Molecular Basis for Arbovirus Transmission by Aedes aegypti Mosquitoes.

Mosquitoes are considered the most important vectors for the transmission of pathogens to humans. Aedes aegypti is a unique species, not only by its highly anthropophilic and peridomestic habits but also because it can transmit an important variety of pathogenic viruses. Examples are dengue, yellow fever, chikungunya, Zika, and Mayaro viruses. After ingesting viremic blood, a wide range of mechanisms are activated in the mosquito to counteract viral infection. Nevertheless, these arboviruses possess strategies to overcome barriers in the mosquito and eventually reach the salivary glands to continue the transmission cycle. However, the infection and eventual transmission of arbovirus depends on multiple factors. The current review focuses in detail on the anatomic, physiological, and molecular characteristics of the mosquito A. aegypti that participate in response to a viral infection. In the past decades, the awareness of the importance of this mosquito as a disease vector and its impact on human health was largely recognized. We need to improve our comprehension of molecular mechanisms that determine the outcome of successful virus replication or control of infection for each arbovirus in the vector; this could lead to the design of effective control strategies in the future.

Chikungunya: Molecular Aspects, Clinical Outcomes and Pathogenesis.

The alarming worldwide emergence of the chikungunya virus began in the last decade. Since the first autochthonous transmission in Mexico in November of 2014, the virus has spread throughout the country, resulted in multiple outbreaks. This virus produces an acute and self-limiting disease characterized by fever, polyarthralgia, myalgia, exanthema, and general malaise. It is transmitted to humans by the bite of Aedes aegypti and A. albopictus mosquitoes. The fact that the clinical presentation is similar to that produced by other arboviruses complicates its clinical diagnosis. The chronic stage of the disease can cause severe consequences lasting months or years, from local arthralgia to rheumatoid arthritis. In this review, we emphasize the public health threat posed by this highly disabling emerging disease, the clinical outcomes, and its possible physiopathological process. We outline the diagnosis and the impact that this virus has had in Mexico since its introduction.

Impact of homologous and heterologous boosters in neutralizing antibodies titers against SARS-CoV-2 Omicron in solid-organ transplant recipients.

Introduction: Booster doses of SARS-CoV-2 vaccines improve seroconversion rates in solid organ transplant recipients (SOTRs) but the impact of homologous and heterologous booster doses in neutralizing antibody (NAb) titers and their ability to interfere with the variant of concern Omicron are not well studied. Methods: We designed a prospective, open-label, observational clinical cohort study. 45 participants received two doses of BNT162b2 or CoronaVac (21-day or 28-day intervals, respectively) followed by a first and second booster with BNT162b2 (5-month apart each) and we analyzed the neutralizing antibody titers against SARSCoV-2 D614G (B.1 lineage) and Omicron (BA.1 lineage). Results: Our results show that SOTRs receiving an initial two-dose scheme of CoronaVac or BNT162b2 generate lower NAbs titers against the ancestral variant of SARS-CoV-2 when compared with healthy controls. Although these NAb titers were further decreased against the SARS-CoV-2 Omicron, a single BNT162b2 booster in both groups was sufficient to increase NAb titers against the variant of concern. More importantly, this effect was only observed in those participants responding to the first two shots but not in those not responding to the initial vaccination scheme. Discussion: The data provided here demonstrate the importance of monitoring antibody responses in immunocompromised subjects when planning booster vaccination programs in this risk group.

Differential neutralizing antibody responses elicited by CoronaVac and BNT162b2 against SARS-CoV-2 Lambda in Chile.

SARS-CoV-2 variant Lambda was dominant in several South American countries, including Chile. To ascertain the efficacy of local vaccination efforts, we used pseudotyped viruses to characterize the neutralization capacity of antibodies elicited by CoronaVac (n = 53) and BNT162b2 (n = 56) in healthcare workers from Clínica Santa María and the Faculty of Medicine at Universidad de Chile, as well as in convalescent plasma from individuals infected during the first wave visiting the Hospital Clínico at Pontificia Universidad Católica (n = 30). We observed that BNT162b2 elicits higher neutralizing antibody titres than CoronaVac, with differences ranging from 7.4-fold for the ancestral spike (Wuhan-Hu-1) to 8.2-fold for the Lambda spike and 13-fold for the Delta spike. Compared with the ancestral virus, neutralization against D614G, Alpha, Gamma, Lambda and Delta variants was reduced by between 0.93- and 4.22-fold for CoronaVac, 1.04- and 2.38-fold for BNT162b2, and 1.26- and 2.67-fold for convalescent plasma. Comparative analyses among the spike structures of the different variants suggest that mutations in the spike protein from the Lambda variant, including the 246-252 deletion in an antigenic supersite at the N-terminal domain loop and L452Q/F490S within the receptor-binding domain, may account for immune escape. Interestingly, analyses using pseudotyped and whole viruses showed increased entry rates into HEK293T-ACE2 cells, but reduced replication rates in Vero-E6 cells for the Lambda variant when compared with the Alpha, Gamma and Delta variants. Our data show that inactivated virus and messenger RNA vaccines elicit different levels of neutralizing antibodies with different potency to neutralize SARS-CoV-2 variants, including the variant of interest Lambda.

Accuracy of a RT-qPCR SARS-CoV-2 detection assay without prior RNA extraction.

The current COVID-19 pandemic constitutes a threat to the population worldwide with over 21 million infected people. There is an urgent need for the development of rapid and massive detection tools as well as the identification and isolation of infected individuals. we sought to evaluate different RT-qPCR kits and protocols to evaluate the best approach to be used omitting an RNA extraction step. We have investigated the sensitivity and performance of different commercially available RT-qPCR kits in detecting SARS-CoV-2 using 80 extracted RNA and NSS from COVID-19 diagnosed patients. We evaluated the ability of each kit to detect viral RNA from both kit-extracted or directly from a pre-boiled NSS observing that direct RNA detection is possible when Ct values are lower than 30 with the three kits tested. Since SARS-CoV-2 testing in most locations occurs once COVID-19 symptoms are evident and, therefore, viral loads are expected to be high, our protocol will be useful in supporting SARS-CoV-2 diagnosis, especially in America where COVID-19 cases have exploded in the recent weeks as well as in low- and middle-income countries, which would not have massive access to kit-based diagnosis. The information provided in this work paves the way for the development of more efficient SARS-CoV-2 detection approaches avoiding an RNA extraction step.

Neurological Complications Associated with the Blood-Brain Barrier Damage Induced by the Inflammatory Response During SARS-CoV-2 Infection.

The main discussion above of the novel pathogenic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has focused substantially on the immediate risks and impact on the respiratory system; however, the effects induced to the central nervous system are currently unknown. Some authors have suggested that SARS-CoV-2 infection can dramatically affect brain function and exacerbate neurodegenerative diseases in patients, but the mechanisms have not been entirely described. In this review, we gather information from past and actual studies on coronaviruses that informed neurological dysfunction and brain damage. Then, we analyzed and described the possible mechanisms causative of brain injury after SARS-CoV-2 infection. We proposed that potential routes of SARS-CoV-2 neuro-invasion are determinant factors in the process. We considered that the hematogenous route of infection can directly affect the brain microvascular endothelium cells that integrate the blood-brain barrier and be fundamental in initiation of brain damage. Additionally, activation of the inflammatory response against the infection represents a critical step on injury induction of the brain tissue. Consequently, the virus' ability to infect brain cells and induce the inflammatory response can promote or increase the risk to acquire central nervous system diseases. Here, we contribute to the understanding of the neurological conditions found in patients with SARS-CoV-2 infection and its association with the blood-brain barrier integrity.

N6 -Methyladenosine Negatively Regulates Human Respiratory Syncytial Virus Replication.

N6-methyladenosine (m6A) is the most abundant internal modification described in eukaryotic mRNA and several viral RNA including human respiratory syncytial virus (HRSV). Here, we evaluated the impact of m6A writers, erasers and readers on HRSV genomic RNA accumulation and inclusion bodies assembly during viral replication. We observed that the METTL3/METTL14 m6A writer complex plays a negative role in HRSV protein synthesis and viral titers, while m6A erasers FTO and ALKBH5 had the opposite effect. We also observed that m6A readers YTHDF1-3 bind to the viral genomic RNA inducing a decrease in its intracellular levels and thus, inhibiting viral replication. Finally, we observed that overexpression of YTHDFs proteins caused a decrease in the size of inclusion bodies (IBs), accompanied by an increase in their number. METTL3 knockdown cells showed an opposite effect indicating that the dynamics of IBs assembly and coalescence are strongly affected by m6A readers in a mechanism dependent on m6A writers. Taken together, our results demonstrated that the m6A modification negatively affects HRSV replication, possibly through a mechanism involving the assembly of inclusion bodies, the main factories of viral genomic RNA synthesis.

Evaluation of the Immune Response Induced by CoronaVac 28-Day Schedule Vaccination in a Healthy Population Group.

CoronaVac vaccine from Sinovac Life Science is currently being used in several countries. In Chile, the effectiveness of preventing hospitalization is higher than 80% with a vaccination schedule. However, to date, there are no data about immune response induction or specific memory. For this reason, we recruited 15 volunteers without previous suspected/diagnosed COVID-19 and with negative PCR over time to evaluate the immune response to CoronaVac 28 and 90 days after the second immunization (dpi). The CoronaVac administration induces total and neutralizing anti-spike antibodies in all vaccinated volunteers at 28 and 90 dpi. Furthermore, using ELISpot analysis to assay cellular immune responses against SARS-CoV-2 spike protein, we found an increase in IFN-gamma- and Granzyme B-producing cells in vaccinated volunteers at 28 and 90 dpi. Together, our results indicate that CoronaVac induces a robust humoral immune response and cellular immune memory of at least 90 dpi.

Crosstalk between RNA Metabolism and Cellular Stress Responses during Zika Virus Replication.

Zika virus (ZIKV) is a mosquito-borne virus associated with neurological disorders such as Guillain-Barré syndrome and microcephaly. In humans, ZIKV is able to replicate in cell types from different tissues including placental cells, neurons, and microglia. This intricate virus-cell interaction is accompanied by virally induced changes in the infected cell aimed to promote viral replication as well as cellular responses aimed to counteract or tolerate the virus. Early in the infection, the 11-kb positive-sense RNA genome recruit ribosomes in the cytoplasm and the complex is translocated to the endoplasmic reticulum (ER) for viral protein synthesis. In this process, ZIKV replication is known to induce cellular stress, which triggers both the expression of innate immune genes and the phosphorylation of eukaryotic translation initiation factor 2 (eIF2α), shutting-off host protein synthesis. Remodeling of the ER during ZIKV replication also triggers the unfolded protein response (UPR), which induces changes in the cellular transcriptional landscapes aimed to tolerate infection or trigger apoptosis. Alternatively, ZIKV replication induces changes in the adenosine methylation patterns of specific host mRNAs, which have different consequences in viral replication and cellular fate. In addition, the ZIKV RNA genome undergoes adenosine methylation by the host machinery, which results in the inhibition of viral replication. However, despite these relevant findings, the full scope of these processes to the outcome of infection remains poorly elucidated. This review summarizes relevant aspects of the complex crosstalk between RNA metabolism and cellular stress responses against ZIKV and discusses their possible impact on viral pathogenesis.