title: The effect of age on the pathogenesis of a highly pathogenic avian influenza (HPAI) H5N1 virus in Pekin ducks (Anas platyrhynchos) infected experimentally.
abstract: BACKGROUND
  Highly pathogenic avian influenza (HPAI) H5N1 viruses have recently displayed increased virulence for wild waterfowl.
  
  
  OBJECTIVE
  To study the effect of host age on the shedding and tissue dissemination of a HPAI H5N1 virus in infected Pekin ducks.
  
  
  METHODS
  Pekin ducks in two age-matched groups (n = 18), 8 and 12 weeks old (wo) were each infected with 10(6) EID(50)/0.1 ml of HPAI A/turkey/Turkey/1/05 (H5N1, clade 2.2). Each day for 5 days, birds were monitored clinically, and cloacal and oropharyngeal swabs collected, before three birds from each group were selected randomly for post-mortem examination. Tissue samples were collected for examination by real-time RT-PCR, histopathology and immunohistochemistry (IHC).
  
  
  RESULTS
  Severe clinical signs, including incoordination and torticollis were observed in the 8 wo group resulting in 100% mortality by 4 dpi. Mild clinical signs were observed in the 12 wo group with no mortality. Real-time RT-PCR and IHC results demonstrated the systemic spread of H5N1 virus in birds of both age groups. Higher levels of virus shedding were detected in oropharyngeal swabs than in cloacal swabs, with similar levels of shedding detected in both age groups. Variations in level and temporal dissemination of virus within tissues of older ducks, and the presence of the virus in brain and heart were observed, which coincided with the appearance of clinical signs preceding death in younger birds.
  
  
  CONCLUSIONS
  These results are consistent with reports of natural infections of wild waterfowl and poultry possibly indicating an age-related association with dissemination and clinical outcome in ducks following infection with H5N1 HPAI virus.
authors.affiliation: Veterinary Laboratories Agency-Weybridge, Addlestone, Surrey KT15 3NB, UK.
authors.forename: Brandon Z
authors.initials: BZ
authors.lastname: Löndt
authors.forename: Alejandro
authors.initials: A
authors.lastname: Núñez
authors.forename: Jill
authors.initials: J
authors.lastname: Banks
authors.forename: Dennis J
authors.initials: DJ
authors.lastname: Alexander
authors.forename: Christine
authors.initials: C
authors.lastname: Russell
authors.forename: Angela C
authors.initials: AC
authors.lastname: Richard-Löndt
authors.forename: Ian H
authors.initials: IH
authors.lastname: Brown
mesh_terms: D000367:Age Factors; D000818:Animals; D004372:Ducks / Q000821:virology*; D053124:Influenza A Virus, H5N1 Subtype / Q000302:isolation & purification / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000473:pathology / Q000821:virology*; D014774:Virulence; D017201:Virus Shedding