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PubMed2026

First Fatal Case of Adult Meningoencephalitis Caused by Pasteurella canis: An Autopsy Case Report.

Pasteurella canis is a Gram-negative bacterium commonly found as a commensal organism in the oral cavity of dogs and cats. Human infections are rare and typically occur following skin breaches, with bacteremia reported less frequently. To date, fatal central nervous system infections in adults caused by P. canis have not been reported. We report the case of a 25-year-old immunocompetent man with no significant medical history. The patient developed otitis a few days after his dog licked his ear. Twenty days later, he died at home following a febrile illness with headaches. An autopsy revealed purulent meningitis. Bacteriological cultures from the ear and subdural empyema isolated P. canis and Streptococcus anginosus group. To our knowledge, this is the first reported case of fatal adult meningoencephalitis caused by P. canis. The case highlights the pathogen's invasive potential and underscores the importance of prompt evaluation of otitis with neurological involvement.

Humans↗
PubMed2026

Estimated prevalence and distribution of causes of immune-mediated hypertrophic pachymeningitis in São Paulo, Brazil.

BACKGROUND: The prevalence of hypertrophic pachymeningitis (HP) remains poorly defined worldwide. In Japan, the estimated prevalence is 0.949 cases per 100,000 inhabitants, with most cases related to ANCA-associated vasculitis or IgG4-related disease. In contrast, epidemiological data from other regions, including Latin America, are scarce. METHODS: This study was conducted at a tertiary referral center in the city of São Paulo, Brazil. The prevalence of HP was estimated by comparison with the known prevalence of multiple sclerosis (MS), based on the number of patients with each condition followed at our institution. The etiological distribution of HP was also analyzed. In addition, HP prevalence was compared with that of tuberculous meningoencephalitis, a compulsory notifiable disease and a well-established cause of chronic meningitis in Brazil, using data from the national surveillance system (SINAN). RESULTS: We identified 55 patients with HP: 36 (65%) idiopathic, 10 (18%) IgG4-related disease, 4 (7%) ANCA-associated pachymeningitis, 4 (7%) probable or definite neurosarcoidosis, and 1 (2%) secondary to rheumatoid arthritis. Among 968 registered MS patients and assuming an MS prevalence of 15 per 100,000 inhabitants in São Paulo, the estimated HP prevalence was 0.85 per 100,000 inhabitants. This estimate was comparable to the prevalence of tuberculous meningoencephalitis in the same region. CONCLUSION: The estimated prevalence of HP in São Paulo (0.85 per 100,000) is consistent with reports from other regions and is comparable to that of tuberculous meningeal disease, although with a distinct etiological profile. IgG4-related disease was the most frequent systemic association, differing from previous reports. ANCA-associated HP appears to be less frequent than in other geographic regions, possibly reflecting differences in disease phenotype. Key Points • The estimated prevalence of HP in São Paulo was 0.85 per 100,000 inhabitants. • IgG4-related disease was the most common systemic disease identified among patients with HP. • ANCA-associated HP was less common than reported in Asian and European cohorts. • The prevalence of HP was comparable to that of tuberculous meningoencephalitis in São Paulo.

Humans↗
PubMed2025

Detection and identification of Naegleria species along with Naegleria fowleri in the tap water samples.

Naegleria fowleri, the causative agent of Primary Amoebic Meningoencephalitis (PAM), is commonly found in warm freshwater environments and can enter the brain through nasal passages during activities like swimming or ablution. PAM has a high fatality rate, raising concerns about its global health impact. In Pakistan, particularly in Karachi, a significant number of cases have been reported, often with no history of recreational water exposure, but with regular ablution using tap water. This study analyzed the physicochemical parameters, abundance of total and fecal coliforms, and detected N. fowleri and other Naegleria species in tap water samples from Karachi using PCR with ITS- and Naegl-primers. Almost all samples exhibited high temperatures, low chlorine levels, and a high presence of coliforms. N. fowleri and other Naegleria species were detected in 11 out of 39 samples. Sequence analysis identified N. fowleri in tap water from the Golimar and Lyari areas of Karachi, while the other nine samples revealed different Naegleria species. This study suggests that the combination of high temperatures, insufficient chlorination, and the presence of coliforms may create favorable conditions for N. fowleri growth. However, these factors are not exclusive to the Golimar and Lyari areas, indicating that other environmental or infrastructural factors, not detailed in this study, may have contributed to the presence of N. fowleri in that specific location.

Naegleria fowleri↗
PubMed2025

Efficient Expression of Oropouche Virus Nonstructural Proteins NSs and NSm.

Oropouche fever, a mosquito- or midge-borne emerging zoonotic disease endemic to South and Central America, manifests as a dengue-like acute febrile illness with occasional occurrences of meningitis or meningoencephalitis. The causative agent, Oropouche virus (OROV), belongs to the genus Orthobunyavirus within the family Peribunyaviridae. Its tripartite negative-sense RNA genome comprises small (S), medium (M), and large (L) segments, encoding structural N, Gn/Gc, and L proteins, respectively. Additionally, the S- and M-segments encode nonstructural proteins: NSs and NSm, which may act as virulence factors. OROV NSs functions as an interferon antagonist with an unknown mechanism, while the roles of OROV NSm remain elusive. This chapter introduces efficient expression systems for OROV NSm and NSs proteins. Validating the presence of a signal peptide at the N-terminus of NSm protein is essential for its expression. Furthermore, expressing OROV NSs protein independently of an RNA polymerase II promoter is crucial to prevent restricted gene expression, potentially caused by NSs inhibiting cellular RNA polymerase II, as observed in closely related bunyavirus NSs proteins. These protein expression strategies offer insights into the molecular characterization of OROV NSm and NSs proteins, facilitating a deeper understanding of their virulence mechanisms.

Viral Nonstructural Proteins↗
PubMed2025

Meiosis-specific genes play roles in ploidy reduction in Cryptococcus neoformans titan cells.

Cryptococcus neoformans is a fungal pathogen of humans that causes life-threatening meningoencephalitis. During infection, enlarged, polyploid titan cells are produced that promote survival, evade immune cells, and generate diverse progeny. These titan cells divide to produce haploid, aneuploid or diploid daughter cells with enhanced stress tolerance; however, how ploidy reduction occurs is poorly understood. Here, we show that titan cells developed from diploid strains predominantly produce diploid daughter cells with haploid daughters observed infrequently. We further demonstrate that meiosis-specific genes, including DMC1 and SPO11, are critical for stable inheritance of a diploid genome in the daughter cells. Specifically, deletion of these genes in a heterozygous diploid background results in: 1) titan cells with a significantly reduced capacity to produce daughter cells; 2) increased phenotypic variation among daughter cells produced by the titan cells, including traits that could be relevant to cell growth and viability; and 3) daughter cells produced by the titan cells exhibiting high levels of loss of heterozygosity (LOH) and aneuploidy, suggested elevated genome instability. Taken together, these findings demonstrate the importance of meiosis-specific genes in the ploidy reduction process of titan cells derived from a heterozygous diploid background in an important human fungal pathogen.

Dmc1↗
PubMed2026

H5N1 Clade 2.3.4.4b Infections in Domestic Cats During an Avian Influenza Outbreak in Italy: Implications for One Health Surveillance.

BACKGROUND: H5Nx goose/Guangdong (Gs/GD) lineage highly pathogenic avian influenza (HPAI) viruses pose a significant public health threat due to their global spread, mutation accumulation, and expanding host range. The descendant clade 2.3.4.4b has been causing widespread infections in birds and increasing spillover events in mammals. METHODS: This report documents the first fatal case of highly pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b infection in a domestic cat in Italy, detected in early January 2025. The cat (CAT 1) resided on a backyard poultry farm experiencing a high pathogenicity avian influenza outbreak and succumbed rapidly following the onset of respiratory signs. A second exposed cat (CAT 2) developed clinical disease without fatal outcome. Comprehensive outbreak investigations were conducted, including pathological, serological, molecular analyses, and genomic characterization. RESULTS: Pathological examination of CAT 1 revealed acute necrotizing bronchointerstitial pneumonia, non-suppurative meningoencephalitis, and disseminated foci of hepatic necrosis. Interestingly, the PB2-E627K mutation associated with mammalian virus adaptation was observed in the feline viral isolate compared to avian isolates. Such polymerase complex mutations are key determinants of host range and increase pathogenicity in mammals. CAT 2 from the same farm tested negative for AIV genome detection but subsequently seroconverted for antibodies against NPA, H5, and N1. CONCLUSION: Sharing these findings is crucial for surveillance aimed at enabling early identification of increased risks to human and animal health, preventing cross-species viral transmission and mitigating the risk of potential spillover events.

Animals↗
PubMed2026

Continuous Intrathecal Infusion of Nivolumab in Advanced Melanoma With Concomitant Leptomeningeal Disease: Efficacy, Safety, and Pharmacokinetics.

BACKGROUND AND OBJECTIVES: Prognosis of melanoma with leptomeningeal disease (LMD) is poor (median overall survival of 5.1 months). Intrathecal (IT) nivolumab appears safe, although its efficacy remains uncertain. We investigated the feasibility, safety, and efficacy of continuous IT nivolumab. METHODS: This was a retrospective analysis of 11 melanoma patients with progressive LMD (MelBase; NCT02828202) treated as part of the patients' care with continuous IT nivolumab administered through spinal (n = 10) or ventricular catheter (n = 1). RESULTS: Patients (5 women, median age 52) with Eastern Cooperative Oncology Group &#x2264;1 (except for 1) and stable extracranial disease (except for 4) were treated over a median duration of 1.5 months and followed for 2.5 months. Seven presented symptomatic LMD. Primary tumors were mostly cutaneous (n = 8) and BRAF-mutated (n = 10). All patients had progressed on systemic immunotherapy; 7 had received brain radiotherapy (whole brain radiotherapy [n = 3]; stereotactic radiosurgery [n = 4]). Concomitant therapies included corticosteroids >10 mg (n = 5), intravenous nivolumab (first 3 months of IT therapy, n = 1), and targeted therapies (n = 7). The median overall survival was 2.5 months, with 3 patients surviving for more than a year. Reversible treatment-related adverse events occurred in 5 patients: meningoencephalitis (grade 3, n = 1), intracranial hemorrhage (grade 1, n = 1), intracranial hypotension (grade 2, n = 2; grade 1, n = 1). Baseline levels of nivolumab in the cerebrospinal fluid (CSF) were <2 &#xb5;g/mL, even among patients with plasma detection. CSF concentrations of nivolumab at steady state varied from 36 to 97 &#xb5;g/mL, with clearances of 4.3-15.7 mL/h. Next-generation sequencing identified CSF genomic profiles correlating with clinical progression in 4 patients. CONCLUSION: These findings warrant further trials on IT nivolumab.

Humans↗
PubMed2025

Eating the brain - A multidisciplinary study provides new insights into the mechanisms underlying the cytopathogenicity of Naegleria fowleri.

Naegleria fowleri, the causative agent of primary amoebic meningoencephalitis (PAM), requires increased research attention due to its high lethality and the potential for increased incidence as a result of global warming. The aim of this study was to investigate the interactions between N. fowleri and host cells in order to elucidate the mechanisms underlying the pathogenicity of this amoeba. A co-culture system comprising human fibrosarcoma cells was established to study both contact-dependent and contact-independent cytopathogenicity. Proteomic analyses of the amoebas exposed to human cell cultures or passaged through mouse brain were used to identify novel virulence factors. Our results indicate that actin dynamics, regulated by Arp2/3 and Src kinase, play a considerable role in ingestion of host cells by amoebae. We have identified three promising candidate virulence factors, namely lysozyme, cystatin and hemerythrin, which may be critical in facilitating N. fowleri evasion of host defenses, migration to the brain and induction of a lethal infection. Long-term co-culture secretome analysis revealed an increase in protease secretion, which enhances N. fowleri cytopathogenicity. Raman microspectroscopy revealed significant metabolic differences between axenic and brain-isolated amoebae, particularly in lipid storage and utilization. Taken together, our findings provide important new insights into the pathogenic mechanisms of N. fowleri and highlight potential targets for therapeutic intervention against PAM.

Naegleria fowleri↗