Balamuthia Mandrillaris Encephalitis Post‐Raw Beef Ingestion

A 35-year-old male presented with a 1.5-month history of fever, right limb convulsions, and progressive quadriparesis. The patient had consumed raw beef approximately 10 days before the onset of symptoms. Magnetic resonance imaging of the brain revealed multiple supratentorial and infratentorial lesions, characterized by ring and patchy enhancement (see Fig 1A,B), coupled with diffusion restriction (see Fig 1C). The cerebrospinal fluid (CSF) analysis demonstrated an elevated total cell count of 65 cells/μL (reference ≤20 cells/μL, 6% polymorphonuclear cells and 94% mononuclear cells), a white blood cell count of 34 cells/μL (reference <10 cells/μL), a protein concentration of 465.6 mg/dL (reference ≤400 mg/dL), and a slightly decreased glucose level of 2 mmol/L (reference 2.8–4.48 mmol/L). Metagenomic next-generation sequencing (mNGS) of CSF detected 462 Stenotrophomonas maltophilia sequences. A biopsy of the left parietal lobe lesion confirmed Balamuthia mandrillaris encephalitis (BAE) via periodic acid-Schiff stain (see Fig 1D) and mNGS. The patient received a combination of meropenem, azithromycin, co-trimoxazole, and fluconazole for anti-infection treatment, along with mannitol to reduce intracranial pressure. Despite aggressive treatment measures, the patient experienced rapid clinical deterioration, developing the absence of spontaneous respiration, hypotension, and loss of pupillary light reflex. Unfortunately, the patient's family decided to discontinue further treatment and requested discharge, and the patient passed away a few weeks after discharge. BAE is an extremely rare and severe parasitic infection of the central nervous system, with a high mortality rate of around 95%.1 Transmission of B. mandrillaris typically occurs through the respiratory tract or skin lesions, with subsequent dissemination via the bloodstream. Recent animal studies suggest a rare possibility of entry through the gastrointestinal tract as well.2 This is the suspected route of infection in the current case. The clinical manifestations of BAE are lack of specificity, including fever, headache, vomiting, and abnormal mental behavior, seizures, etc. Neuroimaging typically reveals nonspecific findings such as ring-enhancing lesions, multifocal or space-occupying lesions both supratentorially and infratentorially.3 The lack of specificity in clinical manifestations, laboratory tests, and neuroimaging often lead to delayed diagnosis. When a patient presents with symptoms suggestive of central nervous system infection, and brain imaging shows multiple supratentorial and infratentorial lesions with significant enhancement, but standard pathogen tests are negative, free-living amoeba infections like BAE should be considered. Currently, brain tissue and skin biopsies remain the gold standard for diagnosis. Treatment guidelines for BAE are not well established, but a combination therapy using miltefosine, fluconazole, and pentamidine isethionate is often recommended by several authorities.4 In some cases, surgical excision of isolated brain lesions may also be effective. X.L., contributed to the study concept and design. X.Y., contributed to data acquisition and analysis. X.Y., and X.L., contributed to drafting the manuscript and preparing figures. Nothing to report. Data generated or analyzed during the study are available from the corresponding author by request.