Protecting Livestock. Improving Human Lives

Newcastle disease vaccine virus I-2 fails to acquire virulence during repeated passage in vivo.

Author: Bisschop SPR, Peters A, Domingue G, Pearce MC, Verwey J, Poolman P

Year: 2021

About this Publication:

We determined if naturally attenuated, thermotolerant Newcastle disease vaccine virus I-2 could acquire virulence after five in vivo passages through SPF chickens. Compliant with international requirements including Ph EU, v9.0 04/2013:0450, 2013, I-2 working seed (WS) was compared with 5X-passaged I-2 WS (5XP-WS) using intracerebral pathogenicity index (ICPI), F0 cleavage site sequencing and safety tests. The first passage which used a 50% brain: 50% tracheal tissue challenge homogenate was unsuccessful; I-2 was not detected after the fourth passage. The second passage used 10% brain: 90% tracheal tissue homogenates; I-2 was isolated from tracheal tissue in each passage but harvested titres were below the minimum challenge (107 EID50) specified for ICPI and safety tests. Given this, the WS and 5XP-WS comparisons proceeded. ICPI values were 0.104 and 0.073 for the WS group and the 5XP-WS group respectively confirming that I-2, passaged or not, expressed low pathogenicity. F0 amino-acid sequences for both WS and 5XP-WS were 112R-K-Q-G-R-?-L-I-G119 and compatible with avirulent ND viruses. In safety tests, no abnormal clinical signs were observed in either group except for two chicks in the 5XP-WS group: one bird was withdrawn due to a vent prolapse; the other died with inconclusive necropsy results. These data, low passage titres with little or no virus isolation from brain tissues and the genomic copy approach suggest a need to amend Ph. Eur. v9.0 04/2013:0450, 2013 for naturally attenuated, low pathogenicity vaccine viruses such as I-2. These results demonstrate that Newcastle Disease vaccine virus I-2 is safe for use.

Grant: VITAL

Subject Areas: Research and Development

Diseases: Newcastle Disease



Newcastle, Vaccine, passage, virulence, virus

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