Zika virus causes testicular atrophy

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus that has recently been found to cause fetal infection and neonatal abnormalities, including microcephaly and neurological dysfunction. ZIKV persists in the semen months after the acute viremic phase in humans. To further understand the consequences of ZIKV persistence in males, we infected Ifnar1−/− mice via subcutaneous injection of a pathogenic but nonlethal ZIKV strain. ZIKV replication persists within the testes even after clearance from the blood, with interstitial, testosterone-producing Leydig cells supporting virus replication. We found high levels of viral RNA and antigen within the epididymal lumen, where sperm is stored, and within surrounding epithelial cells. Unexpectedly, at 21 days post-infection, the testes of the ZIKV-infected mice were significantly smaller compared to those of mock-infected mice, indicating progressive testicular atrophy. ZIKV infection caused a reduction in serum testosterone, suggesting that male fertility can be affected. Our findings have important implications for nonvector-borne vertical transmission, as well as long-term potential reproductive deficiencies, in ZIKV-infected males.

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Genome sequencing reveals Zika virus diversity and spread in the Americas

Despite great attention given to the recent Zika virus (ZIKV) epidemic in the Americas, much remains unknown about its epidemiology and evolution, in part due to a lack of genomic data. We applied multiple sequencing approaches to generate 100 ZIKV genomes from clinical and mosquito samples from 10 countries and territories, greatly expanding the observed viral genetic diversity from this outbreak. We analyzed the timing and patterns of introductions into distinct geographic regions, confirming phylogenetic evidence for the origin and rapid expansion of the outbreak in Brazil, and for multiple introductions from Brazil into Honduras, Colombia, Puerto Rico, other Caribbean islands, and the continental US. We find that ZIKV circulated undetected in many regions of the Americas for up to a year before the first locally transmitted cases were confirmed, highlighting the challenge of effective surveillance for this virus. We further characterize genetic variation across the outbreak to identify mutations with possible functional implications for ZIKV biology and pathogenesis.

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ImageSource=RCSB PDB; StructureID=5mrk; DOI=http://dx.doi.org/10.2210/pdb5mrk/pdb;

Structural basis of Zika virus methyltransferase inhibition by sinefungin

New high resolution structure of ZIKV NS5 methyltransferase with the inhibitor sinefugin is available in Protein Data Bank (PDB ID: 5MRK).

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The clinically approved antiviral drug sofosbuvir inhibits Zika virus replication

Zika virus (ZIKV) is a member of the Flaviviridae family, along with other agents of clinical significance such as dengue (DENV) and hepatitis C (HCV) viruses. Since ZIKV causes neurological disorders during fetal development and in adulthood, antiviral drugs are necessary. Sofosbuvir is clinically approved for use against HCV and targets the protein that is most conserved among the members of the Flaviviridae family, the viral RNA polymerase. Indeed, we found that sofosbuvir inhibits ZIKV RNA polymerase, targeting conserved amino acid residues. Sofosbuvir inhibited ZIKV replication in different cellular systems, such as hepatoma (Huh-7) cells, neuroblastoma (SH-Sy5y) cells, neural stem cells (NSC) and brain organoids. In addition to the direct inhibition of the viral RNA polymerase, we observed that sofosbuvir also induced an increase in A-to-G mutations in the viral genome. Together, our data highlight a potential secondary use of sofosbuvir, an anti-HCV drug, against ZIKV.

Figure 1

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Potential use of saliva samples to diagnose Zika virus infection

Serological diagnosis of ZIKV in countries where dengue virus (DENV) is endemic is challenging, because antibodies elicited by a prior DENV infection may cross-react against ZIKV. Therefore, molecular techniques, such as conventional or real-time reverse transcriptase polymerase chain reaction (RT-PCR/qRT-PCR), remain the reference methods for the diagnosis of ZIKV. However, the sensitivity of ZIKV RT-PCR in serum samples is not optimal due to low and short viremia. Here, we describe findings from a case series of acute febrile illness patient’s whose saliva and blood samples were tested for ZIKV by qRT-PCR.


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Mathematical model for Zika virus dynamics with sexual transmission route

Zika virus is a flavivirus transmitted to humans primarily through the bite of infected Aedes mosquitoes. In addition to vector-borne spread, however, the virus can also be transmitted through sexual contact. In this paper, we formulate and analyze a new system of ordinary differential equations which incorporates both vector and sexual transmission routes. Theoretical analysis of this model when there is no disease induced mortality shows that the disease-free equilibrium is locally and globally asymptotically stable whenever the associated reproduction number is less than unity and unstable otherwise. However, when we extend this same model to include Zika induced mortality, which have been documented in Latin America, we find that the model exhibits a backward bifurcation. Specifically, a stable disease-free equilibrium co-exists with a stable endemic equilibrium when the associated reproduction number is less than unity. To further explore model predictions, we use numerical simulations to assess the importance of sexual transmission to disease dynamics. This analysis shows that risky behavior involving multiple sexual partners, particularly among male populations, substantially increases the number of infected individuals in the population, contributing significantly to the disease burden in the community.

Flow diagram of the Zika virus model (2.5) with sexual transmission route.

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ImageSource=RCSB PDB; StructureID=5mfx; DOI=http://dx.doi.org/10.2210/pdb5mfx/pdb;

Zika NS3 helicase:RNA complex

New high resolution structure of ZIKV NS3 helicase is available in Protein Data Bank (PDB ID: 5MFX)

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Vulnerability of primitive human placental trophoblast to Zika virus

Infection of pregnant women by Asian lineage strains of Zika virus (ZIKV) has been linked to brain abnormalities in their infants, yet it is uncertain when during pregnancy the human conceptus is most vulnerable to the virus. We have examined two models to study susceptibility of human placental trophoblast to ZIKV: cytotrophoblast and syncytiotrophoblast derived from placental villi at term and colonies of trophoblast differentiated from embryonic stem cells (ESC). The latter appear to be analogous to the primitive placenta formed during implantation. The cells from term placentas, which resist infection, do not express genes encoding most attachment factors implicated in ZIKV entry but do express many genes associated with antiviral defense. By contrast, the ESC-derived trophoblasts possess a wide range of attachment factors for ZIKV entry and lack components of a robust antiviral response system. These cells, particularly areas of syncytiotrophoblast within the colonies, quickly become infected, produce infectious virus and undergo lysis within 48 h after exposure to low titers (multiplicity of infection > 0.07) of an African lineage strain (MR766 Uganda: ZIKVU) considered to be benign with regards to effects on fetal development. Unexpectedly, lytic effects required significantly higher titers of the presumed more virulent FSS13025 Cambodia (ZIKVC). Our data suggest that the developing fetus might be most vulnerable to ZIKV early in the first trimester before a protective zone of mature villous trophoblast has been established. Additionally, MR766 is highly trophic toward primitive trophoblast, which may put the early conceptus of an infected mother at high risk for destruction.

Fig. 2.

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Characterization of cytopathic factors through genome-wide analysis of the Zika viral proteins in fission yeast

The Zika virus (ZIKV) causes various neurologic defects including microcephaly and the Guillain-Barré syndrome. However, little is known about how ZIKV causes those diseases or which viral protein(s) is responsible for the observed cytopathic effects involved in restricted neuronal cellular growth, dysregulation of the cell cycle, and induction of cell hypertrophy or cell death. A genome-wide analysis of ZIKV proteins and peptides was conducted using fission yeast as a surrogate host. Seven ZIKV proteins conferred various cytopathic effects in which NS4A-induced cellular hypertrophy and growth restriction were mediated through the target of rapamycin (TOR) cellular stress-response pathway. These findings provide a foundation for identifying viral pathogenicity factors associated with the ZIKV diseases.

Fig. 1.

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Researchers identify key proteins that may make Zika so deadly

Until it burst onto the scene earlier this year, Zika was an obscure, little-known virus. As a result, scientists know little about how it works. Over the past year, they have learned that it can cause a range of dangerous health problems, including birth defects such as microcephaly and neurological problems such as Guillain-Barré syndrome. But they don’t know which Zika protein or proteins are causing harm, or exactly how these proteins cause damage.

Now, a new study by scientists at the University of Maryland School of Medicine (UM SOM) has for the first time identified seven key proteins in the virus that may be the culprits behind this damage. The study is the first comprehensive description of the Zika virus genome. The study was published today in the journal Proceedings of the National Academy of Sciences.

Zika virus