Age and season predict influenza A virus dynamics in urban gulls: consequences for natural hosts in unnatural landscapes

Abstract

Gulls are ubiquitous in urban areas due to a growing reliance on anthropogenic feeding sites, which has led to changes in their abundance, distribution, and migration ecology, with implications for disease transmission. Gulls offer a valuable model for testing hypotheses regarding the dynamics of influenza A virus (IAV) – for which gulls are a natural reservoir in urban areas. We sampled sympatric populations of Ring‐billed (Larus delawarensis), Herring (L. argentatus), and Great Black‐backed Gulls (L. marinus) along the densely populated Atlantic rim of North America to understand how IAV transmission is influenced by drivers such as annual cycle, host species, age, habitat type, and their interplay. We found that horizontal transmission, rather than vertical transmission, played an outsized role in the amplification of IAV due to the convergence of gulls from different breeding grounds and age classes. We detected overlapping effects of age and season in our prevalence model, identifying juveniles during autumn as the primary drivers of the seasonal epidemic in gulls. Gulls accumulated immunity over their lifespan, however short‐term fluctuations in seroprevalence were observed, suggesting that migration may impose limits on the immune system to maintain circulating antibodies. We found that gulls in coastal urban habitats had higher viral prevalence than gulls captured inland, correlating with higher richness of waterbird species along the coast, a mechanism supported by our movement data. The peak in viral prevalence in newly fledged gulls that are capable of long‐distance movement has important implications for the spread of pathogens to novel hosts during the migratory season as well as for human health as gulls increasingly utilize urban habitats.

Ecological divergence of wild birds drives avian influenza spillover and global spread

“…involved in onward transmission. Adaptive immunity in gulls accumulates with each successive annual cycle, reaching 70% seropositivity in adult birds [51]. Introduction of novel strains coupled with the absence of broadly-neutralizing immunity, particularly in younger birds, may translate to conditions that favor rapid dispersal that are unusual in the reservoir host.…”

“…-71.06) at urban habitats that attract migratory and over-wintering gulls. Herring Gulls (L. smithsonianus), Ring-billed Gulls (L. delawarensis) and Greater Black-backed Gulls (L. marinus) were captured with a net launcher and birds were sampled as per Ineson, Hill [51]. Sampling was performed weekly from October to April coinciding with the non-breeding season between 2012 and 2014.…”

Avian influenza virus circulation and immunity in a wild urban duck population prior to and during a highly pathogenic H5N1 outbreak

“…infected with an H4N6 virus exhibited minimal viral shedding and antibody levels increased to a level considered seropositive at 7 days post infection (dpi), peaked at 10 dpi, then waned over the next several months and reached undetectable levels one year after the infection. Other studies on wild gulls have found detectable AIV antibody levels for up to a year, demonstrating that responses in some individuals can be long-lived, likely boosted through re-exposure [29,65].…”

“…Dabbling ducks using human-dominated landscapes in Atlantic Canada show notably high survival rates and strong annual site fidelity to wintering areas [63], leading to a population with an older age distribution than usual. This older age structure may have contributed to the higher seroprevalence overall and over time, as antibody levels are elevated and persist longer in older individuals [28,64,65]. With low seroprevalence of H5-specific antibodies from 2012-2014, assumed to be due to occasional circulation of LPAI H5 viruses, most individuals were likely infected for the first time with an H5 virus, explaining the shorter period in which these specific antibodies persisted.…”

Research on the propagation model of COVID-19 based on virus dynamics

“…It can easily pass through the nasal hair and mucosal secretions and reach the upper respiratory tract. It is the particle size range that is most likely to cause infection [11,12].…”