Victims and Vectors: Highly Pathogenic Avian Influenza H5N1 and the Ecology of Wild Birds

Abstract

The emergence of highly pathogenic avian influenza (HPAI) viruses has raised concerns about the role of wild birds in the spread and persistence of the disease. In 2005, an outbreak of the highly pathogenic subtype H5N1 killed more than 6,000 wild waterbirds at Qinghai Lake, China. Outbreaks have continued to periodically occur in wild birds at Qinghai Lake and elsewhere in Central China and Mongolia. This region has few poultry but is a major migration and breeding area for waterbirds in the Central Asian Flyway, although relatively little is known about migratory movements of different species and connectivity of their wetland habitats. The scientific debate has focused on the role of waterbirds in the epidemiology, maintenance and spread of HPAI H5N1: to what extent are they victims affected by the disease, or vectors that have a role in disease transmission? In this review, we summarise the current knowledge of wild bird involvement in the ecology of HPAI H5N1. Specifically, we present details on: (1) origin of HPAI H5N1; (2) waterbirds as LPAI reservoirs and evolution into HPAI; (3) the role of waterbirds in virus spread and persistence; (4) key biogeographic regions of outbreak; and (5) applying an ecological research perspective to studying AIVs in wild waterbirds and their ecosystems.

Ecophysiology of avian migration in the face of current global hazards

“…debate on the importance of migratory birds in the spread of the H5N1 highly pathogenic subtype of avian influenza virus, a pathogen of significant concern for both public health and domestic poultry production [32,33]. Importantly, migratory waterbirds (waterfowl Anseriformes and waders/gulls Charadriiformes) are considered an important reservoir for low-pathogenic avian influenza viruses, certain strains of which represent precursors for highly pathogenic avian influenza viruses [34,35].…”

Bird Migration and Risk for H5N1 Transmission into Qinghai Lake, China

“…The conclusion that oropharyngeal excretion is the main source of transmissible virus is supported by experimental studies of captive swans and ducks (Brown et al 2008, Kalthoff et al 2008). However, virus shedding from the oral cavity may promote transmission between poultry in a wet market or in a crowded breeding colony, but it is unlikely to be as efficient as fecal shedding in dispersing viral particles in the aquatic habitats occupied by waterfowl (Takekawa et al 2010). Feeding habit is closely related with the fecal-oral route of transmission, so it was included in the calculation of Ei.…”

“…Quantity of virus shedding is highly strain and species specific in the experimental test , Swayne 2007, Swayne and Slemons 2008. Two important factors: titers and duration of shedding virus were included in the equation to differentiate the susceptibility of wild bird species (Takekawa et al 2010).…”

“…On the circumstance that we do not know the genotype of the newly introduced H5N1 isolate into Qinghai Lake, it is difficult to assess the susceptibility of different species, so we used the morbidity rate data from experimental studies to estimate the difference of susceptibility between species. Based on experimental exposure trials on wild bird species, there were a series of differences in exposure responses ranging from asymptomatic periods, shedding periods, and development of clinical signs, morbidity rates and mortality rates (Takekawa et al 2010). However, most of the experimental studies of the exposure responses were conducted on the species from order of Anseriformes (ducks and geese), Galliformes (chickens), and Passeriformes (songbirds) (Perkins and Swayne 2003, Boon et al 2007).…”

A new method for discovering behavior patterns among animal movements

“…These contributions could serve as the basis of further studies on the intrinsic link between animal movement and the long-term spread of disease (Prosser et al . 2009, Takekawa et al . 2010, Altizer et al .…”