Gallid Alphaherpesvirus 2 in the Egyptian Turkeys: Molecular Characterization and Establishment of a Universal System for Phylogenetic Classification

Abstract

<b><i>Introduction:</i></b> Gallid alphaherpesvirus 2 (GaHV-2) is a highly contagious oncogenic virus that causes Marek’s disease in chickens and occasionally in turkeys. Among 100 genes identified in GaHV-2 genome, the Meq gene appears to involve viral virulence, oncogenicity, and genetic diversity. Despite the use of Meq gene sequences in phylogenetic classification of GaHV-2 strains circulating in many countries worldwide, no integrated system exists yet. <b><i>Methods:</i></b> Turkeys from 2 commercial Egyptian farms were presented with signs of dullness, dehydration, and emaciation. Samples prepared from the internal organs were examined by histopathology and immunohistochemistry. Pools of the internal organs were analyzed by PCR for identification of GaHV-2, avian leucosis virus, and reticuloendotheliosis virus. The Meq gene of an Egyptian strain was sequenced and analyzed in comparison to 40 reference strains for generation of a universal system for phylogenetic classification of GaHV-2 strains. <b><i>Results:</i></b> Gross and histopathological examination revealed grayish-white soft masses in the internal organs characterized by diffuse infiltration of pleomorphic neoplastic cells. All lymphoma cells were identified as T-lymphocytes of CD3+ phenotype. Samples of both farms were only positive for GaHV-2 by PCR. Sequence analysis of the Meq gene has classified the current turkey strain as related to the Egyptian strains identified in chicken in 2012. A universal phylogenetic system for classification of GaHV-2 strains into 4 clusters was proposed. The vaccine strains were all grouped in cluster 2, and most of the classical American strains belonged to cluster 4. Cluster 1 was further divided into 3 subclusters (1.1–1.3). <b><i>Conclusion:</i></b> GaHV-2 was identified in turkeys for the first time in Africa and the Middle East. Sequence analysis of the Meq gene of the Egyptian strain along with a wide array of the global strains has enabled the construction of a novel phylogenetic classification system.

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

“…Phylogenetic analyses based on the Meq gene demonstrated that MDV‐1 field strains circulating in Thailand between 2013 and 2021 could be divided into four clusters, whereas small numbers of MDV‐1 clusters were reported in several other countries (Abd‐Ellatieff et al., 2018; Bayoumi et al., 2021; Mescolini et al., 2020; Ozan et al., 2021). This finding suggests that MDV‐1 circulating in Thailand exhibited a high level of genetic diversity compared to those circulating in some other countries.…”

“…Phylogenetic analyses based on the Meq gene demonstrated that MDV-1 field strains circulating in Thailand between 2013 and 2021 could be divided into four clusters, whereas small numbers of MDV-1 clusters were reported in several other countries (Abd-Ellatieff et al, 2018;Bayoumi et al, 2021;Mescolini et al, 2020;Ozan et al, 2021).…”

First report of Serotype-1 Marek’s disease virus (MDV-1) with oncogenic form in backyard turkeys in Turkey: a molecular analysis study

“…In spite of the fact that MD is rarely seen in turkeys, it has been reported in some countries including Netherlands, France, the UK, Israel, Germany, Scotland, Egypt and the USA [ 14 , 22 , 26 , 27 ]. Severe outbreaks of the disease have been reported in commercial turkey flocks in Europe and Israel between 1997 and 2002 [ 1 , 28 ].…”

“…By the means of molecular based methods such as PCR and real–time PCR (qPCR), it is possible to obtain a good indication of pathotype/virulence of the virus owing to the amplification of oncogenicity/pathogenicity related genes followed by sequencing. This also enables us to better understand why protection is not provided in some vaccinated flocks and then develop more efficient vaccines containing the correct pathotype based on molecular characterization [ 14 ]. The PCR analysis of the BamH1-H and BamH1-D regions of the viral genome flanking the 132-bp tandem repeat region is an important criterion that can be used to distinguish between pathogenic and non-pathogenic strains of MDV-1.…”

Potential Use of CRISPR/Cas13 Machinery in Understanding Virus–Host Interaction

“…They also validated using various Cas13 orthologs simultaneously, which could open the way to target more than one transcript as segmented RNA viruses, including influenza (Yang et al, 2019;Ahmed et al, 2020). Additionally, combining the catalytically inactive Cas13 (dCas13) with the dCas9 version could open new avenues for tracking RNA and DNA simultaneously in DNAreplicating viruses, including herpesvirus models (Yang et al, 2019;Bayoumi et al, 2020aBayoumi et al, , 2021.…”