Efficacy Of A Bivalent Newcastle Disease And lnfectious Bronchitis Vaccine Against A Challenge Of Genotype VIl Newcastle Disease Virus
SHEAU Wie Tan, RAHMAN Omar Abdul, YIP Karen, LEE Michael, LEMlERE Stephane
An increase in the incidence of velogenic viscerotropic Newcastle disease (ND) in Malaysia involving high morbidity and mortality even in routinely vaccinated flocks was observed beginning from 2009. The causative ND virus was identified to belong to the genotype VIl group. These raised doubts on the protection provided by current existing live ND vaccines against the prevalent genotype VIl field virus. This trial investigates the efficacy of a live bivalent ND and infectious bronchitis (lB) vaccine against the current genotype VIl field virus. The live vaccine (AVINEW strain) contained a strain of ND virus and H120 strain of lB virus. The ND live vaccine strain has bath enteric and respiratory tropisms in chickens. The challenge virus, NDV IBS002/2011, was isolated from an outbreak in Malaysia in 2011 and is classified as velogenic NDV with two pairs of basic amino-acids, lysine (K) or arginine (R), at the fusion (F) cleavage site at residues 112 to 113 and 115 to 116, as weil as a phenylalanine at residue 117 (GenBank accession no: JQ809695). The experimental design included 3 groups of SPF birds. One group of birds were bled and euthanized at day old for serological purposes. The second group was vaccinated at day old with a single dose of the vaccine via eye drop. The third group was left unvaccinated as positive contrais. At day 21, bath the groups were challenged via the intra-ocular route with 105 EID50 of the challenge virus. The birds were then monitored daily for clinical signs and mortality up to 10 days post-challenge. Only 1 out of 25 birds in the vaccinated group exhibited transient mild depression lasting for 3 days. This bird recovered at day 5 post challenge and remained clinically normal until the end of trial. No mortality was observed in the vaccinated group. ln contrast, ali the non-vaccinated control birds displayed severe depression starting from day 2 post challenge. 100% mortality was recorded by day 5 post challenge. Therefore, this trial shows that a bivalent vaccine (ND and lB H120) provided good heterologous protection against a velogenic genotype VIl challenge.
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