Emerging and reemerging respiratory viral infections up to Covid-19.

Infectious diseases remain as the significant causes of human and animal morbidity and mortality, leading to extensive outbreaks and epidemics. Acute respiratory viral diseases claim over 4 million deaths and cause millions of hospitalizations in developing countries every year. Emerging viruses, especially the RNA viruses, are more pathogenic since most people have no herd immunity. The RNA viruses can adapt to the rapidly changing global and local environment due to the high error rate of their polymerases that replicate their genomes. Currently, coronavirus disease 2019 (COVID-19) is determined as an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which was first identified in 2019 in Wuhan. Herein we discuss emerging and reemerging respiratory viral infections till to SARS-CoV-2.