Abstract:
Dongola strain is a lentogenic Newcastle disease virus. A series of selection procedures was carried out at 56?C to enhance heat resistance. The study was therefore conducted to determine the effect of serial passage on thermostability of the strain. The virus was passaged and at intervals samples were subjected to heat treatment by two methods; stepwise method in which the virus was exposed to increasing temperatures for 15min and extreme heat at 56?C for increasing time for 10 passages. After selection, recovered virions from the last passage were propagated and tested for thermostability. The results showed that extreme heat selection was better since infectivity titre of the 10th passages decreased by one logarithmic order within 15min of incubation at 56?C, while the titre decreased by two logarithmic orders in stepwise method.
