DOI: 10.5061/dryad.j855b
title: Data from: Juveniles and migrants as drivers for seasonal epizootics of avian influenza virus

description: 1. Similar to other infectious diseases, the prevalence of low pathogenic
 avian influenza viruses (LPAIV) has been seen to exhibit marked seasonal
 variation. However, mechanisms driving this variation in wild birds have
 yet to be tested. We investigated the validity of three previously
 suggested drivers for the seasonal dynamics in LPAIV infections in wild
 birds: (1) host density, (2) immunologically-naïve young, and (3)
 increased susceptibility in migrants. 2. To address these questions, we
 sampled a key LPAIV host species, the mallard Anas platyrhynchos, on a
 small spatial scale, comprehensively throughout a complete annual cycle,
 measuring both current and past infection (i.e. viral and seroprevalence
 respectively). 3. We demonstrate a minor peak in LPAIV prevalence in
 summer, a dominant peak in autumn, during which half of the sampled
 population was infected, and no infections in spring. Seroprevalence of
 antibodies to a conserved gene-segment of AIV peaked in winter and again
 in spring. 4. The summer peak of LPAIV prevalence coincided with the
 entrance of unfledged naïve young in the population. Moreover, juveniles
 were more likely to be infected, shed higher quantities of virus, and were
 less likely to have detectable antibodies to AIV than adult birds. The
 arrival of migratory birds, as identified by stable hydrogen isotope
 analysis, appeared to drive the autumn peak in LPAIV infection, with both
 temporal coincidence and higher infection prevalence in migrants.
 Remarkably, seroprevalence in migrants was substantially lower than viral
 prevalence throughout autumn migration, further indicating that each wave
 of migrants amplified local AIV circulation. Finally, while host abundance
 increased throughout autumn, it peaked in winter, showing no direct
 correspondence with either of the LPAIV infection peaks. 5. At an
 epidemiologically-relevant spatial scale, we provide strong evidence for
 the role of migratory birds as key drivers for seasonal epizootics of
 LPAIV, regardless of their role as vectors of these viruses. This study
 exemplifies the importance of understanding host demography and migratory
 behaviour when examining seasonal drivers of infection in wildlife
 populations.
description: Year-round mallard
 sampling for low pathogenic avian influenza virus (LPAIV) in The
 NetherlandsMallards were caught at
 a duck decoy located near Oud Alblas in the Alblasserwaard, The
 Netherlands, from March 2010 until February 2011. Each captured mallard
 was marked with a metal ring, sexed and aged. Cloacal and oropharyngeal
 samples were taken for detection of current LPAIV infection, and blood
 samples collected for detection of antibodies to AIV. The cycle threshold
 (Ct) value, which is the first real-time amplification cycle in which
 matrix gene amplification was detected, was used to assess the degree of
 viral shedding from the cloaca and oropharynx. The Ct-value is inversely
 proportional to the number of virus particles in a sample. Feather samples
 were taken to assess the origin of birds (resident, local migrant, distant
 migrant) using stable hydrogen isotope analysis. For more details see
 Appendix 2.Raw data
 JAE.xlsx