Virus infections

Viruses spread in several ways viruses in plants are often transmitted from plant to plant through insects which feed on plant sap like as aphids viruses in animals can be carried through blood-sucking bacteria. These disease-bearing organisms are known as vectors. Influenza viruses are spread through sneezing and coughing. Rotavirus and Norovirus, general causes of viral gastroenteritis, are transmitted through the faecal–oral route and are passed from person to person through contact, entering the body in food or water. HIV is one of various viruses transmitted by sexual contact and through exposure to infected blood. The range of host cells in which a virus can infect is called its host range. This can be narrow or as when a virus is capable of infecting several species wide.

Viral infections in animals provoke an immune response which commonly eliminates the infecting virus. Immune responses can be produced through vaccines that confer an artificially acquired immunity to the exact viral infection. Moreover, some viruses involving those which cause AIDS and viral hepatitis evade these immune responses and result in chronic infections. Antibiotics have no effect on viruses, but various antiviral drugs have been established.