One can not generalize this that easy. Because virus co-evolves together with its host at a very specific manner. I am working on the following area so giving example in the same: HIV need CD4 and CXCR4/CCR5 receptors to infect T-cells (of human). when these receptors are missing (example B cells) HIV wont infect those cell types. So the infection of a particular virus to enter its host cell requires specific receptors!
Once it enter the cell, the virus face restriction factors(proteins fight against virus), so virus need to have or evolve counteraction, otherwise it will not be able to replicate. Same HIV example, it has Vif protein to fight against APOBECs of human T cells. Unfortuantely APOBEC of B cell will kill HIV rapidly irrespective of vif presence, hence HIV avoid infecting B cells.
Inside a host cell.
They are active only when they are inside a living host cell.
Viruses are cellular parasites.
host cells!
Viruses are small infectious agents that can only replicate inside living cells of organisms. They consist of genetic material (DNA or RNA) enclosed in a protein coat. Viruses can cause a wide range of diseases in humans, plants, and animals.
Viruses van cause diesease and so can bacteria they are both microscopic they can evolve they have DNA they can reporduce (even though viruses can only reporduce in a cell) they are passed through the air They have both caused plagues
Viruses can affect animals, and some viruses can affect plants.
There are currently 20 families of viruses that infect humans. There are two additional viruses (Hepatitis D and Hepatitis E) which have not yet been assigned to a families but are clearly distinct from the other families infecting humans. Viruses replicate inside cells by hijacking strands of RNA to duplicate themselves. See the related link for more details on viral diseases.
the virus is active when they are inside living things (host cell)
Virus's effect every living creature, including reptiles and fish!
Viruses are small infectious agents that can only replicate inside the cells of living organisms. They consist of genetic material (DNA or RNA) surrounded by a protein coat. Viruses can infect all types of life forms, from animals and plants to bacteria. They are responsible for a wide range of diseases in humans, animals, and plants.
viruses replicate inside respiratory cells.