ABSTRACT
In Egypt, efforts to control highly pathogenic H5N1 avian influenza virus in poultry and in humans have failed despite increased biosecurity, quarantine, and vaccination at poultry farms. The ongoing circulation of HP H5N1 avian influenza in Egypt has caused >100 human infections and remains an unresolved threat to veterinary and public health. Here, we describe that the failure of commercially available H5 poultry vaccines in Egypt may be caused in part by the passive transfer of maternal H5N1 antibodies to chicks, inhibiting their immune response to vaccination. We propose that the induction of a protective immune response to H5N1 is suppressed for an extended period in young chickens. This issue, among others, must be resolved and additional steps must be taken before the outbreaks in Egypt can be controlled.
Subject(s)
Influenza A Virus, H5N1 Subtype/immunology , Influenza A Virus, H5N1 Subtype/pathogenicity , Influenza Vaccines/pharmacology , Influenza in Birds/prevention & control , Poultry Diseases/prevention & control , Animal Husbandry , Animals , Animals, Newborn , Antibodies, Viral/blood , Chickens , Cross Reactions , Disease Outbreaks/prevention & control , Disease Outbreaks/veterinary , Egypt/epidemiology , Female , Humans , Immunization, Passive , Influenza in Birds/epidemiology , Influenza in Birds/immunology , Influenza in Birds/transmission , Influenza, Human/epidemiology , Influenza, Human/immunology , Influenza, Human/prevention & control , Influenza, Human/transmission , Male , Poultry Diseases/immunology , Poultry Diseases/transmission , Yolk Sac/immunologyABSTRACT
The highly pathogenic influenza virus H5N1 that infected chickens in Egypt in 2006 was characterized at immunologic and molecular levels. Cloacal swabs from chicken were analyzed by rapid antigen detection and RT-PCR using H5- and N1-specific primers, which confirmed the presence of an H5N1 influenza virus in infected chickens. Sequencing results revealed 100% homology of both genes with previously published sequences of H5N1 isolates from Egypt and the Middle East. The virus was isolated and propagated in MDBK cells in culture. Host cells showed a substantial cytopathic effect within 2 days of infection, which increased dramatically by the fourth day. Plaque infectivity titers of virus harvested from cell culture were initially 10(5)PFUs/ml and increased to 10(8)PFUs/ml after two additional passages and ultrafiltration. Formaldehyde treatment completely inactivated the virus, and MDBK cells inoculated with the killed virus showed no cytopathic effect. Two days after chickens were immunized with the killed virus, their sera showed that the killed Egyptian isolate was highly immunogenic. Western blot analysis showed that sera had antibodies reacting to four viral peptides: hemagglutinin (61.5kDa), RNA-binding protein (56kDa), neuraminidase (50kDa), and 45-kDa protein. In a challenge infection, the vaccine protected immunized chickens from death and reduced viral shedding.
