SummaryZika virus (ZIKV) remained obscure until the recent explosive outbreaks in French Polynesia (2013-2014) and South America (2015-2016). Phylogenetic studies reveal that ZIKV has evolved into African and Asian lineages. The Asian lineage of ZIKV is responsible for the recent epidemics in the Americas. However, the underlying mechanisms through which ZIKV rapidly and explosively spread from Asia to the Americas are limited. We have recently shown that nonstructural protein 1 (NS1) facilitates flavivirus acquisition by mosquitoes from an infected mammalian host and subsequently enhances viral prevalence in mosquitoes. Here, we report that the antigenemia of NS1 determines ZIKV infectivity in its mosquito vector Aedes aegypti, which acquires ZIKV via a blood meal. Clinical isolates from the most recent outbreak in the Americas were much more infectious in mosquitoes than the FSS13025 strain, which was isolated in Cambodia in 2010. Further analyses showed that these epidemic strains have more robust NS1 antigenemia than the FSS13025 strain because of an alanine-to-valine amino acid substitution at the 188th residue in NS1. ZIKV infectivity was enhanced by this residue substitution in the ZIKV FSS13025 strain in mosquitoes that acquired ZIKV from a viremic Type I and II interferon receptor-deficient (ifnagr-/-) C57BL/6 (AG6) mouse. Our results reveal that ZIKV evolved to acquire a spontaneous mutation in its NS1 protein, resulting in increased antigenemia of the protein. Enhancement of NS1 antigenemia in infected hosts promotes ZIKV infectivity and prevalence in mosquitoes, which potentially facilitates transmission during the recent ZIKV epidemics.

SUMMARY Background Avian influenza A(H7N9) virus has caused human infections in China since 2013, and a large epidemic in 2016–17 has prompted concerns of whether the epidemiology has changed to suggest an increasing pandemic threat. Our study aimed to describe the epidemiological characteristics, clinical severity, and time-to-event distributions of A(H7N9) case-patients in the 2016–17 epidemic wave compared with previous waves. Methods We obtained information about all laboratory-confirmed human cases of A(H7N9) virus infection reported in mainland China as of 23 February 2017. We described the epidemiological characteristics across epidemic waves, and estimated the risk for death, mechanical ventilation, and admission to the intensive care unit for patients who required hospitalization for medical reasons. We estimated the incubation periods, and time delays from illness onset to hospital admission, illness onset to initiation of antiviral treatment, and hospital admission to death or discharge. Findings The 2016–17 A(H7N9) epidemic wave began earlier, spread to more counties in affected provinces and had more confirmed cases than previous epidemic waves. There was an increase in the proportion of cases in middle-aged adults and in semi-urban and rural residents. The clinical severity of hospitalized cases in 2016–17 was comparable to the previous epidemic waves. Interpretation Age distribution and case sources changed gradually across epidemic waves, while clinical severity has not changed substantially. Continued vigilance and sustained intensive control efforts are needed to minimize the risk of human infection with A(H7N9) virus. Funding The National Science Fund for Distinguished Young Scholars (grant no. 81525023).

The ongoing coronavirus disease 2019 (COVID-19) pandemic has caused >20 million infections and >750,000 deaths. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiological agent of COVID-19, has been found closely related to the bat coronavirus strain RaTG13 (Bat-CoV RaTG13) and a recently identified pangolin coronavirus (Pangolin-CoV-2020). Here we first investigated the ability of SARS-CoV-2 and three related coronaviruses to utilize animal orthologs of angiotensin-converting enzyme 2 (ACE2) for cell entry. We found that ACE2 orthologs of a wide range of domestic and wild mammals, including camels, cattle, horses, goats, sheep, cats, rabbits and pangolins, were able to support cell entry of SARS-CoV-2, suggesting that these species might be able to harbor and spread this virus. In addition, the pangolin and bat coronaviruses, Pangolin-CoV-2020 and Bat-CoV RaTG13, were also found able to utilize human ACE2 and a number of animal-ACE2 orthologs for cell entry, indicating risks of spillover of these viruses into humans in the future. We then developed potently anti-coronavirus ACE2-Ig proteins that are broadly effective against the four distinct coronaviruses. In particular, through truncating ACE2 at its residue 740 but not 615, introducing a D30E mutation, and adopting an antibody-like tetrameric-ACE2 configuration, we generated an ACE2-Ig variant that neutralizes SARS-CoV-2 at picomolar range. These data demonstrate that the improved ACE2-Ig variants developed in this study could potentially be developed to protect from SARS-CoV-2 and some other SARS-like viruses that might spillover into humans in the future. IMPORTANCE The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the etiological agent of the currently uncontrolled coronavirus disease 2019 (COVID-19) pandemic. It is important to study the host range of SARS-CoV-2 because some domestic species might harbor the virus and transmit it back to humans. In addition, insight into the ability of SARS-CoV-2 and SARS-like viruses to utilize animal orthologs of the SARS-CoV-2 receptor ACE2 might provide structural insight into improving ACE2-based viral entry inhibitors. In this study, we found that ACE2 orthologs of a wide range of domestic and wild animals can support cell entry of SARS-CoV-2 and three related coronaviruses, providing insights into identifying animal hosts of these viruses. We also developed recombinant ACE2-Ig proteins that are able to potently block these viral infections, providing a promising approach to developing antiviral proteins broadly effective against these distinct coronaviruses.

Increasing evidence suggests that dysregulated immune responses are associated with the clinical outcome of coronavirus disease 2019 (COVID-19). Nucleocapsid protein (NP)-, spike (S)-, receptor binding domain (RBD)- specific immunoglobulin (Ig) isotypes, IgG subclasses and neutralizing antibody (NAb) were analyzed in 123 serum from 63 hospitalized patients with severe, moderate, mild or asymptomatic COVID-19. Mild to modest correlations were found between disease severity and antigen specific IgG subclasses in serum, of which IgG1 and IgG3 were negatively associated with viral load in nasopharyngeal swab. Multiple cytokines were significantly related with antigen-specific Ig isotypes and IgG subclasses, and IL-1β was positively correlated with most antibodies. Furthermore, the old patients (≥ 60 years old) had higher levels of chemokines, increased NAb activities and SARS-CoV-2 specific IgG1, and IgG3 responses and compromised T cell responses compared to the young patients (≤ 18 years old), which are related with more severe cases. Higher IgG1 and IgG3 were found in COVID-19 patients with comorbidities while biological sex had no effect on IgG subclasses. Overall, we have identified diseases severity was related to higher antibodies, of which IgG subclasses had weakly negative correlation with viral load, and cytokines were significantly associated with antibody response. Further, advancing age and comorbidities had obvious effect on IgG1 and IgG3.

Sensitive and accurate detection of highly contagious virus is urgently demanded for disease diagnosis and treatment. Herein, based on a multifunctional aggregation-induced emission luminogen (AIEgen), a dual-modality readout immunoassay platform for ultrasensitive detection of viruses has been successfully demonstrated. The platform is relied on virions immuno-bridged enzymatic hydrolysis of AIEgen, accompanying with the in situ formation of highly emissive AIE aggregates and shelling of silver on gold nanoparticles. As a result, robust turn-on fluorescence and naked-eye discernible plasmonic colorimetry composed dual-signal is achieved. By further taking advantage of effective immunomagnetic enrichment, EV71 virions, as an example, can be specifically detected with a limit of detection down to 1.4 copies/μL under fluorescence modality. Additionally, semiquantitative discerning of EV71 virions is realized in a broad range from 1.3 × 10 to 2.5 × 10 copies/μL with the naked eye. Most importantly, EV71 virions in 24 real clinical samples are successfully diagnosed with 100% accuracy. Comparing to the gold standard polymerase chain reaction (PCR) assay, our immunoassay platform do not need complicated sample pretreatment and expensive instruments. This dual-modality strategy builds a good capability for both colorimetry based convenient preliminary screening and fluorescence based accurate diagnosis of suspect infections in virus-stricken areas.

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Transmission from an infected mosquito to a host is an essential process in the life cycle of mosquito-borne flaviviruses. Numerous studies have demonstrated that mosquito saliva facilitates viral transmission. Here we find that a saliva-specific protein, named Aedes aegypti venom allergen-1 (AaVA-1), promotes dengue and Zika virus transmission by activating autophagy in host immune cells of the monocyte lineage. The AG6 mice (ifnar1–/–ifngr1–/–) bitten by the virus-infected AaVA-1-deficient mosquitoes present a lower viremia and prolonged survival. AaVA-1 intracellularly interacts with a dominant negative binder of Beclin-1, known as leucine-rich pentatricopeptide repeat-containing protein (LRPPRC), and releases Beclin-1 from LRPPRC-mediated sequestration, thereby enabling the initialization of downstream autophagic signaling. A deficiency in Beclin-1 reduces viral infection in mice and abolishes AaVA-1-mediated enhancement of ZIKV transmission by mosquitoes. Our study provides a mechanistic insight into saliva-aided viral transmission and could offer a potential prophylactic target for reducing flavivirus transmission.

Background Virological detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through RT-PCR has limitations for surveillance. Serological tests can be an important complementary approach. We aimed to assess the practical performance of RT-PCR-based surveillance protocols and determine the extent of undetected SARS-CoV-2 infection in Shenzhen, China.Methods We did a cohort study in Shenzhen, China and attempted to recruit by telephone all RT-PCR-negative close contacts (defined as those who lived in the same residence as, or shared a meal, travelled, or socially interacted with, an index case within 2 days before symptom onset) of all RT-PCR-confirmed cases of SARS-CoV-2 detected since January, 2020, via contact tracing. We measured anti-SARS-CoV-2 antibodies in serum samples from RT-PCR-negative close contacts 2-15 weeks after initial virological testing by RT-PCR, using total antibody, IgG, and IgM ELISAs. In addition, we did a serosurvey of volunteers from neighbourhoods with no reported cases, and from neighbourhoods with reported cases. We assessed rates of infection undetected by RT-PCR, performance of RT-PCR over the course of infection, and characteristics of individuals who were seropositive on total antibody ELISA but RT-PCR negative.Findings Between April 12 and May 4, 2020, we enrolled and collected serological samples from 2345 (53•0%) of 4422 RT-PCR-negative close contacts of cases of RT-PCR-confirmed SARS-CoV-2. 1175 (50•1%) of 2345 were close contacts of cases diagnosed in Shenzhen with contact tracing details, and of these, 880 (74•9%) had serum samples collected more than 2 weeks after exposure to an index case and were included in our analysis. 40 (4•5%) of 880 RT-PCR-negative close contacts were positive on total antibody ELISA. The seropositivity rate with total antibody ELISA among RT-PCR-negative close contacts, adjusted for assay performance, was 4•1% (95% CI 2•9-5•7), which was significantly higher than among individuals residing in neighbourhoods with no reported cases (0•0% [95% CI 0•0-1•1]). RT-PCR-positive individuals were 8•0 times (95% CI 5•3-12•7) more likely to report symptoms than those who were RT-PCR-negative but seropositive, but both groups had a similar distribution of sex, age, contact frequency, and mode of contact. RT-PCR did not detect 48 (36% [95% CI 28-44]) of 134 infected close contacts, and false-negative rates appeared to be associated with stage of infection.Interpretation Even rigorous RT-PCR testing protocols might miss a substantial proportion of SARS-CoV-2 infections, perhaps in part due to difficulties in determining the timing of testing in asymptomatic individuals for optimal sensitivity. RT-PCR-based surveillance and control protocols that include rapid contact tracing, universal RT-PCR testing, and mandatory 2-week quarantine were, nevertheless, able to contain community spread in Shenzhen, China.