Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 10 3 2016 06 18 317 329 EN Farzaneh Ahmadnejad Viral Vaccines Production Department, Pasteur Institute, Tehran, Iran AND TIMC-IMAG Team EPSP, VetAgroSup, Campus Vétérinaire de Lyon, France Vahid Otarod Quarantine and Biosafety Directorate General, Iran Veterinary Organization, Tehran, Iran Amanollah Fathnia Department of Geography, Razi University, Kermanshah, Iran Ali Ahmadabadi Faculty of Geography, Kharazmi University, Tehran, Iran Mohammad H. Fallah Department of Poultry Viral Diseases, Razi Vaccine and Serum Research Institute, Alborz, Iran Alireza Zavareh Viral Vaccines Production Department, Pasteur Institute, Tehran, Iran Nargess Miandehi Viral Vaccines Production Department, Pasteur Institute, Tehran, Iran Benoit Durand University Paris Est, Anses, Laboratory of Animal Health, Epidemiology unit, Maisons-Alfort, France Philippe Sabatier TIMC-IMAG Team EPSP, VetAgroSup, Campus Vétérinaire de Lyon, France 2015 10 14 2015 10 14 Background: Geographic distribution of West Nile virus (WNV) is heterogeneous in Iran by a high circulation in the southern-western areas. The objective of our study was to determine environmental and climatic factors associ­ated with the risk of WNV equine seropositivity in Iran. Methods: Serological data were obtained from a serosurvey conducted in equine population in 260 districts in Iran. The climate and environmental parameters included in the models were distance to the nearest wetland area, type of stable, Normalized Difference Vegetation Index (NDVI), annual mean temperature, humidity and precipitation. Results: The important risk factors included annual mean temperature, distance to wetlands, local and seasonal NDVI differences. The effect of local NDVI differences in spring was particularly notable. This was a normalized difference of average NDVI between two areas: a 5 km radius area centered on the stable and the 5–10 km sur­rounding area. Conclusion: The model indicated that local NDVI’s contrast during spring is a major risk factor of the transmission of West-Nile virus in Iran. This so-called oasis effect consistent with the seasonal production of vegetation in spring, and is associated to the attractiveness of the local NDVI environment for WNV vectors and hosts.   https://jad.tums.ac.ir/index.php/jad/article/view/165 https://jad.tums.ac.ir/index.php/jad/article/download/165/149