Avian influenza A virus (AIV) is a member of the Orthomyxoviridae family and can be classified according to the antigenicity of its surface proteins haemagglutinin (H) and neuraminidase (N), and on the basis of its pathogenicity in chicken. Highly pathogenic avian influenza (HPAI), an acute generalised disease in which mortality may be as high as 100%, is restricted to subtype H5 and H7, although not all viruses of these subtypes necessarily cause HPAI. Over the last three years outbreaks of HPAI have also occurred in Europe. Zoo animals, esp. birds are at risk through importation of birds, inflying wild birds or whole prey feeds (e.g. chicken). Vaccination against HPAI has repeatedly been advocated and tested as a preventive measure. From the current literature it becomes obvious that there is a need for further data on the effect of HPAI vaccine in bird species other than chicken and turkey. Of special interest are seroconversion, and duration and persistence of titres in relation to the second vaccine, and modified dosages in very large birds such as ratites.
The proposed study involves avian collections from the Zoological Gardens of Basel, Berne, Goldau and Zurich (ZooSchweiz). A maximum of 488 birds are intended to be vaccinated with the Nobilis Influenza H5N2 (Intervet, Boxmeer, NL), an inactivated vaccine with the strain A/chicken/Mexico/232/94/CPA with liquid paraffin adjuvant. Vaccination will be carried out by veterinarians at the respective zoos. Dosages will be 0.25 ml for birds with a body weight < 1.5 kg, 0.5 ml for birds between 1.5 and 20 kg body weight, and 1 ml for birds > 20 kg body weight. The vaccine will be injected s.c. A second vaccination will be given after 5 weeks. From every species vaccinated, 10% or a minimum of 5 birds will be sampled for antibody measurement on day 0, after 5 weeks, 10 weeks and 26 weeks. Cloacal swabs will be collected on day 0 and after 26 weeks for antigen determination by a real time RT-PCR against the matrix gene of Avian Influenza.
The proposed study is aimed to improve our understanding on the dynamics of avian influenza and to increase the scientific evidence needed to make the decision if vaccination may be a viable control measure in the face of a HPAI outbreak - a question which will continue to be of importance considering the current epizootics of HPAI in Southeast Asia and its threat for transmission to the human population. Furthermore the involved zoos see this vaccination trial as a measure to protect selected avian species from complete eradication measures should a positive case occur.
