Risk factors for the occurrence of highly pathogenic avian influenza H5N1 in Nigeria: Results of a case-control study conducted in April and May 2009 in Kano and Lagos States - Métras, Raphaëlle; Abdu, P.; Okike, Iheanacho; Stevens, K.; Costard, Solenne; Grace, Delia; Pfeiffer, Dirk U.; Randolph, Thomas F. (International Livestock Research Institute, 2009)