Antigenic content of 500 HA units in H5N1 reassortant AI vaccine enhances protection and reduces shedding of HPAI H5N1 clade 2.2.1.2 in broiler chickens
Antigenic content of 500 HA units in H5N1 reassortant AI vaccine enhances protection and reduces shedding of HPAI H5N1 clade 2.2.1.2 in broiler chickens
Hussein A. Hussein, Maha Khedr, Reem A. Suliman, Marwa F. Mohamed, Mounir D. El
Safty
ABSTRACT
Background: Egyptian poultry industry has suffered from high economic losses as a result of the wide
spread of highly pathogenic H5N1. Determination of the optimal antigen content of avian influenza virus
vaccines is urgent to reach protective antibody titers and reduce virus shedding.
Methods: Groups of one-day old commercial broiler chicks were divided in to 8 groups 1, 2 and 3 were
vaccinated with a prepared vaccine contain 500HAU of H5N1 reassortant antigen; while group 4, 5 and 6
were vaccinated with an imported reassortant vaccine with 500HAU antigen content of H5N1 at 1, 5 and 10
days of age; respectively. A group 7 was positive challenged control and group 8 negative challenged
groups. All chicken groups were maintained at isolators along the experiment study. Blood samples were
collected for weekly for 4 weeks and antibody titers were determined by HI test. All vaccinated groups
were challenged 4 weeks post vaccination and tracheal and cloacal swabs were taken at 3, 5, 7, and 10 days
post challenge and tested by real time RT-PCR (rRT-PCR) and virus isolation and titration in SPF ECE.
Results: Results of HI demonstrated significant difference between groups in relation to age of vaccination,
where the groups vaccinated at 10 days of age were significantly higher compared to others with maximum
titers at 4 weeks post vaccination. The protection % post challenge revealed 0, 20, 86 % and 0, 20 and 86 %
in groups 1, 2, 3 and groups 4, 5, and 6; respectively. Results of rRT-PCR and virus isolation revealed that
all chicken groups vaccinated at 1 and 5 days of age revealed 100% shedding at 3rd, 5th, 7th and 10th days
post challenge. However, groups 3 and 6 which were vaccinated at 10 days of age demonstrated different
shedding pattern where group 3 (vaccinated with local prepared 500HAU vaccine) showed at the 3rd and
5th days shedding by rRT-PCR and 80% and 20 % of the chickens in tracheal swabs and 80% and 40% in
cloacal swabs when tested by virus isolation in eggs at 3 and 5 days post challenge; respectively. Whereas
swabs of 7 and 10 days post challenge of group 3 were negative by rRT-PCR and virus isolation. On the
other hand, group 6 (vaccinated with imported 500HAU vaccine) demonstrated shedding % at 3 and 5 days
post challenge by rRT-PCR and for virus isolation were positive in 60% for tracheal swabs 3 day post
challenge and no shedding at 5th post challenge and 60% and 20% for cloacal swabs; respectively. At 7th
and 10th days post challenge shedding of all chickens in group 6 were negative by both rRT-PCR and virus
isolation.
Conclusion: Vaccination against H5N1 AIV is greatly affected by both antigen content of vaccine and level
of maternal immunity in vaccinated chicks.
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July 2018
Vol. 4, Pages 1-71
