Dengue virus infections pose a significant threat to human health at present, which is reported from nearly 140 countries. The genome of this virus encodes three structural and seven non-structural (NS) proteins along with two un-translated regions, one each on both ends. Among them, dengue protease (NS3) plays a pivotal role in polyprotein processing and virus multiplication. NS3 is also known to regulate several host proteins to induce and maintain pathogenesis.Certain viral proteins are known to interact with mitochondrial membrane proteins and interfere with their functions. But the association of a virus-coded protein with the mitochondrial matrix is not known. In this report, by using in silico analysis, we show that NS3pro alone is capable of mitochondrial import; however, dependent on its innate mitochondrial transport signal (MTS). Transient transfection and protein import studies confirm the import of NS3pro to the mitochondrial matrix. Similarly, NS3pro-helicase (1-464 amino acids of NS3) also targets the mitochondria. Intriguingly, reduced levels of the matrix localized GrpEL1, a co-chaperone of mtHsp70, were noticed in NS3pro, NS3pro-helicase expressing, and virus-infected cells. Upon using purified components, GrpEL1 undergoes cleavage, and the sites have been mapped to KR81A and QR 92S. Importantly, the levels of GrpEL1 are seriously compromised in severe dengue infected clinical samples. Our studies provide novel insights into the import of NS3 into host mitochondria and identify a hitherto unknown factor, GrpEL1 as a cleavage target, and thereby providing new avenues for the dengue research and the design of potential therapeutics. IMPORTANCE About 40% of the world's population is at the risk of dengue virus infections. There is no specific drug or potential vaccine for these infections until now. Lack of complete understanding about the pathogenesis is one of the hurdles for developing antivirals for this virus infection. In the present study, we show that the virus-coded protease imports to the mitochondrial matrix, which is the first-ever report with reference to the animal and human viruses. The analysis indicated that the observed mitochondrial import is due to the inherited mitochondrial transport signal. We also show that the matrix localized GrpEL1, a co-chaperone of mtHsp70, is also the substrate of dengue virus protease, as observed in in vitro, ex vivo, virus-infected cells, and dengue virus-infected clinical samples. Hence our studies reveal an essential aspect of the pathogenesis of dengue virus infections, which may aid in developing anti-dengue therapeutics.

Viruses that emerge pose challenges for treatment options as their uniqueness would not know completely. Hence, many viruses are causing high morbidity and mortality for a long time. Despite large diversity, viruses share common characteristics for infection. At least 12 different respiratory-borne viruses are reported belonging to various virus taxonomic families. Many of these viruses multiply and cause damage to the upper and lower respiratory tracts. The description of these viruses in comparison with each other concerning their epidemiology, molecular characteristics, disease manifestations, diagnosis and treatment is lacking. Such information helps diagnose, differentiate, and formulate the control measures faster. The leading cause of acute illness worldwide is acute respiratory infections (ARIs) and are responsible for nearly 4 million deaths every year, mostly in young children and infants. Lower respiratory tract infections are the fourth most common cause of death globally, after non-infectious chronic conditions. This review aims to present the characteristics of different viruses causing respiratory infections, highlighting the uniqueness of SARS-CoV-2. We expect this review to help understand the similarities and differences among the closely related viruses causing respiratory infections and formulate specific preventive or control measures.

Dengue virus reportedly circulates as four genetically distinct serotypes for which there is no widely accepted vaccine or drug at present. Morbidity and mortality caused by this virus are alarming for the possible increased threat to human health. A suitable diagnostic test is the prerequisite for designing and developing control measures. But, the tests being employed at present possess one or the other drawback for this disease diagnosis. During the dengue virus infections, NS2B is essential for the stability and catalytic activity of the NS3 protease. N‐terminal 185 amino acids of NS3 protease domain along with hydrophilic portion of NS2B (NS2BNS3pro) is being used to screen dengue inhibitors but not for diagnosis until now. In the present study, we have used purified NS2BNS3pro as an antigen to trap anti‐NS2BNS3pro antibodies of the clinical samples. Antibodies were detected successfully in both Western blot analysis and enzyme‐linked immunosorbent assay (ELISA) tests. In ELISA, antibodies were detected in both primary and secondary infections of all serotypes. Interestingly, 17 samples declared as other febrile infections by NS1 and IgM/IgG tests were found to be positive in present test, which were further confirmed by reverse‐transcription polymerase chain reaction. In silico studies suggested the absence of conserved epitopes between NS2BNS3pro and the counterpart in JEV, Zika, and CHIKV, indicating less possibility of crossreaction, which was in turn confirmed by using synthetic peptides representing the above epitopes. Statistical analysis with 76% specificity, 87% sensitivity, and 95% concordance also supported the present test as a suitable test for large scale diagnosis of dengue virus infections.

Dengue virus infections are recorded as hyper-endemic in many countries, including India. Research pertaining to the reasons for frequent outbreaks and severe dengue is ongoing. Hyderabad city, India, has been recorded as a ‘hotspot’ for dengue virus infections. Dengue virus strains circulating over the past few years in Hyderabad city have been characterized at the molecular level to analyze the serotype/genotypes; 3′UTRs were further amplified and sequenced. The disease severity in patients infected with dengue virus strains with complete and 3′UTR deletion mutants was analyzed. Genotype I of the serotype 1 replaced genotype III, which has been circulating over the past few years in this region. Coincidentally, the number of dengue virus infections significantly increased in this region during the study period. Nucleotide sequence analysis suggested twenty-two and eight nucleotide deletions in the 3′UTR of DENV-1. The eight nucleotide deletions observed in the case of DENV-1 3′UTR were the first reported in this instance. A 50 nucleotide deletion was identified in the case of the serotype DENV-2. Importantly, these deletion mutants were found to cause severe dengue, even though they were found to be replication incompetent. This study emphasized the role of dengue virus 3′UTRs on severe dengue and emerging outbreaks.

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