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==Description==

==Description==

Newcastle disease virus is the causative agent of Newcastle Disease, an acute viral disease of domestic poultry and many other bird species that is usually fatal.

Newcastle disease virus (NDV) is the causative agent of Newcastle Disease, an acute viral disease of domestic poultry and many other bird species that is usually fatal. It is characterised primarily by respiratory disease but neurological and gastrointestinal signs may also be a feature of Newcastle Disease.  Virulent strains of the virus are endemic in most of Asia, Africa and South, Central and North America. Hosts of the virus include gallinaceous birds, pigeons, parrots and finches and the disease may be carried subclinically by ducks and ostriches.

==Transmission==

==Transmission==

==Clinical signs==

==Clinical signs==

NDV affects the gastrointestinal, respiratory and nervous systems and clinical signs reflect the system(s) affected. Clinical signs are usually acute and may appear throughout the flock within 2-12 days. Respiratory signs may include dyspnoea, sneezing, nasal discharge and coughing and are common with low virulence infections.

NDV affects the gastrointestinal, respiratory and nervous systems and clinical signs reflect the system(s) affected. Clinical signs are usually acute and may appear throughout the flock within 2-12 days. Respiratory signs may include dyspnoea, sneezing, nasal discharge and coughing and are common with low virulence infections. Neurological signs such as tremors, paralysis, circling and depression may accompany respiratory signs and are often seen in cormorants and exotic bird species. Pigeons frequently display neurological signs accompanied by diarrhoea.

[[Image:Newcastle Disease.jpg|150px|thumb|right|''Newcastle Disease'' <br> L. Mahin, Wikimedia Commons]]

[[Image:Newcastle Disease.jpg|150px|thumb|right|''Newcastle Disease'' <br> L. Mahin, Wikimedia Commons]]

==Pathogenesis==

==Pathogenesis==