Serological Evidence of Infectious Laryngotracheitis Infection and Associated Risk Factors in Chickens in Northwestern Ethiopia oleh Mastewal Birhan, Ashenafi Syoum, Saddam Mohammed Ibrahim, Tewodros Fentahun, Addisu Mohammed, Nega Berhane, Molalegne Bitew, Esayas Gelaye, Malede Birhan Atanaw, Belayneh Getachew, Bereket Dessalegn, Anmaw Shite Abat, Kassahun Berrie, Kassaye Adamu, Takele Abayneh