The avian response to Newcastle disease virus

Newcastle disease virus (NDV) is classified as a member of the superfamily Mononegavirales in the family Paramyxoviridae. This virus family is divided into two subfamilies, the Paramyxovirinae and the Pneumovirinae. In 1993 t he International Committee on the Taxonomy of Viruses rearranged the order of the Paramyxovirus genus and placed NDV within the Rubulavirus genus amon g the Paramyxovirinae. The enveloped virus has a negative sense single-stra nded RNA genome of 15,186 kb which codes for an RNA directed RNA polymerase , hemagglutinin-neuraminidase protein, fusion protein, matrix protein, phos phoprotein and nucleoprotein in the 5' to 3' direction. The virus has a wid e host range with most orders of birds reported to have been infected by ND V. Isolates are characterized by virulence in chickens and are categorized into three main pathotypes depending on severity of disease. Lentogenic iso lates are of low virulence while viruses of intermediate virulence are term ed mesogenic. Highly virulent viruses that cause high mortality in birds ar e termed neurotropic or viscerotropic velogenic. Velogenic NDV are List A p athogens that require reporting to the Office of International Epizootics a nd outbreaks result in strict trade embargoes. The primary molecular determ inant for NDV pathogenicity is the fusion protein cleavage site amino acid sequence. Vaccination for NDV is primarily by mass application of live-viru s vaccines among commercial poultry. Although protection is measured by pre sence of antibodies to NDV, vaccinated B-cell depleted chickens are resista nt to disease. Consequently, immune protection involves responses that are presently incompletely defined. (C) 2000 Elsevier Science Ltd. All rights r eserved.