warrants cautious interpretation. This association remains consistent across sensitivity analyses (bootstrap 95% CI 1·06–8·74; E-value 4·62). Asthma demonstrates a protective association in univariable analysis (OR 0·37; p = 0·021), though this finding remains hypothesis-generating. Early treatment (≤2 days) shows a trend toward improved survival (p = 0·084). Inflammatory biomarkers show no association with outcome, though CSF pathogen burden correlates significantly with admission neurological severity. Conclusions Under standardised treatment, diabetes mellitus emerges as a key host determinant of PAM mortality. The dissociation between inflammatory markers and outcomes suggests neurological fate may be determined early in infection, with immediate clinical implications as climate change expands the geographic range of N. fowleri. Plain language summary Naegleria fowleri is an amoeba found in warm freshwater that can cause a rare but usually fatal brain infection. Historically, more than 97% of people who develop this infection die. In 2025, a large outbreak occurred in Kerala, India, affecting 200 people. We studied these patients to understand what factors influenced survival. The death rate was 45.5%, much lower than expected, likely because all patients received the same standard drug treatment. People with diabetes were roughly twice as likely to die as those without. Surprisingly, common markers of inflammation did not help predict who would survive. As climate change warms freshwater sources worldwide, understanding what determines survival from this infection becomes increasingly important . (Continue . . . )

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