These do not have a cell structure with a nucleus like bacteria and are simpler and much smaller. Unlike living organisms, viruses are not able to take in food, get rid of waste, or reproduce by themselves. They direct their host cell to do their reproduction for them and, in doing so, the host cell can be destroyed. The virus attaches itself to the host cell and injects its genetic material, which forces the cell to produce more viruses. Different viruses have the ability to infect plants, animals, and bacteria. They are very specialized in that they can only infect specific hosts and only certain cells within that host. The host’s immune system typically keeps viruses at bay. When they infect humans, the viruses are considered pathogens. Person-to-person contact is the most usual way in which viral infections are transmitted. Viruses found in water include Hepatitis A and E, and Poliovirus. They can be inactivated by disinfection.