Marek's disease is an
infectious disease in poultry that usually appears in neural and visceral
tumors. This disease is caused by Gallid alphaherpesvirus 2
infection in lymphocytes, and its meq gene is commonly used in virulent studies for coding the key
protein functional in oncogenic transformation of the lymphocytes. Although
vaccines have been introduced in many countries to control its spread and are proven to be efficient, recent records show a decline of such efficiency due to viral evolution. In this study, we reviewed the outbreak of
Marek's disease in Asia for the last 10 years, together with associated meq sequences, finding a total of 36 studies recording outbreaks with 132 viral strains in 12 countries. The visceral type is the most common (13 in 16 studies) form of
Marek's disease, but additional unobserved neural changes may exist. MD induces liver
lymphoma most frequently (11 in 14 studies), and
tumors were also found in spleen, kidney, heart, gizzard, skin, intestine, lung, and sciatic nerve. Twelve viral strains distributed in China have been reported to escape the CVI988
vaccine, reaching a mortality rate of more than 30%. Phylogenetic analyses show the internal connection between the Middle East (Turkey, Iraq, Iran, Saudi Arabia), South Asia (India, Indonesia), and East Asia (China and Japan), while external viral communications might occasionally occur. In 18 strains with both sequential and mortality data,
amino acid alignment showed several point substitutions that may be related to its virulence. We suggest more behavioral monitoring in
Marek's disease-endemic regions and further studies on strain virulence, together with its Meq
protein structural changes.