title: Chronic infections of West Nile virus detected in California dead birds.
abstract: During 2010 and 2011, 933 recently deceased birds, submitted as part of the dead bird surveillance program, tested positive for West Nile virus RNA at necropsy. The relative amount of RNA measured by qRT-PCR cycles ranged from 8.2 to 37.0 cycle threshold (Ct) and formed a bimodal frequency distribution, with maxima at 20 and 36 Ct and minima at 28-30 Ct. On the basis of frequency distributions among different avian species with different responses to infection following experimental inoculation, field serological data indicating survival of infection, and the discovery of persistent RNA in experimentally infected birds, dead birds collected in nature were scored as "recent" or "chronic" infections on the basis of Ct scores. The percentage of birds scored as having chronic infections was highest during late winter/spring, when all birds were after hatching year, and lowest during late summer, when enzootic transmission was typically highest as indicated by mosquito infections. Our data indicated that intervention efforts should not be based on dead birds with chronic infections unless supported by additional surveillance metrics.
authors.affiliation: Center for Vectorborne Diseases, Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, California, USA. wkreisen@ucdavis.edu
authors.forename: William K
authors.initials: WK
authors.lastname: Reisen
authors.forename: Kerry
authors.initials: K
authors.lastname: Padgett
authors.forename: Ying
authors.initials: Y
authors.lastname: Fang
authors.forename: Leslie
authors.initials: L
authors.lastname: Woods
authors.forename: Leslie
authors.initials: L
authors.lastname: Foss
authors.forename: Jaynia
authors.initials: J
authors.lastname: Anderson
authors.forename: Vicki
authors.initials: V
authors.lastname: Kramer
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology*; D001715:Bird Diseases / Q000453:epidemiology* / Q000401:mortality / Q000635:transmission / Q000821:virology; D001717:Birds; D002140:California / Q000453:epidemiology; D002522:Chlorocebus aethiops; D002908:Chronic Disease; D009033:Culicidae / Q000382:microbiology*; D062665:Epidemiological Monitoring / Q000662:veterinary; D015277:Hotlines; D006801:Humans; D007303:Insect Vectors / Q000382:microbiology*; D012367:RNA, Viral / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D012621:Seasons; D014709:Vero Cells; D014901:West Nile Fever / Q000453:epidemiology / Q000401:mortality / Q000635:transmission / Q000662:veterinary*; D014902:West Nile virus / Q000276:immunology / Q000302:isolation & purification* / Q000502:physiology; D015047:Zoonoses
chemical_list: D000914:Antibodies, Viral; D012367:RNA, Viral