COVID-19: Causes, Transmission, Diagnosis, and Treatment

Over the past two decades, coronavirus-associated diseases such as SARS and MERS have challenged the public health systems globally. Around 2002-2003, a near-pandemic of a previously unknown β-coronavirus, named SARS-CoV, arose in China and 29 other countries. Not much attention was paid to it post-disappearance of this outbreak. An understanding of the coronavirus began only after alarming predictions of the virus’s re-emergence began in 2007. Identification from previous studies revealed that bats have proven to be a major reservoir of animal coronavirus. SARS-related bat coronaviruses have all the essential components of SARS-virus, have along with similar genome sequences to that of SARS-CoV and SARS-CoV-2, and thus, are able to cause infection and transmit between humans directly. Later in 2012, another unknown β-coronavirus named Middle East respiratory syndrome (MERSCoV), with close relation to the SARS-CoV, caused an epidemic limited to the MiddleEast. The emergence of yet another bat-origin coronavirus, α-coronavirus, in China caused epizootic disease in pigs, thus named swine acute diarrhea syndrome coronavirus (SADS-CoV). Subsequently, unattended warnings of 12 years led to the most fatal bat-derived sarbecovirus, recognized as SARS CoV-2, springing up in November 2019, sweeping the globe. The predictions of SARS-CoV-2 to be a natural event with association to transmission directly from bats to humans or through an intermediate host have been essentially proven to be true. SARS-Cov-2 shares genetic properties with many other sarbecoviruses; this slies fully within their genetic cluster and is, thus, a naturally emerged virus.

Based on the genomic structure coronavirus is mainly divided into four subgroups alpha, beta, gamma, and delta.

CoVs are fall under the family Coronaviridae, and subfamily Orthocoronavirinae. The virus is protected by receptor binding domain (RBD) that binds to ACE2 receptor found in kidneys, lungs, heart and gastrointestinal tract, which that promote viral entry into target cells. Domestic animals can act as intermediary hosts in the transmission of viruses from natural hosts to people. Porcine Epidemic Diarrhea CoV(PEDC), which originated in pigs, was found to be similar to SADS-CoV. It has been transferred from bats to pigs. SADS-CoV was first found in rhinolophids or horseshoe bat, before the SARS epidemic Recombination of bat SARSr-CoVs, or recombined virus, infected and adapted to civets and humans. MERS-CoV is a zoonotic virus. It was transferred from dromedary camels to humans. The first confirmed cases of SARS-CoV-like viruses were found in raccoon dogs in live animal markets and palm civets. Another bat coronavirus, CoV RaTG13, was isolated from the Rhinolophus affinis bats.

Corona variants are classified into variants of concern (VOCS), variants of interest (VOI), variants of high consequence (VOHC), and variants being monitored (VBM).

Some common coronaviruses of human are 229E, NL63, OC43, and HKU1, which infect the upper-respiratory tract.  

 More than 600 million people have contracted the COVID-19, and a substantial level of fatalities have occurred on a global scale. The pandemic has grown to pose a serious risk to humankind. Gaining knowledge about the dynamics of virus transmission and clinical manifestation, as well as possible causes of severe illness and mortality, requires an understanding of coronavirus epidemiology. To create global health policies that work, it is imperative to understand these elements. It is believed that bats are the original host of the coronavirus that causes severe acute respiratory syndrome. The most prevalent means of transmission is through airborne droplets. Other potential routes of infection include the fecal-oral pathway, sexual transmission, the vertical chain, and so forth. The incubation period of COVID-19 is two to fourteen days, during which asymptomatic carriers may spread the virus to other people. From mild symptoms like fever, coughing, and fatigue to life-threatening illness necessitating hospitalization, COVID-19 respiratory illness can range widely in severity. The impacts of the disease are more likely to affect the elderly and people with underlying medical disorders including Type 2 diabetes, obesity, or chronic heart disease. New strains of SARS-CoV-2 have evolved as the pandemic has expanded, wreaking havoc on countries with weak healthcare systems and low incomes. Social isolation, the use of masks, and vaccination campaigns have all helped reduce the spread of the virus.

The COVID-19 pandemic has led to widespread illness, death, and economic disruption worldwide, leading to a critical need for effective treatments, vaccines, and diagnostic tools. SARS-CoV-2, belonging to the class of β-CoVs, is the virus accountable for COVID-19, and mediates entry into the host cell via its surface spike protein. Understanding its replication and pathogenesis is crucial for developing effective treatments and curbing the microbe’s spread. Here, we dive deep into the genomic organisation of the SARS-Cov2 virion and its various structural components, highlighting the molecular mechanism involved in replication, ultimately leading to pathogenesis.

The COVID-19 infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), progressed to a global pandemic and led to millions of deaths worldwide over the years since its COVID-19 origin. Coronavirus transmission is a zoonotic spillover, which means that virus transmission can occur from a vertebrate animal to a human host. The CoV genome underwent continuous recombination and evolution, which resulted in interspecies transmission and the virus' recurrent emergence as a pandemic. The SARS-CoV-2 infection primarily results in respiratory symptoms, like pneumonia, that range from mild to severe in severity, along with alveolar injury ultimately leading to acute respiratory distress syndrome (ARDS) and death. This chapter outlines the SARS-CoV-2 transmission pathways, how the disease spreads by infected people, and the consequences for the prevention and control of infection, both inside and outside healthcare facilities. This section also covers modes of transmission like horizontal, fomite, fecal-oral, nosocomial, and animal-to-human transmission of SARS-CoV-2.

COVID-19, an outbreak that has disrupted people's normal lives and lifestyles worldwide, has evolved to rank among the top few major causes of death. The virus spreads through direct and contact transmission and is thought to have a zoonotic origin. Fever, cough, and myalgia are symptoms of the symptomatic phase, which progresses to severe respiratory failure. It also includes pulmonary symptoms, which involve the severe acute respiratory syndrome coronavirus 2.

Human antibody detection, viral antigen detection, and viral gene detection are used as the foundation for the diagnostic tools developed thus far; however, viral gene detection via RT-PCR has proven to be the most reliable method. It is one of the more delicate approaches, which is also well-known for being highly advised for both qualitative and quantitative products. There is another sensitive method too that can precisely amplify a target nucleic acid known as loop-mediated isothermal amplification or LAMP.

On the other hand, amplification of nucleic acid tests is the test that identifies COVID19, which works by identifying the RNA (ribonucleic acid) sequences responsible for generating the viral genetic material. Diagnostic systems based on CRISPR for COVID-19 have advantages like early screening (30 minutes from crude extract to result), sensitivity and accuracy, mobility, and the absence of specific laboratory equipment. Some other diagnostic techniques are CBNAAT and TruNAT, along with some other serological assays that use the ELISA KIT. Lateral flow immunoassay, Enzyme-linked immunosorbent assay, and chemiluminescence immunoassay (CLIA) are some of the other reliable diagnostic techniques.

The world witnessed the outbreak of the most dreadful zoonotic infection, COVID-19, by the last month of 2019. The prompt dissemination of SARS-CoV-2 by intermediate hosts in the human community paved the way for the WHO declaration of a pandemic in 2020. In patients, the severity of this infection ranges from asymptomatic to critical state, leading to complications like acute respiratory distress syndrome (ARDS). The different diagnostics investigated the rapid spread and complexity of the disease. The omics and sequencing technologies helped to identify the virus's structure and potential targets for drug discovery against the virus. Different therapeutic agents like antivirals, antibiotics, etc., are administered to reduce the infection. The various treatment options discussed in this chapter include different types of drugs and their combinational therapies, monoclonal antibodies, immune modulating treatments, promising vaccine developments, CRISPR-Cas13 therapy, experimental therapeutic interventions, non-pharmacological interventions, etc. This study also concentrates on the various challenges these clinical medications have faced. By rectifying each challenge, new beneficial treatments can be made possible with the fewest side effects.

SARS-CoV-2, the viral inciting agent of one of the deadliest pulmonary infections known as novel Coronavirus Disease (COVID-19) has resulted in millions of deaths. With the first incidence being reported in the city of Wuhan, China, in December 2019 and dealing with a pathogen capable of quick as well as easy transmissibility, undefined symptoms, non-availability of therapeutics and acclimatization/adaptation to COVID-19 scenario can be acknowledged as the phase I challenges faced by the world. The novel and enduring COVID-19 pandemic that the world has been witnessing for the past few years has advanced to the huge and exhaustive phase II challenges that encompass the implementation of one of the longest complete global shutdowns, unusual practice of work-from-home practices, immense pressure on the healthcare sector, suspension of daily activities, majorly closing of schools and colleges, no social gatherings, the urgency to develop anti-COVID therapeutic/vaccine, lack of awareness/negligence, antimicrobial resistance and emergence of variants that fuelled the spread of the infection. Despite the combined efforts that might have flattened the curve of the infection, it remains a major trigger for rolling out post-COVID challenges, being a serious concern for every facet of the society that includes continuous deterioration of mental health, financial instability, and fear of death. This chapter focuses on addressing the challenges and threats that prevailed during and post-COVID period. Additionally, it also summarizes strategies to combat the setbacks posed by SARS-CoV-2 infection.

An enormous global economic crisis was brought on by the COVID-19 epidemic, which first appeared in 2020. This paper analyzes the challenges standing in the way of an efficient recovery while also looking at the many economic effects. Severe economic contractions were first caused by widespread lockdowns and supply chain disruptions, mainly impacting the services, tourism, and hospitality industries. Fiscal and monetary measures were swiftly implemented by governments and central banks to lessen the effects, but a number of barriers to recovery have persisted.

In this research, several obstacles are outlined, such as unequal vaccination coverage, enduring health fears, and uneven economic recovery rates. The public's uneven adherence to safety measures and inconsistent worldwide response coordination have added to ongoing uncertainty. The pandemic has also highlighted pre-existing disparities and the need for extensive policy changes. In order to provide fair access to vaccines, the report promotes targeted aid for vulnerable sectors, investments in digital infrastructure, and international cooperation.

In conclusion, the COVID-19 outbreak highlighted weaknesses in the world's economies and prompted a reassessment of traditional economic paradigms. Despite continued recovery efforts, a number of challenges—from health issues to structural inequalities—remain in the way. Building a more robust and inclusive post-pandemic economy requires an integrated strategy that includes both short-term alleviation and long-term systemic improvements.

The therapeutic value of artificial intelligence (ML) in the diagnosis of viral illnesses has been illustrated by the outbreak of COVID-19. This chapter digs into the modern uses of Artificial Intelligence and Machine Learning (ML) algorithms for COVID-19 diagnosis, with a focus on chest imaging procedures like as CT and X-rays. Additionally, we explored ML's strengths, such as its capacity to analyze enormous datasets and detect patterns in medical imagery. But there are still issues to deal with, like the scarcity of data, privacy issues, and machine learning's incapacity to evaluate the severity of health conditions. However, several machine learning methods, such as decision trees, random forests, and convolutional neural networks, are reviewed in this research concerning COVID-19 diagnosis. Subsequently, we highlight the efficacy of several models in COVID-19 screening, such as XGBoost and Truncated Inception Net. Moreover, the chapter discusses potential strategies for machine learning in COVID-19 diagnosis, emphasizing the crucial role of collaboration among data scientists and healthcare experts. It is imperative to confront data bias and incorporate more comprehensive patient data than just chest imaging. All things considered, machine learning presents a potential pathway toward quick and precise COVID-19 diagnosis; nonetheless, conquering existing obstacles is necessary for ML to be widely used in healthcare institutions. 

The world has witnessed the most devastating pandemic due to the rapid spread of COVID-19, an infectious disease caused by severe acute respiratory syndrome coronavirus (SARS-CoV2 virus). The public health emergency of international concern arose due to the sudden outbreak of COVID-19 where both medical and socio-economic structures remain entirely altered not only in developed countries but also in developing countries. In this crucial scenario, advanced technologies like machine learning (ML) and deep learning (DL) assisted the researchers and helped governments and other health officials (including frontline workers) to manage the outbreak. ML is a sub-branch of computer science, where, machines can analyze large datasets and derive inference from that variable data structures. With the help of suitable algorithms, computers can imitate human behavior by analyzing results and the machines can perform in less time with great accuracy. During the pandemic, due to the scarcity of human resources, ML aided in the diagnosis of patients, forecasted communal transmission, and also helped in the development of effective antivirals and vaccines. In this chapter, we have highlighted the importance of various state-of-the-art ML tools, algorithms and computational models useful in the diagnosis and management of COVID-19. The circumstantial applications of ML are also discussed with real-time case studies. Lastly, the challenges faced by ML in COVID-19 supervision and future directions are also discussed. This chapter will help the researchers and students to understand how this powerful tool is employed to fight COVID-19 and can assist in future health emergencies due to emerging pathogens.

The ongoing battle against coronaviruses demands innovative approaches and cutting-edge technologies to enhance our ability to detect, prevent, and respond to outbreaks effectively. This chapter explores the forefront of advancements in robotics, drones, Genetic Engineering technologies, and nano-technology, presenting a comprehensive overview of their potential roles in shaping the future of pandemic management. By embracing these innovative solutions, we have paved the way to not only enhance our response capabilities during the current pandemic but also to establish a robust framework for tackling future viral threats.