ABSTRACT
The stability of shipping and port operations are crucial for international trade and global supply chain. However, the COVID-19 pandemic hit the shipping and port industry enormously in late 2019, and continues till now. It is important to identify the impacts of the pandemic on shipping and port operations and evaluate the potential economic impacts for better setting future development strategies and policies. A System Dynamics (SD) model is proposed to depict the impact transmission within the supply chain considering 5 sub-systems (shipping, port, transportation, manufacturing and social). Potential economic impacts which are represented by the shipping loss and port loss will be assessed. 6 scenarios with different epidemic durations and capacity recovery degrees have been set to investigate the economic impacts. The port of Shanghai, together with the container shipping business is selected as input for case study. Results indicate that in the first few months the port and carriers may suffer economic loss due to shrunken demand caused by COVID-19. But later carriers may enjoy an increase of income compared to non-pandemic scenario owing to strong recovery in most scenarios. Moreover, we found that manufacturing, transportation and port operation capacities would jointly affect the recovery process and economic impacts. The findings can facilitate policy makers in making port management and future industry development decisions.
ABSTRACT
Sea ports are key nodes of global trade and economy, but are vulnerable to hazards, catastrophes and epidemic outbreaks. Since the emergence of COVID-19 infection at the end of 2019, the operations of seaports, especially container ports have been hit hard. This paper aims to explore the impacts of COVID-19 on container ports' operations, clarify the potential economic losses of ports and propose coping suggestions for recovery. Five scenarios of port recovery have been set and the revenues of the port under epidemic outbreaks are estimated. The economic loss could be modeled as the difference between original revenue a port should obtained without the impact of COVID-19 and the actual revenue considering the impact of COVID-19. The container port of Shanghai is selected as the case study. Results and sensitivity analysis reveal that slower the recovery develops, much more loss will be borne by the port. However, there is also a possibility that the port achieves increased income with a surging boom of shipping demand. The loss of port due, handling service, facility security fee and berthage charge are major losses. Besides, port handling efficiency and fleet structure are also found crucial for reducing economic losses. Reducing containership's handling time and serving larger ships would also help the port reduce economic losses.
ABSTRACT
RNA viruses, such as hepatitis C virus (HCV), influenza virus, and SARS-CoV-2, are notorious for their ability to evolve rapidly under selection in novel environments. It is known that the high mutation rate of RNA viruses can generate huge genetic diversity to facilitate viral adaptation. However, less attention has been paid to the underlying fitness landscape that represents the selection forces on viral genomes, especially under different selection conditions. Here, we systematically quantified the distribution of fitness effects of about 1,600 single amino acid substitutions in the drug-targeted region of NS5A protein of HCV. We found that the majority of nonsynonymous substitutions incur large fitness costs, suggesting that NS5A protein is highly optimized. The replication fitness of viruses is correlated with the pattern of sequence conservation in nature, and viral evolution is constrained by the need to maintain protein stability. We characterized the adaptive potential of HCV by subjecting the mutant viruses to selection by the antiviral drug daclatasvir at multiple concentrations. Both the relative fitness values and the number of beneficial mutations were found to increase with the increasing concentrations of daclatasvir. The changes in the spectrum of beneficial mutations in NS5A protein can be explained by a pharmacodynamics model describing viral fitness as a function of drug concentration. Overall, our results show that the distribution of fitness effects of mutations is modulated by both the constraints on the biophysical properties of proteins (i.e., selection pressure for protein stability) and the level of environmental stress (i.e., selection pressure for drug resistance).IMPORTANCE Many viruses adapt rapidly to novel selection pressures, such as antiviral drugs. Understanding how pathogens evolve under drug selection is critical for the success of antiviral therapy against human pathogens. By combining deep sequencing with selection experiments in cell culture, we have quantified the distribution of fitness effects of mutations in hepatitis C virus (HCV) NS5A protein. Our results indicate that the majority of single amino acid substitutions in NS5A protein incur large fitness costs. Simulation of protein stability suggests viral evolution is constrained by the need to maintain protein stability. By subjecting the mutant viruses to selection under an antiviral drug, we find that the adaptive potential of viral proteins in a novel environment is modulated by the level of environmental stress, which can be explained by a pharmacodynamics model. Our comprehensive characterization of the fitness landscapes of NS5A can potentially guide the design of effective strategies to limit viral evolution.