Marek's Disease Virus and Reticuloendotheliosis Virus Coinfection Enhances Viral Replication and Alters Cellular Protein Profiles

Onset and long-term duration of immunity provided by a single vaccination with recombinant a Marek's disease virus with REV-LTR insertion

Marek's Disease (MD), caused by Marek's disease virus (MDV), is a highly contagious lymphoproliferative disease in poultry. Despite the fact that MD has been effectively controlled by vaccines, the virulence of field isolates of MDV has continued to evolve, becoming more virulent under the immune pressure of vaccines. Our previous research has confirmed that the recombinant rMDV strain with REV-LTR insertion can be used as a live attenuated vaccine candidate. The aim of this research was to evaluate the onset and duration of immunity of the rMDV strain through two experiments. In both experiments, 1-day-old SPF chickens were vaccinated subcutaneously with the rMDV strain at a dose of 3,000 Plaque Formation Unit (PFU) per chick in 0.2 mL of the MD diluent. Then, in Experimental design 1, the chicks in the groups Vac-3d/CC-3d, Vac-5d/CC-5d, and Vac-7d/CC-7d were challenged separately with 500 PFU vvMDV strain MD5 at 3 days, 5 days, and 7 days after vaccination; in Experimental design 2, the chicks in group Vac-60d/CC-60d, Vac-120d/CC-120d, and Vac-180d/CC-180d were challenged at 60 days, 120 days, and 180 days after vaccination. The clinical symptoms and weight gain of chickens in each group were observed and recorded. The results showed that the rMDV strain with REV-LTR insertion provides protection starting from 3 days of age and achieves good immune effects at 5 days of age after 1-day-old immunization, and the immunization duration can reach for at least 180 days. Given age-related resistance, it can be confirmed that our vaccine can actually provide lifelong immunity. This study provides valuable insights into the onset and duration of immunity of the rMDV strain, which will provide a basis for the development and improvement of MD vaccines.

Diversity of Marek's Disease Virus Strains in Infections in Backyard and Ornamental Birds

Marek's disease is caused by Mardivirus gallidalpha2, commonly known as Marek's disease virus (MDV). This pathogen infects various bird species resulting in a range of clinical manifestations. The meq gene, which is crucial for oncogenesis, has been extensively studied, but molecular investigations of MDV in noncommercial South American birds are limited. This study detected MDV in backyard and ornamental birds from Brazil and Peru and characterized the meq gene. MDV was confirmed in all seven outbreaks examined. Three isoforms of meq (S-meq, meq, and L-meq) and two to seven proline repeat regions (PRRs) were detected among the sequenced strains. At the amino acid level, genetic profiles with low and high virulence potential were identified. Phylogenetic analysis grouped the sequences into three distinct clusters. Selection pressure analysis revealed 18 and 15 codons under positive and negative selection, respectively. The results demonstrate significant MDV diversity in the studied birds, with both high and low virulence potentials. This study highlights the importance of monitoring and characterizing circulating MDV in backyard and ornamental birds, as they can act as reservoirs for future epidemiological outbreaks.

Co-infection of H9N2 subtype avian influenza virus and QX genotype live attenuated infectious bronchitis virus increase the pathogenicity in SPF chickens

Avian influenza virus (AIV) infection and vaccination against live attenuated infectious bronchitis virus (aIBV) are frequent in poultry worldwide. Here, we evaluated the clinical effect of H9N2 subtype AIV and QX genotype aIBV co-infection in specific-pathogen-free (SPF) white leghorn chickens and explored the potential mechanisms underlying the observed effects using by 4D-FastDIA-based proteomics. The results showed that co-infection of H9N2 AIV and QX aIBV increased mortality and suppressed the growth of SPF chickens. In particular, severe lesions in the kidneys and slight respiratory signs similar to the symptoms of virulent QX IBV infection were observed in some co-infected chickens, with no such clinical signs observed in single-infected chickens. The replication of H9N2 AIV was significantly enhanced in both the trachea and kidneys, whereas there was only a slight effect on the replication of the QX aIBV. Proteomics analysis showed that the IL-17 signaling pathway was one of the unique pathways enriched in co-infected chickens compared to single infected-chickens. A series of metabolism and immune response-related pathways linked with co-infection were also significantly enriched. Moreover, co-infection of the two pathogens resulted in the enrichment of the negative regulation of telomerase activity. Collectively, our study supports the synergistic effect of the two pathogens, and pointed out that aIBV vaccines might increased IBV-associated lesions due to pathogenic co-infections. Exacerbation of the pathogenicity and mortality in H9N2 AIV and QX aIBV co-infected chickens possibly occurred because of an increase in H9N2 AIV replication, the regulation of telomerase activity, and the disturbance of cell metabolism and the immune system.

Exosomal miR-7-25207 Increases Subgroup J Avian Leukosis Virus Titers by Targeting the Akt-CyclinQ1 and PRC1-YAF2 Dual Pathways

Subgroup J avian leukosis virus (ALV-J) is a major pathogen in poultry, causing substantial economic losses to the poultry industry worldwide. Exosomal small RNAs derived from virus-infected cells or biological fluids can serve as viral transmission vectors. However, the role and mechanism of exosomal miRNA in ALV-J infection are unclear. In this study, we demonstrated that exosomal microRNA-7-25207 (miR-7-25207) could increase the titers of ALV-J. Exosomes isolated from ALV-J-infected DF-1 cells (Exo-ALV-J) contained partial viral proteins from ALV-J and could transmit the infection to uninfected DF-1 cells, leading to productive infection. Additionally, the RNA expression profile of exosomes was altered following ALV-J infection. miRNA analysis revealed that the expression of exosomal miR-7-25207 increased. Overexpression of miR-7-25207 significantly increased the titers of ALV-J in transfected cells. Furthermore, miR-7-25207 directly suppressed the expression of Akt and PRC1. Akt, in turn, directly inhibited CyclinQ1 expression, while PRC1 directly interfered with YAF2 expression. In conclusion, ALV-J infection activates the expression of miR-7-25207, which is subsequently delivered via exosomes to uninfected cells, increasing ALV-J titers by targeting Akt-CyclinQ1 and PRC1-YAF2 dual pathways. These findings suggest that exosomal miR-7-25207 may serve as a potential biomarker for clinical parameters in ALV-J infection.

Dynamic Changes in Viral Loads during Co-Infection with a Recombinant Turkey Herpesvirus Vector Vaccine and Very Virulent Marek's Disease Virus In Vivo

Marek's disease (MD), caused by the Marek's disease virus (MDV), is a common infectious tumor disease in chickens and was the first neoplastic disease preventable by vaccination. However, the vaccine cannot completely prevent virulent MDV infections, allowing both the vaccine and virulent MDV to coexist in the same chicken for extended periods. This study aims to investigate the changes in viral load of the very virulent strain Md5 and the rHVT-IBD vaccine in different chicken tissues using a real-time PCR assay. The results showed that the rHVT-IBD vaccine significantly reduced the viral load of MDV-Md5 in different organs, while the load of rHVT-IBD was significantly increased when co-infected with Md5. Additionally, co-infection with Md5 and rHVT-IBD in chickens not only changed the original viral load of both viruses but also affected the positive rate of Md5 at 14 days post-vaccination. The positive rate decreased from 100% to 14.29% (feather tips), 0% (skin), 33.33% (liver), 16.67% (spleen), 28.57% (thymus), 33.33% (bursa), and 66.67% (PBL), respectively. This study enhances our understanding of the interactions between HVT vector vaccines and very virulent MDV in chickens and provides valuable insights for the future development of MD vaccines.

Molecular characterization of Marek's Disease virus reveals reticuloendotheliosis virus-long terminal repeat integration in the genome of the field isolates in Egypt

The highly contagious, immunosuppressive, and cancer-causing Marek's disease virus (MDV) infects chickens. The financial costs of Marek's disease (MD) are significant for the chicken industry. In this study, a total of 180 samples from chicken farms suspected to be MDV-infected were collected. The chickens were sampled during the period between the months of October 2016 and February 2018 at Dakahlia and Damietta Governorates, Egypt. A total of 36 pooled samples were created. The prepared samples were inoculated into embryonated chicken eggs (ECEs). Indirect fluorescent antibody technique (IFAT) and ICP4 gene-based polymerase chain reaction (PCR) were used for MDV identification. For the genetic characterization of the identified virus, The ICP4 gene sequence was identified and compared with the sequences available from various regions of the world. Furthermore, the genomes of all detected MDVs were screened for the long terminal repeat (LTR) region of reticuloendotheliosis (REV) in their genomes. The results showed that 31 out of 36 pooled samples (86.1%) inoculated into ECEs displayed the characteristic pock lesions. By using IFAT and PCR to identify MDV in ECEs, positive results were found in 27 samples (75%). The Egyptian virus is thought to be genetically closely related to MDVs circulating in Ethiopia, China, and India. REV-LTR was amplified from 6 out of 27 field isolates genomes (22.2 %) while MDV vaccine strains were free from REV-LTR insertion. The integrated REV-LTRs depicted a close genetic relationship with those integrated in fowl poxvirus (FWPV) circulating in Egypt as well as those integrated in FWPVs and MDVs from China, USA, South Africa, and Australia. To the best of our knowledge, this investigation represents the first identification and characterization of REV-LTR insertions in Egyptian MDV field isolates. Given the findings above, additional research in the future seems crucial to determine how the REV-LTR insertions affect MDV pathogenesis, virulence, and insufficient vaccination protection.

miR-155 facilitates the synergistic replication between avian leukosis virus subgroup J and reticuloendotheliosis virus by targeting a dual pathway

IMPORTANCE

The synergy of two oncogenic retroviruses is an essential phenomenon in nature. The synergistic replication of ALV-J and REV in poultry flocks increases immunosuppression and pathogenicity, extends the tumor spectrum, and accelerates viral evolution, causing substantial economic losses to the poultry industry. However, the mechanism of synergistic replication between ALV-J and REV is still incompletely elusive. We observed that microRNA-155 targets a dual pathway, PRKCI-MAPK8 and TIMP3-MMP2, interacting with the U3 region of ALV-J and REV, enabling synergistic replication. This work gives us new targets to modulate ALV-J and REV's synergistic replication, guiding future research on the mechanism.

Viral Co-Infection in Bats: A Systematic Review

Co-infection is an underappreciated phenomenon in contemporary disease ecology despite its ubiquity and importance in nature. Viruses, and other co-infecting agents, can interact in ways that shape host and agent communities, influence infection dynamics, and drive evolutionary selective pressures. Bats are host to many viruses of zoonotic potential and have drawn increasing attention in their role as wildlife reservoirs for human spillover. However, the role of co-infection in driving viral transmission dynamics within bats is unknown. Here, we systematically review peer-reviewed literature reporting viral co-infections in bats. We show that viral co-infection is common in bats but is often only reported as an incidental finding. Biases identified in our study database related to virus and host species were pre-existing in virus studies of bats generally. Studies largely speculated on the role co-infection plays in viral recombination and few investigated potential drivers or impacts of co-infection. Our results demonstrate that current knowledge of co-infection in bats is an ad hoc by-product of viral discovery efforts, and that future targeted co-infection studies will improve our understanding of the role it plays. Adding to the broader context of co-infection studies in other wildlife species, we anticipate our review will inform future co-infection study design and reporting in bats. Consideration of detection strategy, including potential viral targets, and appropriate analysis methodology will provide more robust results and facilitate further investigation of the role of viral co-infection in bat reservoirs.

A Multiplex Quantitative Polymerase Chain Reaction for the Rapid Differential Detection of Subgroups A, B, J, and K Avian Leukosis Viruses

Avian leukosis (AL), caused by avian leukosis virus (ALV), is a contagious tumor disease that results in significant economic losses for the poultry industry. Currently, ALV-A, B, J, and K subgroups are the most common in commercial poultry and cause possible coinfections. Therefore, close monitoring is necessary to avoid greater economic losses. In this study, a novel multiplex quantitative polymerase chain reaction (qPCR) assay was developed to detect ALV-A, ALV-B, ALV-J, and ALV-K with limits of detection of 40, 11, 13.7, and 96 copies/µL, respectively, and no cross-reactivity with other ALV subtypes and avian pathogens. We detected 852 cell cultures inoculated with clinical samples using this method, showing good consistency with conventional PCR and ELISA. The most prevalent ALV strain in Hubei Province, China, was still ALV-J (11.74%). Although single infections with ALV-A, ALV-B, and ALV-K were not found, coinfections with different subgroup strains were identified: 0.7% for ALV-A/J, 0.35% for ALV-B/J, 0.25% for ALV-J/K, and 0.12% for ALV-A/B/K and ALV-A/B/J. Therefore, our novel multiplex qPCR may be a useful tool for molecular epidemiology, clinical detection of ALV, and ALV eradication programs.

Serum amyloid A regulates TLR2/4-mediated IFN-β signaling pathway against Marek's disease virus

Serum amyloid A (SAA), an acute response phase protein (APP), is crucial for the innate immune response during pathogenic microorganisms' invasion. Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus that activates multiple innate immune molecules, including SAA, in the host during infection. However, the pathway through which SAA participates in MDV-induced host innate immunity remains unknown. The present study aimed to elucidate the pathway through which SAA exerts its anti-MDV function. We observed that MDV infection in vivo and in vitro significantly elevated SAA expression. Furthermore, through SAA overexpression and knockdown experiments, we demonstrated that SAA could inhibit MDV replication. Subsequently, we found that SAA activated Toll-Like Receptor 2/4 (TLR2/4) -mediated Interferon Beta (IFN-β) promoter activity and IFN regulatory factor 7 (IRF7) promoter activity. During MDV infection, SAA enhanced TLR2/4-mediated IFN-β signal transduction and messenger RNAs (mRNAs) expression of type I IFN (IFN-I) and interferon-stimulated genes (ISGs). Finally, TLR2/4 inhibitor OxPAPC inhibits the anti-MDV activity of SAA. These results demonstrated that SAA inhibits MDV replication and enhancing TLR2/4-mediated IFN-β signal transduction to promote IFNs and ISGs expression. This finding is the first to demonstrate the signaling pathway by which SAA exerts its anti-MDV function. It also provides new insights into the control of oncogenic herpesviruses from the perspective of acute response phase proteins.

Viral Coinfections

In nature, viral coinfection is as widespread as viral infection alone. Viral coinfections often cause altered viral pathogenicity, disrupted host defense, and mixed-up clinical symptoms, all of which result in more difficult diagnosis and treatment of a disease. There are three major virus-virus interactions in coinfection cases: viral interference, viral synergy, and viral noninterference. We analyzed virus-virus interactions in both aspects of viruses and hosts and elucidated their possible mechanisms. Finally, we summarized the protocol of viral coinfection studies and key points in the process of virus separation and purification.

RIOK3-mediated Akt phosphorylation facilitates synergistic replication of Marek's disease and reticuloendotheliosis viruses

Co-infection of Marek’s disease virus (MDV) and reticuloendotheliosis virus (REV) synergistically drives disease progression, yet little is known about the mechanism of the synergism. Here, we found that co-infection of REV and MDV increased their replication via the RIOK3-Akt pathway. Initially, we noticed that the viral titres of MDV and REV significantly increased in REV and MDV co-infected cells compared with single-infected cells. Furthermore, tandem mass tag peptide labelling coupled with LC/MS analysis showed that Akt was upregulated in REV and MDV co-infected cells. Overexpression of Akt promoted synergistic replication of MDV and REV. Conversely, inhibition of Akt suppressed synergistic replication of MDV and REV. However, PI3K inhibition did not affect synergistic replication of MDV and REV, suggesting that the PI3K/Akt pathway is not involved in the synergism of MDV and REV. In addition, we revealed that RIOK3 was recruited to regulate Akt in REV and MDV co-infected cells. Moreover, wild-type RIOK3, but not kinase-dead RIOK3, mediated Akt phosphorylation and promoted synergistic replication of MDV and REV. Our results illustrate that MDV and REV activated a novel RIOK3-Akt signalling pathway to facilitate their synergistic replication.