Submitted to: American Association of Avian Pathologists
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2005
Publication Date: 7/15/2005
Citation: Cruz-Coy, J.S., Pritchard, N., Suarez, D.L., Swayne, D.E., Bublot, M. 2005. Efficacy of avian influenza-fowl pox vaccines, live fowl pox vector, h7 subtype, administered to one-day-old spf chickens [abstract]. American Association of Avian Pathologists. p.29.
Technical Abstract: The purpose of the study was to determine whether recombinant avian influenza-fowl pox (FP) experimental vaccines, expressing genes (HA, M1 and/or NA) from the three different H7 avian influenza lineages (Eurasian, American and Australian), were able to protect against a highly pathogenic (HP) Avian Influenza (AI) Eurasian challenge. One-day-old SPF chickens (10 birds per group) were vaccinated by the subcutaneous (SQ) route with 103.0 TCID50 of FP recombinant and challenged intranasally three weeks later with 106.0 EID50 of the Eurasian HP AI H7N1 isolate A/Turkey/Italy/ 4580/99. All control birds vaccinated with the parental FP died 2 or 3 days after challenge. The three FP recombinants expressing the HA (with or without M1) gene(s) from the Eurasian H7N1 A/Turkey/Italy/4426/00 isolate provided 80-90% protection against morbidity and mortality. In contrast, only 20% protection were induced by FP expressing the HA gene from an Australian (H7N7 A/Chicken/Victoria/1/85) or an American isolate (H7N2 A/Turkey/Virginia/66/02). Similar level of protection (10-20%) were also induced by a FP recombinant expressing the neuraminidase (NA) gene from the Eurasian H7N1 A/Turkey/Italy/ 4426/00 isolate or by a combination of FP expressing HA (Australian lineage) or NA (Eurasian lineage). The mean time to death was delayed in all vaccinated groups compared to the controls. Pre-challenge Hemagglutination Inhibition (HI) Geometric Mean Titers (GMT's) had a range of 5 to 11, when the Eurasian strain A/Turkey/Italy/3283/99 was used as the antigen. GMT's lower than 8 were considered negative. Post-challenge HI GMT's had a range of 128 to 2048. Oral and cloacal viral isolations of the HP AI challenge were taken from the birds in the groups that showed good protection (80-90%) and the challenge control group. Vaccination reduced significantly the virus load in oral (from 106.7 EID50 to 102.1-2.7 EID50 per ml) and in cloacal swabs (from 103.5 EID50 to 101.1-1.3 EID50 per ml) compared to the challenged controls. Altogether, these results indicate that acceptable levels of protection against the Eurasian HP AI H7N1 challenge could be achieved only when FP recombinants were expressing an homologous Eurasian HA gene. Protection was not improved by addition of the M1 gene. Heterologous (Australian or American) HA genes induced a poor protection which was similar to that induced by the homologous NA gene. Furthermore, mixing heterologous HA with homologous NA did not improve protection.