Title: An in-depth review of NDV, including epidemiology and molecular diagnostics Author
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 15, 2012
Publication Date: N/A
Technical Abstract: Birds infected with virulent strains of avian paramyxovirus serotype 1 (APMV-1), also known as Newcastle disease virus (NDV), and pigeon PMV-1 (PPMV-1)are defined as having Newcastle disease (ND), which in the United States is sometimes called Exoctic Newcastle disease (END). Infections with virulent forms of the virus (vNDV) are reportable to regulatory agencies because of the potential of rapid spread and devastating losses. ND in poultry impacts international trade. Newcastle disease viruses of low virulence (loNDV) cause infections that have mild or inapparent clinical signs,unless exacerbated by complicating infections. Virus shed from respiratory and intestinal tract of infected birds is transmitted by aerosol and/or ingestion. Species and the breed of the infected host have some affect on clinical disease observed. Chickens are most the most susceptible species, turkeys more resistant, and generally waterfowl are believed to be quite resistant although there were severe outbreaks of ND in geese in Israel and China. Gross lesions are usually unremarkable except in birds infected with viscerotropic velogenic viruses which may have eyelid edema, perithymic hemorrhage and occasionally edema, splenic necrosis, and necrohemorrhagic lesions localized at the sites of lymphoid aggregation. The primary lesions of neurotropic velogenic ND are neuronal degeneration and variable disruption of heartmuscle. Gross lesions of the viscerotropic strains are similar to lesions of highly pathogenic avian influenza and are only suggestive of a possible diagnosis. Definitive diagnosis requires virus isolation, most often from oropharyngeal and/or cloacal swabs from live birds, or tissue samples from necropsied birds. Detection of hemagglutination in culture fluids and inhibition of that hemagglutination with NDV specific antiserum confirms the diagnosis of an APMV-1 infection. Characterization of the virulence of an isolate usually requires chicken inoculation but a presumptive indication of virulence potential may be accomplished by noting the time to death of inoculated embryos (more rapid death usually indicates a more virulent virus) and by determining the deduced amino acid sequence of the fusion protein cleavage site from nucleotide sequence analysis of reverse transcriptase polymerase chain reaction (RT-PCR)product of fusion gene. Real time RT-PCR procedures were developed and validated to detect most NDV strains and within that broad grouping the END virus in swab samples during the outbreak in California. Biosecurity is a critical component of any disease control program even when there are efficacious vaccines available as is the case with ND. A complete program includes for example limiting visitors to any production facility, rodent and free-flying bird control to prevent entry into bird housing, preventing feed contamination, and avoiding use of shared equipment as well as use of vaccines where appropriate and providing surveillance for all diseases of concern. Low virulence strains of NDV, B1, La Sota and VG/GA, are used in live vaccines and in the preparation of inactivated whole virus vaccines prepared as oil emulsions. Both live and inactivated vaccines are used widely in chicken and turkey flocks. These vaccines are protective against disease but not against infection therefore use of vaccines in flocks exposed to virulent challenge can make it more difficult to detect virulent infections. Vaccine use also prevents the use of serum as in indication of ND infection. A rent analysis of NDV isolates groups known strains into two classes with one of the classes being further broken down into XV genotypes (ten of which were previously defined). An in-depth review of NDV, including epidemiology and molecular diagnostics will be presented.