Immunogenic potential of a thermostable Mesogenic Newcastle disease virus genotype xiii isolate from Assam

Abstract

Newcastle disease (ND) is a devastating viral disease affecting poultry and has a substantial economic impact on production because of the high morbidity and mortality rates. Only biosecurity measures and adequate vaccination can effectively reduce the economic threat posed by ND. To prevent ND outbreaks, many effective live vaccines are still routinely used. But the use of these vaccines, which are phylogenetically divergent and thermolabile, remains a constraint for controlling ND outbreaks. Therefore, addressing the need for a thermostable genotype-matched vaccine, the present study was undertaken to thermoadapt and attenuate a mesogenic (Genotype XIII) NDV isolate in Vero cells and evaluate its immunogenic potential in chickens. newlineIn the present study, the thermostability profile of the NDV isolates was assessed by subjecting them to various temperatures at different time intervals. Of the five NDV isolates, AS/KM/18/32 retained the highest thermal stability based on HA (Log2) titer and infectivity (Log TCID50/ml) at 560C for 30 minutes. The isolate was selected for thermoadaptation and attenuation in Vero cells. In the present study, the selected NDV isolate AS/KM/18/32 was adapted and attenuated in the Vero cells by serial passaging 50 times. The cytopathic effects (CPE) were observed from the 3rd passage onwards. At every 5th passage, the confirmation of adaptation of NDV isolates in Vero cells was done by performing RT-PCR targeting the F gene (363bp). The HA titer (Log2/50µl) and infectivity (Log TCID50/ml) of the NDV isolates increased with progressive passages up to the 50th passage (8.750 ± 0.250 and 9.15 log TCID50 /ml). Simultaneously, thermoadaptation of the AS/KM/18/32 was done by selective heat treatment by exposing the isolate to 560C for 30 minutes before each passage in Vero cells. After thermoadaptation, the NDV isolate AS/KM/18/32 was stable for 120 minutes at 400C and 15 minutes at 560C. The half-life of HA activity and infectivity of the isolate at 560C was 99.72 minutes and 100.92 minut