Monitoring avian influenza virus in a small Spanish wetland using non-invasive sampling methods

Abstract

Anseriformes and Charadriiformes are known to be the main reservoirs for Avian Influenza Virus (AIV) in which the transmission within these occurs via faecal/oral contact in contaminated water. Understanding the Avian Influenza Virus (AIV) persistence and transmission dynamics is crucial for predicting disease outbreaks and improving surveillance strategies. The aim of this work was to monitor the presence and persistence of AIV in its natural environment in relation to ecology of its reservoir hosts. During a 23 month period (March 2012-January 2014) the relationship between AIV presence and wildfowl population movements was studied in a small wetland in the north of Spain where the presence of different AIV had previously been recorded. This water ecosystem is considered of special interest as it is an important site for wintering and breeding of waterfowl and as a stopover for waterfowl migrating further south, being considerably small (209 Ha) and close to an urbanised area. Fresh faeces were collected monthly from islets scattered along the wetland, used as roosting sites by the birds. Bird censuses and meteorological data were gathered in parallel in order to relate AIV detection to waterfowl ecology. For AIV detection RNA was extracted from the faecal matter and analysed by influenza A specific rRT-PCR. Positive samples were then tested for H5 and H7 subtypes and inoculated into embrionated SPF chicken eggs for virus isolation. During the 23 months, a total of 2096 samples were analysed and AIV was detected in 0.29%. In regard to the wild bird population movements, the highest AIV prevalence occurred along the breeding season (0.67%) and autumn migration (0.35%). The highest prevalence 3.23% was recorded in June 2012. All positive samples contained low pathogenic AIV. The concentration of positive results during the two above mentioned periods may be related to two scenarios in waterfowl ecology; on one hand, high water bird aggregation densities and therefore a greater virus titre input to the environment during migration and fledging of chicks and on the other hand, the presence of a naïve juvenile population with a still less efficient immune system that will make them more susceptible towards an AIV infection. More research is deemed necessary clarify the complex AIV ecology. In this regard, further studies are presently being undertaken.