Evaluation of a Vaccination Program Against Avian Influenza in Three Danish Zoos: Serologic Response to Vaccination with an Inactivated H5N9 Vaccine
Abstract
Avian influenza (AI, Influenzavirus A, Orthomyxoviridae) is a highly contagious disease of poultry, which may infect most, if not all, bird species. Between October 2005 and July 2006, highly pathogenic (HP) AIV of subtype H5N1 spread in wild birds and poultry in Europe. Within the EU, AI is a notifiable disease normally handled by culling.1 Vaccination of birds is generally not allowed, but based on a desire to protect genetically unique populations, an emergency vaccination permission was issued in the spring of 2006.2 In Denmark, an inactivated H5N9 AI vaccine (Gallimune Flu H5N9, Merial) designated for domestic poultry3 was used.
Five hundred and forty birds in three zoos were vaccinated twice with a 6-wk interval. Vaccine doses were based on body weight (1–99 g: 0.1 ml; 100–2999 g: 0.3 ml; 3 kg–20 kg: 0.6 ml; >20 kg: 1 ml), and were administered subcutaneously. All individuals were blood sampled 4–6 wk following the second administration. To evaluate the humoral response to vaccination, H5-antibody titers were determined in a hemagglutination inhibition test (HI) following EU guidelines.1 Geometric mean titer (GMT), seroconversion rate (SR), and protection rate (PR) were calculated. Undetectable titers (<16) were regarded as 4 for the calculation of GMT.
The GMT following vaccination varied greatly among species, ranging from 5 in cockatiels (Nymphicus hollandicus, n=29) to 2195 in Amazon parrots (Amazona spp., n=10). Overall GMT was 137. 84% of the birds seroconverted, and the PR was 76%. No side effects related to vaccine administration or blood sampling were observed.
Significant differences in post-vaccination titers were observed among and indeed within orders, and species-specific data appears to be the clinically relevant parameter rather than values based on higher taxonomic classification.
In the current investigation, penguins, pelicans, ducks, geese, herons, Guinea fowl, cranes, cockatiels, lovebirds, and barbets showed very poor response to vaccination, while very high titers and seroconversion rates were seen in flamingos, ibis, rheas, Congo peafowl, black-winged stilts, Amazon parrots, and kookaburras.
The overall PR and GMT reported here are similar to the response reported following the administration of inactivated H7N14 and H5N25,6 vaccines to various zoo birds. However, the marked species differences in serologic response make such comparisons dubious, as mean results are likely to reflect the composition of collections more than the immunogenicity of the vaccines in question.
Acknowledgments
The authors thank Helle Flaga, Eddie Bach, Henrik Futtrup, Brian Zacho, Janus Hansen, Jesper Nielsen, Julie Bertelsen, Mille Krambeck Hansen, Kirstin Anderson Hansen, Kamilla Westarp Zornhagen, Stine Nielsen, Lidija Vestergaard, Kirsten Brock, Hans Åge Hjeresen, Frands Carlsen, Louise Fisker, and Francesco Prandini.
Literature Cited
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2. Commission Decision 2005/744/EC of 21 October 2005 laying down the requirements for the prevention of highly pathogenic avian influenza caused by influenza A virus of subtype H5N1 in susceptible birds kept in zoos in the Member States. Official Journal of the European Commission, L279, Pp. 75–78.
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