title: Zoonotic potential of highly pathogenic avian H7N3 influenza viruses from Pakistan.
abstract: H5 and H7 avian influenza viruses can become highly pathogenic in chickens after interspecies transmission. These viruses have transmitted directly to humans from birds in Eurasia and Africa (H5N1), the Netherlands (H7N7), and Canada (H7N3). Here we report antigenic, sequence, and phylogenetic analyses of H7N3 viruses isolated from chickens in Pakistan from 1995 to 2002. We compared the pathogenic and zoonotic potential of the Pakistani viruses in avian and mammalian hosts. In chickens, all of the isolates showed high pathogenicity with poor transmissibility to contact birds. Viral shedding from the trachea and cloaca was equivalent, but cloacal shedding occurred longer; dissemination of virus into the tissues was widespread. In contrast, the viruses replicated poorly in 6-week-old mallard ducks. In mammalian hosts, of the two Pakistani H7N3/02 viruses that caused weight loss, one also caused 40% mortality in mice without prior adaptation, and preliminary experiments in ferrets showed significant virus multiplication in the lungs, intestine, and conjunctiva. We conclude that the H7N3/02 isolates from Pakistan show limited antigenic drift and have evolved slowly during their 8-year circulation in chickens; however, these viruses have the potential to infect mammals.
authors.affiliation: Division of Virology, Department of Infectious Diseases, MS 330, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105-2794, USA.
authors.forename: Uzma B
authors.initials: UB
authors.lastname: Aamir
authors.forename: Khalid
authors.initials: K
authors.lastname: Naeem
authors.forename: Zaheer
authors.initials: Z
authors.lastname: Ahmed
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Obert
authors.forename: John
authors.initials: J
authors.lastname: Franks
authors.forename: Scott
authors.initials: S
authors.lastname: Krauss
authors.forename: Patrick
authors.initials: P
authors.lastname: Seiler
authors.forename: Robert G
authors.initials: RG
authors.lastname: Webster
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology; D002645:Chickens; D002988:Cloaca / Q000821:virology; D003228:Conjunctiva / Q000821:virology; D004372:Ducks; D005289:Ferrets; D006801:Humans; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification* / Q000472:pathogenicity*; D005585:Influenza in Birds / Q000635:transmission* / Q000821:virology*; D007422:Intestines / Q000821:virology; D008168:Lung / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D010154:Pakistan; D010802:Phylogeny; D012367:RNA, Viral; D017422:Sequence Analysis, DNA; D016019:Survival Analysis; D014132:Trachea / Q000821:virology; D017201:Virus Shedding; D015047:Zoonoses / Q000821:virology*
chemical_list: D000956:Antigens, Viral; D012367:RNA, Viral