Bridge hosts for avian influenza viruses at the wildlife/domestic interface : an eco-epidemiological framework implemented in southern Africa

Abstract

Wild terrestrial birds can act as potential local spreaders or bridge hosts for avian influenzaviruses (AIVs) between waterfowl (the maintenance hosts of AIVs) and domestic avianpopulations in which AIVs may cause disease. Few studies have investigated this hypothesis,although it is an important knowledge gap in our understanding of AIV spread within socio-ecosystems. We designed a simple and reproducible approach in an agro-ecosystem inZimbabwe based on: (1) bird counts at key target sites (i.e., wetlands, villages, intensivepoultry production buildings and ostrich farms) to identify which wild birds species co-occur in these different sites and seasons when the risk of AIV transmission through thesepotential bridge hosts is maximal and (2) targeted sampling and testing for AIV infectionin the identified potential bridge hosts. We found that 12 wild bird species represented thevast majority (79%) of co-occurrences in the different sites, whereas 230 bird species wererecorded in this ecosystem. Specifically, three species – barn swallow, Hirundo rustica, red-billed quelea, Quelea quelea and cattle egret, Bubulcus ibis – represented the main potentialbridge host species (65% of co-occurrences). In two out of these three species (i.e., barnswallow and red-billed quelea), we detected AIV infections, confirming that they can play abridge function between waterfowl and domestic species in the ecosystem. Our approachcan be easily implemented in other ecosystems to identify potential bridge hosts, and ourresults have implications in terms of surveillance, risk management and control of AIVspread in socio-ecosystems.