Chicken embryo origin-like strains are responsible for Infectious laryngotracheitis virus outbreaks in Egyptian cross-bred broiler chickens

Fibroblast test cells of embryo of Super Java Chicken as an indicator to test toxicity and malignancy

Fibroblast is one component of connective tissue cells in polygonal or stellate with cytoplasmic processes or projections. In vitro, tissue culture is an excellent medium used in biomedical research. The goal of this study was to analyze Toxicity and Malignancy in Embryo of Super Java Chicken as Potential Candidates of Strong Poultry in Indonesia. This study used Preparation of fibroblast primary cell culture of Java super chicken embryos, Pathogenicity test using fibroblast cells from Super Java chicken, Toxicity test using fibroblast cells from Super Java Chicken. Primary fibroblast cell culture of Java super chicken embryos was prepared from 10-day-old brood chicken eggs free of pathogens. Cells were prepared in 96-well microplates with minimal essential medium (MEM) containing 10 % fetal calf serum (FCS) 100 IU/ug penicillin/streptomycinVirus isolates were diluted in stages from 10-2 to 10-5 and inoculated into Java Super Chicken Fibroblast cell culture. The result showed that the negative control of the samples had a faster proliferative power than the fibroblast cell culture of Java super chicken, which was treated with concentrations of 10-2; 10-3; 10-4; 10-5. Moreover, before being inoculated with the virus, the confluent fibroblast cells of Java super chicken looked oval and regular. The day after infection, syncytia (large multinucleated cells) began to form on a small scale and became more pronounced on the second and third post-infection days. CPE was found in the 10-2,10-3 and 10-4 virus dilutions, and CPE was not found in the 10-5 dilution.

Molecular and genetic detection of infectious laryngeotrachitis disease virus in broiler farms after a disease outbreak in Egypt

Infectious laryngotracheitis (ILT) is a viral respiratory illness in poultry that causes massive financial losses. This research aimed to isolate and identify the ILT virus in suspected outbreaks of broiler flocks in Egypt during 2020-2021, besides investigating its genetic link with other circulating strains. Real-time-PCR was used to test 57 samples taken from unvaccinated broiler farms. Ten samples are positive for ILTV, and the virus is being isolated in SPF chicken embryos. The Sanger sequencing was used to conduct (partial) sequencing of the infected cell protein4 gene (ICP4) for eight isolates. Phylogenetic analysis conducted Maximum Likelihood, comparative sequencing analysis of ICP4 of strains under study with vaccination ILT reference strains reveled that all isolates were clustered into two major groups. The (OM291843and OM291846) clustered together with the chicken embryo origin vaccine strains (IV and V group). The remaining six strains belong to the TCO vaccine(I, II and III group). The total sequence similarity between the strains under study and the various Egyptian strains varied from (97 to 100%) while the similarity with TCO or chicken embryo origin -vaccine strains ranged from (95to 100%). There were no deletions detected in the 272-283-bp region of the ICP4 gene. Detection of arginine to methionine substitutions at position 180 (R180M) and change of Serine to Asparagine at position 227 (S227N) in the (OM291843 and OM291846) which were previously described in chicken embryo origin -vaccine strains. This reveals that field strains may have evolved from vaccine strains, notably identification of non-synonymous substitutions which might be linked to the virulence strains' attenuation. Finally, independent of geographical distribution, both chicken embryo origin-vaccine-like and TCO-Vaccine-like virus strains were circulating in Egyptian non-vaccinated broiler flocks in 2020 and 2021. Despite their genetic differences, both viruses caused significant illnesses in the field.

Comparative full genome sequence analysis of wild-type and chicken embryo origin vaccine-like infectious laryngotracheitis virus field isolates from Canada

Infectious laryngotracheitis (ILT), caused by infectious laryngotracheitis virus (ILTV), occurs sporadically in poultry flocks in Canada. Live attenuated chicken embryo origin (CEO) vaccines are being used routinely to prevent and control ILTV infections. However, ILT outbreaks still occur since vaccine strains could revert to virulence in the field. In this study, 7 Canadian ILTV isolates linked to ILT outbreaks across different time in Eastern Canada (Ontario; ON and Quebec; QC) were whole genome sequenced. Phylogenetic analysis confirmed the close relationship between the ON isolates and the CEO vaccines, whereas the QC isolates clustered with strains previously known as CEO revertant and wild-type ILTVs. Recombination network analysis of ILTV sequences revealed clear evidence of historical recombination between ILTV strains circulating in Canada and other geographical regions. The comparison of ON CEO clustered and QC CEO revertant clustered isolates with the LT Blen® CEO vaccine reference sequence showed amino acid differences in 5 and 12 open reading frames (ORFs), respectively. Similar analysis revealed amino acid differences in 32 ORFs in QC wild-type isolates. Compared to all CEO vaccine strains in the public domain, the QC wild-type isolates showed 15 unique mutational sites leading to amino acid changes in 13 ORFs. Our outcomes add to the knowledge of the molecular mechanisms behind ILTV genetic variance and provide genetic markers between wild-type and vaccine strains.

Pathogenicity and vaccine efficacy of two virulent infectious laryngotracheitis virus strains in Egypt

Infectious laryngotracheitis (ILT) is an economically crucial respiratory disease of poultry that affects the industry worldwide. Vaccination is the principal tool in the control of the disease outbreak. In an earlier study, we comprehensively characterized the circulating strains in Egypt and identified both CEO-like and recombinant strains are dominant. Herein, we investigated the pathogenicity of two virulent strains representing the CEO-like (Sharkia_2018) and recombinant strain (Qalubia_2018). Additionally, we evaluated the efficacy of different commercial vaccines (HVT-LT, CEO, and TCO) against the two isolates in terms of the histopathological lesion scores and the viral (gC) gene load. A total of 270 White Leghorn-specific pathogen-free male chicks were divided into nine groups of 30 birds, each housed in separate isolators. Birds were distributed as follows; one group was non-vaccinated, non-challenged, and served as a negative control. Two groups were non-vaccinated and infected with the two isolates of interest and served as a positive control to test the pathogenicity. Six groups were vaccinated and challenged; two groups were vaccinated with vector vaccine at one day old. The other four groups were vaccinated with either the CEO- or TCO- vaccine (two groups each) at four weeks of age. Three weeks after vaccination, birds were infected with the virulent ILTV isolates. The larynx, trachea, and harderian gland samples were taken at 1, 3, and 7 days post-infection for histopathological lesion score and molecular detection. Notably, The recombinant strain was more virulent and pathogenic than CEO-like ILTV strains. Moreover, the TCO vaccine was less immunogenic than the vector and CEO vaccines.

Characterization of infectious laryngotracheitis virus isolates from laying hens during 2019-2020 outbreaks in Tamil Nadu, India

Infectious laryngotracheitis (ILT) is an acute respiratory disease in chickens that is a serious threat to poultry-producing countries worldwide. In the present study, we isolated and characterized infectious laryngotracheitis (ILTV) virus isolates by sequencing and restriction fragment length polymorphism analysis of PCR-amplified products (PCR-RFLP). A total of 26 ILTV outbreaks were investigated that occurred between 2019 and 2020 in flocks that had not been vaccinated against ILTV. ILTV was isolated by cultivating tracheal samples in embryonated chicken eggs, which showed multiple opaque pock lesions and thickening of the chorioallantoic membrane after 120 hours of infection. The ILTV isolates were identified and characterized by PCR and sequencing a portion of the ICP4 and TK genes. Phylogenetic analysis based on the ICP4 region showed that the sequences clustered with chicken-embryo-origin vaccine-like strains. Sequence analysis of the ICP4 region differentiated chicken-embryo-origin (CEO), tissue-culture-origin (TCO), and field ILTV strains, with significant differences in nucleotide and amino acid sequences. Furthermore, PCR-RFLP analysis of the TK gene showed that the patterns were identical to those obtained with low-virulence and vaccine strains. In conclusion, sequencing of a portion of the ICP4 region of ILTV allowed differentiation of ILTV field, CEO, and TCO vaccine strains. In this study, CEO-vaccine-like strains were found to be the cause of ILTV outbreaks between 2019 and 2020 in Tamil Nadu in southern India.

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.

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.

Pathogenic and Transmission Potential of Wildtype and Chicken Embryo Origin (CEO) Vaccine Revertant Infectious Laryngotracheitis Virus

Infectious laryngotracheitis (ILT) is an infectious upper respiratory tract disease that impacts the poultry industry worldwide. ILT is caused by an alphaherpesvirus commonly referred to as infectious laryngotracheitis virus (ILTV). Vaccination with live attenuated vaccines is practiced regularly for the control of ILT. However, extensive and improper use of live attenuated vaccines is related to vaccine viruses reverting to virulence. An increase in mortality and pathogenicity has been attributed to these vaccine revertant viruses. Recent studies characterized Canadian ILTV strains originating from ILT outbreaks as related to live attenuated vaccine virus revertants. However, information is scarce on the pathogenicity and transmission potential of these Canadian isolates. Hence, in this study, the pathogenicity and transmission potential of two wildtype ILTVs and a chicken embryo origin (CEO) vaccine revertant ILTV of Canadian origin were evaluated. To this end, 3-week-old specific pathogen-free chickens were experimentally infected with each of the ILTV isolates and compared to uninfected controls. Additionally, naïve chickens were exposed to the experimentally infected chickens to mimic naturally occurring infection. Pathogenicity of each of these ILTV isolates was evaluated by the severity of clinical signs, weight loss, mortality, and lesions observed at the necropsy. The transmission potential was evaluated by quantification of ILTV genome loads in oropharyngeal and cloacal swabs and tissue samples of the experimentally infected and contact-exposed chickens, as well as in the capacity to produce ILT in contact-exposed chickens. We observed that the CEO vaccine revertant ILTV isolate induced severe disease in comparison to the two wildtype ILTV isolates used in this study. According to ILTV genome load data, CEO vaccine revertant ILTV isolate was successfully transmitted to naïve contact-exposed chickens in comparison to the tested wildtype ILTV isolates. Overall, the Canadian origin CEO vaccine revertant ILTV isolate possesses higher virulence, and dissemination potential, when compared to the wildtype ILTV isolates used in this study. These findings have serious implications in ILT control in chickens.

Molecular detection and genetic characterization of infectious laryngotracheitis virus in poultry in Myanmar

BACKGROUND

Avian infectious laryngotracheitis (ILT) is a highly contagious viral disease that causes severe economic losses to the poultry industry worldwide. In Southeast Asian countries, including Myanmar, poultry farming is a major industry. Although it is known that infectious respiratory pathogens, including infectious laryngotracheitis virus (ILTV), are a major threat to poultry farms, there are no data currently available on the epidemiology of ILTV in Myanmar. Therefore, in this study, we conducted a molecular detection of ILTV in 20 poultry farms in Myanmar.

RESULTS

Of the 57 tested oropharyngeal swabs, 10 were positive for ILTV by polymerase chain reaction of a 647 bp region of the thymidine kinase (TK) gene, giving a prevalence of ILTV of 17.5% (10/57). Further sequencing analysis of infected cell protein 4 (ICP4) gene and glycoprotein B, G, and J (gB, gG, and gJ) genes indicated that these isolates were field strains. Phylogenetic analysis revealed that the Myanmar strains clustered together in a single branch and were closely related to other reference strains isolated from Asian countries.

CONCLUSIONS

This study demonstrated the presence of ILTV in poultry farms in Myanmar. The genetic characterization analysis performed provides the fundamental data for epidemiological studies that monitor circulating strains of ILTV in Myanmar.

Superinfection and recombination of infectious laryngotracheitis virus vaccines in the natural host

Infectious laryngotracheitis virus (ILTV, Gallid alphaherpesvirus 1) causes severe respiratory disease in chickens and has a major impact on the poultry industry worldwide. Live attenuated vaccines are widely available and are administered early in the life of commercial birds, often followed by one or more rounds of revaccination, generating conditions that can favour recombination between vaccines. Better understanding of the factors that contribute to the generation of recombinant ILTVs will inform the safer use of live attenuated herpesvirus vaccines. This study aimed to examine the parameters of infection that allow superinfection and may enable the generation of recombinant progeny in the natural host. In this study, 120 specific-pathogen free (SPF) chickens in 8 groups were inoculated with two genetically distinct live-attenuated ILTV vaccine strains with 1-4 days interval between the first and second vaccinations. After inoculation, viral genomes were detected in tracheal swabs in all groups, with lowest copies detected in swabs collected from the groups where the interval between inoculations was 4 days. Superinfection of the host was defined as the detection of the virus that was inoculated last, and this was detected in tracheal swabs from all groups. Virus could be isolated from swabs at a limited number of timepoints, and these further illustrated superinfection of the birds as recombinant viruses were detected among the progeny. This study has demonstrated superinfection at host level and shows recombination events occur under a very broad range of infection conditions. The occurrence of superinfection after unsynchronised infection with multiple viruses, and subsequent genomic recombination, highlight the importance of using only one type of vaccine per flock as the most effective way to limit recombination.

Genotyping of Infectious Laryngotracheitis Virus (ILTV) Isolates from Western Canadian Provinces of Alberta and British Columbia Based on Partial Open Reading Frame (ORF) a and b

Simple Summary

Infectious laryngotracheitis virus is an economically important acute upper respiratory tract disease in chickens. To control the disease, there are two types of vaccines commercially available, the recombinant viral vector and the live attenuated vaccines. The live attenuated vaccines are effective in disease control, but because of their residual virulence, they can replicate, cause disease, and revert to their original virulent form. Strains of the virus can be categorized as vaccine-related or wild type related. Information is scarce on the type of strains that are circulating in Canada. This study aims to discriminate between wild type and vaccine strains associated with infectious laryngotracheitis cases in the provinces of Alberta and British Columbia between the years 2009–2018. To accomplish this objective, the sequencing of two specific partial genes was performed. As a result, 27 samples from Alberta, and 5 samples from British Columbia were successfully sequenced. From the total samples, ~85% were related to vaccine strains and the rest categorized as wild type. These results reinforce the concern on current practices surrounding vaccination and the need to implement better biosecurity measures.

Abstract

Infectious laryngotracheitis virus (ILTV) causes an acute upper respiratory disease in chickens called infectious laryngotracheitis (ILT). Live attenuated vaccines are effective in disease control; however, they have residual virulence, which makes them able to replicate, cause disease and revert to the original virulent form. Information is scarce on the molecular nature of ILTV that is linked to ILT in Canada. This study aims to determine whether isolates originating from ILT cases in Western Canada are a wild type or vaccine origin. Samples submitted for the diagnosis of ILT between 2009–2018 were obtained from Alberta (AB, n = 46) and British Columbia (BC, n = 9). For genotyping, a Sanger sequencing of open reading frame (ORF) a and b was used. A total of 27 from AB, and 5 from BC samples yielded a fragment of 1751 base pairs (bp). Three of the BC samples classified as group IV (CEO vaccine strains) and 2 as group V (CEO revertant). Of the AB samples, 22 samples clustered with group V, 3 with group VI (wild type), and 2 with group VII, VIII, and IX (wild type). Overall, 17 non-synonymous single nucleotide polymorphisms (SNPs) were detected. Further studies are underway to ascertain the virulence and transmission potential of these isolates.

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.

Investigation of infectious laryngotracheitis outbreaks in Namibia in 2018

Between July and August 2018, two outbreaks of infectious laryngotracheitis caused the death of over 116,000 commercial poultry (layers and broilers) near the city of Windhoek, Namibia. A third outbreak occurred in September 2018 in the north of the country approximately 800 km from the original outbreaks. Sample collection and molecular epidemiological analyses revealed that the outbreaks were most likely caused by poor vaccination practices leading to the reversion to virulence of an ILT vaccine strain. The analyses also indicate that inaccurate declarations were made by one of the farms involved and that illegal movement of animals most likely occurred.

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.

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.

Enhanced infection of avian influenza virus H9N2 with infectious laryngeotracheitis vaccination in chickens

Avian influenza and infectious laryngeotracheitis viruses are common causes of respiratory diseases in chickens with economical importance worldwide. In this study, we investigated the effect of experimental co-infection of avian influenza virus-H9N2 (AIV-H9N2) with infectious laryngeotracheitis virus (ILTV) live-attenuated vaccine (LAR-VAC^®) on chickens. Four experimental groups were included in this study: negative control group, AIV-H9N2 group, AIV-H9N2+LAR-VAC^® group, and LAR-VAC^® group. AIV-H9N2 was inoculated intranasally to challenged groups at 35 days of age. On the same day, LAR-VAC^® was ocularly administered to vaccinated groups. Chickens were observed for clinical signs, changes in body weight and mortality rates. Tissue samples, sera, tracheal and cloacal swabs, and blood were also collected at 3, 6, 9 and 12 days post-infection (PI). A significant increase in clinical signs and mortality rates were observed in the AIV-H9N2 + LAR-VAC^® group. Moreover, chickens coinfected with AIV-H9N2 and LAR-VAC^® showed a significant decrease in body weight and lymphoid organs indices. The tracheal gross and histopathological lesions and the shedding titer and period of AIV-H9N2 were significantly higher in AIV-H9N2 + LAR-VAC^® group when compared to other groups. Furthermore, AIV-H9N2 infection leads to humoral and cellular immunosuppression as shown by a significant decrease in the CD4⁺/CD8⁺ ratio and antibody responses to ILTV and a significant increase in H/L ratio. In conclusion, this is the first report of co-infection of AIV-H9N2 and ILTV vaccine in chickens, which leads to increased pathogenicity, pathological lesions, and AIV-H9N2 shedding titer and period, which can lead to severe economic losses due to poor weight gain and mortality.

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.

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.

Molecular epidemiology of infectious laryngotracheitis: a review

Infectious laryngotracheitis (ILT) is an economically important respiratory disease of poultry that affects the poultry industry worldwide. The disease is caused by gallid herpesvirus I (GaHV-1), a member of the genus Iltovirus, family Herpesviridae, subfamily Alphaherpesvirinae. The current incidence of the disease is heavily influenced by live attenuated vaccines, which have been used extensively since their introduction in the mid-twentieth century. The capability of current live attenuated vaccine viruses to revert to virulence and spread from bird to bird has shaped the molecular epidemiology of ILT. Because of the antigenic homogeneity among GaHV-1 strains, differentiation of strains has been achieved by targeting genomic differences between outbreak-related isolates and vaccine strains. Numerous genes and genomic regions have been utilized in the development of DNA-based diagnostic assays to differentiate outbreak-related isolates from vaccine strains in countries where ILT outbreaks have occurred. More recently, full genome sequences have allowed determination of the origin of some of the outbreak-related isolates circulating in some poultry production countries. Overall, molecular typing data collected worldwide have identified live attenuated vaccine-related isolates as the primary source for outbreaks of the disease.