A Review on the Marek’s Disease Outbreak and Its Virulence-Related meq Genovariation in Asia between 2011 and 2021

Abstract

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.

Genetic characterization of Marek's disease virus in chickens in Thailand reveals a high genetic diversity of circulating strains

“…Four clusters of MDV-1 were found to be circulating in Thailand, but only cluster 1 was predominant in chicken populations. Consistent with previous observations (Mescolini et al, 2020;Murata et al, 2020;Padhi & Parcells, 2016;Song et al, 2022;Trimpert et al, 2017), it seems to be likely that MDV-1 strains tended to be grouped by geographical regions, suggesting the geographic restricted evolution of MDV-1 field strains. We also found that most Thai MDV-1 strains showed higher identity and were grouped with Chinese and Eurasian MDV-1 strains rather than US strains, indicating that these Thai strains may share the same ancestor and evolve towards the same direction with those strains.…”

“…This indicates the wide distribution and endemicity of MDV-1 field strains in chickens in Thailand. Corresponding to this finding, widespread MDV-1 infection in chickens has been reported in several countries worldwide (Lopez-Osorio et al, 2017;Mescolini et al, 2020;Song et al, 2022). It should be noted that MDV-1 field strain positive samples were all collected from MD-affected chickens vaccinated with both CVI988 and HVT strains.…”

“…These distinct mutations along with a low number of PPPP likely affected the binding capacity and transcriptional activity of Meq protein, reported to be correlated with high virulence characteristics of MDV‐1 (Conradie et al., 2020; Mescolini et al., 2020; Renz et al., 2012; Shamblin et al., 2004). It should be noted that these Thai strains had the same mutations in the basic region (77E and 80Y) and the PRR (176R and 217A), reported to be the main characteristics of Chinese virulent MDV‐1 strains (Cui et al., 2016; Lv et al., 2017; Song et al., 2022; Tian et al., 2011; Zhang et al., 2016). This finding also supported the virulent potential of these Thai strains.…”

Ochratoxin A and Aflatoxin B1 Detection in Laying Hens for Omega 3-Enriched Eggs Production

“…Moreover, our findings showed that infectious diseases can be excluded. Indeed, in the episode we described, anemia and weight loss were not associated with the typical lesions induced by the viruses responsible for avian neoplasms (Marek's Disease Virus or avian leukosis virus) [50,51], nor with the medullary hypoplasia described in the case of gyrovirus infections [52]. Furthermore, although infectious bronchitis can induce kidney lesions similar to those described [53], the animals were treated with a vaccine with a wide antigenic panel.…”

Differential Replication and Cytokine Response between Vaccine and Very Virulent Marek’s Disease Viruses in Spleens and Bursas during Latency and Reactivation

“…Marek’s disease (MD), caused by Marek’s disease virus (MDV) in chickens, is a lymphoproliferative, oncogenic disease [ 1 ]. MDV infection leads to oncogenic immunosuppression, which seriously affects the production performance of the poultry industry and results in huge economic losses [ 2 ]. MDV replicates in lymphoid tissues, resulting in lymphocytosis, which shows many considerable biological similarities with lymphoid neoplasms related to the Epstein-Barr virus and contributes substantially to the understanding of herpes virus-associated oncogenicity [ 3 ].…”