Abstract

Newcastle disease virus (NDV) causes major losses in the poultry industry and is regarded as endemic in many parts of Africa. Differences in virulence of the virus occur and during any disease outbreak, determining virulence is essential for effectively controlling the disease. The virulence of the virus is dependent on cleavage of the fusion site and is characterised by different sequences in the genome. Thus a reliable and rapid method to determine virulence is to sequence the fusion site. The alternative method is to do a conventional mean death time (MDT) study, which is time consuming. Furthermore, the molecular techniques required for the sequencing of the fusion glycoprotein are not within reach of many regional laboratories in developing countries, where NDV is a serious problem. Thus a simple method is described in which the virulence of a NDV field virus can be determined, using conventional MDT methods, more rapidly. In this study viral samples were treated with 0.25% trypsin free of EDTA, and the MDT was compared to untreated control samples. Results indicate that if the viral isolate is lentogenic in nature, and treated with 0.25% trypsin it caused mortalities in eggs within 70 h post inoculation, whereas control samples resulted in mortalities from 96 h. By using this technique, the time to identify lentogenic isolates is substantially reduced.

Key words: Newcastle disease virus, rapid diagnosis, mean death time, fusion site, trypsin, pathogenicity, virulence.