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Sericin, a silk-derived non-immunogenic protein, has been used to improve cell culture performance by increasing viability, cell concentration, and promoting adherence of several cell lines. Here, we hypothesized that the properties of sericin can enhance the amplification of flaviviruses in cell cultures. The propagation of flavivirus is inefficient and limits scientific research. Zika virus (ZIKV) is an important human pathogen that has been widely studied because of its high impact on public health. There is a need to amplify Zika virus both for research and vaccine development. In this work, we show that sericin improves ZIKV amplification in insect (C6/36) and mammalian (Vero) cell cultures, and that it has a cryoprotectant capacity. Supplementation of cell culture media with sericin at 80 µg/mL resulted in a significant increase of 1 log in the concentration of ZIKV infectious particles produced from both cell lines. Furthermore, final virus yields increased between 5 and 10-fold in Vero cells and between 7 and 23-fold in C6/36 cells when sericin was supplemented, compared to control conditions. These results show that sericin is an effective supplement to increase ZIKV production by Vero and C6/36 cells. Additionally, sericin was a suitable cryoprotective agent, and hence an alternative to FBS and DMSO, for the cryopreservation of C6/36 cells but not for Vero cells.

The dengue virus NS1 is a multifunctional protein that forms part of replication complexes. NS1 is also secreted, as a hexamer, to the extracellular milieu. Circulating NS1 has been associated with dengue pathogenesis by several mechanisms. Cell binding and internalization of soluble NS1 result in endothelial hyperpermeability and in the downregulation of the innate immune response. In this work, we report that the HDL scavenger receptor B1 (SRB1) in human hepatic cells and a scavenger receptor B1-like in mosquito C6/36 cells act as cell surface binding receptors for dengue virus NS1. The presence of the SRB1 on the plasma membrane of C6/36 cells, as well as in Huh7 cells, was demonstrated by confocal microscopy. The internalization of NS1 can be efficiently blocked by anti-SRB1 antibodies, and previous incubation of the cells with HDL significantly reduces NS1 internalization. Significant reduction in NS1 internalization was observed in C6/36 cells transfected with siRNAs specific for SRB1. In addition, the transient expression of SRB1 in Vero cells, which lacks the receptor, allows NS1 internalization in these cells. Direct interaction between soluble NS1 and the SRB1 in Huh7 and C6/36 cells was demonstrated in situ by proximity ligation assays and in vitro by surface plasmon resonance. Finally, results are presented indicating that the SRB1 also acts as a cell receptor for Zika virus NS1. These results demonstrate that dengue virus NS1, a bona fide lipoprotein, usurps the HDL receptor for cell entry and offers explanations for the altered serum lipoprotein homeostasis observed in dengue patients. IMPORTANCE Dengue is the most common viral disease transmitted to humans by mosquitoes. The dengue virus NS1 is a multifunctional glycoprotein necessary for viral replication. NS1 is also secreted as a hexameric lipoprotein and circulates in high concentrations in the sera of patients. Circulating NS1 has been associated with dengue pathogenesis by several mechanisms, including favoring of virus replication in hepatocytes and dendritic cells and disruption of the endothelial glycocalyx leading to hyperpermeability. Those last actions require NS1 internalization. Here, we identify the scavenger cell receptor B1, as the cell-binding receptor for dengue and Zika virus NS1, in cultured liver and in mosquito cells. The results indicate that flavivirus NS1, a bona fide lipoprotein, usurps the human HDL receptor and may offer explanations for the alterations in serum lipoprotein homeostasis observed in dengue patients.

Dengue virus nonstructural protein 1 (NS1) is a multifunctional glycoprotein. For decades, the notion in the field was that NS1 is secreted exclusively from vertebrate cells and not from mosquito cells. However, recent evidence shows that mosquito cells also secrete NS1 efficiently. In this review, we discuss the evidence for secretion of NS1 of dengue virus, and of other flaviviruses, from mosquito cells, differences between NS1 secreted from mosquito and NS1 secreted from vertebrate cells, and possible roles of soluble NS1 in the insect flavivirus vector.

Background The role of rotavirus as main etiologic agent of diarrhea has been well documented worldwide, including in Venezuela. However, information about the prevalence of gastrointestinal viruses such as calicivirus, adenovirus and astrovirus is limited and the contribution of other agents as Aichi virus and klassevirus is largely unknown. To explore the etiological spectrum of diarrhea associated with agents other than rotaviruses, 227 stool samples from children under 5 years old with acute gastroenteritis, collected in Valencia (Venezuela) from 2001 to 2005, and previously tested as rotavirus-negative, were analyzed for caliciviruses, adenoviruses, astroviruses, Aichi viruses, klasseviruses, picobirnaviruses and enteroviruses by specific RT-PCRs. Results At least one viral agent was detected in 134 (59%) of the samples analyzed, mainly from children under 24 months of age and most of them belonging to the lowest socioeconomic status. Overall, enterovirus was identified as the most common viral agent (37.9%), followed by calicivirus (23.3%), adenovirus (11.5%), astrovirus (3.5%), klassevirus (1.3%) and Aichi virus (0.4%), while no picobirnavirus was detected. Klasseviruses were found during 2004 and 2005 and Aichi viruses only in 2005, indicating their circulation in Venezuela; meanwhile, the rest of the viruses were detected during the whole study period. Coinfections with two or more viruses were found in 39 (29.1%) of the infected children, most under 24 months of age. Adenovirus was involved as the coinfecting agent in at least 46.9% of the cases, but no differences concerning socio-demographic variables were observed between the coinfected and the single infected children. Conclusions The results show that various enteric viruses, including enteroviruses, caliciviruses and adenoviruses, accounted for a significant proportion of infantile diarrhea cases in Venezuela before rotavirus vaccine implementation. In addition, emerging viruses as Aichi virus and klassevirus were found, indicating the need to continue monitoring their spreading into the communities. Efforts are needed to develop more accurate methods to identify the major causes of diarrhea and to provide tools for more effective preventive measures.

Dengue virus NS1 is a glycoprotein of 46-50 kDa that is conserved among flaviviruses, associates as a dimer to cell membranes and is secreted as a hexamer to the extracellular milieu. Recent evidence showed that NS1 is secreted efficiently from infected mosquito cells. To explore the secretory route of NS1 in mosquito cells, infected cells were treated with brefeldin A (BFA) and methyl-beta-cyclodextrin (MβCD). The results showed that MβCD, but not BFA, significantly reduced the release of NS1. Moreover, silencing the expression of caveolin-1 (CAV1; a key component of the caveolar system that transports cholesterol inside the cell), but not SAR1 (a GTPase that participates in the classical secretory pathway), also results in a significant reduction of the secretion of NS1. These results indicate that NS1 is released from mosquito cells via an unconventional secretory route that bypasses the Golgi complex, with the participation of CAV1. In agreement with this notion, differences were observed in the glycosylation status between secreted NS1 and E proteins. Classical mechanics and docking simulations suggested highly favoured interactions between the caveolin-binding domain present in NS1 and the scaffolding domain of CAV1. Finally, proximity ligation assays showed direct interaction between NS1 and CAV1 in infected mosquito cells. These findings are in line with the lipoprotein nature of secreted NS1 and provide new insights into the biology of NS1.

Porcine enteric sapovirus (PES) has been shown to cause diarrhea under experimental conditions in gnotobiotic piglets. However, the role of PES as enteric pathogens in porcine farms remains unclear. To further understand the PES-host interactions under field conditions, a serological survey was carried out. To this end the capsid gene of a PES isolate was cloned in the baculovirus expression system and an ELISA was developed based on virus-like particles from the baculovirus-expressed PES capsid protein. A total of 85 serum samples collected from pigs ranging from 8 weeks to over 54 weeks of age were analyzed. An overall seroprevalence to PESs of 62% was found, with significant differences (p0.05) found between ages. Pigs younger than 10 weeks old and older than 12 weeks old showed high seroprevalences (70-100%), while pigs aged 10-12 weeks showed no detectable serum antibodies levels. Our results suggest that PES infections are common in pigs and that passively acquired maternal antibodies are soon replaced by actively acquired antibodies, whose titers increase gradually with age and that probably are maintained during lifetime.

Hospital-based studies to determine the etiology of deaths from diarrhea are scarce. In this study we specifically analyzed deaths due to rotavirus to assess the rotavirus impact on diarrhea mortality. To determine the rotavirus proportion contributing to mortality due to diarrhea we analyzed data obtained from a hospital-based mortality surveillance conducted over 7 years in the Ciudad Hospitalaria Dr. Enrique Tejera Valencia Venezuela. Rotavirus was identified in stool samples collected from children who died of diarrhea by a confirmatory ELISA and/or reverse transcription polymerase chain reaction. Our results show that rotavirus (21%; 21/100) is the leading cause of death due to diarrhea among children < 5 years of age; rotavirus also has an important impact (2%; 21/1336) on deaths from all causes in this age group. Shigella spp. (19%; 13/69) was the second most important cause of death followed by calicivirus (6%; 3/53). Furthermore this study documents a seasonal pattern in the deaths due to rotavirus (odds ratio 3.28; 95% confidence interval 1.13-9.76). For Venezuela it is estimated that approximately 300 children < 5 years of age die of rotavirus each year which means that 1 in 1800 children die by the age of 5. Rotavirus was found to be the main cause of death due to diarrhea which supports previous estimations. This is the first study to present data of cause-specific mortality due to diarrhea based on hospital surveillance of diarrhea etiologies. (authors)

Caliciviruses are a well-established cause of respiratory, vesicular and hemorrhagic diseases in animals. In addition, these viruses are an important cause of enteric diseases in humans. Recently, molecular analysis of several porcine enteric caliciviruses indicated that they are closely related to human enteric caliciviruses. The objective of this work was to determine the frequency, age distribution, and association with diarrhea of enteric calicivirus infections in piglets and to partially characterize the detected isolates. A total of 203 stool samples from animals 0 to 9 weeks of age, collected between 1993 and 2003 in seven porcine farms located in the central region of Venezuela were tested for enteric caliciviruses by reverse transcription-polymerase chain reaction (RT-PCR) amplification using primers designed to detect both norovirus and sapovirus. Selected amplicons were sequenced to establish phylogenetic relationships with reference strains. Calicivirus were detected in 18% (36/204) of the samples. Viruses were detected more frequently in animals between 3 and 4 weeks of age, and were detected in samples from animals with diarrhea and without diarrhea with equal frequencies (14 versus 19%, p > 0.5). Phylogenetic studies based on partial RNA polymerase gene sequences indicated that the Venezuelan isolates were most closely related (75-95% identity) to the sapovirus Cowden reference strain. These results provide evidence that caliciviruses of the genus sapovirus circulate frequently in piglets but further studies are needed to clarify their importance as cause of diarrhea.

The importance of enteric viral infections in HIV-related diarrhea is uncertain. Human caliciviruses have emerged as a leading cause of acute diarrhea worldwide.To evaluate the importance of calicivirus infections in HIV-related diarrhea. Study design 151 fecal samples collected from children and adults infected with HIV, with and without diarrhea, were examined. In addition, 89 fecal samples from non HIV-infected children and adults were also tested. Samples were analyzed by RT-PCR using primer sets specific to Norovirus genogroup I or genogroup II as well as primers designed to react with both Noroviruses and Sapovirus genus.Viruses were detected with equal frequencies in stools from HIV infected and non-infected adults (12%). However, specimens from HIV infected children were more likely than those of HIV-negative children to have caliciviruses (51% versus 24%, P0.05). Viral infections were not significantly associated with diarrhea neither in children nor in adults, regardless of HIV status. Viruses genetically related to the common Lordsdale virus (Norovirus genogroup II) and London/92 virus (Sapovirus) clusters were detected circulating among children.These results suggest that caliciviruses may be an important opportunistic pathogen in children infected with HIV.

Caliciviruses are a well-established cause of respiratory, vesicular and hemorrhagic diseases in animals. In addition, these viruses are an important cause of enteric diseases in humans. Recently, molecular analysis of several bovine enteric calicivirus isolates indicated that they are genetically close to human enteric calicivirus. To investigate if bovine enteric caliciviruses circulate in Venezuela, 129 stool samples collected between 1994 and 2000 were assayed by reverse transcription-polymerase chain reaction amplification. The presence of calicivirus was confirmed in one of the samples analyzed, collected in the Lara State from a healthy calf, 2 months old. Phylogenetic studies based on partial RNA polymerase sequences indicated that the Venezuelan isolate (Bo/NV/Lara/2000/VE) is most closely related to the genogroup III, genus Noroviruses.

A primer pair (p289-p290) designed to detect both noroviruses and sapoviruses by reverse transcription-PCR (Jiang et al., J. Virol. Methods 83: 145, 1999) cross-reacts with rotaviruses. The rotavirus amplicon corresponds to genome segment 1. Furthermore, primer pair p289-p290 detected rotaviruses as efficiently as rotavirus-specific primers directed to rotavirus gene 4.