Abstract
Simple SummaryMarek’s disease is continuously causing an economic loss in Asia, despite the wide use of vaccines in the last decade. This review aims at summarizing the outbreak, the virulence-related meq gene variation, and the pathological information of Marek’s disease in the last decade in Asia. We found that a total of 132 viral strains emerged in 12 countries with different meq sequences. Among the evidence we have collected, 12 strains found in China were vaccine-resistant, reaching a mortality rate of 30% and above. This evidence requires the related region in China to consider the renewal of its vaccination type; however, more studies regarding the vaccination efficiency in other Asian countries are recommended, as the current information is not enough. The visceral tumor is the most common pathological type (13 in 16 studies) in Asia, while it is possible that a neural type may exist. We suggest that farmers monitor the behavioral changes of chickens to identify this harmful disease at the early stage. The phylogenetic analysis shows interconnection between Middle Eastern, South Asian, and East Asian countries that are geologically connected—poultry trading managers should consider the potential of viral transmitting.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.
Highlights
Marek’s disease (MD) is a threatening infectious disease for the poultry industry
Overall MD Outbreaks in Asia between 2011 and 2021 and Associated Phylogeny Based on meq Gene
The lymphoma induced by Marek’s disease virus (MDV) occured most frequently in the liver (11 studies), followed by spleen (9 studies), bursa of Fabricius (5 studies), kidney (4 studies), skin (4 studies), heart (4 studies), gizzard (4 studies), intestine (3 studies), and lung (2 studies), as shown in MD incidence rates ranged from 0.1% to 40%, and MD mortality rates were distributed from 1% to 80% depending on the specific viral strains and vaccination status
Summary
Marek’s disease (MD) is a threatening infectious disease for the poultry industry. MD was first reported in a chicken farm in Hungary in 1907 and rapidly spread around the world, with recorded mortalities ranging from 10 to 30% and occasionally above 60% in infected chickens. The monitoring of MD in farms relies first on clinical pathology detection and is followed by genetic confirmation. In neural MD, the main clinical symptoms include a complete or partial paralysis of the neck, wings, and limbs. Such paralyses are mainly induced by lesions of the vagus, brachial, and sciatic plexuses that show enlargement and yellowish color on the surface. Sometimes in more severe infections, gray or cloudy eyes and small tumors in the ovary, heart, liver, lung, and other tissues can be found and, usually, iridocyclitis and lymphomas are further detected under microscopic observation. In visceral MD, the gross tumors can be observed in the gonads, liver, kidney, lung, heart, spleen, and proventriculus in larger sizes and higher numbers
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