Oncolytic viruses are viruses that preferably infect cancer cells. Bacteriophages are viruses that infect bacteria and archaea. Viruses infect host cells and reproduce inside them. They mostly infect other primates, but humans can be infected. H3N2 viruses can infect birds and mammals. Both these viruses infect amoebas specifically. Bacteriophages are viruses that infect and replicate within a bacterium. Bacteriophages are the viruses that infect and replicate in bacteria. The virophages are a group of viruses that infect other viruses. These viruses likely infect single-celled eukaryotes. One possibility is that the virus does not infect human cells directly. There is no evidence that this virus can infect humans. Another group of viruses that infect fish has been described. Gregarines infect the gut and may cause blockage and secondary infection. Apart from humans, the bacteria can also infect primates.