Seasonality dynamics of avian influenza occurrences in Central and West Africa
Understanding seasonal cycles of viruses originating in wildlife can provide insight into their likelihood of persistence in animal populations and inform policies to limit spillover to human populations. Avian influenza virus (AIV) is an important zoonotic agent causing seasonal occurrence of avian influenza (AI) in wild birds in temperate areas. Although the seasonality of AIV transmission in tropical birds is largely unknown, peaks of influenza activity in human populations in the tropics coincide with the rainy season. To assess the seasonality of AI in tropical birds, from 2010-14, we sampled 40,099 birds at 32 sites in Central Africa (Cameroon, Central African Republic, Congo-Brazzaville, and Gabon) and West Africa (Benin, Cote dIvoire, and Togo). Although AIV was not isolated by egg culture, in Central Africa, detection rates by real-time RT-PCR were 3.57% for passerine songbirds and 8.74% for Anatid ducks. RT-PCR positivity in resident birds increased when Palearctic migrants arrived in Central Africa. At sampling sites with two annual wet seasons, the positive rate in wild birds was greatest during the big rainy season in September - October. This study provides the first evidence that AI is present in Central African birds and identifies environmental factors associated with cases.