Identification and functional analysis of membrane proteins gD, gE, gI, and pUS9 of Infectious laryngotracheitis virus

Isolation, identification, molecular and pathogenicity characteristics of an infectious laryngotracheitis virus from Hubei province, China

Multiple outbreaks of avian infectious laryngotracheitis (ILT) in chickens, both domestically and internationally, have been directly correlate to widespread vaccine use in affected countries and regions. Phylogenetic and recombination event analyses have demonstrated that avian infectious laryngotracheitis virus (ILTV) field strains are progressively evolving toward the chicken embryo-origin (CEO) vaccine strain. Even with standardized biosecurity measures and effective prevention and control strategies implemented on large-scale farms, continuous ILT outbreaks result in significant economic losses to the poultry industry worldwide. These outbreaks undoubtedly hinder efforts to control and eradicate ILTV in the future. In this study, an ILTV isolate was successfully obtained by laboratory PCR detection and virus isolation from chickens that exhibited dyspnea and depression on a broiler farm in Hubei Province, China. The isolated strain exhibited robust propagation on chorioallantoic membranes of embryonated eggs, but failed to establish effective infection in chicken hepatocellular carcinoma (LMH) cells. Phylogenetic analysis revealed a unique T441P point mutation in the gJ protein of the isolate. Animal experiments confirmed the virulence of this strain, as it induced mortality in 6-wk-old chickens. This study expands current understanding of the epidemiology, genetic variations, and pathogenicity of ILTV isolates circulating domestically, contributing to the elucidate of ILTV molecular basis of pathogenicity and development of vaccine.

Construction and characterisation of glycoprotein E and glycoprotein I deficient mutants of Australian strains of infectious laryngotracheitis virus using traditional and CRISPR/Cas9-assisted homologous recombination techniques

In alphaherpesviruses, glycoproteins E and I (gE and gI, respectively) form a heterodimer that facilitates cell-to-cell spread of virus. Using traditional homologous recombination techniques, as well as CRISPR/Cas9-assisted homologous recombination, we separately deleted gE and gI coding sequences from an Australian field strain (CSW-1) and a vaccine strain (A20) of infectious laryngotracheitis virus (ILTV) and replaced each coding sequence with sequence encoding green fluorescent protein (GFP). Virus mutants in which gE and gI gene sequences had been replaced with GFP were identified by fluorescence microscopy but were unable to be propagated separately from the wildtype virus in either primary chicken cells or the LMH continuous chicken cell line. These findings build on findings from a previous study of CSW-1 ILTV in which a double deletion mutant of gE and gI could not be propagated separately from wildtype virus and produced an in vivo phenotype of single-infected cells with no cell-to-cell spread observed. Taken together these studies suggest that both the gE and gI genes have a significant role in cell-to-cell spread in both CSW-1 and A20 strains of ILTV. The CRISPR/Cas9-assisted deletion of genes from the ILTV genome described in this study adds this virus to a growing list of viruses to which this approach has been used to study viral gene function.

Glycoprotein-C-gene-deleted recombinant infectious laryngotracheitis virus expressing a genotype VII Newcastle disease virus fusion protein protects against virulent infectious laryngotracheitis virus and Newcastle disease virus

To develop an alternative vectored vaccine against both Newcastle disease virus (NDV) and infectious laryngotracheitis virus (ILTV), the glycoprotein C (gC) gene was first deleted from an avirulent ILTV. Based on this gC-deleted ILTV mutant, a recombinant ILTV expressing the fusion protein (F) of a genotype VII NDV (designated ILTV-ΔgC-F) was then constructed. Expression of the NDV F protein in ILTV-ΔgC-F-infected LMH cells was examined with an immunofluorescence assay and western blotting. The F gene was stably maintained in the genome of ILTV-ΔgC-F and the F protein was stably expressed. Compared with the parental virus, ILTV-ΔgC-F demonstrated an increased penetration capacity in vitro, and an increased replication rate in vitro and in vivo. Both the parental virus and ILTV-ΔgC-F were avirulent in chickens. Vaccination of specific-pathogen-free chickens with ILTV-ΔgC-F induced ILTV-specific antibodies, detected with an enzyme-linked immunosorbent assay (ELISA), and provided complete clinical protection against virulent ILTV, although viral shedding and replication were detected in the respiratory tract in the early stage of infection in a very small number of birds. Vaccination with ILTV-ΔgC-F also provided significant protection against challenge with a virulent genotype VII NDV, although the level of NDV-specific antibodies detected with an ELISA was low. Notably, the numbers of birds that were positive for the virulent genotype VII NDV and the replication of the challenge virus NDV in selected target tissues were significantly lower in the ILTV-ΔgC-F-vaccinated chickens than in the control birds. Our results indicate that ILTV-ΔgC-F has potential utility as a bivalent candidate vaccine against both infectious laryngotracheitis and Newcastle disease.

Multilocus analysis of Gallid herpesvirus 1 in layer chickens in Iraq

Background and Aim:

Infectious laryngotracheitis virus (ILTV) causes a highly pathogenic respiratory disease that affects poultry. It is also known as Gallid herpesvirus 1. ILT prophylaxis measures often include using live attenuated vaccines. The live attenuated vaccine can, however, lead to the formation of new strains of ILTV as a result of vaccine reversion and recombination with field strains. Therefore, this study was performed to explore the multilocus variation of ILTV strains of field and vaccine origin. Samples were tested from two distinctive geographical areas in Iraq as little is known about the ILTV genetic diversity within these areas.

Materials and Methods:

The polymerase chain reaction method was utilized to generate sequencing templates of six highly polymorphic genes, including UL54, UL52, gB, ICP18.5, ICP4, and gJ in the layer chicken sample (n=15). The Western blotting technique was also employed to detect and estimate the native molecular weight of gE.

Results:

The results revealed an important degree of genetic relatedness between the field and vaccine strains across all genes. In addition, gE was found to be expressed natively at 49 kDa.

Conclusion:

The findings of this study may be used to improve the production process of the vaccine for more effective ILT prophylaxis and could further the understanding of epidemiologists and immunologists to better control ILT in the future.

Genetic stability of a Newcastle disease virus vectored infectious laryngotracheitis virus vaccine after serial passages in chicken embryos

Previously, we have demonstrated that the recombinant Newcastle disease virus (NDV) expressing the infectious laryngotracheitis virus (ILTV) glycoprotein D (gD) conferred protection against both virulent NDV and ILTV challenges in chickens. In this study, we evaluated the genetic stability of the recombinant vaccine after eight serial passages in embryonated chicken eggs (ECE). The vaccine master seed virus at the original egg-passage level 3 (EP3) was diluted and passaged in three separate repetitions (A, B and C) in ECE eight times (EP4 to EP11). RT-PCR analysis of the vaccine seed and egg-passaged virus stocks showed that there was no detectable insertion/deletion in the ILTV gD insert region. Next-generation sequencing analysis of the EP3 and EP11 virus stocks confirmed their genome integrity and revealed a total of thirteen single-nucleotide polymorphisms (SNPs). However, none of these SNPs were located in the ILTV gD insert or any of the known critical biological determinant positions. Virological and immunofluorescent assays provided additional evidence that the EP11 virus stocks retained their growth kinetics, low pathogenicity, and robust level of gD expression comparable to that of the vaccine master seed virus. This indicated that the SNPs were non-detrimental sporadic mutations. These results demonstrated that the insertion of ILTV gD gene into the NDV LaSota backbone did not significantly affect the genetic stability of the recombinant virus and that the rLS/ILTV-gD virus is a safe and genetically stable vaccine candidate after at least eight serial passages in ECE.

Comparative genome analysis of Korean field strains of infectious laryngotracheitis virus

Attenuated live infectious laryngotracheitis (ILT) virus (ILTV) vaccines have been used to prevent and control the outbreak of ILT worldwide. Recent studies using high-throughput sequencing technology have increased the number of complete genome sequences of ILTVs, enabling comparative genome analysis. Although 37 complete genome sequences of ILTV, including vaccine strains, have been reported, the complete genome sequence of any field strain of ILTV in South Korea is yet to be published. In this study, we determined and analyzed the complete genome sequences of three virulent Korean field strains of ILTV (40798/10/Ko, 0206/14/Ko, and 30678/14/Ko). Two of the Korean field strains (40798/10/Ko and 0206/14/Ko) displayed fewer non-synonymous single nucleotide polymorphisms than those of the Serva vaccine strain, indicating that these Korean field strains of ILTV most likely originated from the vaccine strain. The third ILTV strain, 307678/14/Ko, had two regions in the genome showing recombination between the Serva vaccine-like strain and the Australian A20 vaccine-like strain. Comparative genome analysis of ILTV using the Korean field strains with variable virulence can shed light on the recent trend of the emergence of virulent ILTV strains in the field. A few amino acid changes in the genome of ILTV vaccines could enhance the virulence in the vaccine strain, and natural recombination should be considered one of the major risks for the generation of revertant strains of ILTV under field conditions.

Recombinant infectious laryngotracheitis virus expressing Newcastle disease virus F protein protects chickens against infectious laryngotracheitis virus and Newcastle disease virus challenge

In this study, we isolated and identified an infectious laryngotracheitis virus (ILTV) that was naturally avirulent in specific pathogen-free (SPF) chickens, with the aim of developing a more efficacious vaccine against ILTV and Newcastle disease virus (NDV). We constructed a US9-deleted ILTV mutant based on this avirulent ILTV, and then constructed a recombinant ILTV (designated ILTV-ΔUS9-F) expressing the fusion protein (F) of the genotype VII NDV based on the US9-deleted ILTV mutant. Expression of the F protein in ILTV-ΔUS9-F-infected cells was confirmed by indirect immunofluorescence assay and western blotting. The inserted F gene was stably expressed in ILTV-ΔUS9-F. The growth kinetics of ILTV-ΔUS9-F were comparable to those of the wild-type ILTV strain. Vaccination of SPF chickens with ILTV-ΔUS9-F produced no clinical signs but did induce low levels of NDV-specific enzyme-linked immunosorbent assay and neutralizing antibodies. A single vaccination with 10⁴ plaque-forming units (PFU) of ILTV-ΔUS9-F provided good protection against both genotype VII and IX NDVs based on clinical signs, similar to the protection provided by the commercial live La Sota vaccine. Notably, ILTV-ΔUS9-F limited the replication and shedding of genotype VII NDV from oropharyngeal swabs more efficiently than the La Sota vaccine. In addition, vaccination with lower doses (10³ and 10² PFU) of ILTV-ΔUS9-F also provided sufficient clinical protection. These results indicated that ILTV-ΔUS9-F may be a bivalent vaccine candidate against both ILTV and NDV.

Impairment of infectious laryngotracheitis virus replication by deletion of the UL[-1] gene

Infectious laryngotracheitis virus (ILTV) encodes several unique genes, including a pair of unique nuclear proteins UL0 and UL[-1] that are expressed during replication in cell culture. Although the UL0 gene has been shown to be dispensable for replication, the role of UL[-1] has not been elucidated. In this study a deletion mutant of ILTV lacking the UL[-1] gene was constructed using homologous recombination. The coding sequences of the gene were replaced with the gene for enhanced green fluorescent protein and the cytomegalovirus major immediate early promoter element. The progeny virus carrying the reporter gene was readily identified using fluorescent microscopy, but was unable to propagate in the permissive cells in the absence of wild type ILTV. Even after plaque purification and fluorescent associated cell sorting the recombinant virus deficient in UL[-1] gene could not be successfully isolated. Our findings suggest that the UL[-1] gene has an important role in ILTV replication.

Viral proteins expressed in the protozoan parasite Eimeria tenella are detected by the chicken immune system

Background

Eimeria species are parasitic protozoa that cause coccidiosis, an intestinal disease commonly characterised by malabsorption, diarrhoea and haemorrhage that is particularly important in chickens. Vaccination against chicken coccidiosis is effective using wild-type or attenuated live parasite lines. The development of protocols to express foreign proteins in Eimeria species has opened up the possibility of using Eimeria live vaccines to deliver heterologous antigens and function as multivalent vaccine vectors that could protect chickens against a range of pathogens.

Results

In this study, genetic complementation was used to express immunoprotective virus antigens in Eimeria tenella. Infectious bursal disease virus (IBDV) causes Gumboro, an immunosuppressive disease that affects productivity and can interfere with the efficacy of poultry vaccination programmes. Infectious laryngotracheitis virus (ILTV) causes a highly transmissible respiratory disease for which strong cellular immunity and antibody responses are required for effective vaccination. Genes encoding the VP2 protein from a very virulent strain of IBDV (vvVP2) and glycoprotein I from ILTV (gI) were cloned downstream of 5’Et-Actin or 5’Et-TIF promoter regions in plasmids that also contained a mCitrine fluorescent reporter cassette under control of the 5’Et-MIC1 promoter. The plasmids were introduced by nucleofection into E. tenella sporozoites, which were then used to infect chickens. Progeny oocysts were sorted by FACS and passaged several times in vivo until the proportion of fluorescent parasites in each transgenic population reached ~20 % and the number of transgene copies per parasite genome decreased to < 10. All populations were found to transcribe and express the transgene and induced the generation of low titre, transgene-specific antibodies when used to immunise chickens.

Conclusions

E. tenella can express antigens of other poultry pathogens that are successfully recognised by the chicken immune system. Nonetheless, further work has to be done in order to improve the levels of expression for its future use as a multivalent vaccine vector.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1756-2) contains supplementary material, which is available to authorized users.

Full Genome Sequence-Based Comparative Study of Wild-Type and Vaccine Strains of Infectious Laryngotracheitis Virus from Italy

Infectious laryngotracheitis (ILT) is an acute and highly contagious respiratory disease of chickens caused by an alphaherpesvirus, infectious laryngotracheitis virus (ILTV). Recently, full genome sequences of wild-type and vaccine strains have been determined worldwide, but none was from Europe. The aim of this study was to determine and analyse the complete genome sequences of five ILTV strains. Sequences were also compared to reveal the similarity of strains across time and to discriminate between wild-type and vaccine strains. Genomes of three ILTV field isolates from outbreaks occurred in Italy in 1980, 2007 and 2011, and two commercial chicken embryo origin (CEO) vaccines were sequenced using the 454 Life Sciences technology. The comparison with the Serva genome showed that 35 open reading frames (ORFs) differed across the five genomes. Overall, 54 single nucleotide polymorphisms (SNPs) and 27 amino acid differences in 19 ORFs and two insertions in the UL52 and ORFC genes were identified. Similarity among the field strains and between the field and the vaccine strains ranged from 99.96% to 99.99%. Phylogenetic analysis revealed a close relationship among them, as well. This study generated data on genomic variation among Italian ILTV strains revealing that, even though the genetic variability of the genome is well conserved across time and between wild-type and vaccine strains, some mutations may help in differentiating among them and may be involved in ILTV virulence/attenuation. The results of this study can contribute to the understanding of the molecular bases of ILTV pathogenicity and provide genetic markers to differentiate between wild-type and vaccine strains.