A viral infection that affects the digestive, intestinal, and respiratory tracts and the neurological system of birds. The causative agent is an enveloped ribonucleic acid (RNA) virus that is classified as a paramyxovirus. Paramyxovirus

Newcastle disease occurs in five forms based on a virulence in chickens ranging from inapparent infection to severe disease and death. Viscerotropic-velogenic Newcastle disease causes a very severe infection, producing hemorrhagic lesions in the intestinal tract and high mortality. The neurotropic-velogenic type is also highly lethal and produces neurologic and respiratory signs in infected birds. The mesogenic form causes an acute respiratory or neurologic infection that may be lethal only in young birds. The lentogenic type is a mild or inapparent respiratory infection of chickens. The last group includes the viruses causing inapparent or asymptomatic infections of the digestive tract.

The wide susceptibility of avian species to infection with Newcastle disease has complicated control. Newcastle disease is spread worldwide by the international transportation of live birds disseminating the virus. Control of and protection from Newcastle disease can be achieved by the correct use of vaccines. Lentogenic and some mesogenic strains are used to produce vaccines that can be administered by aerosol, intranasal drops, or intramuscular injection, or as an additive to the drinking water. Animal virus