Avian infectious laryngotracheitis

Spray vaccination with a Newcastle disease virus (NDV)-vectored infectious laryngotracheitis (ILT) vaccine protects commercial chickens from ILT in the presence of maternally-derived antibodies

Infectious laryngotracheitis (ILT) poses a significant threat to the poultry industry, and vaccines play an important role in protection. However, due to the increasing scale of poultry production, there is an urgent need to develop vaccines that are suitable for convenient immunization methods such as spraying. Previous studies have shown that Newcastle disease virus (NDV)-ILT vaccines administered via intranasal and intraocular routes to commercial chickens carrying maternally-derived antibodies (MDAs) are still protective against ILT. In this study, a recombinant NDV (rNDV) was generated to express infectious laryngotracheitis virus (ILTV) glycoprotein B (gB), named rLS-gB, based on a full-length cDNA clone of the LaSota strain. The protective effect of different doses of rLS-gB administered by spray vaccination to commercial chickens at 1 d of age (doa) was evaluated. The chickens were exposed to 160-μm aerosol particles for 10 min for spray vaccination, and no adverse reactions were observed after vaccination. Despite the presence of anti-NDV MDAs and anti-ILTV MDAs in chickens, the ILTV- and NDV-specific antibody titres were significantly greater in the vaccinated groups than in the unvaccinated group. After challenge with a virulent ILTV strain, no clinical signs were observed in the 107 EID50/ml group compared to the other groups. Furthermore, vaccination with 107 EID50/ml rLS-gB significantly reduced the ILTV viral load and ameliorated gross and microscopic lesions in the trachea of chickens. Overall, these results suggested that rLS-gB is a safe and efficient candidate spray vaccine for ILT and is especially suitable for scaled chicken farms.

A meta-analysis for prevalence of infectious laryngotracheitis in chickens in mainland China in 1981-2022

BACKGROUND

Infectious laryngotracheitis (ILT) is a highly infectious upper respiratory tract disease of chickens caused by infectious laryngotracheitis virus or Gallid herpesvirus 1 (GaHV-1). ILT is an important respiratory disease of chickens and annually causes significant economic losses in the chicken industry. Although numerous relevant studies have been published, the overall prevalence of ILT infection among chicken in mainland China is still unknown, and associated risk factors need to be evaluated to establish preventive measures.

RESULTS

The present study reviewed the literature on the prevalence of ILT in chickens in China as of December 20, 2022, retrieved from six databases-CNKI, Wanfang, VIP, PubMed, Web of Science, and ScienceDirect-were used to retrieve relevant studies published between January 1, 1981 and December 20, 2022. The literature quality of studies was assessed, and 20 studies with a total of 108,587 samples were included in the meta-analysis. Results of the meta-analysis showed that the overall prevalence of ILT was 10% (95% confidence interval: 8 -12%) through the random-effects model, which showed high heterogeneity, I2 = 99.4%. Further subgroup analyses showed that the prevalence of ILT decreased over time; furthermore, the prevalence in Northwest China was slightly lower than that in North China and South China, and the prevalence estimated using the diagnostic technique AGP was higher than that reported using other diagnostic techniques.

CONCLUSIONS

ILT is prevalent to some extent in mainland China. Given that the ILT attenuated live vaccine has a certain level of virulence and the prevalence differences between regions, we recommend controlling breeding density, improving immunization programs and continuously monitoring viruses and to prevent ILT prevailing in mainland China.

Characterization of the Effects of Host p53 and Fos on Gallid Alpha Herpesvirus 1 Replication

Treatment options for herpesvirus infections that target the interactions between the virus and the host have been identified as promising. Our previous studies have shown that transcription factors p53 and Fos are essential host determinants of gallid alpha herpesvirus 1 (ILTV) infection. The impact of p53 and Fos on ILTV replication has 'not been fully understood yet. Using the sole ILTV-permissive chicken cell line LMH as a model, we examined the effects of hosts p53 and Fos on all phases of ILTV replication, including viral gene transcription, viral genome replication, and infectious virion generation. We achieved this by manipulating the expression of p53 and Fos in LMH cells. Our results demonstrate that the overexpression of either p53 or Fos can promote viral gene transcription at all stages of the temporal cascade of ILTV gene expression, viral genome replication, and infectious virion production, as assessed through absolute quantitative real-time PCR, ILTV-specific RT-qPCR assays, and TCID50 assays. These findings are consistent with our previous analyses of the effects of Fos and p53 knockdowns on virus production and also suggest that both p53 and Fos may be dispensable for ILTV replication. Based on the synergistic effect of regulating ILTV, we further found that there is an interaction between p53 and Fos. Interestingly, we found that p53 also has targeted sites upstream of ICP4, and these sites are very close to the Fos sites. In conclusion, our research offers an in-depth understanding of how hosts p53 and Fos affect ILTV replication. Understanding the processes by which p53 and Fos regulate ILTV infection will be improved by this knowledge, potentially paving the way for the development of novel therapeutics targeting virus-host interactions as a means of treating herpesvirus infections.

Reconstitution and Mutagenesis of Avian Infectious Laryngotracheitis Virus from Cosmid and Yeast Centromeric Plasmid Clones

The genomes of numerous herpesviruses have been cloned as infectious bacterial artificial chromosomes. However, attempts to clone the complete genome of infectious laryngotracheitis virus (ILTV), formally known as Gallid alphaherpesvirus-1, have been met with limited success. In this study, we report the development of a cosmid/yeast centromeric plasmid (YCp) genetic system to reconstitute ILTV. Overlapping cosmid clones were generated that encompassed 90% of the 151-Kb ILTV genome. Viable virus was produced by cotransfecting leghorn male hepatoma (LMH) cells with these cosmids and a YCp recombinant containing the missing genomic sequences - spanning the TRS/UL junction. An expression cassette for green fluorescent protein (GFP) was inserted within the redundant inverted packaging site (ipac2), and the cosmid/YCp-based system was used to generate recombinant replication-competent ILTV. Viable virus was also reconstituted with a YCp clone containing a BamHI linker within the deleted ipac2 site, further demonstrating the nonessential nature of this site. Recombinants deleted in the ipac2 site formed plaques undistinguished from those viruses containing intact ipac2. The 3 reconstituted viruses replicated in chicken kidney cells with growth kinetics and titers similar to the USDA ILTV reference strain. Specific pathogen-free chickens inoculated with the reconstituted ILTV recombinants succumbed to levels of clinical disease similar to that observed in birds inoculated with wildtype viruses, demonstrating the reconstituted viruses were virulent. IMPORTANCE Infectious laryngotracheitis virus (ILTV) is an important pathogen of chicken with morbidity of 100% and mortality rates as high as 70%. Factoring in decreased production, mortality, vaccination, and medication, a single outbreak can cost producers over a million dollars. Current attenuated and vectored vaccines lack safety and efficacy, leaving a need for better vaccines. In addition, the lack of an infectious clone has also impeded understanding viral gene function. Since infectious bacterial artificial chromosome (BAC) clones of ILTV with intact replication origins are not feasible, we reconstituted ILTV from a collection of yeast centromeric plasmids and bacterial cosmids, and identified a nonessential insertion site within a redundant packaging site. These constructs and the methodology necessary to manipulate them will facilitate the development of improved live virus vaccines by modifying genes encoding virulence factors and establishing ILTV-based viral vectors for expressing immunogens of other avian pathogens.

Characterization of a Recombinant Thermostable Newcastle Disease Virus (NDV) Expressing Glycoprotein gB of Infectious Laryngotracheitis Virus (ILTV) Protects Chickens against ILTV Challenge

Infectious laryngotracheitis (ILT) and Newcastle disease (ND) are two important avian diseases that have caused huge economic losses to the poultry industry worldwide. Newcastle disease virus (NDV) has been used as a vector in the development of vaccines and gene delivery. In the present study, we generated a thermostable recombinant NDV (rNDV) expressing the glycoprotein gB (gB) of infectious laryngotracheitis virus (ITLV) based on the full-length cDNA clone of the thermostable TS09-C strain. This thermostable rNDV, named rTS-gB, displayed similar thermostability, growth kinetics, and pathogenicity compared with the parental TS09-C virus. The immunization data showed that rTS-gB induced effective ILTV- and NDV-specific antibody responses and conferred immunization protection against ILTV challenge in chickens. The efficacy of rTS-gB in alleviating clinical signs was similar to that of the commercial attenuated ILTV K317 strain. Furthermore, rTS-gB could significantly reduce viral shedding in cloacal and tracheal samples. Our study suggested that the rNDV strain rTS-gB is a thermostable, safe, and highly efficient vaccine candidate against ILT and ND.

Diagnosis of Infectious Laryngotracheitis Outbreaks on Layer Hen and Broiler Breeder Farms in Vojvodina, Serbia

Infectious laryngotracheitis (ILT) is a respiratory disease of poultry characterized by high morbidity and variable mortality. ILT is caused by Gallid alpha herpesvirus-1 (GaHV-1), which is transmitted horizontally and most susceptible are chickens older than 4 weeks. After almost two decades since last appearance of this disease in Vojvodina, an outbreak occurred from April 2020 to August 2021 on five laying hen farms and one broiler breeder flock farm. Clinical signs were mild to severe respiratory symptoms, unilateral or bilateral head swelling, serous nasal discharge, conjunctivitis and increased tearing. There was a decrease in feed consumption (2.1-40.0%) and egg production (2.7-42.0%), weight loss and mortality increased (0.8-31.5%). Pathomorphological changes were localized in the upper respiratory tract. Total of 200 carcasses were examined; 40 pooled samples were analyzed by PCR, and 40 by bacteriological analysis. ILT virus was confirmed in tracheal tissue samples. Infected flocks were not vaccinated against this disease. Five flocks had coinfection with Avibacterium paragallinarum. Three-to-four weeks after the first reported case in the flock, clinical symptoms had ceased. Future control and prevention strategies will involve the procurement of flocks vaccinated by recombinant vaccine or the registration of live attenuated vaccines and their use during the rearing period.

Detection and molecular characterization of infectious laryngotracheitis virus (ILTV) in chicken with respiratory signs in Brazil during 2015 and 2016

Avian infectious laryngotracheitis (ILT) is a respiratory disease that causes severe economic losses in the poultry industry, mainly due to high morbidity and mortality and reduced egg production. Molecular characterization was performed on samples collected from flocks in the Brazilian States of São Paulo, Pernambuco, and Minas Gerais during 2015 and 2016 that presented clinical signs of respiratory disease. End-point PCR was used for viral detection, and DNA sequencing was used for differentiation of vaccine and field strains. Molecular analysis based on the infected cell protein (ICP4) gene separated four of the nine samples together with previous Brazilian isolates (São Paulo and Minas Gerais), one sample was grouped on the same branch as Minas Gerais strains (along with another related sample), one sample was separately branched but still related to the tissue culture origin (TCO) vaccine strain, and two samples were grouped on the same branch as the TCO vaccine strain. Molecular analysis of the thymidine kinase (TK) gene showed the existence of strains of both high and low virulence. The characterization of two fragments of the ICP4 gene and a fragment of the TK gene in this study suggested that the virus circulating in Guatapará, as well as those in Barretos and Itanhandu, that is causing respiratory problems in birds is a highly virulent field strain. The clinical signs point to a TCO vaccine strain that most likely underwent some reversal event and is a latent reactivated infection.

Field Application of qPCR Monitoring of Infectious Laryngotracheitis Virus in Settled Chicken House Dust and Its Role in Control of a Major Outbreak

Population-level sampling based on qPCR detection of infectious laryngotracheitis virus (ILTV) in poultry dust can be used to assess ILT vaccination outcomes following mass administration in drinking water. We report on the field application of this approach to assess the success of vaccine administration and its use in ILT outbreak control in meat chickens. In Study 1, dust samples were collected from 26 meat chicken flocks at 0, 4, 7, 14, and 21 days post drinking water vaccination (DPV) given between 7 to 13 days of age with the Serva or A20 live attenuated ILT vaccines. Unexpectedly, ILTV DNA was detected in dust samples collected prior to vaccination in 22/26 flocks. Typing revealed that the detected ILTV was different from the vaccine virus. To determine whether the detected ILTV DNA was from active infection or carryover of a noninfectious virus, Study 2 was implemented in 14 additional flocks with dust samples collected at 0, 7, 14, and 21 DPV and tracheal swabs collected from 15 birds/flock at 0 and 21 DPV. The results indicated that there was active infection with ILTV in those flocks before vaccination. This approach contributed to a statewide control program resulting in the eradication of ILT from South Australia as confirmed by negative ILTV test results for dust samples from 50 flocks and the absence of clinical ILT. These findings show that ILTV infection prior to vaccination is common in outbreak situations and that dust samples must be collected at 0 and 7 DPV for meaningful interpretation of vaccination outcomes and ILTV status. Comparatively low-cost dust testing during an outbreak, coupled with typing information, greatly assisted with decision making and control strategies during a major outbreak, including confirmation of the absence of infection in the final stages.

Biological Characteristics of Infectious Laryngotracheitis Viruses Isolated in China

Infectious laryngotracheitis virus (ILTV) causes severe respiratory disease in chickens and results in huge economic losses in the poultry industry worldwide. To correlate the genomic difference with the replication and pathogenicity, phenotypes of three ILTVs isolated from chickens in China from 2016 to 2018 were sequenced by high-throughput sequencing. Based on the entire genome, the isolates GD2018 and SH2017 shared 99.9% nucleotide homology, while the isolate SH2016 shared 99.7% nucleotide homology with GD2018 and SH2017, respectively. Each virus genome contained 82 ORFs encoding 77 kinds of protein, 31 of which share the same amino acid sequence in the three viruses. GD2018 and SH2017 shared 57 proteins with the same amino acid sequence, while SH2016 shared 42 and 41 proteins with the amino acid sequences of GD2018 and SH2017, respectively. SH2016 propagated efficiently in allantoic fluid and on chorioallantoic membranes (CAMs) of SPF chicken embryo eggs, while GD2018 and SH2017 proliferated well only on CAMs. GD2018 propagated most efficiently on CAMs and LMH cells among three isolates. SH2016 caused serious clinical symptoms, while GD2018 and SH2017 caused mild and moderate clinical symptoms in chickens, although the sero of the chickens infected with those three isolates were all positive for anti-ILTV antibody at 14 and 21 days after challenge. Three ILTVs with high genetic homology showed significant differences in the replication in different culture systems and the pathogenicity of chickens, providing basic materials for studying the key determinants of pathogenicity of ILTV.

Host Responses Following Infection with Canadian-Origin Wildtype and Vaccine Revertant Infectious Laryngotracheitis Virus

Infectious laryngotracheitis (ILT) is caused by Gallid herpesvirus-1 (GaHV-1) or infectious laryngotracheitis virus (ILTV) and was first described in Canadian poultry flocks. In Canada, ILTV infection is endemic in backyard flocks, and commercial poultry encounters ILT outbreaks sporadically. A common practice to control ILT is the use of live attenuated vaccines. However, outbreaks still occur in poultry flocks globally due to ILTV vaccine strains reverting to virulence and emergence of new ILTV strains due to recombination in addition to circulating wildtype strains. Recent studies reported that most of the ILT outbreaks in Canada were induced by the chicken-embryo-origin (CEO) live attenuated vaccine revertant strains with the involvement of a small percentage of wildtype ILTV. It is not known if the host responses induced by these two ILTV strains are different. The objective of the study was to compare the host responses elicited by CEO revertant and wildtype ILTV strains in chickens. We infected 3-week-old specific pathogen-free chickens with the two types of ILTV isolates and subsequently evaluated the severity of clinical and pathological manifestations, in addition to host responses. We observed that both of the isolates show high pathogenicity by inducing several clinical and pathological manifestations. A significant recruitment of immune cells at both 3 and 7 days post-infection (dpi) was observed in the tracheal mucosa and the lung tissues of the infected chickens with wildtype and CEO vaccine revertant ILTV isolates when compared to uninfected controls. Overall, this study provides a better understanding of the mechanism of host responses against ILTV infection.

Quantitative real-time PCR assays for the concurrent diagnosis of infectious laryngotracheitis virus, Newcastle disease virus and avian metapneumovirus in poultry

Newcastle disease (ND), infectious laryngotracheitis (ILT) and avian metapneumovirus (aMPV) can be similar making it critical to quickly differentiate them. Herein, we adapted pre-existing molecular-based diagnostic assays for NDV and ILTV, and developed new assays for aMPV A and B, for use under synchronized thermocycling conditions. All assays performed equivalently with linearity over a 5 log₁₀ dynamic range, a reproducible (R² > 0.99) limit of detection of ≥ 10 target copies, and amplification efficiencies between 86.8%–98.2%. Using biological specimens for NDV and ILTV showed 100% specificity. Identical amplification conditions will simplify procedures for detection in diagnostic laboratories.

A preliminary study of the localisation of infectious laryngotracheitis virus glycoprotein E within specific peripheral blood lymphocytes

Infectious laryngotracheitis virus (ILTV) DNA has been detected in blood fractions, but the cell phenotype with which the virus is associated is unknown. This study investigated the presence of ILTV antigen in peripheral blood cells of six acutely ILTV-infected chickens (5 or 9 days post ocular inoculation with a virulent isolate and three sham-inoculated chickens using immunofluorescent staining. Blood fractions were separated by Ficoll-Paque density gradient centrifugation, and smears were prepared from erythrocyte and leukocyte fractions. The smears were stained for ILTV glycoprotein E and the leukocyte markers CD4, CD8, Bu-1 (B cell), KUL01 (monocyte/macrophage), TCRγδ, and TCRαβ/Vβ₂ and examined under a confocal microscope. In samples from infected birds, ILTV gE specific fluorescence was localised in B cells and all evaluated T cell types, but not in monocytes and erythrocytes. The percentage of CD4, CD8, TCRγδ, TCRαβ/Vβ₁, TCRαβ/Vβ₂ and B cells colocalised with ILTV antigen ranged from 13.3% to 22.3%. None of the samples from the sham-inoculated chickens exhibited fluorescence for ILTV gE. The results of this pilot study suggest that ILTV has a tropism for peripheral blood T and B cells. Further research is required to investigate whether these cells support ILTV productive replication.

Evaluation of Recombinant Herpesvirus of Turkey Laryngotracheitis (rHVT-LT) Vaccine against Genotype VI Canadian Wild-Type Infectious Laryngotracheitis Virus (ILTV) Infection

In Alberta, infectious laryngotracheitis virus (ILTV) infection is endemic in backyard poultry flocks; however, outbreaks are only sporadically observed in commercial flocks. In addition to ILTV vaccine revertant strains, wild-type strains are among the most common causes of infectious laryngotracheitis (ILT). Given the surge in live attenuated vaccine-related outbreaks, the goal of this study was to assess the efficacy of a recombinant herpesvirus of turkey (rHVT-LT) vaccine against a genotype VI Canadian wild-type ILTV infection. One-day-old specific pathogen-free (SPF) White Leghorn chickens were vaccinated with the rHVT-LT vaccine or mock vaccinated. At three weeks of age, half of the vaccinated and the mock-vaccinated animals were challenged. Throughout the experiment, weights were recorded, and feather tips, cloacal and oropharyngeal swabs were collected for ILTV genome quantification. Blood was collected to isolate peripheral blood mononuclear cells (PBMC) and quantify CD4+ and CD8+ T cells. At 14 dpi, the chickens were euthanized, and respiratory tissues were collected to quantify genome loads and histological examination. Results showed that the vaccine failed to decrease the clinical signs at 6 days post-infection. However, it was able to significantly reduce ILTV shedding through the oropharyngeal route. Overall, rHVT-LT produced a partial protection against genotype VI ILTV infection.

A Cell Line Adapted Infectious Laryngotracheitis Virus Strain (BΔORFC) for in ovo and Hatchery Spray Vaccination Alone or in Combination with a Recombinant HVT-LT Vaccine

To produce more-stable, live attenuated vaccines for infectious laryngotracheitis virus (ILTV), deletion of genes related to virulence has been extensively pursued. Although its function remains unknown, the open reading frame C (ORF C) is among the genes potentially associated with viral virulence that is nonessential for replication in vitro. Earlier results indicated that the ILT virus with deletion of the ORF C gene (BΔORFC) was suitable and safe for eye drop administration but was not sufficiently attenuated for in ovo administration. The objective of this study was to evaluate the safety and protection efficacy of a cell line-adapted, gene-deleted strain (BΔORFC) of ILTV when administered in ovo and/or spray (SP) by itself, or in combination with the recombinant HVT-LT (rHVT-LT) vaccine. Results indicated that vaccination with the BΔORFC strain, either by itself or in combination with an rHVT-LT vaccine, did not affect hatchability, and only marginal signs of respiratory distress were recorded for groups of chickens that received the BΔORFC strain via SP. The replication and seroconversion induced by the BΔORFC strain after in ovo and SP administration was very limited, whereas the replication of the rHVT-LT vaccine was delayed when combined with the BΔORFC strain in ovo. Compared to rHVT-LT or BΔORFC when administered alone, dual vaccination with rHVT-LT + BΔORFC was more effective in mitigating clinical signs of the disease and reducing challenge virus load in the trachea. To our knowledge, this study provides the first proof of concept that ILTV strains can be sufficiently attenuated for early vaccination in ovo or at hatch; also, this study documented the benefits of using a dual (recombinant and live attenuated) hatchery vaccination strategy for ILTV.

Review of Poultry Recombinant Vector Vaccines

The control of poultry diseases has relied heavily on the use of many live and inactivated vaccines. However, over the last 30 yr, recombinant DNA technology has been used to generate many novel poultry vaccines. Fowlpox virus and turkey herpesvirus are the two main vectors currently used to construct recombinant vaccines for poultry. With the use of these two vectors, more than 15 recombinant viral vector vaccines against Newcastle disease, infectious laryngotracheitis, infectious bursal disease, avian influenza, and Mycoplasma gallisepticum have been developed and are commercially available. This review focuses on current knowledge about the safety and efficacy of recombinant viral vectored vaccines and the mechanisms by which they facilitate the control of multiple diseases. Additionally, the development of new recombinant vaccines with novel vectors will be briefly discussed.

Assessing the infiltration of immune cells in the upper trachea mucosa after infectious laryngotracheitis virus (ILTV) vaccination and challenge

The types of immune cells that populate the trachea after ILTV vaccination and infection have not been assessed. The objective of this study was to quantify CD4⁺, CD8α⁺, CD8β⁺, TCRγδ⁺, and MRC1LB⁺ cells that infiltrate the trachea after vaccination with chicken embryo origin (CEO), tissue culture origin (TCO), and recombinant herpesvirus of turkey-laryngotracheitis (rHVT-LT) vaccines, and after challenge of vaccinated and non-vaccinated chickens with a virulent ILTV strain. Eye-drop vaccination with CEO, or TCO, or in ovo vaccination with rHVT-LT did not alter the number of CD4⁺, CD8α⁺, CD8β⁺, TCRγδ⁺, and MRC1LB⁺ cells in the trachea. After challenge, the CEO vaccinated group of chickens showed swift clearance of the challenge virus, the mucosa epithelium of the trachea remained intact, and a limited number of CD4⁺, CD8α⁺, and CD8β⁺ cells were detected in the upper trachea mucosa. The TCO and rHVT-LT vaccinated groups of chickens showed narrow viral clearance with moderate disruption of the trachea epithelial integrity, and a significant increase in CD4⁺, CD8α⁺, CD8β⁺, and TCRγδ⁺ cells infiltrated the upper trachea mucosa. Non-vaccinated challenged chickens showed high levels of viral replication, the epithelial organization of the upper trachea mucosa was heavily disrupted, and the predominant infiltrates were CD4⁺, TCRγδ⁺, and MRC1LB⁺ cells. Hence, the very robust protection provided by CEO vaccination was characterized by minimal immune cell infiltration to the trachea mucosa. In contrast, partial protection induced by the TCO and rHVT-LT vaccines requires a prolonged period of T cell expansion to overcome the established infection in the trachea mucosa.

Infectious laryngotracheitis of chickens: Pathologic and immunohistochemistry findings

Infectious laryngotracheitis (ILT) is an important upper respiratory disease of chickens. Gross and histologic lesions of ILT in chickens are compared to immunohistochemistry to evaluate the diagnostic test sensitivity. A total of 31 separate ILT-confirmed necropsy submissions (12 commercial meat-type flocks, 13 egg-type producers, and 6 backyard flocks) were arbitrarily selected. Each submission ranged from 1 to 18 birds, for a total of 246 chickens. Cases with available formalin-fixed tissues were selected to include a range of bird production types, ages, clinical histories, and severity of macroscopic and histologic lesions. Macroscopic findings in the respiratory tract varied from increased mucus (55.6%) to fibrinonecrotic exudate (20.3%) and hemorrhages in the larynx and trachea (13.0%). Syncytia with intranuclear inclusion bodies were present in the respiratory tract epithelium with or without hemorrhages. Sections of conjunctiva, sinus, larynx, trachea, lung, and air sac were analyzed by immunohistochemistry (IHC) to detect gallid alphaherpesvirus 1 (GaHV-1) antigen. Positive immunolabeling was detected in the cytoplasm and nuclei of syncytia and epithelial cells in 18/22 conjunctivae (82%), 12/13 sinuses (92%), 18/22 larynxes (82%), 23/25 tracheas (92%), 10/21 lungs (57%), and 3/8 air sacs (37%). Of the 34 tissues with no visible syncytia or inclusion bodies, 8 were positive by IHC. In conclusion, IHC was useful to study the viral antigen tissue distribution and support the diagnosis of ILT when the histopathologic interpretation was doubtful.

Surveillance on respiratory diseases reveals enzootic circulation of both H5 and H9 avian influenza viruses in small-scale commercial layer farms of Bangladesh

Poultry production in Bangladesh has been experiencing H5N1 highly pathogenic avian influenza (HPAI) and H9N2 low pathogenic avian influenza (LPAI) for the last 14 years. Vaccination of chickens against H5 HPAI is in practice since the end of 2012. Subsequently, the official reporting of HPAI outbreaks gradually decreased. However, the true extent of circulation of avian influenza virus (AIV) in commercial poultry production is not clear. To explore this, we conducted active surveillance in 422 small-scale commercial layer farms in 20 villages of Mymensingh and Tangail districts of Bangladesh during 2017 and 2018 for the presence of diseases with respiratory signs. A total of 88 farms with respiratory disease problems were identified and investigated during the surveillance. In addition, 22 small-scale commercial layer farms in the neighbouring areas with respiratory disease problem were also investigated on request from the farmers. Pooled samples of oropharyngeal swabs from live birds or respiratory tissues from dead birds of the farm suffering from respiratory disease problem were tested for molecular detection of avian influenza virus (AIV), Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious laryngotracheitis virus (ILTV), Mycoplasma gallisepticum and Avibacterium paragallinarum. A total of 110 farms (88 in the surveillance site and 22 in the neighbouring region) were investigated, and one or more respiratory pathogens were detected from 89 farms. AIV was detected in 57 farms often concurrently with other pathogens. Among these 57 farms, H5, H9, both H5 and H9 or non-H5 and non-H9 AIV were detected in 28, 9, 13 or 7 farms, respectively. Birds of most of the H5 AIV-positive farms did not present typical clinical signs or high mortality. Twenty such farms were observed longitudinally, which had only 1.05%-5.50% mortality but a marked drop in egg production. This widespread circulation of H5 AIV along with H9 AIV and other pathogens in small-scale commercial layer farms, often with low mortality, reaffirms the enzootic circulation of AIV in Bangladesh, which may escape syndromic surveillance focused on unusual mortality only. To reduce public health risks, strengthening of the control programme with comprehensive vaccination, enhanced biosecurity, improved surveillance and outbreak response is suggested.

Transmission of infectious laryngotracheitis virus vaccine and field strains: the role of degree of contact and transmission by whole blood, plasma and poultry dust

Understanding the mechanisms of transmission of infectious laryngotracheitis virus (ILTV) is critical to proper control as both vaccine and wild-type strains circulate within chicken flocks with potential adverse consequences. The relative efficiency of transmission by direct contact between chickens and airborne transmission has not been investigated. Furthermore, relatively high levels of ILTV DNA have been detected in poultry dust and blood but the infectivity of these is unknown. In this study, comparison of in-contact and airborne transmission of two vaccine and one field strain of ILTV revealed that all transmitted to 100% of in-contact birds by 6 days post-exposure (dpe). Airborne transmission without contact resulted in 100% transmission by 14 and 17 dpe for the wild-type and Serva vaccine virus but only 27% transmission by 21 dpe for the A20 vaccine virus. The infectivity of dust or extracts of dust and blood or plasma from infected chickens at various stages of infection was assessed by inoculation into susceptible chickens. There was no transmission by any of these materials. In conclusion, direct contact facilitated efficient ILTV transmission but the virus was unable to be transmitted by dust from infected chickens suggestive of a limited role in the epidemiology of ILTV.

Fos Facilitates Gallid Alpha-Herpesvirus 1 Infection by Transcriptional Control of Host Metabolic Genes and Viral Immediate Early Gene

Gallid alpha-herpesvirus 1, also known as avian infectious laryngotracheitis virus (ILTV), continues to cause huge economic losses to the poultry industry worldwide. Similar to that of other herpesvirus-encoded proteins, the expression of viral genes encoded by ILTV is regulated by a cascade, and the underlying regulatory mechanism remains largely unclear. The viral immediate-early (IE) gene ICP4 plays a prominent role in the initiation of the transcription of early and late genes during ILTV replication. In this study, we identified AP-1 as the key regulator of the transcription of ILTV genes by bioinformatics analysis of genome-wide transcriptome data. Subsequent functional studies of the key members of the AP-1 family revealed that Fos, but not Jun, regulates ILTV infection through AP-1 since knockdown of Fos, but not Jun, by gene silencing significantly reduced ICP4 transcription and subsequent viral genome replication and virion production. Using several approaches, we identified ICP4 as a bona fide target gene of Fos that regulated Fos and has Fos response elements within its promoter. Neither the physical binding of Jun to the promoter of ICP4 nor the transcriptional activity of Jun was observed. In addition, knockdown of Fos reduced the transcription of MDH1 and ATP5A1, genes encoding two host rate-limiting enzymes essential for the production of the TCA intermediates OAA and ATP. The biological significance of the transcriptional regulation of MDH1 and ATP5A1 by Fos in ILTV infection was supported by the fact that anaplerosis of OAA and ATP rescued both ICP4 transcription and virion production in infected cells under when Fos was silenced. Our study identified the transcription factor Fos as a key regulator of ILTV infection through its transcription factor function on both the virus and host sides, improving the current understanding of both avian herpesvirus–host interactions and the roles of AP-1 in viral infection.

Infectious laryngotracheitis: Etiology, epidemiology, pathobiology, and advances in diagnosis and control - a comprehensive review

Infectious laryngotracheitis (ILT) is a highly contagious upper respiratory tract disease of chicken caused by a Gallid herpesvirus 1 (GaHV-1) belonging to the genus Iltovirus, and subfamily Alphaherpesvirinae within Herpesviridae family. The disease is characterized by conjunctivitis, sinusitis, oculo-nasal discharge, respiratory distress, bloody mucus, swollen orbital sinuses, high morbidity, considerable mortality and decreased egg production. It is well established in highly dense poultry producing areas of the world due to characteristic latency and carrier status of the virus. Co-infections with other respiratory pathogens and environmental factors adversely affect the respiratory system and prolong the course of the disease. Latently infected chickens are the primary source of ILT virus (ILTV) outbreaks irrespective of vaccination. Apart from conventional diagnostic methods including isolation and identification of ILTV, serological detection, advanced biotechnological tools such as PCR, quantitative real-time PCR, next generation sequencing, and others are being used in accurate diagnosis and epidemiological studies of ILTV. Vaccination is followed with the use of conventional vaccines including modified live attenuated ILTV vaccines, and advanced recombinant vector vaccines expressing different ILTV glycoproteins, but still these candidates frequently fail to reduce challenge virus shedding. Some herbal components have proved to be beneficial in reducing the severity of the clinical disease. The present review discusses ILT with respect to its current status, virus characteristics, epidemiology, transmission, pathobiology, and advances in diagnosis, vaccination and control strategies to counter this important disease of poultry.

Indicators and risk factors of infectious laryngotracheitis in layer hen flocks in Algeria

Background and Aim

Since 2017, there have been epidemics with respiratory disorders in the laying hen farms in Algeria, as signs and lesions, respiratory difficulties, and hemorrhagic tracheitis, which closely like laryngotracheitis. This study aimed to analyze the epidemiological, serological, and clinical indicators, as well as the risk factors, of infectious laryngotracheitis (ILT) in layer hen flocks in Algeria.

Materials and Methods

A total of 1728 layer hens were sampled randomly from 48 poultry houses. Blood samples were collected from each hen at the wing vein area, and an indirect enzyme-linked immunosorbent assay was done using an IDvet^® kit.

Results

The flocks showed 56.25% seroprevalence. Clinical signs and gross lesions of ILT suspect cases included respiratory signs characterized by hemorrhagic tracheitis and sinusitis; conjunctivitis; egg drop; and a low mortality rate varying from 5% to 20%. Statistical analyses showed the effect of risk factors on the seropositivity for ILT in 48 layer flocks. When the vaccination was not applied, flocks were significantly more seropositive by 54% (odds ratio OR=1.54, p=0.01) compared to vaccinated flocks. Furthermore, flocks with poor hygiene were more seropositive by 68% (OR=1.68, p=0.002) compared to those with good hygiene. Finally, flocks with decreased egg production between 10% and 30% were significantly more seropositive by 42% (OR=1.42, p=0.04) than those with egg production >30%.

Conclusion

The serological survey revealed anti-ILT virus antibodies, signifying the circulation of this virus in layer hen farms in Algeria. Correct vaccination protocol, strict biosecurity measures, rapid diagnosis, and detection of latent carriers are necessary to control and eradicate the disease from layer farms.

Detection of infectious laryngotracheitis virus (ILTV) in tissues and blood fractions from experimentally infected chickens using PCR and immunostaining analyses

The ability of infectious laryngotracheitis virus (ILTV) to replicate in organs outside of the upper respiratory tract and conjunctiva associated-lymphoid tissues is still not well understood. This study investigated the tissue distribution of an Australian field strain of ILTV (class 9) on birds experimentally inoculated via eye-drop at 7 days of age by using quantitative PCR (qPCR) and immunohistochemistry. Tissues including conjunctiva, caecal tonsil, kidney, liver, lung, spleen, thymus, trachea and blood were collected from sham-inoculated (control group; n = 2) and ILTV-inoculated (n = 8) birds at 7 days post-inoculation (dpi). Blood was collected from 13 infected birds at 14 dpi and fractionated using ficoll-paque. At 7 dpi, the highest detection rate and genomic copies (GC) were in conjunctiva (8/8; 8.08 ± 0.48 log₁₀ GC/mg) followed by trachea (8/8; 4.64 ± 0.48) and thymus (8/8; 4.52 ± 0.48), kidney (8/8; 3.97 ± 0.48), lung (8/8; 3.65 ± 0.48), spleen (8/8; 3.55 ± 0.48), liver (8/8; 3.51 ± 0.48), caecal tonsil (7/8; 3.76 ± 0.48) and plasma (4/8; 2.40 ± 0.48 log₁₀ GC/ml). ILTV antigen was only detected in conjunctiva (7/8), trachea (6/8) and lung (4/8) samples. At 14 dpi, ILTV detection rate and genomic copies in buffy coat cells were 12/13 and 2.86 ± 0.39 log₁₀ GC/mg, respectively while those of plasma were 11/13 and 4.29 ± 0.39 log₁₀ GC/ml and red blood cell were 3/13 and 0.36 ± 0.39 log₁₀ GC/mg. In conclusion, ILTV DNA was detected in a wide range of tissues and blood fractions but ILTV antigen was only detected in respiratory organs and conjunctiva.

Recombinant Fowlpox Virus Expressing gB Gene from Predominantly Epidemic Infectious Larygnotracheitis Virus Strain Demonstrates Better Immune Protection in SPF Chickens

Background: Infectious laryngotracheitis (ILT) is a highly contagious acute respiratory disease of chickens. Antigenic mutation of infectious laryngotracheitis virus (ILTV) may result in a vaccination failure in the poultry industry and thus a protective vaccine against predominant ILTV strains is highly desirable. Methods: The full-length glycoprotein B (gB) gene of ILTV with the two mutated synonymous sites of fowlpox virus (FPV) transcription termination signal sequence was cloned into the insertion vector p12LS, which was co-transfected with wild-type (wt) FPV into chicken embryo fibroblast (CEF) to develop a recombinant fowlpox virus-gB (rFPV-gB) candidate vaccine strain. Furthermore, its biological and immunological characteristics were evaluated. Results: The results indicated that gB gene was expressed correctly in the rFPV by indirect immunofluorescent assay and Western blot, and the rFPV-gB provided a 100% protection in immunized chickens against the challenge of predominant ILTV strains that were screened by pathogenicity assay when compared with the commercialized rFPV vaccine, which only provided 83.3%. Conclusion: rFPV-gB can be used as a potential vaccine against predominant ILTV strains.

Avian Viruses that Impact Table Egg Production

Eggs are a common source of protein and other nutrient components for people worldwide. Commercial egg-laying birds encounter several challenges during the long production cycle. An efficient egg production process requires a healthy bird with a competent reproductive system. Several viral pathogens that can impact the bird's health or induce reversible or irreversible lesions in the female reproductive organs adversely interfere with the egg industry. The negative effects exerted by viral diseases create a temporary or permanent decrease in egg production, in addition to the production of low-quality eggs. Several factors including, but not limited to, the age of the bird, and the infecting viral strain and part of reproductive system involved contribute to the form of reproductive disease encountered. Advanced methodologies have successfully elucidated some of the virus-host interactions relevant to the hen's reproductive performance, however, this branch needs further research. This review discusses the major avian viral infections that have been reported to adversely affect egg productivity and quality and aims to summarize the current understanding of the mechanisms that underlie the observed negative effects.

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.

Airborne Transmission of Vaccinal and Wild Type Infectious Laryngotracheitis Virus and Noninfectivity of Extracts of Excreta from Infected Chickens

Infectious laryngotracheitis virus (ILTV) is thought to exit the host in respiratory aerosols and enter by inhalation of these. High levels of ILTV DNA have been detected in excreta, raising the possibility of alternative routes of shedding from the host. However, it is not known whether or not the ILTV DNA in excreta represents infective virus. This study investigated transmission of wild type and vaccinal ILTV from infected to susceptible commercial meat chickens. Airborne- and excreta-mediated transmission of two field isolates of ILTV (Classes 9 and 10) and three vaccine strains (SA2, A20, and Serva) were tested. To test airborne transmission, air from isolators containing infected birds was ducted through a paired isolator containing uninfected chickens. To test excreta transmission, aliquots were prepared from excreta containing a high level of ILTV DNA within the first week after infection. Chicks were infected bilaterally by eye drop. Clinical signs were monitored daily and choanal cleft swab samples for ILTV detection by quantitative PCR were collected at 4, 8, 15, 22, and 28 days postinfection (DPI) in the airborne transmission study and at 7 and 14 DPI from the excreta transmission studies. There was no transmission of ILTV from excreta, suggesting that ILTV is inactivated during passage through the gut. All strains of ILTV were transmitted by the airborne route but only to a limited extent for the vaccine viruses. The field viruses induced clinical signs, pathology, and greatly elevated ILTV genome copies in swabs. In summary, these findings confirm the suspected airborne transmission of ILTV, demonstrate differential transmission potential between wild type and vaccine strains by this route, and indicate that excreta is unlikely to be important in the transmission of ILTV and the epidemiology of ILT.

Seroprevalence of infectious laryngotracheitis disease in backyard chickens in villages of Ada'a district, Oromia, Ethiopia: first report

As per the report from the OIE in 2005, infectious laryngotracheitis (ILT) has not been yet reported in Ethiopia. Hence, considering the evident clinical signs on-field associated with the disease, it felt that there is a need to identify the disease and to protect the chicken population. The study was, therefore, aimed at identifying the seroprevalence of ILT virus from the samples collected from chickens in backyard system, so as to notify its prevalence and setup recommendations for further research in the future. Consequently, cross-sectional study was conducted in eleven purposefully selected peasant associations (PA) of Ada'a district from January to May 2019 to determine ILT in backyard chickens. A total number of 426 sera sample of backyard chickens were randomly collected from 11 PA and each sera was exposed to an indirect enzyme-linked immunosorbent assay (iELISA), at the National Animal Health Diagnostic and Investigation Center, Ethiopia. Out of 426 samples, 233 (54.7%) samples were found positive for ILT virus-specific antibody. The highest prevalence was recorded in Wajitu (83.3%), whereas the least was in Giche (40.7%) PA. There was a statistically significant difference (p < 0.05) among seroprevalence and study PA. The result of this study revealed that a high prevalence of ILT virus is circulating among backyard chickens in the selected PA of Ada'a district, which could significantly affect the poultry sector. Thus, further studies on the circulating strains and the epidemiology of the disease should be carried using a molecular diagnostic test.

Methods to prevent PCR amplification of DNA from non-viable virus were not successful for infectious laryngotracheitis virus

Molecular-based testing of poultry dust has been used as a fast, sensitive and specific way to monitor viruses in chicken flocks but it provides no information on viral viability. Differentiation of viable and nonviable virus would expand the usefulness of PCR-based detection. This study tested three treatments (1. DNAse, 2. propidium monoazide [PMA], 3. immunomagnetic separation [IMS]) applied to dust or virus stock prior to nucleic acid extraction for their ability to exclude nonviable virus from PCR amplification. Infectious laryngotracheitis virus (ILTV) was used as a model. These treatments assume loss of viral viability due to damage to the capsid or to denaturation of epitope proteins. DNAse and PMA assess the integrity of the capsid to penetration by enzyme or intercalating dye, while IMS assesses the integrity of epitope proteins. Treatments were evaluated for their ability to reduce PCR signal, measured as ILTV log₁₀ genomic copies (ILTV GC), of heat and chemically inactivated ILTV in poultry dust and virus stock. Compared to untreated dust samples, there was an overall reduction of 1.7 ILTV GC after IMS treatment (p<0.01), and a reduction of 2.0 ILTV GC after PMA treatment (p<0.0001). DNAse treatment did not reduce ILTV GC in dust (p = 0.68). Compared to untreated virus stocks, there was an overall reduction of 0.5 ILTV GC after DNAse treatment (p = 0.04), a reduction of 1.8 ILTV GC after IMS treatment (p<0.001) and a reduction of 1.4 ILTV GC after PMA treatment (p<0.0001). None of the treatments completely suppressed the detection of inactivated ILTV GC. In conclusion, treatments that use capsid integrity or protein epitope denaturation as markers to assess ILTV infectivity are unsuitable to accurately estimate proportions of viable virus in poultry dust and virus stocks.

A modified loop-mediated isothermal amplification method for detecting avian infectious laryngotracheitis virus

This study was aimed to establish a highly specific and sensitive loop-mediated isothermal amplification (LAMP) method for diagnosing avian infectious laryngotracheitis (AILT). DNA was extracted from isolated infectious laryngotracheitis virus (ILTV) strains and control samples, followed by PCR using three sets of six specific primers. The detection efficiency of the LAMP assay was evaluated by the turbidity and calcein methods. The sensitivity of LAMP was then assessed using a concentration gradient followed by a specificity analysis. Furthermore, the detection efficiency of LAMP and PCR was compared. Finally, a clinical test was performed to evaluate the value of the LAMP assay. The optimal temperature for the LAMP reaction was 66 °C. Meanwhile, the primers selected for the LAMP assay were highly specific for the target virus. The sensitivity of the turbidity and calcein methods for LAMP was consistent. The minimum detection concentration of LAMP was 0.06 pg/μL, which was 100-fold higher than that of PCR. Furthermore, the results from clinical samples showed that the LAMP method could identify AILT from many samples. The newly designed LAMP assay was an effective method for AILT detection at an optimal temperature of 66 °C with a minimum detection concentration of 0.06 pg/µL.

Development and application of a colloidal gold test strip for the rapid detection of the infectious laryngotracheitis virus

Infectious laryngotracheitis disease is an acute, highly contagious viral disease seriously affecting poultry industry worldwide. In this study, a rapid and simple immune colloidal gold test strip for detecting infectious laryngotracheitis virus (ILTV) was developed based on membrane chromatography with monoclonal antibodies (mAbs) against gJ protein of ILTV and systematically evaluated for the detection of ILTV from clinical samples. mAb 2D4 1D7 was conjugated with colloidal gold as the detector antibody on the test strip. Another mAb, 1D8 1G3, was used as the capture complex at the test line (T-line), and goat antimouse IgG antibody was used as the capture antibody at the control line (C-line). The colloidal gold test strip showed high specificity in the detection of ILTV, with no cross-reaction with other avian pathogens, including infectious bronchitis virus, infectious bursal disease virus, avian influenza virus, Newcastle disease virus, fowl adenoviruses, and Marek's disease virus. Besides, the detection limit of this method was as low as 60 ELD₅₀/mL for the ILTV Wanggang strain. Furthermore, we evaluated its application in 260 clinical samples suspected of infection with ILTV. Results from the strip test were nearly identical with those from real-time PCR (coincidence rate 99.6%) and showed higher sensitivity than conventional PCR. All the results obtained in this study indicated that the colloidal gold test strip can be applied as a simple, rapid, sensitive, and specific diagnostic tool for the detection of ILTV, especially in resource-limited areas.

Molecular characterization and genetic diversity of the infectious laryngotracheitis virus strains circulating in Egypt during the outbreaks of 2018 and 2019

Infectious laryngotracheitis (ILT) is a respiratory disease that causes significant economic losses in the poultry industry worldwide. In this study, ILT outbreaks were reported on 30 farms located in eight Egyptian governorates between January 2018 and May 2019. Gross examination of diseased chickens revealed congestion and hemorrhage of laryngeal and tracheal mucosa with fibrinohemorrhagic casts and/or caseous material in the lumens. Histopathological examination showed epithelial sloughing, syncytium formation, heterophilic exudation, and development of eosinophilic intranuclear inclusion bodies. Infectious laryngotracheitis virus (ILTV) antigen was detected in the tracheal epithelium, infiltrated inflammatory cells, and syncytial cells, using immunohistochemistry. PCR targeting a portion of the thymidine kinase gene was further utilized to confirm the presence of ILTV DNA. The complete coding sequences of three envelope glycoprotein genes, gG, gD, and gJ, and a partial sequence of the infected cell polypeptide 4 (ICP4) gene from samples representing all of the farms and disease outbreaks were determined. Five prototype strains with unique sequences were chosen for detailed molecular characterization. Sequence comparisons and phylogenetic analysis of the partial ICP4 gene revealed that two strains were chicken embryo origin (CEO)-vaccine-like strains, and three were tissue culture origin (TCO)-vaccine-like strains. Analysis of the gJ gene sequence indicated that all of the strains were CEO vaccine-like strains. It was predicted that the latter three strains were recombinants of CEO- and TCO-vaccine-like strains. In conclusion, immunohistochemistry coupled with multi-genomic PCR sequencing proved to be efficient for identification and typing of ILTV strains during disease outbreaks. Both CEO-vaccine-like and recombinant virus strains were circulating in Egypt during the 2018 and 2019 outbreaks.

Phylogenetic Evidence of a Close Relationship between the Peruvian Strain Vfar-043 and Two U.S. Origin Iltv Field Strains

Infectious laryngotracheitis virus (ILTV) is the causative agent of an acute respiratory avian disease known as infectious laryngotracheitis (ILT), which has been associated with economic losses in poultry. The presence of ILTV has been widely reported in South American countries; however, only one full genomic sequence (VFAR-043 strain) has been recently published, from an outbreak in Peru. The aim of this study was to determine the genetic relationship of the Peruvian strain with other ILTV strains from different geographic regions. The phylogenetic analyses revealed a close relationship between VFAR-043 and two U.S. origin strains (1874C5 and J2) using only the whole genome, Unique Long (UL), and Unique Short (US) genomic regions. Then these three genomic sequences were compared to evaluate their genetic variations using the USDAref as a reference strain. Genetic variations such as synonymous and nonsynonymous single-nucleotide polymorphisms, insertions, deletions, and nucleotide-codon variations were identified among these three strains. Moreover, the phylogenetic tree analysis using gene sequences of the US5 and ICP4 coding regions from South American isolates showed that VFAR-043 does not have a close relationship with either the Argentinian (US5) or Brazilian (ICP4) reported sequences. However, a close relationship was observed between VFAR-043 and another Peruvian isolate (USP-81) when the ICP4 gene sequence was analyzed. All these results suggest that VFAR-043 together with 1874C5 and J2 are closely related. These findings contribute to our understanding of the epidemiology of ILTV in South America.

Spatial and temporal variation of Marek's disease virus and infectious laryngotracheitis virus genome in dust samples following live vaccination of layer flocks

Monitoring of Marek's disease virus (MDV) and infectious laryngotracheitis virus (ILTV) genome using poultry dust can be useful to monitor on-farm vaccination protocols but there are no set guidelines for collection of this sample type. This study assessed different dust collection methods for MDV and ILTV detection in a vaccinated layer flock (n = 1700) from day-old to 50 weeks of age. Birds were vaccinated against MDV at day-old, and ILTV by drinking water at week 6 and eye drop at week 12. Dust samples were collected weekly by settle plates (1-3 plates/15 m²) or by scraping surfaces in the poultry shed and tested for ILTV and MDV genomic copies (GC) by PCR. ILTV GC were detected 4 weeks post water vaccination, peaked at weeks 12-14 and became mostly undetectable after week 18. MDV was detected in dust on week 1, peaked at weeks 3-6, declined 3 logs by week 26 and remained detectable at this level until week 50. There was no difference in the detection rates of ILTV and MDV collected from settle plates in different locations of the shed (P > 0.10). There was no difference between settle plate and scraped samples in ILTV GC load but higher MDV GC were found in scraped samples. The settle plate method appears to reflect the current level of vaccine virus in the flock while the scrape method likely represents a cumulative record of shedding. Assessment of viral GC in dust samples is a good candidate for a practical method of estimating successful vaccine administration.

Glycoprotein D peptide-based diagnostic approach for the detection of avian infectious laryngotracheitis antibodies

Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens, pheasants, and peafowl. It is caused by the alpha herpesvirus, infectious laryngotracheitis virus (ILTV). Glycoprotein D (gD) of ILTV is immunogenic and helps in its binding to the susceptible host cell receptor. In the present study, a recombinant gD protein was expressed in a prokaryotic system to develop a single serum dilution ELISA. In addition, two immunogenic peptides, corresponding to regions 77-89 and 317-328, were identified in gD protein. The peptides were synthesized using solid-phase peptide synthesis, purified using reversed-phase HPLC, and characterized using mass spectrometry. The peptides displayed a good titre and were found to be promising antigens to coat the ELISA plate to detect the ILTV antibodies in the serum sample. The developed ELISA showed 96.9% sensitivity, 87.5% specificity, and 95.3% accuracy as compared to OIE referenced standard indirect ILTV ELISA (whole viral coated). The assay may not differentiate vaccinated from infected birds when the flocks are administered with live attenuated vaccines. However, the assay could be useful to detect the disease condition in birds vaccinated with recombinant vaccine expressing glycoproteins other than gD. The developed ILTV single serum dilution ELISA could be an alternative to the existing diagnostics for the detection of ILTV antibodies.

Immunoinformatics Approach for Multiepitopes Vaccine Prediction against Glycoprotein B of Avian Infectious Laryngotracheitis Virus

Infectious laryngotracheitis virus (ILTV) is a gallid herpesvirus type 1, a member of the genus Iltovirus. It causes an infection in the upper respiratory tract mainly trachea which results in significant economic losses in the poultry industry worldwide. Vaccination against ILTV produced latent infected carriers' birds, which become a source of virus transmission to nonvaccinated flocks. Thus this study aimed to design safe multiepitopes vaccine against glycoprotein B of ILT virus using immunoinformatic tools. Forty-four sequences of complete envelope glycoprotein B were retrieved from GenBank of National Center for Biotechnology Information (NCBI) and aligned for conservancy by multiple sequence alignment (MSA). Immune Epitope Database (IEDB) analysis resources were used to predict and analyze candidate epitopes that could act as a promising peptide vaccine. For B cell epitopes, thirty-one linear epitopes were predicted using Bepipred. However eight epitopes were found to be on both surface and antigenic epitopes using Emini surface accessibility and antigenicity, respectively. Three epitopes (₁₉₀KKLP₁₉₃, ₃₈₆YSSTHVRS₃₉₃, and ₃₁₇KESV₃₂₀) were proposed as B cell epitopes. For T cells several epitopes were interacted with MHC class I with high affinity and specificity, but the best recognized epitopes were ₁₁₈YVFNVTLYY₁₂₆, ₃₃₅VSYKNSYHF₃₄₃, and ₆₂₂YLLYEDYTF₆₃₀. MHC-II binding epitopes, ₃₀₁FLTDEQFTI₃₀₉,₂₇₇FLEIANYQV₂₈₅, and ₇₄₃IASFLSNPF₇₅₁, were proposed as promising epitopes due to their high affinity for MHC-II molecules. Moreover the docked ligand epitopes from MHC-1 molecule exhibited high binding affinity with the receptors; BF chicken alleles (BF2 2101 and 0401) expressed by the lower global energy of the molecules. In this study nine epitopes were predicted as promising vaccine candidate against ILTV. In vivo and in vitro studies are required to support the effectiveness of these predicted epitopes as a multipeptide vaccine through clinical trials.

MinION sequencing to genotype US strains of infectious laryngotracheitis virus

Over the last decade the US broiler industry has fought long-lasting outbreaks of infectious laryngotracheitis (ILTV). Previously, nine genotypes (I-IX) of ILTVs have been recognized using the polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP) method with three viral alleles (gB, gM and UL47/gG). In this study, the genotyping system was simplified to six genotypes by amplicon sequencing and examining discriminating single nucleotide polymorphisms (SNPs) within these open reading frames. Using phylogenomic analysis of 27 full genomes of ILTV, a single allele (ORF A/ORF B) was identified containing SNPs that could differentiate ILTVs into genotypes congruent with the phylogenetic partitioning. The allelic variations allowed for the cataloging of the 27 strains into 5 genotypes: vaccinal TCO, vaccinal CEO, virulent CEO-like, virulent US and virulent US backyard flocks from 1980 to 1990, correlating with the PCR-RFLP genotypes I/ II/ III (TCO), IV (CEO), V (virulent CEO-like), VI (virulent US) and VII/VIII/IX (virulent US backyard flock isolates). With the unique capabilities of third generation sequencing, we investigated the application of Oxford Nanopore MinION technology for rapid sequencing of the amplicons generated in the single-allele assay. This technology was an improvement over Sanger-based sequencing of the single allele amplicons due to a booster amplification step in the MinION sequencing protocol. Overall, there was a 90% correlation between the genotyping results of the single-allele assay and the multi-allele assay. Surveillance of emerging ILTV strains could greatly benefit from real-time amplicon sequencing using the single-allele assay and MinION sequencing. RESEARCH HIGHLIGHTS A multi-allelic assay identified nine ILTV genotypes circulating in the US Single-allele genotyping is congruent with whole genome phylogenetic partitioning US ILTV strains can be grouped into five genotypes using the single-allele assay The single-allele assay can be done using MinION sequencing of barcoded amplicons.

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.

Development and application of high-resolution melting analysis for the classification of infectious laryngotracheitis virus strains and detection of recombinant progeny

Live attenuated vaccines against infectious laryngotracheitis virus (ILTV) are widely used in the poultry industry to control disease and help prevent economic losses. Molecular epidemiological studies of currently circulating strains of ILTV within poultry flocks in Australia have demonstrated the presence of highly virulent viruses generated by genomic recombination events between vaccine strains. In this study, high-resolution melting (HRM) analysis was used to develop a tool to classify ILTV isolates and to investigate ILTV recombination. The assay was applied to plaque-purified progeny viruses generated after co-infection of chicken embryo kidney (CEK) monolayers with the A20 and Serva ILT vaccine strains and also to viruses isolated from field samples. The results showed that the HRM analysis is a suitable tool for the classification of ILTV isolates and can be used to detect recombination between ILTV vaccine strains in vitro. This method can be used to classify a broad range of ILTV strains to facilitate the classification and genotyping of ILTV and help to further understand recombination in these viruses.

A Review of Eight High-Priority, Economically Important Viral Pathogens of Poultry within the Caribbean Region

Viral pathogens cause devastating economic losses in poultry industries worldwide. The Caribbean region, which boasts some of the highest rates of poultry consumption in the world, is no exception. This review summarizes evidence for the circulation and spread of eight high-priority, economically important poultry viruses across the Caribbean region. Avian influenza virus (AIV), infectious bronchitis virus (IBV), Newcastle disease virus (NDV), infectious laryngotracheitis virus (ILTV), avian metapneumovirus (aMPV), infectious bursal disease virus (IBDV), fowl adenovirus group 1 (FADV Gp1), and egg drop syndrome virus (EDSV) were selected for review. This review of serological, molecular, and phylogenetic studies across Caribbean countries reveals evidence for sporadic outbreaks of respiratory disease caused by notifiable viral pathogens (AIV, IBV, NDV, and ILTV), as well as outbreaks of diseases caused by immunosuppressive viral pathogens (IBDV and FADV Gp1). This review highlights the need to strengthen current levels of surveillance and reporting for poultry diseases in domestic and wild bird populations across the Caribbean, as well as the need to strengthen the diagnostic capacity and capability of Caribbean national veterinary diagnostic laboratories.

Patterns of genomic site inheritance in HIV-1M inter-subtype recombinants delineate the most likely genomic sites of subtype-specific adaptation

Recombination between different HIV-1 group M (HIV-1M) subtypes is a major contributor to the ongoing genetic diversification of HIV-1M. However, it remains unclear whether the different genome regions of recombinants are randomly inherited from the different subtypes. To elucidate this, we analysed the distribution within 82 circulating and 201 unique recombinant forms (CRFs/URFs), of genome fragments derived from HIV-1M Subtypes A, B, C, D, F, and G and CRF01_AE. We found that viruses belonging to the analysed HIV-1M subtypes and CRF01_AE contributed certain genome fragments more frequently during recombination than other fragments. Furthermore, we identified statistically significant hot-spots of Subtype A sequence inheritance in genomic regions encoding portions of Gag and Nef, Subtype B in Pol, Tat and Env, Subtype C in Vif, Subtype D in Pol and Env, Subtype F in Gag, Subtype G in Vpu-Env and Nef, and CRF01_AE inheritance in Vpu and Env. The apparent non-randomness in the frequencies with which different subtypes have contributed specific genome regions to known HIV-1M recombinants is consistent with selection strongly impacting the survival of inter-subtype recombinants. We propose that hotspots of genomic region inheritance are likely to demarcate the locations of subtype-specific adaptive genetic variations.

Genotyping of infectious laryngotracheitis virus using allelic variations from multiple genomic regions

Live attenuated vaccines are extensively used worldwide to control the outbreak of infectious laryngotracheitis. Virulent field strains showing close genetic relationship with the infectious laryngotracheitis virus (ILTV) vaccines of chicken embryo origin have been detected in the poultry industry. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, a reliable molecular epidemiological method, of multiple genomic regions was performed. The PCR-RFLP is a time-consuming method that requires considerable amount of intact viral genomic DNA to amplify genomic regions greater than 4 kb. In this study, six variable genomic regions were selected and amplified for sequencing. The multi-allelic PCR-sequence genotyping showed better discrimination power than that of previous PCR-sequencing schemes using single or two target regions. The allelic variation patterns yielded 16 strains of ILTV classified into 14 different genotypes. Three Korean field strains, 550/05/Ko, 0010/05/Ko and 40032/08/Ko, were found to have the same genotype as the commercial vaccine strain, Laryngo Vac (Zoetis, Florham Park, NJ, USA). Three other Korean field strains, 40798/10/Ko, 12/07/Ko, and 30678/14/Ko, showed recombined allelic patterns. The multi-allelic PCR-sequencing method was proved to be an efficient and practical procedure to classify the different strains of ILTV. The method could serve as an alternate diagnostic and differentiating tool for the classification of ILTV, and contribute to understanding of the epidemiology of the disease at a global level.

Presence of DNA extracellular traps but not MUC5AC and MUC5B mucin in mucoid plugs/casts of infectious laryngotracheitis virus (ILTV) infected tracheas of chickens

Although it has been speculated that the tracheal obstructions and asphyxiation during acute infectious laryngotracheitis (ILT) are due to mucoid plugs/casts formed by mucus hypersecretion, there are no reports demonstrating this. Hence, in the present study, we first examined if the main respiratory mucins, MUC5AC and MUC5B, are expressed in the mucosae of larynx, trachea and bronchi of mock-inoculated and ILTV infected chickens. Second, the tracheas with plugs/casts were stained for mucins (MUC5AC and MUC5B) and nuclear material (traps). MUC5AC and MUC5B were produced by the mucosae of larynx, trachea and bronchi of mock-inoculated chickens. Interestingly, MUC5AC and MUC5B were exclusively present in the dorsal tracheal region of the cranial and middle part of trachea of mock-inoculated chickens. In ILTV infected chickens, the tracheal lumen diameter was almost 40% reduced and was associated with a strongly increased tracheal mucosal thickness. MUC5AC and MUC5B were scarcely observed in larynx, trachea and bronchi, and in tracheal plugs/casts of ILTV infected birds. Surprisingly, DNA fibrous structures were observed in connection with nuclei of 10.0±7.3% cells, present in tracheal plugs/casts. Upon inoculation of isolated blood heterophils with ILTV, DNA fibrous structures were observed in 2.0±0.1% nuclei of ILTV inoculated blood heterophils at 24hours post inoculation (hpi). In conclusion, the tracheal obstructions and suffocation of ILTV infected chickens are due to a strong thickening of the mucosa (inflammation) resulting in a reduced tracheal lumen diameter and the presence of mucoid plugs/casts containing stretched long DNA-fibrous structures (traps) but not MUC5AC and MUC5B mucins.

Companion Animals as a Source of Viruses for Human Beings and Food Production Animals

Companion animals comprise a wide variety of species, including dogs, cats, horses, ferrets, guinea pigs, reptiles, birds and ornamental fish, as well as food production animal species, such as domestic pigs, kept as companion animals. Despite their prominent place in human society, little is known about the role of companion animals as sources of viruses for people and food production animals. Therefore, we reviewed the literature for accounts of infections of companion animals by zoonotic viruses and viruses of food production animals, and prioritized these viruses in terms of human health and economic importance. In total, 138 virus species reportedly capable of infecting companion animals were of concern for human and food production animal health: 59 of these viruses were infectious for human beings, 135 were infectious for food production mammals and birds, and 22 were infectious for food production fishes. Viruses of highest concern for human health included hantaviruses, Tahyna virus, rabies virus, West Nile virus, tick-borne encephalitis virus, Crimean-Congo haemorrhagic fever virus, Aichi virus, European bat lyssavirus, hepatitis E virus, cowpox virus, G5 rotavirus, influenza A virus and lymphocytic choriomeningitis virus. Viruses of highest concern for food production mammals and birds included bluetongue virus, African swine fever virus, foot-and-mouth disease virus, lumpy skin disease virus, Rift Valley fever virus, porcine circovirus, classical swine fever virus, equine herpesvirus 9, peste des petits ruminants virus and equine infectious anaemia virus. Viruses of highest concern for food production fishes included cyprinid herpesvirus 3 (koi herpesvirus), viral haemorrhagic septicaemia virus and infectious pancreatic necrosis virus. Of particular concern as sources of zoonotic or food production animal viruses were domestic carnivores, rodents and food production animals kept as companion animals. The current list of viruses provides an objective basis for more in-depth analysis of the risk of companion animals as sources of viruses for human and food production animal health.

Attenuation and protection efficacy of ORF C gene-deleted recombinant of infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is a highly contagious respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV). The disease is controlled by the use of live-attenuated vaccines. Previously we reported the complete nucleotide sequence of the ILTV vaccine strain (TCO) and identified a nonsense mutation in the gene encoding the ORF C protein. This suggested that the ORF C protein might be associated with viral virulence. To investigate this, an ILTV recombinant with a deletion in the gene encoding ORF C was constructed using the genome of the virulent United States Department of Agriculture (USDA) challenge strain (USDAch). Compared to the parental virus, the ΔORF C recombinant replicated in chicken kidney (CK) cells with similar kinetics and generated similar titres. This demonstrated that the ORF C deletion had no deleterious effects on replication efficacy in vitro. In chickens, the recombinant induced only minor microscopic tracheal lesions when inoculated via the intra-tracheal/ocular route, while the parental strain induced moderate to severe microscopic tracheal lesions, even though virus load in the tracheas were comparable. Groups of chickens vaccinated via eye-drop with the ∆ORFC-ILTV were protected to levels comparable to those elicited by TCO vaccination. To our knowledge, this is the first report that demonstrates the suitability of ∆ORFC as a live-attenuated vaccine to prevent the losses caused by ILTV.

Real-time PCR quantification of infectious laryngotracheitis virus in chicken tissues, faeces, isolator-dust and bedding material over 28 days following infection reveals high levels in faeces and dust

Infectious laryngotracheitis (ILT) is an important disease of chickens caused by ILT virus (ILTV). We used the Australian SA2 and A20 vaccine strains of ILTV to determine tissue distribution and excretion characteristics of ILTV in specific-pathogen-free chickens and to determine whether ILTV is readily detectable in environmental samples such as faeces, bedding material and dust using real-time quantitative PCR. Three groups of 10 freshly hatched chicks were placed in isolators and infected orally with high doses of the two strains of vaccine virus or left unchallenged as controls. Over a 28-day post-infection (p.i.) period, faecal and serum samples were collected at frequent intervals from six individually identified chickens in each group. Dust and litter samples from the isolators were collected less frequently. Tissue samples were collected from three to four sacrificed or dead/euthanized birds at 6, 14 and 28 days p.i. Infection resulted in clinical ILT, a pronounced antibody response and sustained qPCR detection of the viral genome in the trachea, Harderian gland, lung and kidney up to 28 days p.i. A high level of the viral genome was also detected in faeces between 2 and 7 days p.i., declining by about approximately four orders of magnitude to low, but detectable, levels at 21 and 28 days p.i. The finding of high-level shedding of ILTV in faeces warrants further investigation into the epidemiological role of this, and the sustained high levels of ILTV observed in dust suggest that it may be a useful sample material for monitoring ILTV status in flocks.