Publikationsdatenbank

Highly pathogenic H5N1 avian influenza virus epidemic in Egypt:
detection and protection studies (2012)

Art

Hochschulschrift

Autor

Abd El-Whab, El-Sayed Mohammed (WE 15)

Quelle

Berlin: Mensch und Buch Verlag, 2012 — 92 Seiten

ISBN: 978-3-86387-107-9

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/12282

Kontakt

Nutztierklinik: Abteilung Geflügel

Königsweg 63
14163 Berlin
+49 30 838 62676
gefluegelkrankheiten@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Poultry is the major source of animal protein in under-resourced countries. Introduction of highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 into such countries had a severe negative impact on the poultry industry and posed a serious threat to public health. Vaccination of poultry was used successfully to reduce the socioeconomic losses during the first wave of the disease in Egypt. However, vaccines as a sole tool to eradicate the HPAIV H5N1 are insufficient to delineate circulation of the virus in vaccinated birds, on the contrary replication of the virulent virus in presence of antibodies induced by the vaccine lead to increase in the mutation rate in genes, such as the hemagglutinin (HA). This is also had negative effects on the sensitivity of molecular diagnostic tools aiming at the HA gene. Second, passive transfer of maternal immunity through eggs to the newly hatched chicks could interfere with their vaccination in the early stage of life. In this study, to match the divergent Egyptian HPAI H5N1 viruses, we adapted primers and probes of the internationally recommended RT-qPCR assay targeting the H5 gene. As a result the sensitivity to detect the Egyptian variant and classical strains was dramatically increased. Furthermore, phylogenetic analyses of the H5 gene of the Egyptian viruses indicated that two major groups of H5N1 viruses are currently co-circulating in poultry in Egypt. We developed a versatile multiplex real time RT-PCR assay to detect all Egyptian HPAI H5N1 viruses and differentiate between the classic 2.2.1 group (isolated mainly from backyard birds and humans) and the genetic variant 2.2.1 group (isolated mainly from commercial vaccinated chickens). Furthermore, we showed that multiple dose vaccination of broiler breeder chickens with an inactivated H5N2 vaccine induced broad humoral immune responses against different antigens; yet, sufficient clinical protection against the newly emerging variant Egyptian HPAIV H5N1 was not induced. Moreover, we demonstrate that the virus is disseminated in and on eggs of infected vaccinated birds after challenge. H5N2 maternal derived immunity didn’t protect chicks challenged with the Egyptian variant HPAI H5N1 virus and interfered with vaccination of 3 days old chicks with homologous H5N2 vaccine. However, vaccine seeded with the recent Egyptian variant H5N1 strain was more highly effective. In countries with endemic status of HPAIV H5N1 in poultry, regular optimization and development of sensitive molecular diagnostics is a real challenge to ensure early detection and control of infected birds. Vaccination of poultry could be a part of a comprehensive control plan but biosecurity measures should be enforced rigorously. The vaccines should be re-evaluated according to their antigenic match with circulating field viruses. Eggs obtained from infected flocks should be considered as a risk factor for silent virus transmission. Maternal immunity could reduce the vaccine efficacy and should be considered when formulating vaccination regimes against HPAIV H5N1.