An Acute Case of Granulomatous Amoebic Encephalitis-Balamuthia mandrillaris Infection

Metagenomic next-generation sequencing for diagnosis of fatal Balamuthia amoebic encephalitis

INTRODUCTION

Balamuthia amoebic encephalitis (BAE), caused by Balamuthia mandrillaris, is a rare and life-threatening infectious disease with no specific and effective treatments available. The diagnosis of BAE at an early stage is difficult because of the non-specific clinical manifestations and neuroimaging.

CASE DESCRIPTION

A 52-year-old male patient, who had no previous history of skin lesions, presented to the emergency department with an acute headache, walking difficulties, and disturbance of consciousness. The patient underwent a series of examinations, including regular cerebrospinal fluid (CSF) studies and magnetic resonance imaging, and tuberculous meningoencephalitis was suspected. Despite being treated with anti-TB drugs, no clinical improvement was observed in the patient. Following corticosteroid therapy, the patient developed a rapid deterioration in consciousness with dilated pupils. Metagenomic next-generation sequencing (mNGS) revealed an unexpected central nervous system (CNS) amoebic infection, and the patient died soon after the confirmed diagnosis.

CONCLUSION

This study highlights the application of mNGS for the diagnosis of patients with suspected encephalitis or meningitis, especially those caused by rare opportunistic infections.

Immunogens in Balamuthia mandrillaris: a proteomic exploration

Balamuthia mandrillaris is the causative agent of granulomatous amoebic encephalitis, a rare and often fatal infection affecting the central nervous system. The amoeba is isolated from diverse environmental sources and can cause severe infections in both immunocompromised and immunocompetent individuals. Given the limited understanding of B. mandrillaris, our research aimed to explore its protein profile, identifying potential immunogens crucial for early granulomatous amoebic encephalitis diagnosis. Cultures of B. mandrillaris and other amoebas were grown under axenic conditions, and total amoebic extracts were obtained. Proteomic analyses, including two-dimensional electrophoresis and mass spectrometry, were performed. A 50-kDa band showed a robust recognition of antibodies from immunized BALB/c mice; peptides contained in this band were matched with elongation factor-1 alpha, which emerged as a putative key immunogen. Besides, lectin blotting revealed the presence of glycoproteins in B. mandrillaris, and confocal microscopy demonstrated the focal distribution of the 50-kDa band throughout trophozoites. Cumulatively, these observations suggest the participation of the 50-kDa band in adhesion and recognition mechanisms. Thus, these collective findings demonstrate some protein characteristics of B. mandrillaris, opening avenues for understanding its pathogenicity and developing diagnostic and therapeutic strategies.

Distribution and Current State of Molecular Genetic Characterization in Pathogenic Free-Living Amoebae

Free-living amoebae (FLA) are protozoa widely distributed in the environment, found in a great diversity of terrestrial biomes. Some genera of FLA are linked to human infections. The genus Acanthamoeba is currently classified into 23 genotypes (T1-T23), and of these some (T1, T2, T4, T5, T10, T12, and T18) are known to be capable of causing granulomatous amoebic encephalitis (GAE) mainly in immunocompromised patients while other genotypes (T2, T3, T4, T5, T6, T10, T11, T12, and T15) cause Acanthamoeba keratitis mainly in otherwise healthy patients. Meanwhile, Naegleria fowleri is the causative agent of an acute infection called primary amoebic meningoencephalitis (PAM), while Balamuthia mandrillaris, like some Acanthamoeba genotypes, causes GAE, differing from the latter in the description of numerous cases in patients immunocompetent. Finally, other FLA related to the pathologies mentioned above have been reported; Sappinia sp. is responsible for one case of amoebic encephalitis; Vermamoeba vermiformis has been found in cases of ocular damage, and its extraordinary capacity as endocytobiont for microorganisms of public health importance such as Legionella pneumophila, Bacillus anthracis, and Pseudomonas aeruginosa, among others. This review addressed issues related to epidemiology, updating their geographic distribution and cases reported in recent years for pathogenic FLA.

Subacute Balamuthia mandrillaris encephalitis in an immunocompetent patient diagnosed by next-generation sequencing

Balamuthia mandrillaris is a free-living heterotrophic amoeba found in soil that causes a rare and usually fatal granulomatous amebic encephalitis. We report an immunocompetent patient infected with B. mandrillaris encephalitis diagnosed by next-generation sequencing (NGS). Clinical manifestations included sudden headache and epilepsy with disturbance of consciousness. The opening pressure of cerebrospinal fluid (CSF) was 220 mmH₂O, with mildly elevated white blood cell numbers and elevated protein levels. Cranial magnetic resonance imaging revealed abnormal signals in the right frontal lobe, left parietal lobe, and left occipital lobe. CSF NGS detected B. mandrillaris. Albendazole and metronidazole combined with fluconazole were administered to the patient immediately, but his condition deteriorated and he eventually died. Encephalitis caused by B. mandrillaris is rare and has a high mortality rate. Clinical manifestations are complex and diverse, but early diagnosis is very important for successful treatment. This can be aided by the metagenomic NGS of CSF.

A case of fatal amoebic encephalitis caused by Balamuthia mandrillaris, China

We reported a case of B.mandrillaris amoebic encephalitis in mainland China. Metagenomics next-generation sequencing helped initial diagnosis and then polymerase chain reaction of the B.mandrillaris in the infected nasal skin tissues reported positive and amoeba cysts were found in the tissue under microscopic observation.

Balamuthia mandrillaris: An opportunistic, free-living ameba - An updated review

Balamuthia mandrillaris is an opportunistic, free-living ameba that is pathogenic to humans. It has a worldwide distribution but is mainly detected in warmer regions. Balamuthia infections are rare but have been reported in both immunocompetent and immunocompromised individuals of all ages. B. mandrillaris can enter through wounds on the skin or the nose and cause cutaneous lesions and the usually fatal Balamuthia amebic encephalitis (BAE). Infection usually spreads from the lungs or through nerve fibers, and attacks the central nervous system, forming granulomatous lesions and necrosis in the brain. Balamuthia infection is usually chronic, and patients initially present with nonspecific symptoms, including headache, nausea, myalgia, and low-grade fever. As the disease progresses, the patient becomes paralyzed and comatose, often leading to death. Lack of knowledge of predisposing factors, specific treatment, and standardized detection tools have resulted in a nearly cent percent fatality rate. Although only about 200 cases have been reported worldwide since its characterization in the 1990s, the number of reported cases has increased over the years. BAE is an emerging disease and a major health concern. Few patients have survived Balamuthia infections with antimicrobial treatment that has largely been empirical. Early diagnosis is the key and requires familiarity with the disease and a high degree of suspicion on the part of the diagnostician. There are currently no specific treatment and prevention recommendations. This review highlights our current understanding of B. mandrillaris in terms of its pathogenicity, genomics, and novel diagnostic and therapeutic approaches against BAE infections.

Applications of medicinal chemistry for drug discovery against Acanthamoeba infections

Acanthamoeba is a genus of free-living amoebae, pervasively found in the environment. Most of its pathogenic species are the causative agent of sight-threatening Acanthamoeba keratitis and fatal granulomatous amoebic encephalitis. Despite the advancements in the field of chemotherapy, treating Acanthamoeba infections is still challenging due to incomplete knowledge of the complicated pathophysiology. In case of infection, the treatment regimen for the patients is often ineffective due to delayed diagnosis, poor specificity, and side-effects. Besides the resistance of Acanthamoeba cysts to most of the drugs, the recurrence of infection further complicates the recovery. Thus, it is necessary to develop an effective treatment which can eradicate these rare, but serious infections. Based on various computational and in vitro studies, it has been established that the synthetic scaffolds such as heterocyclic compounds may act as potential drug leads for the development of antiamoebic drugs. In this review, we report different classes of synthetic compounds especially heterocyclic compounds which have shown promising results against Acanthamoeba. Moreover, the antiamoebic activities of synthetic compounds with their possible mode of actions against Acanthamoeba, have been summarized and discussed in this review.

Balamuthia mandrillaris infection in China: a retrospective report of 28 cases

Balamuthia mandrillaris infection is a rare and fatal disease. We have recorded 28 cases of Balamuthia mandrillaris infection during the past 20 years. Eighteen patients (64%) were male and 10 (36%) were female. Patient age ranged from 3 to 74 (mean, 27) years. Patient locations were distributed among 12 Provinces in China. Twenty-seven (96%) patients lived in rural areas, and 17 (61%) patients reported a history of trauma before the appearance of skin lesions. All cases presented with skin lesions as the primary symptom, and 16 (57%) cases developed encephalitis. Histopathology of skin lesions revealed granulomatous changes with histiocytes, lymphocytes, and plasma cells infiltration. Amebas were identified in all cases with immunohistochemical staining. Follow-up information was available in 27 (96%) cases. Fifteen (56%) patients died due to encephalitis and 12 (44%) were free of disease after treatment. Our results show that the clinical characteristics of Balamuthia mandrillaris infection in China are very different from those in the US. Infection of traumatized skin may play an important role in the pathogenesis of the disease in China. Encephalitis usually develops 3–4 years after skin lesions in Chinese cases. Patients with only skin lesions have a higher cure rate than patients with encephalitis.

A Japanese case of amoebic meningoencephalitis initially diagnosed by cerebrospinal fluid cytology

Microscopy can detect the presence of amoebic trophozoites in cerebrospinal fluid and tissue. The infection was confirmed in the present case by polymerase chain reaction and immunohistochemistry, but we were unable to achieve a cure. Our case rapidly progressed without any skin lesions.

Discovery of Anti-Amoebic Inhibitors from Screening the MMV Pandemic Response Box on Balamuthia mandrillaris, Naegleria fowleri, and Acanthamoeba castellanii

Pathogenic free-living amoebae, Balamuthia mandrillaris, Naegleria fowleri, and several Acanthamoeba species are the etiological agents of severe brain diseases, with case mortality rates > 90%. A number of constraints including misdiagnosis and partially effective treatments lead to these high fatality rates. The unmet medical need is for rapidly acting, highly potent new drugs to reduce these alarming mortality rates. Herein, we report the discovery of new drugs as potential anti-amoebic agents. We used the CellTiter-Glo 2.0 high-throughput screening methods to screen the Medicines for Malaria Ventures (MMV) Pandemic Response Box in a search for new active chemical scaffolds. Initially, we screened the library as a single-point assay at 10 and 1 µM. From these data, we reconfirmed hits by conducting quantitative dose-response assays and identified 12 hits against B. mandrillaris, 29 against N. fowleri, and 14 against A. castellanii ranging from nanomolar to low micromolar potency. We further describe 11 novel molecules with activity against B. mandrillaris, 22 against N. fowleri, and 9 against A. castellanii. These structures serve as a starting point for medicinal chemistry studies and demonstrate the utility of phenotypic screening for drug discovery to treat diseases caused by free-living amoebae.

A homogeneously enhancing mass evolving into multiple hemorrhagic and necrotic lesions in amoebic encephalitis with necrotizing vasculitis

BACKGROUND

Granulomatous amoebic encephalitis (GAE) is a rare and mostly fatal disease. Without specific symptoms, laboratory findings, or radiologic characteristics, establishing a correct diagnosis is challenging. In many cases of GAE, multiple ring-enhancing lesions with perifocal edema are observed on magnetic resonance imaging (MRI); a solitary and homogeneously enhancing mass masquerading as a malignant lymphoma that evolved into multiple hemorrhagic and necrotic lesions has rarely been reported in GAE.

CASE DESCRIPTION

An immunocompetent 68-year-old man presented with transient right hemiparesis due to epilepsy. MRI revealed a well- and homogeneously enhancing mass with perifocal edema and restricted diffusion in the left parietal subcortical region. As malignant lymphoma was suspected based on MRI findings and an elevated β2-microglobulin level in the cerebrospinal fluid, an open biopsy was performed; the pathological diagnosis was inconclusive but suggested a granulomatous disease. Although steroid therapy was administrated, subsequently the mass lesion gradually enlarged. After a second surgery for removal of the mass lesion, multiple hemorrhagic and necrotic lesions developed at the primary site and additionally in the brainstem. The patient entered a comatose state and died 3 months after admission. Histopathological examination and polymerase chain reaction analysis of the specimen revealed posthumously GAE caused by Balamuthia mandrillaris with necrotizing vasculitis.

CONCLUSION

A solitary mass lesion initially mimicked a malignant lymphoma, and subsequently evolved into multiple hemorrhagic and necrotic lesions detected on T2*-weighted and susceptibility-weighted imaging. Such serial changes noted on MRI seem characteristic and suggestive of necrotizing vasculitis of GAE.

Pathogenic free-living amoebic encephalitis in Japan

Over 600 cases of amoebic encephalitis caused by pathogenic free-living amoebas (Balamuthia mandrillaris, Acanthamoeba spp., and Naegleria fowleri) have been reported worldwide, and in Japan, 24 cases have been reported from the first case in 1976 up to 2018. Among these cases, 18 were caused by B. mandrillaris, four by Acanthamoeba spp., one by N. fowleri, and one was of unknown etiology. Additionally, eight cases were diagnosed with encephalitis due to pathogenic free-living amoebas before death, but only three cases were successfully treated. Unfortunately, all other cases were diagnosed by autopsy. These facts indicate that an adequate diagnosis is difficult, because encephalitis due to pathogenic free-living amoebas does not show typical symptoms or laboratory findings. Moreover, because the number of cases is limited, other cases might have been missed outside of those diagnosed by autopsy. Cases of encephalitis caused by B. mandrillaris have been reported from all over Japan, with B. mandrillaris recently isolated from soil in Aomori prefecture. Therefore, encephalitis caused by pathogenic free-living amoebas should be added to the differential diagnosis of encephalitis patients.

Fatal Balamuthia mandrillaris Encephalitis

Balamuthia mandrillaris is a rare cause of granulomatous meningoencephalitis associated with high mortality. We report a 69-year-old Caucasian female who presented with a 3-day history of worsening confusion and difficulty with speech. On admission, she was disoriented and had expressive dysphasia. Motor examination revealed a right arm pronator drift. Cerebellar examination showed slowing of finger-nose testing on the left. She was HIV-negative, but the absolute CD4 count was low. Neuroimaging showed three cavitary, peripherally enhancing brain lesions, involving the right frontal lobe, the left basal ganglia, and the left cerebellar hemisphere. She underwent right frontal craniotomy with removal of tan, creamy, partially liquefied necrotic material from the brain, consistent with granulomatous amoebic encephalitis on tissue staining. Immunohistochemical studies and PCR tests confirmed infection with Balamuthia mandrillaris. She was started on pentamidine, sulfadiazine, azithromycin, fluconazole, flucytosine, and miltefosine. The postoperative course was complicated by an ischemic stroke, and she died a few weeks later.