Haemovigilance survey and screening strategy for arthropod-borne viruses in blood donors from Argentina.

Arthropod-borne viruses (arboviruses) count among emerging infections, which represent a major challenge for transfusion safety worldwide. To assess the risk of arboviruses-transmission by transfusion (ATT), we performed a survey to evaluate the potential threat for transfusion safety. Samples were retrospectively and randomly collected from donors who donated during the peak of dengue incidence in Cordoba (years: 2016 and 2019-2022). A cost-efficient strategy for molecular screening was implemented with a nucleic acid test (NAT) configured with Flavivirus and Alphavirus-universal degenerated primers targeting conserved gene regions. Besides, we evaluated the neutralizing antibody (NAb) prevalence by plaque reduction neutralization test (PRNT). A total of 1438 samples were collected. Among the NAT-screened samples, one resulted positive for Flavivirus detection. Subsequent sequencing of the PCR product revealed Saint Louis Encephalitis Virus (SLEV) infection (GeneBank accession number OR236721). NAb prevalence was 2.95% for anti-Dengue, 9.94% anti-SLEV, 1.09% anti-West Nile Virus, and 0% anti-Chikungunya. One of the NAb-positive samples also resulted positive for IgM against SLEV but negative by ARN detection. This is the first haemovigilance study developed in Argentina that evaluates the potential risk of ATT and the first research to determine the prevalence of NAb against Flavivirus through PNRT to avoid possible cross-reactions between Ab against Flavivirus. Herein, the finding of one SLEV-viremic donor and the detection of anti-SLEV IgM in a different donor demonstrated a potential threat for transfusion safety and emphasized the need for increased vigilance and proactive measures to ensure the safety of blood supplies.

Acute disseminated encephalomyelitis following Saint Louis encephalitis virus infection.

Saint Louis encephalitis virus (SLEV) infection is an arbovirosis associated with a broad spectrum of neurological complications. We present a case of a 55-year-old man hailing from Manaus, a city situated in the heart of the Amazon Rainforest, who exhibited symptoms of vertigo, tremors, urinary and fecal retention, compromised gait, and encephalopathy 3 weeks following SLEV infection. Neuroaxis MRI revealed diffuse, asymmetric, and poorly defined margins hyperintense lesions with peripheral and ring enhancement in subcortical white matter, as well as severe spinal cord involvement. Serology for SLEV was positive both on serum and cerebrospinal fluid. To the best of our knowledge, the present report is the first to show brain lesions along with myelitis as a post-infectious complication of SLEV infection.

Viral Interference between the Insect-Specific Virus Brejeira and the Saint Louis Encephalitis Virus In Vitro.

The Saint Louis encephalitis virus (SLEV) is an encephalitogenic arbovirus (Flaviviridae family) that has a wide geographical distribution in the western hemisphere, especially in the Americas. The negevirus Brejeira (BREV) was isolated for the first time in Brazil in 2005. This study aimed to verify the existence of a possible interfering effect of BREV on the course of SLEV infection and vice versa. We used clone C6/36 cells. Three combinations of MOIs were used (SLEV 0.1 × BREV 1; SLEV 1 × BREV 0.1; SLEV 1 × BREV 1) in the kinetics of up to 7 days and then the techniques of indirect immunofluorescence (IFA), a plaque assay on Vero cells, and RT-PCR were performed. Our results showed that the cytopathic effect (CPE) caused by BREV was more pronounced than the CPE caused by SLEV. Results of IFA, the plaque assay, and RT-PCR showed the suppression of SLEV replication in the co-infection condition in all the MOI combinations used. The SLEV suppression was dose-dependent. Therefore, the ISV Brejeira can suppress SLEV replication in Aedes albopictus cells, but SLEV does not negatively interfere with BREV replication.

Serological survey reveals enzootic circulation of St. Louis encephalitis and West Nile viruses in semiarid Monte ecosystem of Argentina.

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) are arboviruses transmitted by Culex mosquitoes and amplified in avian hosts. The present study aimed to investigate the presence and seasonal circulation of SLEV and WNV in La Rioja province, within the semiarid ecoregion of the Monte, Argentina. Over a two-year period, avian sera were collected and tested for neutralizing antibodies against SLEV and WNV. Our results reveal the enzootic activity of both viruses in this challenging environment. SLEV seroprevalence was 4.5% (35/778), with higher activity in spring (2016) and autumn (2017). WNV seroprevalence was 3.5% (27/778), peaking during the summer 2016-2017. Greater seroprevalence for SLEV in 2016 was detected for the Lark-like Brushrunner (Coryphistera alaudina) and the Short-billed Canastero (Asthenes baeri) and in 2017 for the Black-crested Finch (Lophospingus pusillus) and Lark-like Brushrunner, whereas for WNV greater seroprevalence in 2016 was detected for the Picui Ground Dove (Columbina picui) and in 2017 for the Lark-like Brushrunner and Band-tailed Seedeater (Catamenia analis). Additionally, five avian individuals experienced seroconversion during the sampling period, namely the Lark-like Brushrunner and White-fronted Woodpecker (Melanerpes cactorum) for SLEV, and the Lark-like Brushrunner, Greater Wagtail Tyrant (Stigmatura budytoides) and Many-colored Chaco Finch (Saltatricula multicolor) for WNV. The study highlights the persistence and circulation of these viruses in a semiarid ecosystem, raising questions about overwintering mechanisms and transmission dynamics. This research contributes to understanding arbovirus ecology in diverse environments. Further investigations are needed to assess the specific mechanisms facilitating virus persistence in the Monte ecoregion.

Phenotypical Screening of an MMV Open Box Library and Identification of Compounds with Antiviral Activity against St. Louis Encephalitis Virus.

St. Louis encephalitis virus (SLEV) is a neglected mosquito-borne Flavivirus that may cause severe neurological disease in humans and other animals. There are no specific treatments against SLEV infection or disease approved for human use, and drug repurposing may represent an opportunity to accelerate the development of treatments against SLEV. Here we present a scalable, medium-throughput phenotypic cell culture-based screening assay on Vero CCL81 cells to identify bioactive compounds that could be repurposed against SLEV infection. We screened eighty compounds from the Medicines for Malaria Venture (MMV) COVID Box library to identify nine (11%) compounds that protected cell cultures from SLEV-induced cytopathic effects, with low- to mid-micromolar potencies. We validated six hit compounds using viral plaque-forming assays to find that the compounds ABT-239, Amiodarone, Fluphenazine, Posaconazole, Triparanol, and Vidofludimus presented varied levels of antiviral activity and selectivity depending on the mammalian cell type used for testing. Importantly, we identified and validated the antiviral activity of the anti-flavivirus nucleoside analog 7DMA against SLEV. Triparanol and Fluphenazine reduced infectious viral loads in both Vero CCL81 and HBEC-5i cell cultures and, similar to the other validated compounds, are likely to exert antiviral activity through a molecular target in the host.

Caracterización biológica de cepas del virus Encefalitis San Luis en células de la inmunidad innata / Biological characterization of St. Louis Encephalitis virus strains in cells of innate immunity

Los flavivirus transmitidos por mosquitos son una amenaza actual y emergente en todo el mundo. Dentro de este género, el virus Encefalitis San Luis (VESL) causa una forma severa de enfermedad neuroinvasiva donde la respuesta inmune es un componente crucial de la defensa del huésped. En este trabajo se investigó la interacción entre VESL y células de la inmunidad innata, en un modelo de infección in vitro de monocitos humanos (células U937) con cepas de distinta virulencia y condiciones epidemiológicas de aislamiento (CbaAr-4005 y 78V-6507). Se evaluó la capacidad de infectar y replicar del virus, como también el efecto citopático y la cinética de viabilidad de monocitos durante la infección. Los resultados demostraron la susceptibilidad de los monocitos a la infección, replicación y muerte por ambas cepas virales. Sin embargo, se hallaron diferencias significativas entre ellas. La cepa epidémica y de mayor virulencia CbaAr-4005 registró una tasa de infección y replicación superior a la de la cepa endémica y de menor virulencia 78V-6507. Se comprobó también que el VESL indujo la muerte de monocitos humanos, dependiendo del tiempo post-infección (pi) y de la cepa. Así, CbaAr-4005 provocó a partir del día 3 pi el doble de mortalidad celular que 78V-6507. Además, en los monocitos infectados se observaron alteraciones de parámetros morfológicos que podrían relacionarse con el tipo de mecanismo de muerte celular asociado a la infección por VESL.

Mosquitoes borne Flavivirus infections are an actual and emergent worldwide threat to human health. Within this genus, Saint Louis Encephalitis Virus (SLEV) causes a severe neuroinvasive disease where immune response is crucial for host survival. In this study the interaction between SLEV and innate immune cells was evaluated. An in vitro infection model with human monocytes (U937 cells) and strains with variations in virulence and isolation conditions (CbaAr-4005 and 78V-6507) were used. Infection capacity, replication capacity, cytopathic effect and monocyte viability kinetics were measured. The results showed susceptibility to infection and replication to both strains. However, significant differences were found among them. CbaAr-4005, the epidemic and more virulent strain, showed higher infection and replication ratios compared to 78V-6507. SLEV infection that induces cell death of human monocytes was also found in a post-infection time and in a strain dependent manner. Since day 3 post-infection, twice the mortality in CbaAr-4005 infected cells was observed. Furthermore, infected monocytes showed alterations in morphologic parameters that could be related with apoptosis mechanisms associated to SLEV infections.

Os Flavivírus transmitidos por mosquitos são uma ameaça atual e emergente no mundo todo. Nesse gênero, o vírus Encefalite Saint Louis (VESL) causa uma forma grave de doença neuroinvasiva onde a resposta imune é um componente crucial da defesa do hospedeiro. Neste trabalho nos investigamos a interação entre VESL e células de imunidade inata em um modelo de infecção in vitro de monócitos humanos (células U937) com estirpe de diferentes virulências e condições epidemiológicas de isolamento (CbaAr-4005 e 78V-6507). Foi avaliada a capacidade do vírus de infectar e replicar , assim como o efeito citopático e a viabilidade cinética dos monócitos durante a infecção. Os resultados demonstraram a suscetibilidade dos monócitos à infecção, replicação e morte por ambas as estirpes virais. No entanto, foram detectadas diferenças significativas entre eles. A estirpe epidémica e de maior virulenta CbaAr-4005 teve uma maior taxa de infecção e replicação do que a estirpe endémica e menos virulenta 78V-6507. Foi comprovado também que o VESL induziu a morte de monócitos humanos, dependendo do tempo pós-infecção (pi) e da estirpe. Assim, a CbaAr-4005 causou a partir do dia 3 pi o dobro da mortalidade celular o que a 78V- 6507. Além disso, alterações nos parâmetros morfológicos foram observadas nos monócitos infectados que poderiam estar relacionadas ao tipo de mecanismo de morte celular associado à infecção pelo VESL.

Saint louis encpphalitis virus in mato grosso, central-western Brazil / Vírus da encefalite de Saint Louis em Mato Grosso, Centro-Oeste, Brasil

The dengue virus (DENV), which is frequently involved in large epidemics, and the yellow fever virus (YFV), which is responsible for sporadic sylvatic outbreaks, are considered the most important flaviviruses circulating in Brazil. Because of that, laboratorial diagnosis of acute undifferentiated febrile illness during epidemic periods is frequently directed towards these viruses, which may eventually hinder the detection of other circulating flaviviruses, including the Saint Louis encephalitis virus (SLEV), which is widely dispersed across the Americas. The aim of this study was to conduct a molecular investigation of 11 flaviviruses using 604 serum samples obtained from patients during a large dengue fever outbreak in the state of Mato Grosso (MT) between 2011 and 2012. Simultaneously, 3,433 female Culex spp. collected with Nasci aspirators in the city of Cuiabá, MT, in 2013, and allocated to 409 pools containing 1-10 mosquitoes, were also tested by multiplex semi-nested reverse transcription PCR for the same flaviviruses. SLEV was detected in three patients co-infected with DENV-4 from the cities of Cuiabá and Várzea Grande. One of them was a triple co-infection with DENV-1. None of them mentioned recent travel or access to sylvatic/rural regions, indicating that transmission might have occurred within the metropolitan area. Regarding mosquito samples, one pool containing one Culex quinquefasciatus female was positive for SLEV, with a minimum infection rate (MIR) of 0.29 per 1000 specimens of this species. Phylogenetic analysis indicates both human and mosquito SLEV cluster, with isolates from genotype V-A obtained from animals in the Amazon region, in the state of Pará. This is the first report of SLEV molecular identification in MT.

O vírus da dengue (DENV), frequentemente envolvido em epidemias de grande proporção, e o vírus da febre amarela (YFV), responsável por surtos silvestres esporádicos, são considerados os flavivírus circulantes mais importantes no Brasil. Por este motivo, o diagnóstico laboratorial de doença febril aguda indiferenciada durante períodos epidêmicos é frequentemente direcionado para dengue e febre amarela no país, dificultando a detecção de outros arbovírus possivelmente circulantes, incluindo o vírus da encefalite de Saint Louis (SLEV), que é amplamente disperso nas Américas. O objetivo deste estudo foi investigar molecularmente a presença de 11 flavivírus no soro de 604 pacientes durante grande epidemia de dengue no estado de Mato Grosso (MT), Centro-Oeste do Brasil, entre 2011- 2012. Concomitantemente, 3.433 fêmeas de Culex spp. capturadas com aspirador de Nasci na cidade de Cuiabá, MT e alocadas em 409 pools com 1-10 mosquitos em 2013 foram testadas por multiplex seminested RT-PCR para os mesmos flavivírus. O SLEV foi detectado em três pacientes co-infectados com o DENV-4 das cidades de Cuiabá e Várzea Grande, MT. Um dos pacientes apresentava tripla co-infecção com DENV-1. Nenhum paciente referiu histórico recente de viagem ou acesso a áreas rurais/silvestres. Um pool contendo uma fêmea de Culex quinquefasciatus foi positivo para o SLEV, apresentando taxa de infecção mínima (MIR) de 0,29 por 1000 espécimes desta espécie. A análise filogenética indica que ambas as amostras formam um cluster com isolados do genótipo V-A do SLEV obtidos de animais na região amazônica do estado do Pará. Este é o primeiro relato de identificação molecular do SLEV no MT.

Molecular identification of Saint Louis encephalitis virus genotype IV in Colombia

Saint Louis encephalitis virus (SLEV) is a member of the Japanese-encephalitis virus serocomplex of the genus Flavivirus. SLEV is broadly distributed in the Americas and the Caribbean Islands, where it is usually transmitted by mosquitoes of the genus Culex and primarily to birds and mammalian-hosts. Humans are occasionally infected by the virus and are dead-end hosts. SLEV causes encephalitis in temperate regions, while in tropical regions of the Americas, several human cases and a wide biological diversity of SLEV-strains have been reported. The phylogenetic analysis of the envelope (E) protein genes indicated eight-genotypes of SLEV with geographic overlap. The present paper describes the genotyping of two SLEV viruses detected in mosquito-pools collected in northern Colombia (department of Cordoba). We used reverse transcription-polymerase chain reaction to amplify a fragment of theE-gene to confirm the virus identity and completeE-gene sequencing for phylogenetic analysis and genotyping of the two-SLEV viruses found circulating in Córdoba. This is the first report of SLEV genotype IV in Colombia (Córdoba) in mosquitoes from a region of human inhabitation, implicating the risk of human disease due to SLEV infection. Physicians should consider SLEV as a possible aetiology for undiagnosed febrile and neurologic syndromes among their patients who report exposure to mosquito-bites.

Evidencia serológica de circulación del virus de la encefalitis de San Luis en aves de la Ciudad Autónoma de Buenos Aires, Argentina / Serological evidence of St. Louis encephalitis virus circulation in birds from Buenos Aires City, Argentina

Nuestro objetivo fue conocer la presencia de anticuerpos neutralizantes contra el virus de la encefalitis de San Luis (St. Louis encephalitis virus [SLEV]) y el virus del Nilo Occidental (West Nile virus [WNV]) en sueros de aves silvestres y domésticas de la Ciudad Autónoma de Buenos Aires, Argentina. Desde octubre del 2012 hasta abril del 2013 se colectaron 180 muestras que fueron procesadas por la técnica de microneutralización. El 7,2% de las aves muestreadas resultaron seropositivas para SLEV, mientras que no se detectaron aves seropositivas para WNV

Our goal was to determine the presence of neutralizing antibodies against St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) in sera of wild and domestic birds from Buenos Aires City, Argentina. From October 2012 to April 2013, 180 samples were collected and processed by the microneutralization technique. A 7.2 % of the sampled birds were seropositive for SLEV, while no seropositive birds for WNV were detected

Virulence variation among epidemic and non-epidemic strains of Saint Louis encephalitis virus circulating in Argentina

Saint Louis encephalitis virus caused an outbreak of febrile illness and encephalitis cases in Córdoba, Argentina, in 2005. During this outbreak, the strain CbaAr-4005 was isolated from Culex quinquefasciatus mosquitoes. We hypothesised that this epidemic variant would be more virulent in a mouse model than two other non-epidemic strains (78V-6507 and CorAn-9275) isolated under different epidemiological conditions. To test this hypothesis, we performed a biological characterisation in a murine model, including mortality, morbidity and infection percentages and lethal infection indices using the three strains. Mice were separated into age groups (7, 10 and 21-day-old mice) and analysed after infection. The strain CbaAr-4005 was the most infective and lethal of the three variants, whereas the other two strains exhibited a decreasing mortality percentage with increasing animal age. The strain CbaAr-4005 produced the highest morbidity percentages and no significant differences among age groups were observed. The epidemic strain caused signs of illness in all inoculated animals and showed narrower ranges from the onset of symptoms than the other strains. CbaAr-4005 was the most virulent for Swiss albino mice. Our results highlight the importance of performing biological characterisations of arbovirus strains likely to be responsible for emerging or reemerging human diseases.

Detección molecular de virus de encefalitis de Saint Louis en mosquitos de Buenos Aires, Argentina

Durante el mes de marzo de 2013 una población de palomas torcazas (Zenaida auriculata) se instaló en una zona céntrica de la ciudad de Buenos Aires. Conociendo el rol que poseen estas aves como hospedadores competentes del virus de la encefalitis de Saint Louis (SLEV), fue colocada en el lugar una trampa de luz tipo CDC, a fin de realizar una vigilancia entomológica. Durante ese mes,fueron capturados 5 grupos de mosquitos (n = 48), 3 correspondieron a la especie Culex pipiens (n = 10) y 2 a Culex spp.(n = 38), no pudiéndose determinar en estos últimos con precisión la especie por encontrarse dañados. En un grupo de mosquitos Culex spp. se detectó el SLEV por técnicas moleculares. Posteriormente fue secuenciado y clasificado como perteneciente al genotipo III.

During March 2013 a population of eared doves (Zenaida auriculata) was established in the center of City of Buenos Aires. Considering the role of these birds as host competent for Saint Louis encephalitis virus (SLEV), a CDC light trap was put in place to perform entomologic surveillance. During this month 5 pools of mosquitoes (n = 48) were collected and taxonomically determined. Three of them were classified as Culex pipiens (n = 10) and the other two were Culex spp. (n = 38). In this case, the mosquitoes species could not be determined due to that individuals were damaged. One of the Culex spp. pool was found to be positive for Saint Louis encephalitis virus by molecular techniques. This was then sequenced and classified as genotype III.

A Saint Louis encephalitis and Rocio virus serosurvey in Brazilian horses

Introduction Arboviruses are an important public health problem in Brazil, in especially flaviviruses, including the Saint Louis encephalitis virus (SLEV) and the Rocio virus (ROCV), are especially problematic. These viruses are transmitted to humans or other vertebrates through arthropod bites and may cause diseases with clinical manifestations that range from asymptomatic infection, viral hemorrhagic fever to encephalitis. Methods A serological survey of horses from various regions of Brazil using an enzyme-linked immunosorbent assay (ELISA) with recombinant SLEV domain III peptides and ROCV E protein as antigens. Results Overall, 415 (55.1%) of the 753 horses that were screened were seropositive for flavivirus and, among them, monotypic reactions were observed to SLEV in 93 (12.3%) and to ROCV in 46 (6.1%). These results suggested that these viruses, or other closely related viruses, are infecting horses in Brazil. However, none of the studied horses presented central nervous system infection symptoms. Conclusions Our results suggest that SLEV and ROCV previously circulated among horses in northeast, west-central and southeast Brazil. .

Serological evidence for Saint Louis encephalitis virus in free-ranging New World monkeys and horses within the upper Paraná River basin region, Southern Brazil

Introduction Saint Louis encephalitis virus (SLEV) primarily occurs in the Americas and produces disease predominantly in humans. This study investigated the serological presence of SLEV in nonhuman primates and horses from southern Brazil. Methods From June 2004 to December 2005, sera from 133 monkeys (Alouatta caraya, n=43; Sapajus nigritus, n=64; Sapajus cay, n=26) trap-captured at the Paraná River basin region and 23 blood samples from farm horses were obtained and used for the serological detection of a panel of 19 arboviruses. All samples were analyzed in a hemagglutination inhibition (HI) assay; positive monkey samples were confirmed in a mouse neutralization test (MNT). Additionally, all blood samples were inoculated into C6/36 cell culture for viral isolation. Results Positive seroreactivity was only observed for SLEV. A prevalence of SLEV antibodies in sera was detected in Alouatta caraya (11.6%; 5/43), Sapajus nigritus (12.5%; 8/64), and S. cay (30.8%; 8/26) monkeys with the HI assay. Of the monkeys, 2.3% (1/42) of A. caraya, 6.3% 94/64) of S. nigritus, and 15.4% (4/26) of S. cay were positive for SLEV in the MNT. Additionally, SLEV antibodies were detected by HI in 39.1% (9/23) of the horses evaluated in this study. Arboviruses were not isolated from any blood sample. Conclusions These results confirmed the presence of SLEV in nonhuman primates and horses from southern Brazil. These findings most likely represent the first detection of this virus in nonhuman primates beyond the Amazon region. The detection of SLEV in animals within a geographical region distant from the Amazon basin suggests that there may be widespread and undiagnosed dissemination of this disease in Brazil. .

Serological detection of St. Louis encephalitis virus and West Nile virus in equines from Santa Fe, Argentina

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) present ecological and antigenic similarities and are responsible for serious human diseases. In addition, WNV is a significant pathogen in terms of equine health. The purpose of our study was to analyse the seroprevalence of SLEV and WNV in equine sera collected in Santa Fe Province, Argentina. The seroprevalence determined using the plaque reduction neutralisation test was 12.2% for SLEV, 16.2% for WNV and 48.6% for a combination of both viruses. These results provide evidence of the co-circulation of SLEV and WNV in equines in Santa Fe.

Seroconversion for west Nile and St. Louis encephalitis viruses among sentinel horses in Colombia

We prospectively sampled flavivirus-naïve horses in northern Colombia to detect West Nile virus (WNV) and St. Louis encephalitis virus (SLEV) seroconversion events, which would indicate the current circulation of these viruses. Overall, 331 (34.1 percent) of the 971 horses screened were positive for past infection with flaviviruses upon initial sampling in July 2006. During the 12-month study from July 2006-June 2007, 33 WNV seroconversions and 14 SLEV seroconversions were detected, most of which occurred in the department of Bolivar. The seroconversion rates of horses in Bolivar for the period of March-June 2007 reached 12.4 percent for WNV and 6.7 percent for SLEV. These results comprise the first serologic evidence of SLEV circulation in Colombia. None of the horses sampled developed symptoms of encephalitis within three years of initial sampling. Using seroconversions in sentinel horses, we demonstrated an active circulation of WNV and SLEV in northern Colombia, particularly in the department of Bolivar. The absence of WNV-attributed equine or human disease in Colombia and elsewhere in the Caribbean Basin remains a topic of debate and speculation.

Serologic evidence of the recent circulation of Saint Louis encephalitis virus and high prevalence of equine encephalitis viruses in horses in the Nhecolândia sub-region in South Pantanal, Central-West Brazil

As in humans, sub-clinical infection by arboviruses in domestic animals is common; however, its detection only occurs during epizootics and the silent circulation of some arboviruses may remain undetected. The objective of the present paper was to assess the current circulation of arboviruses in the Nhecolândia sub-region of South Pantanal, Brazil. Sera from a total of 135 horses, of which 75 were immunized with bivalent vaccine composed of inactive Eastern equine encephalitis virus (EEEV) and Western equine encephalitis virus(WEEV) and 60 were unvaccinated, were submitted to thorough viral isolation, reverse transcriptase polymerase chain reaction (RT-PCR) and neutralization tests for Saint Louis encephalitis virus (SLEV), EEEV, WEEV and Mayaro virus (MAYV). No virus was isolated and viral nucleic-acid detection by RT-PCR was also negative. Nevertheless, the prevalence of neutralizing antibodies in horses older than seven months was 43.7 percent for SLEV in equines regardless of vaccine status, and 36.4 percent for WEEV and 47.7 percent for EEEV in unvaccinated horses. There was no evidence of MAYV infections. The serologic evidence of circulation of arboviruses responsible for equine and human encephalitis, without recent official reports of clinical infections in the area, suggests that the Nhecolândia sub-region in South Pantanal is an important area for detection of silent activity of arboviruses in Brazil.

Genetic characterization of St. Louis encephalitis virus isolated from human in São Paulo, Brazil

The molecular characterization of SPH253157, a new strain of St. Louis encephalitis virus (SLEV), isolated in 2004 from the first case of human infection recognized in the state of São Paulo, Brazil, is reported. The patient, presenting a febrile illness without neurological involvement, was hospitalized as a probable case of dengue fever. Genomic RNA was isolated from the supernatant of C6/36 cells infected with acute phase-serum specimen of the patient and the envelope gene was amplified by reverse-transcription-polymerase chain reaction. The complete nucleotide sequence of the envelope gene of this isolate was directly sequenced from the amplified products and compared with other Brazilian and American SLEV strains. Phylogenetic analyses were carried out under maximum likelihood criterion with outgroups both included and excluded. Outgroups comprised four flavivirus of the Japanese encephalitis group. Phylogeny also included Bayesian analysis. The results indicated that the new SLEV isolate belongs to lineage III, being closely related to an Argentinean strain recovered from Culex sp. in 1979. It is concluded that there are at least 3 lineages of SLEV in Brazil.

St. Louis encephalitis vírus: first isolation from a human in São Paulo state, Brasil

O presente estudo relata o isolamento do vírus da encefalite São Luis (SLEV) de um caso febril humano suspeito de dengue, em São Pedro, Estado de São Paulo. MAC-ELISA realizado com soros das fases aguda e convalescente foi inconclusivo e anticorpos IgG foram detectados por inibição da hemaglutinação para flavivirus. Imunofluorescência indireta com cultura de células C6/36 inoculadas com soro da fase aguda foi positivo para flavivirus mas negativo quando testado com anticorpos monoclonais para dengue. O RNA extraído de cultura de células infectadas foi amplificado na presença de primers universais para o gênero Flavivirus, deduzidos de uma região da proteína não estrutural 5 e diretamente sequenciado. Os resultados da pesquisa no BLAST indicaram que a seqüência apresenta 93% de similaridade de nucleotídeos com a seqüência de SLEV (cepa MS1.7), confirmado por RT-PCR, realizado com primers específicos para SLEV. O fato de SLEV ter sido identificado como a causa de doença humana indica a necessidade de aprimorar a vigilância a fim de detectar precocemente esse agente no Estado de São Paulo e no Brasil. Esse caso é também um alerta para os profissionais de saúde sobre a necessidade de investigações clínicas e epidemiológicas mais completas sobre doenças febris como no caso relatado. Infecções por SLEV podem não ser reconhecidas ou confundidas com outras causadas por arbovírus como a dengue.

St. Louis encephalomyelitis in Hermosillo, Sonora, Mexico

This report, which describes an epidemic of St. Louis encephalitis in northwestern Mexico, was prompted by the apparent infrequency of previous Mexican outbreaks of this disease. The site of the epidemic was the Municipality of Hermosillo in the State of Sonora. This municipality, with a population of about 273,000, is situated in a hot flat area which is naturally dry but which is also well-irrigated. Here, over an eithy-week period, 51 persons became ill and were hospitalized with symptoms including fever, vomiting, stiff neck, lethargy, and increased cell/protein levels in their cerebrospinal fluid. Sera from 12 of these patients were tested for SLE antibodies by hemagglutination inhibition, complement fixation, and neutralization. The results of these tests were positive and showed a fairly high degree of correlation. In addition, paired serum samples showed a significant rise in SLE antibody titers. Over half of the cases occurred in the City of Hermosillo, the municipal seat; the remainder occurred in 13 outlying areas, most of them quite nearby. Virtually all of the city dwellers affected were residents of low-income districts. The rate of hospital cases was roughly 19 per 100,000 inhabitants, and the case-fatality rate among these cases was approximately 20 per cent. The ratio of male to female patients was 1.3 to 1; sixty-nine per cent of the patients were under 16 years of age (Au)