Toll-like receptor 4 and lipopolysaccharide from commensal microbes regulate Tembusu virus infection.

Unlike most flaviviruses transmitted by arthropods, Tembusu virus (TMUV) is still active during winter and causes outbreaks in some areas, indicating vector-independent spread of the virus. Gastrointestinal transmission might be one of the possible routes of vector-free transmission, which also means that the virus has to interact with more intestinal bacteria. Here, we found evidence that TMUV indeed can transmit through the digestive tract. Interestingly, using an established TMUV disease model by oral gavage combined with an antibiotic treatment, we revealed that a decrease in intestinal bacteria significantly reduced local TMUV proliferation in the intestine, revealing that the bacterial microbiome is important in TMUV infection. We found that lipopolysaccharide (LPS) present in the outer membrane of Gram-negative bacteria enhanced TMUV proliferation by promoting its attachment. Toll-like receptor 4 (TLR4), a cell surface receptor, can transmit signal from LPS. We confirmed colocalization of TLR4 with TMUV envelope (E) protein as well as their interaction in infected cells. Coherently, TMUV infection of susceptible cells was inhibited by an anti-TLR4 antibody, purified soluble TLR4 protein, and knockdown of TLR4 expression. LPS-enhanced TMUV proliferation could also be blocked by a TLR4 inhibitor. Meanwhile, pretreatment of duck primary cells with TMUV significantly impaired LPS-induced interleukin 6 production. Collectively, our study provides first insights into vector-free transmission mechanisms of flaviviruses.

Flaviviruses hijack the host microbiota to facilitate their transmission.

Flaviviruses, such as Dengue and Zika viruses, infect millions of people worldwide using mosquitos as vectors. In this issue of Cell, Zhang et al. reveal how these viruses manipulate the skin microbiome of infected hosts in a way that increases vector recruitment and viral spread. They propose vitamin A as a way to counteract the virus and decrease transmission.

Thermodynamic stability of domain III from the envelope protein of flaviviruses and its improvement by molecular design.

The Flavivirus genus includes widespread and severe human pathogens like the four serotypes of dengue virus (DENV1 to DENV4), yellow fever virus, Japanese encephalitis virus and West Nile virus. Domain III (ED3) of the viral envelope protein interacts with cell receptors and contains epitopes recognized by virus neutralizing antibodies. Its structural, antigenic and immunogenic properties have been thoroughly studied contrary to its physico-chemical properties. Here, the ED3 domains of the above pathogenic flaviviruses were produced in the periplasm of Escherichia coli. Their thermodynamic stabilities were measured and compared in experiments of unfolding equilibriums, induced with chemicals or heat and monitored through protein fluorescence. A designed ED3 domain, with the consensus sequence of DENV strains from all serotypes, was highly stable. The low stability of the ED3 domain from DENV3 was increased by three changes of residues in the protein core without affecting its reactivity towards DENV-infected human serums. Additional changes showed that the stability of ED3 varied with the DENV3 genotype. The T(m) of ED3 was higher than 69°C for all the tested viruses and reached 86°C for the consensus ED3. The latter, deprived of its disulfide bond by mutations, was predominantly unfolded at 20°C. These results will help better understand and design the properties of ED3 for its use as diagnostic, vaccine or therapeutic tools.

Dengue: aspectos epidemiológicos, diagnostico e alterações laboratoriais em uma região na cidade de São Paulo

A Dengue é uma arbovirose que afeta o homem, constituindo sério problema de saúde pública. Em condições favoráveis, como acúmulo de água em recipientes naturais ou artificiais, condições climáticas adequadas e oferta de alimento há maior desenvolvimento de larvas e proliferação do mosquito transmissor da dengue, o Aedes aegypti, favorecendo assim a disseminação do vírus. O agente etiológico do dengue pertence a família Flaviviridae, gênero Flavivirus, compreendendo 4 sorotipos: DEN1, DEN2, DEN3 e DEN4, sendo DEN1, DEN2 e DEN3 encontrados no estado de São Paulo. Os vetores são mosquitos do gênero Aedes, dos quais o mais importante é o Aedes aegypti, originário da África. Admite-se que na época de 50 esta espécie foi erradicada do Brasil. Devido a paralisação de campanhas houve a reintrodução na década de 60 no Pará, na década de 70 em Salvador/BA e Rio de Janeiro, na década de 80 em Santos. Hoje é considerado o principal vetor da dengue. A dengue apresenta-se de duas fromas clínicas: A Dengue Clássica (DC), com sintomas de dores de cabeça e articulações, febre, mialgia, entre outros. A febre hemorrágica do dengue (FHD), apresenta os mesmos sintomas da dengue clássica, sendo caracterizado por manifestações clínicas principais, como febre alta, manifestações hemorrágias, hepatomegalia e insuficiência circulatória, podendo ocorrer o choque hemorrágico do dengue, nos casos graves. o diagnóstico de dengue é baseado em dados clínicos, epidemiológicos e laboratoriais. Em suspeitas clínicas são realizados exames laboratoriais complementares, tais como hemograma, coagulograma e bioquímica e a coleta de sangue para realização de sorologia específica. A confirmação do caso só é dada após o resultado sorológico positivo. A profilaxia é feita por programa de vigilância com objetivo de alertar a população para possíveis criadouros, evitando asim os focos e a diminuição de infestação do mosquito e a circulação dos diferentes sorotipos virais.

Mapping the Flv locus controlling resistance to flaviviruses on mouse chromosome 5.

Genetically determined resistance to flaviviruses in mice is a dominant trait conferred by alleles at a single autosomal locus designated Flv, but no gene products have been associated with this locus and the mechanism of resistance is not well understood. To further characterize this model of genetic resistance, we conducted mapping studies to determine the chromosomal location of Flv. Because of evidence suggesting that the Flv locus is on chromosome 5, three-point backcross linkage analyses were used to define the location of Flv relative to previously assigned chromosome 5 markers. The results confirm the chromosome 5 location of Flv and indicate a map position between the anchor loci rd and Gus-s. The chromosomal localization of Flv is the first step in the production of a detailed linkage map of the Flv region, which may open approaches to positional cloning of the resistance gene.