This review examines the emergence of drift variants of low pathogenic avian influenza (LPAI) viruses, with particular focus on their occurrence in India. Influenza viruses are dynamic and continuously evolving, and variants emerge from the instability of these viruses due to their constant mutations through antigenic drift. The drift variants emerging from the LPAI viruses gradually acquire higher virulence, inflicting heavy mortality and severe economic losses. Different aspects covered in reference to the Indian observations include mortality, clinical signs, post mortem lesions, and differential diagnosis. In addition, the cause of death based on the typical lesions encountered, and the limitations of any vaccination programme to control the variants are discussed in a global context.
