Rapid Reliable EID50 Determination for live Newcastle Disease Viruses and Vaccines

Abstract

Newcastle disease (ND) was first recognized more than nine decades ago and continues to be a problem for poultry producers besides being enzootic in many countries including Egypt. Diagnostic and ND virus/vaccine titration are core objects in virus evaluation. A rapid assay based on micro plate hemagglutination (HA) activity was applied to investigate its reliability as alternative method for virus titration. A comparative determination of EID50 /0.1ml was carried out via chicken embryo (CE) inoculation for 35 Newcastle disease virus (NDV) strains. They are previously identified by pathogenicity indices and revealed variable virulence (lentogenicmesogenic and velogenic). The data for both methods were analyzed using SPSS version 25. A Wilcoxon signed-rank test showed that HA titer method did not elicit a statistically significant change in median of reading Virus titer of samples with the median of standard embryonated chicken egg (ECE) method (Z = -0.197, p = 0.844). Spearman’s correlation coefficient (r= 0.42, p =0.01) showed a noteworthy moderate correlation between two methods. Heat map showed the differences between each pair of methods and the relationship between them. Bland-Altman plot revealed difference which fit normality distribution W=0.96, p=0.24. Accordingly, the use of HA activity assay for NDV/vaccine titration is a rapid easy and reliable, especially when needed for primary evaluation.