title: Influenza surveillance on 'foie gras' duck farms in Bulgaria, 2008-2012.
abstract: OBJECTIVE
  Ducks can shed and spread influenza A viruses (IAVs) while showing no disease signs. Our objective was to clarify the role of 'foie gras' ducks in the circulation of IAVs in Bulgaria.
  
  
  METHODS
  Monthly avian influenza surveillance was conducted on 63 'foie gras' duck farms, 52 of which were surveyed throughout the study between November 2008 and April 2012. Virologic and serologic samples were collected and tested. During this time, wild bird samples were collected at major wild bird-resting areas near the Black Sea coast and Danube River.
  
  
  RESULTS
  The study showed high isolation frequency of low-pathogenicity avian influenza viruses. In the raising population (<75 days old), subtypes H3, H4, and H6 were detected monthly and H5 LPAIV, sporadically. Different subtypes (H1, H10, H11) were isolated from the fattening premises (75- to 100-day-old ducks), suggesting different routes of introduction. Only 6 of the 52 farms that were surveyed both virologically and serologically were influenza-free throughout the study, possibly due to higher biosecurity measures implemented. No evidence of direct transmission of IAV from wild birds was found. Wild bird surveillance showed low isolation frequency of IAV. IAV prevalence of 0·55% for migratory ducks and 0·53% for migratory geese was estimated in November-December 2011 and January-February 2012, respectively, at two ornithologically important locations near the Black Sea coast.
  
  
  CONCLUSIONS
  The 'foie gras' duck farms in Bulgaria are an optimal niche where Eurasian-like IAVs are maintained and reassorted unapparent to farmers and veterinarians.
authors.affiliation: Bulgarian Food Safety Agency, Sofia, Bulgaria.
authors.forename: Atanaska
authors.initials: A
authors.lastname: Marinova-Petkova
authors.affiliation: Bulgarian Food Safety Agency, Sofia, Bulgaria.
authors.forename: Georgi
authors.initials: G
authors.lastname: Georgiev
authors.affiliation: Bulgarian Society for the Protection of Birds, Sofia, Bulgaria.
authors.forename: Todor
authors.initials: T
authors.lastname: Petkov
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Darnell
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: John
authors.initials: J
authors.lastname: Franks
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Ghazi
authors.initials: G
authors.lastname: Kayali
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: David
authors.initials: D
authors.lastname: Walker
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Seiler
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Angela
authors.initials: A
authors.lastname: Danner
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Allison
authors.initials: A
authors.lastname: Graham
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Pamela
authors.initials: P
authors.lastname: McKenzie
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Krauss
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Webby
authors.affiliation: St. Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Webster
mesh_terms: D000383:Agriculture; D000818:Animals; D000835:Animals, Wild / Q000821:virology; D002031:Bulgaria / Q000453:epidemiology; D004372:Ducks / Q000821:virology; D062665:Epidemiological Monitoring / Q000662:veterinary*; D006801:Humans; D009980:Influenza A virus / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D005585:Influenza in Birds / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D007251:Influenza, Human / Q000453:epidemiology; D008969:Molecular Sequence Data
keywords: European poultry; avian influenza; ducks; influenza surveillance; low-pathogenicity avian influenza viruses; ‘Foie gras’