Despite considerable effort for surveillance of wild birds for avian influenza viruses (AIVs), empirical
investigations of ecological drivers of AIV prevalence in wild birds are still scarce. Here we used a
continental-scale dataset, collected in tropical wetlands of 15 African countries, to test the relative
roles of a range of ecological factors on patterns of AIV prevalence in wildfowl. Seasonal and geographical
variations in prevalence were positively related to the local density of the wildfowl community and to the
wintering period of Eurasian migratory birds in Africa. The predominant influence of wildfowl density
with no influence of climatic conditions suggests, in contrast to temperate regions, a predominant role
for inter-individual transmission rather than transmission via long-lived virus persisting in the environment.
Higher prevalences were found in Anas species than in non-Anas species even when we account
for differences in their foraging behaviour (primarily dabbling or not) or their geographical origin
(Eurasian or Afro-tropical), suggesting the existence of intrinsic differences between wildfowl taxonomic
groups in receptivity to infection. Birds were found infected as often in oropharyngeal as in cloacal
samples, but rarely for both types of sample concurrently, indicating that both respiratory and digestive
tracts may be important for AIV replication.
Keywords: influenza A virus; pathogen transmission; disease ecology; wild birds; tropical; migratio