Chikungunya Virus Exposure Partially Cross-Protects against Mayaro Virus Infection in Mice.

Chikungunya virus (CHIKV) and Mayaro virus (MAYV) are closely related members of the Semliki Forest virus antigenic complex classified as belonging to the genus Alphavirus of the family Togaviridae. These viruses cause human disease, with sudden fever and joint inflammation that can persist for long periods. CHIKV is the causative agent of large outbreaks worldwide, and MAYV infection represents a growing public health concern in Latin America, causing sporadic cases and geographically limited outbreaks. Considering the relationship between CHIKV and MAYV, the present study aimed to evaluate if preexisting CHIKV immunity protects against MAYV infection. Immunocompetent C57BL/6 mice were intraperitoneally infected with CHIKV and, 4 weeks later, they were infected with MAYV in their hind paw. We observed that the preexistence of CHIKV immunity conferred partial cross-protection against secondary MAYV infection, reducing disease severity, tissue viral load, and histopathological scores. Interestingly, CHIKV antibodies from humans and mice showed low cross-neutralization to MAYV, but neutralizing activity significantly increased after secondary infection. Furthermore, depletion of adaptive immune cells (CD4+ T, CD8+ T, and CD19+ B cells) did not alter the cross-protection phenotype, suggesting that distinct cell subsets or a combination of adaptive immune cells stimulated by CHIKV are responsible for the partial cross-protection against MAYV. The reduction of proinflammatory cytokines, such as interferon gamma (IFN-γ), in animals secondarily infected by MAYV, suggests a role for innate immunity in cross-protection. Our findings shed light on how preexisting immunity to arthritogenic alphaviruses may affect secondary infection, which may further develop relevant influence in disease outcome and viral transmission. IMPORTANCE Mosquito-borne viruses have a worldwide impact, especially in tropical climates. Chikungunya virus has been present mostly in developing countries, causing millions of infections, while Mayaro virus, a close relative, has been limited to the Caribbean and tropical regions of Latin America. The potential emergence and spread of Mayaro virus to other high-risk areas have increased the scientific community's attention to an imminent worldwide epidemic. Here, we designed an experimental protocol of chikungunya and Mayaro virus mouse infection, which develops a measurable and quantifiable disease that allows us to make inferences about potential immunological effects during secondary virus infection. Our results demonstrate that previous chikungunya virus infection is able to reduce the severity of clinical outcomes during secondary Mayaro infection. We provide scientific understanding of immunological features during secondary infection with the closely related virus, thus assisting in better comprehending viral transmission and the pathological outcome of these diseases.

Murine and related chapparvoviruses are nephro-tropic and produce novel accessory proteins in infected kidneys.

Mouse kidney parvovirus (MKPV) is a member of the provisional genus Chapparvovirus that causes renal disease in immune-compromised mice, with a disease course reminiscent of polyomavirus-associated nephropathy in immune-suppressed kidney transplant patients. Here we map four major MKPV transcripts, created by alternative splicing, to a common initiator region, and use mass spectrometry to identify "p10" and "p15" as novel chapparvovirus accessory proteins produced in MKPV-infected kidneys. p15 and the splicing-dependent putative accessory protein NS2 are conserved in all near-complete amniote chapparvovirus genomes currently available (from mammals, birds and a reptile). In contrast, p10 may be encoded only by viruses with >60% amino acid identity to MKPV. We show that MKPV is kidney-tropic and that the bat chapparvovirus DrPV-1 and a non-human primate chapparvovirus, CKPV, are also found in the kidneys of their hosts. We propose, therefore, that many mammal chapparvoviruses are likely to be nephrotropic.

Stability of SARS-CoV-2 and other airborne viruses under different stress conditions.

Viral stability under stress conditions may directly affect viral dissemination, seasonality, and pathogenesis. We exposed airborne viruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), mumps virus, coxsackievirus B5, human rhinovirus A16, and respiratory syncytial virus, to different temperatures, UV light exposure time, pH values, and osmotic pressures and measured the remaining viral infectivity. Reduced thermal stability was observed for coxsackievirus B5 at 45 °C, while SARS-CoV-2 demonstrated residual infectivity at 55 °C. UV light exposure was an efficient means of viral inactivation but was less efficient for non-enveloped viruses. Rhinovirus A16 and respiratory syncytial virus demonstrated extreme sensitivity to acid conditions, while SARS-CoV-2, rhinovirus A16, and respiratory syncytial virus were unstable in an alkaline environment. The information obtained in this study will be useful for the development of viral inactivation methods and may be correlated with epidemiological and seasonal viral characteristics.

Fatal Outcome of Chikungunya Virus Infection in Brazil.

BACKGROUND: Chikungunya virus (CHIKV) emerged in the Americas in 2013 and has caused approximately 2.1 million cases and >600 deaths. A retrospective investigation was undertaken to describe clinical, epidemiological, and viral genomic features associated with deaths caused by CHIKV in Ceará state, northeast Brazil. METHODS: Sera, cerebrospinal fluid (CSF), and tissue samples from 100 fatal cases with suspected arbovirus infection were tested for CHIKV, dengue virus (DENV), and Zika virus (ZIKV). Clinical, epidemiological, and death reports were obtained for patients with confirmed CHIKV infection. Logistic regression analysis was undertaken to identify independent factors associated with risk of death during CHIKV infection. Phylogenetic analysis was conducted using whole genomes from a subset of cases. RESULTS: Sixty-eight fatal cases had CHIKV infection confirmed by reverse-transcription quantitative polymerase chain reaction (52.9%), viral antigen (41.1%), and/or specific immunoglobulin M (63.2%). Co-detection of CHIKV with DENV was found in 22% of fatal cases, ZIKV in 2.9%, and DENV and ZIKV in 1.5%. A total of 39 CHIKV deaths presented with neurological signs and symptoms, and CHIKV-RNA was found in the CSF of 92.3% of these patients. Fatal outcomes were associated with irreversible multiple organ dysfunction syndrome. Patients with diabetes appear to die at a higher frequency during the subacute phase. Genetic analysis showed circulation of 2 CHIKV East-Central-South African (ECSA) lineages in Ceará and revealed no unique virus genomic mutation associated with fatal outcome. CONCLUSIONS: The investigation of the largest cross-sectional cohort of CHIKV deaths to date reveals that CHIKV-ECSA strains can cause death in individuals from both risk and nonrisk groups, including young adults.

The NLRP3 inflammasome is involved with the pathogenesis of Mayaro virus.

Mayaro virus (MAYV) is an arbovirus that circulates in Latin America and is emerging as a potential threat to public health. Infected individuals develop Mayaro fever, a severe inflammatory disease characterized by high fever, rash, arthralgia, myalgia and headache. The disease is often associated with a prolonged arthralgia mediated by a chronic inflammation that can last months. Although the immune response against other arboviruses, such as chikungunya virus (CHIKV), dengue virus (DENV) and Zika virus (ZIKV), has been extensively studied, little is known about the pathogenesis of MAYV infection. In this study, we established models of MAYV infection in macrophages and in mice and found that MAYV can replicate in bone marrow-derived macrophages and robustly induce expression of inflammasome proteins, such as NLRP3, ASC, AIM2, and Caspase-1 (CASP1). Infection performed in macrophages derived from Nlrp3-/-, Aim2-/-, Asc-/-and Casp1/11-/-mice indicate that the NLRP3, but not AIM2 inflammasome is essential for production of inflammatory cytokines, such as IL-1ß. We also determined that MAYV triggers NLRP3 inflammasome activation by inducing reactive oxygen species (ROS) and potassium efflux. In vivo infections performed in inflammasome-deficient mice indicate that NLRP3 is involved with footpad swelling, inflammation and pain, establishing a role of the NLRP3 inflammasome in the MAYV pathogenesis. Accordingly, we detected higher levels of caspase1-p20, IL-1ß and IL-18 in the serum of MAYV-infected patients as compared to healthy individuals, supporting the participation of the NLRP3-inflammasome during MAYV infection in humans.

CCR2 Plays a Protective Role in Rocio Virus-Induced Encephalitis by Promoting Macrophage Infiltration Into the Brain.

Rocio virus (ROCV) is a highly neuropathogenic mosquito-transmitted flavivirus responsible for an unprecedented outbreak of human encephalitis during 1975-1976 in Sao Paulo State, Brazil. Previous studies have shown an increased number of inflammatory macrophages in the central nervous system (CNS) of ROCV-infected mice, implying a role for macrophages in the pathogenesis of ROCV. Here, we show that ROCV infection results in increased expression of CCL2 in the blood and in infiltration of macrophages into the brain. Moreover, we show, using CCR2 knockout mice, that CCR2 expression is essential for macrophage infiltration in the brain during ROCV infection and that the lack of CCR2 results in increased disease severity and mortality. Thus, our findings show the protective role of CCR2-mediated infiltration of macrophages in the brain during ROCV infection.

Development of an Enzyme-Linked Immunosorbent Assay To Detect Antibodies Targeting Recombinant Envelope Protein 2 of Mayaro Virus.

Mayaro virus (MAYV) is a neglected arthropod-borne virus (arbovirus) antigenically clustered into the Semliki Forest complex group of Alphavirus genus (Togaviridae family), maintained in an unclear zoonotic cycle involving mosquitoes from Haemagogus genus as the main vector. The genome is composed of a positive single-stranded RNA of 11.5 kb in length, which contains two genes that encode four nonstructural (nsP1 to nsP4) and five structural (C, E3, E2, 6K, and E1) proteins. In the present study, we have developed an enzyme-linked immunosorbent assay (ELISA) using as antigen the recombinant envelope protein 2 of MAYV produced in an Escherichia coli system (rE2-MAYV ELISAs). A panel of 68 human serum samples from suspected arboviral cases was analyzed and titrated for anti-MAYV IgM and IgG antibody detection. The rE2-MAYV ELISA detected 33.8% (23/68) IgG-positive samples, demonstrating 100% sensitivity and 78.95% specificity compared to the MAYV-specific 50% plaque reduction neutralization assay. In addition, the positive MAYV-neutralizing samples showed high titers of detection by rE2-MAYV ELISA, suggesting a highly sensitive test. The rE2-MAYV ELISA also detected 42.5% (29/68) IgM-positive samples, of which 13.8% (4/29) presented high-avidity interactions with rE2-MAYV. Cross-reactivity was observed with Chikungunya virus (CHIKV)-specific murine antibody sample but not with CHIKV-specific human and other Alphavirus murine antibodies. In short, we have developed a rapid, simple, specific, and sensitive MAYV rE2-ELISA, and our preliminary results show its potential applicability to diagnosis of MAYV infections.

Enzyme-linked immunosorbent assay using recombinant envelope protein 2 antigen for diagnosis of Chikungunya virus.

BACKGROUND: Chikungunya (CHIKV) virus is an important mosquito-borne virus causing outbreaks of acute febrile illness with arthropathy. The detection of specific antibodies against CHIKV is used for diagnosis after the acute viremic phase of the disease. However, a major challenge for serologic diagnosis of CHIKV and other alphaviruses is the cross-reactivity of antibodies to common antigens among these viruses. In the present study, we have developed an enzyme-linked immunosorbend assay using a recombinant envelope protein 2 of CHIKV produced in Escherichia coli system, as a capture antigen. RESULTS: High titers (1600 to 12,800) of anti-CHIKV antibodies were detected in human sera analyzed by the CHIKV assay, suggesting it may detect low levels of the antibodies presence. On the other side, cross-reactivity was not observed in mouse hyperimmune sera to Mayaro virus and other alphaviruses analyzed by the CHIKV immunosorbend assay, suggesting it is a CHIKV-specific test. Fifty-nine human serum samples of CHIKV infection suspected cases were tested for immunoglobulin G (IgG) and M (IgM) antibodies detection using the CHIKV immunosorbend assay. A total of 44% (26/59) of samples were positive for IgG to CHIKV, determining 89.66% sensitivity and 100% specificity when the assay is compared to a CHIKV-specific neutralization assay. In addition, 40.6% (24/59) of samples were positive for IgM, determining 92.48% sensitivity and 79.04% specificity by a Bayesian method in the absence of a gold standard. Moreover, CHIKV immunosorbend assay showed similar sensibilities to a commercial immunochromatography assay (Lumiquick, USA) for CHIKV IgG and IgM detection. CONCLUSION: In short, we have developed a rapid, simple, specific and sensitive CHIKV immunosorbend assay for IgG and IgM detection and our results showed potential applicability on the diagnosis of infections by this virus.

A novel polyomavirus in sigmodontine rodents from São Paulo State, Brazil.

The nearly complete genome sequence of a novel polyomavirus from blood samples of Akodon montensis and Calomys tener collected in Brazil was determined by high-throughput sequencing. This virus showed a typical polyomaviruses genome organization, and it was classified as a member of the genus Betapolyomavirus. Our results expand the host range and viral diversity of the family Polyomaviridae.

Chapparvoviruses occur in at least three vertebrate classes and have a broad biogeographic distribution.

Chapparvoviruses are a highly divergent group of parvoviruses (family Parvoviridae) that have recently been identified via metagenomic sampling of animal faeces. Here, we report the sequences of six novel chapparvoviruses identified through both metagenomic sampling of bat tissues and in silico screening of published vertebrate genome assemblies. The novel chapparvoviruses share several distinctive genomic features and group together as a robustly supported monophyletic clade in phylogenetic trees. Our data indicate that chapparvoviruses have a broad host range in vertebrates and a global distribution.

Genetic characterization of Cacipacoré virus from ticks collected in São Paulo State, Brazil.

Cacipacoré virus (CPCV) is a potential emerging virus classified in the genus Flavivirus, family Flaviviridae. In the present study, we present the genetic characterization of a CPCV isolated from ticks (Amblyomma cajennense) collected from a sick capybara (Hydrochoerus hydrochaeris) in São Paulo State, Brazil. The CPCV isolate shares the typical genomic organization of flaviviruses with 10,857 nucleotides in length and a single open reading frame of 10,284 nucleotides encoding a polyprotein of 3,427 amino acids. Phylogenetic analysis revealed that CPCV is unique, as a potentially tick-borne virus, in the Japanese encephalitis virus serogroup.

Development of HEK-293 Cell Lines Constitutively Expressing Flaviviral Antigens for Use in Diagnostics.

Flaviviruses are important human pathogens worldwide. Diagnostic testing for these viruses is difficult because many of the pathogens require specialized biocontainment. To address this issue, we generated 39 virus-like particle (VLP)- and nonstructural protein 1 (NS1)-secreting stable cell lines in HEK-293 cells of 13 different flaviviruses, including dengue, yellow fever, Japanese encephalitis, West Nile, St. Louis encephalitis, Zika, Rocio, Ilheus, Usutu, and Powassan viruses. Antigen secretion was stable for at least 10 cell passages, as measured by enzyme-linked immunosorbent assays and immunofluorescence assays. Thirty-five cell lines (90%) had stable antigen expression over 10 passages, with three of these cell lines (7%) increasing in antigen expression and one cell line (3%) decreasing in antigen expression. Antigen secretion in the HEK-293 cell lines was higher than in previously developed COS-1 cell line counterparts. These antigens can replace current antigens derived from live or inactivated virus for safer use in diagnostic testing. IMPORTANCE Serological diagnostic testing for flaviviral infections is hindered by the need for specialized biocontainment for preparation of reagents and assay implementation. The use of previously developed COS-1 cell lines secreting noninfectious recombinant viral antigen is limited due to diminished antigen secretion over time. Here, we describe the generation of 39 flaviviral virus-like particle (VLP)- and nonstructural protein 1 (NS1)-secreting stable cell lines in HEK-293 cells representing 13 medically important flaviviruses. Antigen production was more stable and statistically higher in these newly developed cell lines than in their COS-1 cell line counterparts. The use of these cell lines for production of flaviviral antigens will expand serological diagnostic testing of flaviviruses worldwide.

CoronaVac and ChAdOx1 Vaccination and Gamma Infection Elicited Neutralizing Antibodies against the SARS-CoV-2 Delta Variant.

The emergence of new SARS-CoV-2 variants represents a constant threat to world public health. The SARS-CoV-2 Delta variant was identified in late 2020 in India; since then, it has spread to many other countries, replacing other predominant lineages and raising concerns about vaccination efficiency. We evaluated the sensitivity of the Delta variant to antibodies elicited by COVID-19 vaccinated (CoronaVac and ChAdOx1) and convalescent individuals previously infected by earlier lineages and by the Gamma variant. No reduction in the neutralizing efficacy of the Delta variant was observed when compared to B lineage and a reduced neutralization was observed for the Gamma variant. Our results indicate that neutralization of the Delta variant is not compromised in individuals vaccinated by CoronaVac or ChAdOx1; however, a reduction in neutralization efficacy is expected for individuals infected by the Gamma variant, highlighting the importance of continuous vaccination even for previously infected individuals.

Understanding Sabiá virus infections (Brazilian mammarenavirus).

BACKGROUND: Only two naturally occurring human Sabiá virus (SABV) infections have been reported, and those occurred over 20 years ago. METHODS: We diagnosed two new cases of SABV infection using metagenomics in patients thought to have severe yellow fever and described new features of histopathological findings. RESULTS: We characterized clinical manifestations, histopathology and analyzed possible nosocomial transmission. Patients presented with hepatitis, bleeding, neurological alterations and died. We traced twenty-nine hospital contacts and evaluated them clinically and by RT-PCR and neutralizing antibodies. Autopsies uncovered unique features on electron microscopy, such as hepatocyte "pinewood knot" lesions. Although previous reports with similar New-World arenavirus had nosocomial transmission, our data did not find any case in contact tracing. CONCLUSIONS: Although an apparent by rare, Brazilian mammarenavirus infection is an etiology for acute hemorrhagic fever syndrome. The two fatal cases had peculiar histopathological findings not previously described. The virological diagnosis was possible only by contemporary techniques such as metagenomic assays. We found no subsequent infections when we used serological and molecular tests to evaluate close contacts.

Linear and Continuous Flavivirus Epitopes From Naturally Infected Humans.

This manuscript is an up-to-date review of experimentally validated linear and continuous epitopes identified from arbovirus members of the Flavivirus genus. We summarized 153 immunoreactive peptides from the Dengue virus, Zika virus, Japanese encephalitis virus, West Nile virus, and tick-borne encephalitis virus described in studies published from 1989 to 2020. We included peptides from structural (envelope, capsid, and pre-membrane) and nonstructural (Ns1-5) viral proteins that demonstrated relevant immunoreactivity with antibodies from naturally infected or vaccinated humans. We included peptides that demonstrated relevant reactivity features, such as indicators of disease severity related to immunological or immunopathological outcomes, differential or group diagnostic markers, immunotherapy candidates, and potential for vaccine formulation. The majority of immunoreactive peptides were described for DENV probably due to its long-lasting impact on human health and the lack of efficient vaccines and therapeutic methods. Immune landscape data regarding linear immunoreactive and continuous flavivirus peptides are still scarce, and a complete and more detailed map remains to be elucidated. Therefore, this review provides valuable data for those investigating the antibody response against flavivirus infection.

Paramyxoviruses from neotropical bats suggest a novel genus and nephrotropism.

Paramyxoviruses have a broad host range and geographic distribution, including human pathogens transmitted by bats, such as Nipah and Hendra viruses. In this study, we combined high-throughput sequencing and molecular approaches to investigate the presence of paramyxoviruses in neotropical bats (Microchiroptera suborder) in Brazil. We discovered and characterized three novel paramyxoviruses in the kidney tissues of apparently healthy common vampire bats (D. rotundus) and Seba's short-tailed bats (C. perspicillata), which we tentatively named Kanhgág virus (KANV), Boe virus (BOEV), and Guató virus (GUATV). In this study, we classified these viruses as putative species into the Macrojêvirus genus, a newly proposed genus of the Orthoparamyxovirinae subfamily. Using RT-PCR, we detected these viruses in 20.9% (9 out of 43) of bats tested, and viral RNA was detected exclusively in kidney tissues. Attempts to isolate infectious virus were successful for KANV and GUATV. Our results expand the viral diversity, host range, and geographical distribution of the paramyxoviruses.

Protective Immunity against Gamma and Zeta Variants after Inactivated SARS-CoV-2 Virus Immunization.

The persistent circulation of SARS-CoV-2 represents an ongoing global threat due to the emergence of new viral variants that can sometimes evade the immune system of previously exposed or vaccinated individuals. We conducted a follow-up study of adult individuals that had received an inactivated SARS-CoV-2 vaccine, evaluating antibody production and neutralizing activity over a period of 6 months. In addition, we performed mice immunization with inactivated SARS-CoV-2, and evaluated the immune response and pathological outcomes against Gamma and Zeta variant infection. Vaccinated individuals produced high levels of antibodies with robust neutralizing activity, which was significantly reduced against Gamma and Zeta variants. Production of IgG anti-S antibodies and neutralizing activity robustly reduced after 6 months of vaccination. Immunized mice demonstrated cellular response against Gamma and Zeta variants, and after viral infection, reduced viral loads, IL-6 expression, and histopathological outcome in the lungs. TNF levels were unchanged in immunized or not immunized mice after infection with the Gamma variant. Furthermore, serum neutralization activity rapidly increases after infection with the Gamma and Zeta variants. Our data suggest that immunization with inactivated WT SARS-CoV-2 induces a promptly responsive cross-reactive immunity response against the Gamma and Zeta variants, reducing COVID-19 pathological outcomes.

Serological evidence of Mayaro virus infection in blood donors from São Carlos, São Paulo, Brazil.

BACKGROUND: Human infections by Mayaro virus (MAYV) occur by insect bites upon exposure to rural or sylvatic areas. Information regarding MAYV transmission is limited due to a lack of commercial diagnostic assays and diagnostic confusion on account of similarities of clinical signs with other co-circulating arboviral diseases. METHODS: A serological survey of MAYV and Chikunguya virus (CHIKV) antibodies was performed by ELISA. Between 2017 and 2018, 5608 blood donor samples were tested. RESULTS: Specific IgM and IgG antibodies to MAYV were detected respectively in 36 and 11 samples, indicating a total seroprevalence of approximately 0.83%. Neutralization activity was observed in two IgG positive sera. Additionally, eight distinct samples had IgM antibodies to CHIKV alone. CONCLUSIONS: Our data suggest previously unreported circulation of MAYV in São Carlos city, from southeastern Brazil.

A Novel Hepacivirus in Wild Rodents from South America.

The Hepacivirus genus comprises single-stranded positive-sense RNA viruses within the family Flaviviridae. Several hepaciviruses have been identified in different mammals, including multiple rodent species in Africa, Asia, Europe, and North America. To date, no rodent hepacivirus has been identified in the South American continent. Here, we describe an unknown hepacivirus discovered during a metagenomic screen in Akodon montensis, Calomys tener, Oligoryzomys nigripes, Necromys lasiurus, and Mus musculus from São Paulo State, Brazil. Molecular detection of this novel hepacivirus by RT-PCR showed a frequency of 11.11% (2/18) in Oligoryzomys nigripes. This is the first identification of hepavivirus in sigmondonine rodents and in rodents from South America. In sum, our results expand the host range, viral diversity, and geographical distribution of the Hepacivirus genus.

Discovery of novel astrovirus and calicivirus identified in ruddy turnstones in Brazil.

Birds are the natural reservoir of viruses with zoonotic potential, as well as contributing to the evolution, emergence, and dissemination of novel viruses. In this study, we applied a high-throughput screening approach to identify the diversity of viruses in 118 samples of birds captured between October 2006 to October 2010 in the North and Northeast regions of Brazil. We found nearly complete genomes of novel species of astrovirus and calicivirus in cloacal swabs of ruddy turnstones (Arenaria interpres) collected in Coroa do Avião islet, Pernambuco State. These viruses are positive-sense single-stranded RNA with a genome of ~7 to 8 kb, and were designated as Ruddy turnstone astrovirus (RtAstV) and Ruddy turnstone calicivirus (RTCV), respectively. Phylogenetic analysis showed that RtAstV and RTCV grouped in a monophyletic clade with viruses identified from poultry samples (i.e., chicken, goose, and turkey), including viruses associated with acute nephritis in chickens. Attempts of viral propagation in monkey and chicken cell lines for both viruses were unsuccessful. Also, we found genomes related with viral families that infect invertebrates and plants, suggesting that they might be ingested in the birds' diet. In sum, these findings shed new light on the diversity of viruses in migratory birds with the notable characterization of a novel astrovirus and calicivirus.