Authorities in Kerala and three other states - Himachal Pradesh, Madhya Pradesh and Rajasthan- have stepped up efforts to contain the spread of bird flu which has led to the death of lakhs of birds. Around 24,000 birds, mostly ducks, were culled in Kerala on Tuesday after the H5N8 strain of Avian Influenza was confirmed in parts of Alappuzha and Kottayam.