Kannaki, TRGowthaman, VasudevanTANUVAS2021-09-162021-09-162020https://krishikosh.egranth.ac.in/handle/1/5810175840TNV_WPSJ_2020_(91-99)Marek’s disease (MD) is one of the re-emerging diseases in Indian poultry. MD outbreaks are reported from different parts of the country in spite of vaccination, causing major economic losses. Flock mortality of 10–40% have still been observed in vaccinated flocks during outbreaks, although MD is considered to be well controlled with vaccination. Almost 100% of the commercial poultry flocks are vaccinated in the hatchery. Bivalent (HVT+SB1 or HVT+301B/1) or monovalent (HVT) vaccines are used in India. In spite of intensive vaccination, outbreaks are still reported from different parts of the world including India. MD virus (MDV) Indian field isolates from different outbreaks during the last decade are categorised into virulent (vMDV) and very virulent (vvMDV) pathotypes, based on different serotype 1 specific gene sequencing and in vivo pathotyping. The emergence of virulence in MDV is attributed to compromised bio-security, concurrent immunosuppressive diseases and vaccination failure. MD outbreaks in vaccinated Indian poultry flocks cause annual losses of approximately 40 million Indian rupees. Country-wide surveillance and reporting of MD outbreaks and further characterisation of the Indian field isolate should be taken as a priority. Reviewing current vaccination strategy and examining the need for the introduction of more effective vaccines that give better protection against more virulent strains should be considered with equal importance along with improved biosecurity measures, management practices and more effective control of immunosuppressive diseases.EnglishVeterinary ScienceArticle