How do viruses cause infections in organisms?
Infection means the invasion and multiplication of an organism my a pathogen like a virus, bacteria, fungus, or a parasite.This includes the transmission of the pathogen from a source to the organism.
Transmission, invasion and multiplication are three essential stages for infection to take place.
Each of these stages can be done through different mechanisms depending on the type of the pathogen including viruses.
Transmission can be through aerosol, direct contact, using the same sharp tool, blood transfusion, saliva, and wounds.
invasion means getting into the body systems then to the cells and this means overcoming the immune defense in the body. Viruses usually get inside the cells via endocytosis.
Multiplication for viruses is done by using the cell protein synthesis machine and the genetic material to produce more viruses. These new viruses leave the cell via exocytosis to go invade new cells and repeat the process.
Of course they damage the first cell when they go out as it raptures, and they go out in bigger numbers so more and more cells are damaged later on.