Infectious viral diseases are the never-ending challenge that can emerge or re-emerge in unpredictable regions and at unpredictable times. Human beings are facing an intractable problem in unexpected time and place due to these viral diseases. Human, ecological, and viral related factors are the contributing factors in the emergence or re-emergence of viral infectious disease. Travel, mass gathering, urbanization, fragile or deteriorated health systems, weak disease surveillance system, limited laboratory diagnostic capacity, war, migration, poor hygienic practice, illegal animal trade, hunting and eating infected animals are among human-related factors that contribute in emergence or re-emergence of viral infectious disease. Deforestation, climate change, invasion of animal habitats, the building of dams and intensive agricultural practice are contributing factors to the emergence or re-emergence of viral infectious disease. The last but not least risk factor for emergence or re-emergence of infectious viral disease is the virus-related factors. RNA viruses are deadly pathogens since they are evolving rapidly in any hostile conditions and exhibit error-prone gene replication. Mutation, reassortment, and recombination attributed to high evolution rate. Among many RNA viruses, coronaviruses are enveloped, helical with large, positive sense, single-stranded RNA genome, and contain clubshaped surface proteins called spikes. Among many coronaviruses, the current emerged coronavirus disease-19 (COVID-19) can be considered as an "inferno" which aims to damage human beings irrespective of wealth, educational status, color, race, gender, religion, and class. This newly emerged virus has a detrimental impact on the economy, health, tourism, social interaction, education, religion, labor, markets, transportation, and human freedom, and in general, every sector is disrupted by COVID-19. Therefore, the aim of this review article is to provide an overview of emerging and re-emerging viral diseases, contributing factors, and a brief overview is also given to coronaviruses with especial emphasis to COVID-19.
