Claudia Nunes Duarte dos Santos

In the early 2015, several cases of patients presenting symptoms of mild fever, rash, conjunctivitis and arthralgia were reported in the northeastern Brazil. Although all patients lived in a dengue endemic area, molecular and serological diagnosis for dengue resulted negative. Chikungunya virus infection was also discarded. Subsequently, Zika virus (ZIKV) was detected by reverse transcription-polymerase chain reaction from the sera of eight patients and the result was confirmed by DNA sequencing. Phylogenetic analysis suggests that the ZIKV identified belongs to the Asian clade. This is the first report of ZIKV infection in Brazil.

An unusually high incidence of microcephaly in newborns has recently been observed in Brazil. There is a temporal association between the increase in cases of microcephaly and the Zika virus (ZIKV) epidemic. Viral RNA has been detected in amniotic fluid samples, placental tissues and newborn and fetal brain tissues. However, much remains to be determined concerning the association between ZIKV infection and fetal malformations. In this study, we provide evidence of the transplacental transmission of ZIKV through the detection of viral proteins and viral RNA in placental tissue samples from expectant mothers infected at different stages of gestation. We observed chronic placentitis (TORCH type) with viral protein detection by immunohistochemistry in Hofbauer cells and some histiocytes in the intervillous spaces. We also demonstrated the neurotropism of the virus via the detection of viral proteins in glial cells and in some endothelial cells and the observation of scattered foci of microcalcifications in the brain tissues. Lesions were mainly located in the white matter. ZIKV RNA was also detected in these tissues by real-time-polymerase chain reaction. We believe that these findings will contribute to the body of knowledge of the mechanisms of ZIKV transmission, interactions between the virus and host cells and viral tropism.

We report that endoplasmic reticulum alpha-glucosidase inhibitors have antiviral effects on dengue (DEN) virus. We found that glucosidase inhibition strongly affects productive folding pathways of the envelope glycoproteins prM (the intracellular glycosylated precursor of M [membrane protein]) and E (envelope protein): the proper folding of prM bearing unprocessed N-linked oligosaccharide is inefficient, and this causes delayed formation of prME heterodimer. The complexes formed between incompletely folded prM and E appear to be unstable, leading to a nonproductive pathway. Inhibition of alpha-glucosidase-mediated N-linked oligosaccharide trimming may thus prevent the assembly of DEN virus by affecting the early stages of envelope glycoprotein processing.

Apoptosis has been suggested as a mechanism by which dengue (DEN) virus infection may cause neuronal cell death (P. Desprès, M. Flamand, P.-E. Ceccaldi, and V. Deubel, J. Virol. 70:4090-4096, 1996). In this study, we investigated whether apoptotic cell death occurred in the central nervous system (CNS) of neonatal mice inoculated intracerebrally with DEN virus. We showed that serial passage of a wild-type human isolate of DEN virus in mouse brains selected highly neurovirulent variants which replicated more efficiently in the CNS. Infection of newborn mice with these neurovirulent variants produced fatal encephalitis within 10 days after inoculation. Virus-induced cell death and oligonucleosomal DNA fragmentation were observed in mouse brain tissue by day 9. Infected mouse brain tissue was assayed for apoptosis by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and for virus replication by immunostaining of viral antigens and in situ hybridization. Apoptotic cell death and DEN virus replication were restricted to the neurons of the cortical and hippocampal regions. Thus, DEN virus-induced apoptosis in the CNS was a direct result of virus infection. In the murine neuronal cell line Neuro 2a, neuroadapted DEN virus variants showed infection patterns similar to those of the parental strain. However, DEN virus-induced apoptosis in these cells was more pronounced after infection with the neurovirulent variants than after infection with the parental strain.

Dengue is one of the most significant health problems in tropical and sub-tropical regions throughout the world. Nearly 390 million cases are reported each year. Although a vaccine was recently approved in certain countries, an anti-dengue virus drug is still needed. Fruits and vegetables may be sources of compounds with medicinal properties, such as flavonoids. This study demonstrates the anti-dengue virus activity of the citrus flavanone naringenin, a class of flavonoid. Naringenin prevented infection with four dengue virus serotypes in Huh7.5 cells. Additionally, experiments employing subgenomic RepDV-1 and RepDV-3 replicon systems confirmed the ability of naringenin to inhibit dengue virus replication. Antiviral activity was observed even when naringenin was used to treat Huh7.5 cells 24 h after dengue virus exposure. Finally, naringenin anti-dengue virus activity was demonstrated in primary human monocytes infected with dengue virus sertoype-4, supporting the potential use of naringenin to control dengue virus replication. In conclusion, naringenin is a suitable candidate molecule for the development of specific dengue virus treatments.