Marek's disease (MD) is a contagious avian viral disease that is responsible for large economic losses to farmers. The disease is caused by Marek's disease virus (species Gallid alphaherpesvirus 2), which causes neurological lesions, immune suppression, and tumor proliferation of lymphoid cells that invade a large number of organs and tissues. Despite widespread vaccination, Marek's disease virus (MDV), has shown a continuous increase in its virulence and has acquired the ability to overcome immune responses induced by vaccines. In the present study, the oncogenic serotype MDV-1 was detected by real-time PCR in DNA samples extracted from organs developing tumor infiltrations. Identification of the pathotype based on a 132-bp tandem repeat and sequencing and phylogenetic analysis of the Meq gene and its encoded protein allowed classification of the isolated viruses as "very virulent", with two new and unique mutations in the Meq gene resulting in amino acid substitutions. Sequencing of pp38, vIl-8, UL1 and UL44 genes did not reveal any new mutations that were characteristic of the Tunisian isolates or correlated with virulence. These results raised concerns about the ability of HVT and CVI988 vaccines, which are currently used in Tunisia and other countries, to protect chickens against highly virulent virus strains.

马立克氏病（MD）是一种传染性禽病毒病，对农民造成重大经济损失。该疾病是由马立克氏病病毒（物种Gallid alphaherpesvirus 2）引起的，该病毒引起神经系统损害，免疫抑制以及淋巴样细胞侵犯大量器官和组织的肿瘤增殖。尽管进行了广泛的疫苗接种，但马立克氏病病毒（MDV）的毒力不断提高，并具有克服疫苗诱导的免疫反应的能力。在本研究中，通过实时PCR在从发生肿瘤浸润的器官中提取的DNA样品中检测到致癌血清型MDV-1。基于132 bp串联重复序列的病原鉴定，Meq的测序和系统发育分析该基因及其编码的蛋白质可以将分离出的病毒分类为“极强毒”，Meq基因中有两个新的独特突变，导致氨基酸置换。pp38，vl-8，UL1和UL44基因的测序未发现突尼斯分离株特征性或与毒力相关的任何新突变。这些结果引起了人们对目前在突尼斯和其他国家使用的HVT和CVI988疫苗保护鸡免受高毒力病毒株影响的担忧。