can cause infectious diseases like flu, common cold and warts, and severe like HIV/AIDS, Ebola and smallpox. Immune system fights against the infection, and the failure to kill the infectious agent can cause several diseases. Viral fever is caused by , and viruses are small infectious agents. Bacterial and have many things in common. Viruses can only survive with a host. The infection type is identified by tests like stool/blood/urine for culture test and it can be identified under the microscope.