ABSTRACT
Infectious diseases remain important causes of human and animal morbidity and mortality, leading to widespread outbreaks and epidemics. For the past several decades, we have seen new emerging viruses causing them, which have also led to several epidemics due to respiratory infections, most of which have occurred in animals. Acute respiratory viral diseases claim more than four million deaths and millions of hospitalizations in developing countries every year. The emerging virus category includes the severe acute respiratory syndrome coronavirus (SARS-CoV), the Middle East respiratory syndrome coronavirus (MERS-CoV) and pandemic influenza A (H1N1) and avian influenza (AI) viruses. One of these, known as Ribonucleic Acid (RNA) virus, is more pathogenic as most people have no herd immunity. RNA viruses can adapt to rapidly changing global and local environments due to the high error rate of their polymerase replicating their genome. These viruses spread infections with epidemic or pandemic potential present a persistent threat to public health and a huge burden on healthcare services in the global region. In addition, their emerging infections have seriously threatened global health and the economy. Currently, Novel Coronavirus Disease 2019 (COVID-19) has emerged as a serious infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This virus first identified on December 30, 2019, as a report indicating a cluster of patients with pneumonia of unknown etiology in Wuhan City, Hubei Province, China. In this chapter, we will study the emergence and recurrence of respiratory viral infections up to SARS-CoV-2.
