Introduction
Viruses have extraordinary host specificity and generally remain within the boundary of a kingdom of living species and based on this feature, viruses are known by their broad host range like animal virus, bacterial virus, human virus, plant virus etc. The genetic material of the viruses is small and is highly prone to rapid changes during their parasitic life process. The changes in the nucleotide sequence alter their mode of persistence in the living host cells. In a rare instance, the changes are so appropriate that enable a virus to overcome the species barrier and jump from one kingdom to another. The interkingdom host switching is known in case of circovirus infecting vertebrates like bird, chimpanzee, dog, fish, human and pig. The molecular evidence shows that the circovirus has originated from a plant virus, nanovirus [7]. It appears that switching host of nanovirus to animal and then recombination with a RNA virus, (calicivirus) in animal resulted in emergence of circovirus in animal. After switching to a novel host, virus adapts through mutation and or recombination for successful proliferation within and between the cells as well as for successful subsequent transmission to healthy individuals of the same species. This sequence of events results in to origin, evolution and emergence of new viruses [10]. There are past instances of interspecies transmission of virus from animal to human that resulted in outbreak of zoonotic viral diseases in human eg., human immunodeficiency virus from chimpanzees [12], H1N1 type influenza A virus from birds (Spanish flu) [14], Nipah virus from fruit bat/pig [2] and measles virus from cattle [6]. Coronavirus from bat or other intermediate animals is the latest episode of zoonotic disease that soon turned pandemic. At present, the fear of coronavirus looms everywhere in the world resulting locked down in human society.