Researchers worldwide have been studying alternatives to detect SARS-CoV-2 (COVID-19), and accurate and timely diagnosis is crucial for controlling the outbreaks of the disease. Surface plasmon resonance (SPR) is an effective strategy based on antibodies, and it can be used for simple and fast detection of antibodies due to COVID-19 infection. Accordingly, this paper reports on the highly sensitive and specific detection of antibody responses to SARS-CoV-2 spike (S) and nucleocapsid (N) proteins in COVID-19 patients. In this methodology, spike (S) and nucleocapsid (N) proteins belonging to the coronavirus genome were immobilized on the surface of a gold sensor using self-assembled monolayers. Previously, serum from COVID-19 patients was screened by immunochromatography-based COVID-19 IgG rapid test and/or ELISA in house to determine the presence of IgG titers. Serum from COVID-19-positive patients presenting with IgG were added on the surface and, at the time they bound to proteins, they caused refractive changes in the SPR angle. The antibody detection limit was determined through successive injections into the SPR apparatus – these injections ranged from pure (without dilution) to 1 : 200 μL. The system has shown good reproducibility between runs after coated surface regeneration with 0.1 M glycine-HCl solution (pH 3.0); all experiments were tested in triplicate. The antibodies targeted both S and N fragments and gave a high assay sensitivity by identifying 19 out of 20 COVID-19-positive patients. Most importantly, the assay time took less than 10 min. The results of this study indicate that the proposed simple strategy demonstrates high sensitivity and time-saving in the detection of SARS-CoV-2 response antibodies.

The aim of this study was to investigate the coinfection of feline retroviruses (feline immunodeficiency virus—FIV, and the feline leukemia virus—FeLV) with Leishmania infantum and Toxoplasma gondii and the factors associated with these pathogens in domestic cats from Mossoró, a city endemic for canine and human leishmaniasis situated in the semiarid region of Northeast Brazil. Blood samples from 120 cats were collected, and an epidemiological questionnaire was applied to investigate the risk factors associated with the infections. Retroviruses, L. infantum, and T. gondii infections were assessed using a point-of-care ELISA and quantitative PCR (qPCR), indirect fluorescent antibody test (IFAT) and qPCR, and IFAT, respectively. The overall seroprevalences observed were 35% (95% CI = 27.0–43.8%) for FIV, 0.8% (95% CI = 0.1–4.5%) for FeLV, 25.8% (95% CI = 18.8–34.3%) for T. gondii, and 4.2% (95% CI = 1.7–9.3%) for L. infantum. Coinfection with FIV and L. infantum was observed in 2.5% (3/120) of the assessed cats, while 12.5% (15/120) were coinfected with FIV and T. gondii. No significant association was found among the investigated agents (p > 0.05). The factors associated with FIV infection in the multivariable analysis were male sex and age above 78 months. The findings of this study demonstrated a high rate of FIV infection in cats from the Brazilian semiarid region and the exposure of these animals to zoonotic and opportunistic agents. Due to the immunosuppressive potential of FIV, cats infected with this retrovirus should be screened for coinfections with L. infantum and T. gondii, and preventative measures should be adopted.

Chloroviruses are large double-stranded DNA (dsDNA) viruses that infect Chlorella -like green algae in freshwater environments. Despite being extensively studied in the Northern Hemisphere, little is known about their diversity and biology in tropical regions. In this study, we report the isolation and characterization of a novel chlorovirus, named Chlorovirus BR-MG-N01, infecting Chlorella variabilis NC64A. The virus was recovered from a freshwater lake in Guanhães, Minas Gerais, Brazil, located in a transition zone between the Atlantic Forest and Cerrado biomes. Electron microscopy revealed icosahedral particles of approximately 160 nm in diameter. The viral growth profile showed a 2-log increase after 24 h of infection. BR-MG-N01 demonstrated high thermal stability, remaining viable from −80°C to 56°C, but showed low tolerance to ultraviolet radiation, with a rapid decrease in titer after 3 min of exposure. Genome sequencing revealed a 318 kbp dsDNA genome containing 384 coding sequences. Gene annotation identified a high number of endonucleases, two of which are putatively novel, as well as genes related to transcription and oxidative stress resistance. Phylogenetic analysis based on the DNA polymerase gene placed BR-MG-N01 within the Alphachlorovirus subgenus, closely related to the species Chlorovirus vanettense . Comparative genomic analysis revealed strong synteny and high sequence similarity with other members of this species. The isolation of Chlorovirus BR-MG-N01 expands the known distribution of chloroviruses and highlights the need for further exploration of tropical environments to uncover the ecological and evolutionary diversity of these enigmatic aquatic viruses. IMPORTANCE: Chloroviruses are large dsDNA viruses that infect algae, with limited available research in tropical environments. This work helps address that gap by presenting the first detailed genomic and biological characterization of a native chlorovirus from Brazil. We show that Brazilian environments harbor viral lineages as complex and diverse as those described in well-studied regions of the Northern Hemisphere. By documenting the isolate’s morphology, stability, replication profile, genomic architecture, and evolutionary placement, this study establishes the basis for future ecological and evolutionary research on algal viruses in the country. Overall, the discovery highlights a hidden viral diversity in Brazilian ecosystems and reinforces the importance of investigating microorganisms from tropical and understudied habitats.

The emergence of new viral strains has been frequently associated with the onset of outbreaks in different epidemiological settings. This study investigated an acute gastroenteritis (AGE) outbreak, which occurred at a university campus in southern Brazil, in 2024, affecting approximately 30–40% of undergraduate students, with over 400 reported cases. The objectives were to describe the epidemiological and molecular features of the outbreak, identify the probable transmission route, and assess the genetic relatedness of the detected strain to recently circulating rotavirus A (RVA) lineages. Clinical, environmental, and food samples were analysed for RVA and norovirus genogroup (G) I and GII. RT-qPCR detected RVA in the three specimen types with concentrations reaching 2.4 × 10 ⁸ genome copies (GC)/g in faeces, 3.5 × 10 ² GC/g in food and 5.5 log₁₀ GC/l in water. Genotyping revealed an equine-like G3P[8] strain in clinical samples with whole genome sequencing establishing a DS-1-like backbone; G3-P[8]-I2-R2-C2-M2-A2-N2-T2-E2-H2. Sequencing data of the VP6 gene of RVA detected in one of the environmental samples confirmed the same genotype (I2), consistent with the genotype found in the clinical stool samples. The detection of RVA in multiple environmental and food specimens suggests that the possible source of contamination was associated with water supply systems. Phylogenetic analyses showed that the outbreak strain clustered with equine-like G3P[8] lineages. These findings highlight the importance of integrating molecular surveillance and environmental monitoring to trace viral transmission pathways and detect the emergence of RVA strains in community outbreaks.