Development and validation of a real-time Taqman PCR assay for the detection and quantitation of infectious laryngotracheitis virus in poultry

Pathological and molecular investigation of infectious bronchitis in broilers: analyzing the impact of biosecurity lapses

Introduction

Infectious Bronchitis (IB) is an acute, highly contagious disease of poultry that leads to significant economic losses in intensive production systems. Preventive biosecurity measures are essential to control its spread, particularly in broiler farms. This study aimed to investigate the relationship between IB outbreaks and biosecurity practices on a broiler farm.

Methods

The farm, housing 96,000 broilers, experienced increased mortality (over 11%) during two consecutive production cycles. Consequently, serological, pathological, molecular and biosecurity investigations were conducted.

Results

Despite a vaccination program using two types of live vaccines (Massachusetts serotype and serotype 793B), serological testing revealed elevated antibody titers against the IB virus, suggesting exposure to a wild viral strain. Necropsy revealed various lesions, including hemorrhagic tracheitis, pulmonary hyperemia, fibrinous pericarditis, splenomegaly, and ascites. Histopathological findings showed necrotic tracheitis, multifocal hepatitis, and purulent bronchopneumonia. By PCR IB viral RNA was detected in all 24 swabs and tissue samples. Biosecurity evaluation revealed significant deficiencies in both external and internal measures, including improper cross-contamination prevention, inadequate flock management, and insufficient vaccination strategies.

Discussion

These biosecurity deficiencies, coupled with the inadequate selection of vaccines not tailored to the prevalent serotypes in the local area, allowed for the introduction and spread of wild IB virus strains. This highlights the critical importance of robust, well-implemented biosecurity protocols in preventing IB on poultry farms.

Isolation and characterization of an avian metapneumovirus subtype C circulating in Cherry Valley ducks

Since 2023, an infectious upper respiratory tract disease has been persisted in outbreaks among in a flock of Cherry Valley ducks in Shandong Province, China. This outbreak was traced to avian metapneumovirus subtype C (aMPV-C), a significant pathogen associated with egg-drop and acute respiratory diseases in poultry. It is noteworthy that prior to this, aMPV-C infection had not been previously documented in Cherry Valley ducks within China. In this study, we successfully isolated and characterized the aMPV-C LY0913 strain from the affected Cherry Valley duck flock. Sequence analysis showed that the fusion (F) protein of LY0913 exhibited a 97.8-98.7 % amino acid similarity with seven other aMPV-C strains, displaying the closest relationship to the strains isolated from Muscovy ducks in southern China in 2010. Furthermore, five concurrent amino acid mutations were identified in the F protein, providing valuable insights into the outbreak of aMPV-C in Cherry Valley ducks. The LY0913 strain demonstrated typical cytopathic effects on Vero cells and caused mortality in Cherry Valley duck embryos. In vivo infection of Cherry Valley ducklings with LY0913 reproduced the typical clinical signs and pathological lesions observed in the original infected cases. This study is the first to identify aMPV-C as a causative agent of respiratory disease in Cherry Valley ducks in China, highlighting its emergence and potential risk to previously unaffected avian populations. Urgent enhanced surveillance and biosecurity measures are strongly recommended to prevent further spread within duck flocks.

Unveiling the genetic landscape of infectious laryngotracheitis virus in Switzerland: Evidence for vaccine-like and wild-type strains

Infectious laryngotracheitis (ILT) is a respiratory disease affecting chickens worldwide. Unlike many countries, Switzerland does not vaccinate against ILT. This study analysed ILT samples from 21 natural outbreaks in Switzerland using restriction fragment length polymorphism (RFLP) and multiple gene sequencing. Chicken embryo origin (CEO) and tissue culture origin (TCO) vaccine strains were included as references. Both vaccine strains were distinguishable, and 14 out of 21 samples resembled the CEO vaccine. Additionally, four distinct non-vaccine-like groups were identified. Sequencing of three genes from selected Swiss samples and those from neighbouring countries revealed four phylogenetic clades. Notably, four Swiss field strains formed two unique clades, not closely related to vaccine strains or ILTV from neighbouring countries. Overall, RFLP results were supported by sequencing data. This study demonstrates the presence of both vaccine-like and wild-type ILT viruses in Switzerland, where vaccination is de facto prohibited.

First detection of D181 genotype of infectious bronchitis in poultry flocks of Morocco

BACKGROUND

This paper reports the first pathological and molecular characterization of the novel variant of infectious bronchitis virus (IBV) D181 in poultry flocks in Morocco and Africa.

METHODS

The study includes six poultry farms, involving three flocks of layers aged between 28 and 67 weeks and three broiler flocks aged 27, 39 and 42 days from different regions of Morocco. In all affected layer flocks, a severe drop in egg production with poor eggshell quality was reported. Necropsy of dead birds was carried out, and samples of trachea, lungs, oviduct, ovaries, and kidneys were fixed in 10% neutral buffered formalin for histopathologic examinations, while other portions were stored at -20 °C for molecular analysis. Real time RT-qPCR for IBV gene group was performed, and IBV variants were identified. Partial S1 gene sequences were amplified by conventional RT-PCR, sequenced, and aligned for phylogenetic and amino acid similarity analysis.

RESULTS

Necropsy of dead birds revealed misshapen and hemorrhagic ovarian follicles with an edematous oviduct and severe reaction in the cecal tonsils. A caseous material accumulation in the sinus was noted in few birds. In contrast, the broiler flocks exhibited respiratory clinical signs such as difficulty in breathing, sneezing, tracheal rales, watery eyes and lethargy, associated with a decrease in feed consumption. Mortality in broiler ranged from 2 to 15%. Histopathological analysis of samples showed a lympho-plasmocytic inflammation in the oviduct, trachea, and lungs. Individual necrosis of epithelial cells, with sloughing of the bronchial epithelium and accumulation of desquamated cells with mucus in the airways, was observed in some birds. Partial S1 gene sequencing and phylogenetic analyses showed that the Moroccan strains were very closely related to D181 strains isolated in Dutch layers and breeders in 2018. Nucleotide sequence identities reached 90.9-95% with the Dutch isolates (strain CK/NL/D181/2018).

CONCLUSION

Our sequencing results demonstrate for the first time that the D181 IBV genotype is circulating in Moroccan poultry. These findings justify permanent monitoring of circulating strains in order to appropriately adjust vaccination strategies to align with the evolving field situation.

Development and Evaluation of Mycoplasma gallisepticum Challenge Model in Layer Pullets

Manufacturers of Mycoplasma gallisepticum (MG) modified live vaccines usually recommend a single application at 8 wk of age. This makes 12-16-wk-old layer pullets suitable for challenge studies intended to evaluate these vaccines. Numerous challenge models in different poultry species and ages have been reported. However, there is not an established layer pullet challenge model for this age. The aim of this study is to develop a suitable challenge model in 12-wk-old layer pullets. MG Rlow strain was used as the challenge strain, and its ability to induce clinical signs and lesions in 12-wk-old Hy-Line W-36 layer pullets was evaluated. Three different doses (low, 7.95 × 104 color-changing units [CCU]/bird; medium, 7.95 × 106 CCU/bird; and high, 7.95 × 108 CCU/bird) via three different routes (eye drop, fine spray, and contact infection) were compared and evaluated using different parameters. At 14 days post-challenge, there were no mortalities in any of the groups throughout the study. Layer pullets directly challenged with the high dose via the fine spray route showed the clearest and most consistent results (clinical signs, positive quantitative real-time PCR [qPCR], seroconversion, air sac scoring, and histopathological changes of the tracheal mucosa). Medium and low challenge doses applied via fine spray or eye drop did not show consistent results. Rlow strain was able to spread to the contact infection birds, as confirmed by the positive qPCR results; however, none of the contact-infected birds showed any clinical signs or gross or microscopic lesions. Our results suggest that a high dose (7.95 × 108 CCU/bird) administered through a fine spray route is the model of choice in any future MG vaccine evaluation trials in 12-wk-old layer pullets.

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

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

Infectious Bronchitis Virus California Variant CA1737 Isolated from a Commercial Layer Flock with Cystic Oviducts and Poor External Egg Quality

False layer syndrome is a condition in which the reproductive tract of chicks is infected with infectious bronchitis virus (IBV) strains that cause permanent damage to the oviduct. These chickens subsequently develop cystic oviducts and do not lay eggs, and affected flocks fail to reach expected egg production peaks. The California Animal Health and Food Safety laboratory, Turlock Branch, received four separate case submissions from a 25-to-28-wk-old commercial ISA Brown layer flock. Birds were submitted for diagnostic evaluation due to suboptimal egg production and vent pecking. Submissions totaled 31 birds and consisted of live layers, recent mortality, and a flat of eggs. No clinical signs were observed in the submitted live birds. The most common gross findings included cystic left oviducts, signs of vent pecking, ovarian regression, and yolk coelomitis. The eggs were abnormally shaped with irregular, white, gritty deposits on the surface of the shell. Microscopically, there was atrophy of the oviducts, glandular hypoplasia, and lymphocytic salpingitis. In addition, lymphoplasmacytic tracheitis was observed, and renal tubules were dilated with multifocal areas of mineralization. IBV was identified by reverse transcription quantitative PCR from cecal tonsil tissue pools and tracheal swab pools. Sequencing of the S1 hypervariable region of IBV and whole-genome IBV sequencing were 97% homologous to the California variant CA1737/04. Definitive proof of the CA1737 strain's causing reproductive abnormalities will require challenge studies with fulfillment of Koch's postulates and evaluation of confounding and risk factors.

Protection Efficacy of the Infectious Laryngotracheitis (ILT) Serva CEO Vaccine Strain in Broiler Chickens Under Different Vaccination Coverage Conditions

Mass vaccination against infectious laryngotracheitis virus (ILTV) in drinking water can result in variable initial vaccine take. Partial initial vaccine coverage of 20% with an Australian ILT vaccine (A20) previously resulted in significant protection against virulent ILTV challenge. This follow-up study used the international Serva ILT vaccine strain in a factorial design testing four levels of vaccination coverage (0%, 10%, 20%, or 100% of chicks eye-drop vaccinated with the live vaccine at 7 days of age) and three levels of ILTV challenge (no challenge or challenge at 7 or 21 days postvaccination [DPV]). The increase in ILTV load in choanal cleft swabs detected by qPCR after challenge was significantly reduced by 20% and 100% but not by 10% vaccination coverage. Vaccination reduced weight gain in unchallenged birds. Daily weight gain of birds was not affected by ILTV challenge at 7 DPV in any group, but following challenge at 21 DPV, it was significantly reduced in unvaccinated and 10% vaccinated groups relative to 20% and 100% vaccinated groups. Vaccination of 20% of the chickens provided substantial but incomplete protection (protective index range 44%-70%) against the severity of clinical signs and mortality following challenge while 10% vaccination coverage provided limited or no protection. Clinical signs were more severe and appeared earlier following challenge at 21 DPV than at 7 DPV. Within the vaccination treatments, eye-drop-vaccinated birds were better protected than their in-contact cohorts. In conclusion, partial vaccination of 20%, but not 10% of chickens, induced substantial protection against subsequent challenge. However, the attendant risks of reduced protection against early challenge and the possible reversion to virulence of vaccine virus when transmitted to unvaccinated chickens make it essential that 100% initial vaccine take be the goal of mass vaccination programs.

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.

Investigation of respiratory disease outbreaks of poultry in Bangladesh using two real-time PCR-based simultaneous detection assays

For rapid and sensitive pathogen screening from field outbreaks, molecular techniques such as qPCR-based simultaneous detections are efficient. Respiratory diseases are the most detrimental diseases to the poultry industry and need to be addressed because of their major economic losses. In the current study, we have applied two different detection assays: one for simultaneous detection of avian influenza virus (AIV; M gene) and subtyping (H5, N1, H9, N2) using TaqMan probe chemistry (TaqMan multitarget) and another for simultaneous detection of Newcastle disease virus (NDV), infectious bronchitis virus (IBV), and infectious laryngotracheitis virus (ILTV) using SYBR Green chemistry (SYBR Green multitarget). Two individual qPCRs were conducted for the detection of four pathogens. Surveillance of tissue (n = 158) and oropharyngeal swab (206) samples from multiple poultry flocks during the years April 2020-July 2022 applying the TaqMan and SYBR Green multitarget qPCRs revealed that 48.9% of samples were positive for respiratory infections, of which 17.2% were positive for NDV, 25.5% were positive for AIV, 9.9% were positive for IBV, and only a single positive (0.3%) for ILTV. Among the AIV, 35% were highly pathogenic subtype H5N1 and 65% were low pathogenic subtype H9N2. Co-infections of 2-3 respiratory viruses were also accurately detected. Respiratory viral pathogens are quite common in Bangladeshi poultry and can be successfully detected using multitarget simultaneous real-time quantitative polymerase chain reaction (RT-qPCR) assays like those adopted in the current study. Increased mass surveillance, along with the molecular characterization of the circulating respiratory viruses, is crucial to control the epidemic and subsequently save the Bangladeshi poultry industry.

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.

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.

Molecular-based monitoring of live vaccines in dust samples from experimental and commercial chicken flocks and its potential use as a screening test

Despite the high cost of vaccination programmes, conventional methods to evaluate vaccine uptake are often impractical and costly. More recently, molecular-based testing of poultry dust has been used to monitor the "take" of Marek's disease virus and infectious laryngotracheitis virus (ILTV) live vaccines. This study aimed to provide proof-of-concept for detecting other poultry pathogens by using molecular detection of vaccine microorganisms in poultry dust of vaccinated flocks. Dust and choanal cleft and cloacal swabs were collected from chickens vaccinated against avian encephalomyelitis virus (AEV), fowlpox virus (FPV), Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) using live vaccines in an experimental flock. Dust samples were collected weekly from 5 commercial breeder or layer flocks from day-old up to 25 weeks of age. These flocks were vaccinated against Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious bursal disease virus (IBDV), ILTV, fowl adenovirus (FAdV), MG and MS. Samples were tested for nucleic acids of these microorganisms by PCR or reverse transcriptase PCR. Genomes of all targeted vaccines were detected in dust samples from the experimental and commercial flocks except for FPV, which was detected only in the experimental flock. FAdV was detected in unvaccinated commercial flocks. These findings suggest that PCR detection of target organisms in dust samples has potential as a relatively simple and inexpensive population-level test to monitor vaccine take and/or pathogen status in chicken flocks. Further studies comparing the detection of each of these microorganisms in poultry dust with individual birds samples are required to validate this approach.

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.

Genomic Stability for PCR Detection of Infectious Laryngotracheitis Virus and Infectious Bronchitis Virus in Poultry Dust Samples Stored Under Different Conditions

Dust collected from the poultry house has been increasingly used as a population-level sample to monitor the presence of pathogens or to evaluate the administration of live vaccines. However, there are no guidelines for the storage of this sample type. This study investigated the stability of infectious laryngotracheitis virus (ILTV), a DNA virus, and infectious bronchitis virus (IBV), an RNA virus, in poultry dust kept under temperature and moisture conditions that mimic on-farm and laboratory storage. Dust samples were collected from chicks spray vaccinated with a live IBV vaccine and inoculated with a field ILTV strain via eye drop. Samples were stored under different moisture conditions (dry = 2% moisture, moist = 22%-71% moisture) and temperatures (-20, 4, 25, and 37 C) for different durations (0, 7, and 14 days, and 1, 2, 3, and 4 mo) in a factorial arrangement, followed by quantitative PCR for detection of virus genome copies (GC). The length of storage, moisture level, and storage temperature affected the viral genome load for ILTV and IBV but did not affect the number of positive samples for each virus. All treatment combinations were ILTV positive for at least 4 mo. In dry dust samples, all storage temperatures or durations had quantifiable ILTV or IBV GC. Moisture addition had a detrimental effect on viral genome load, causing an overall reduction of 0.3 log 10 for ILTV GC (7.29 and 6.97 log 10, P = 0.0001), and 1.3 log 10 for IBV GC (5.95 and 4.66 log 10, P = 0.0001), which are unlikely to have biologic significance. In conclusion, dry dust can be stored at any temperature up to 37 C for at least 4 mo without loss in qPCR detection of ILTV or IBV GC. Collection or storage of moist dust should be avoided, or air drying prior to storage is recommended if only moist dust is available.

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.

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.

Health surveillance of a potential bridge host: Pathogen exposure risks posed to avian populations augmented with captive-bred pheasants

Augmentation of wild populations with captive‐bred individuals presents an inherent risk of co‐introducing novel pathogens to naïve species, but it can be an important tool for supplementing small or declining populations. Game species used for human enterprise and recreation such as the ring‐necked pheasant (Phasianus colchicus) are commonly raised in captivity and released onto public and private wildlands as a method of augmenting naturalized pheasant populations. This study presents findings on pathogen exposure from three sources of serological data collected in California during 2014–2017 including (a) 71 pen‐reared pheasants sampled across seven game bird breeding farms, (b) six previously released pen‐reared pheasants captured at two study sites where wild pheasants occurred and (c) 79 wild pheasants captured across six study sites. In both pen‐reared and wild pheasants, antibodies were detected against haemorrhagic enteritis virus (HEV), infectious laryngotracheitis (ILT), infectious bursal disease virus (IBDV), paramyxovirus type 1 (PMV‐1) and Pasteurella multocida (PM). Previously released pen‐reared pheasants were seropositive for HEV, ILT, and PM. Generalized linear mixed models accounting for intraclass correlation within groups indicated that pen‐reared pheasants were more than twice as likely to test positive for HEV antibodies. Necropsy and ancillary diagnostics were performed in addition to serological testing on 40 pen‐reared pheasants sampled from five of the seven farms. Pheasants from three of these farms tested positive by PCR for Siadenovirus, the causative agent of both haemorrhagic enteritis in turkeys and marble spleen disease of pheasants, which are serologically indistinguishable. Following necropsy, owners from the five farms were surveyed regarding husbandry and biosecurity practices. Farms ranged in size from 10,000 to more than 100,000 birds, two farms raised other game bird species on premises, and two farms used some form of vaccination. Biosecurity practices varied by farm, but the largest farm implemented the strictest practices.

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.

Analysis of Whole-Genome Sequences of Infectious laryngotracheitis Virus Isolates from Poultry Flocks in Canada: Evidence of Recombination

Infectious laryngotracheitis virus (ILTV) is a herpes virus that causes an acute respiratory disease of poultry known as infectious laryngotracheitis (ILT). Chicken embryo origin (CEO) and tissue culture origin (TCO) live attenuated vaccines are routinely used for the control of ILT. However, vaccine virus is known to revert to virulence, and it has been recently shown that ILT field viral strains can undergo recombination with vaccinal ILTV and such recombinant ILT viruses possess greater transmission and pathogenicity potential. Based on complete or partial genes of the ILTV genome, few studies genotyped ILTV strains circulating in Canada, and so far, information is scarce on whole-genome sequencing or the presence of recombination in Canadian ILTV isolates. The objective of this study was to genetically characterize the 14 ILTV isolates that originated from three provinces in Canada (Alberta, British Columbia and Quebec). To this end, a phylogenetic analysis of 50 ILTV complete genome sequences, including 14 sequences of Canadian origin, was carried out. Additional phylogenetic analysis of the unique long, unique short and inverted repeat regions of the ILTV genome was also performed. We observed that 71%, 21% and 7% of the ILTV isolates were categorized as CEO revertant, wild-type and TCO vaccine-related, respectively. The sequences were also analyzed for potential recombination events, which included evidence in the British Columbia ILTV isolate. This event involved two ILTV vaccine (CEO) strains as parental strains. Recombination analysis also identified that one ILTV isolate from Alberta as a potential parental strain for a United States origin ILTV isolate. The positions of the possible recombination breakpoints were identified. These results indicate that the ILTV wild-type strains can recombine with vaccinal strains complicating vaccine-mediated control of ILT. Further studies on the pathogenicity of these ILTV strains, including the recombinant ILTV isolate are currently ongoing.

Assessment of A20 infectious laryngotracheitis vaccine take in meat chickens using swab and dust samples following mass vaccination in drinking water

Infectious laryngotracheitis, caused by the alphaherpesvirus infectious laryngotracheitis virus (ILTV), is an important disease of chickens. Partial control of this disease in meat chickens is commonly achieved by mass vaccination with live virus in drinking water. There is a need for a practical test to evaluate vaccination outcomes. For the Serva ILTV vaccine, quantitative real-time PCR (qPCR) enumeration of ILTV genome copies (GC) in flock level dust samples collected at 7-8 days post vaccination (dpv) can be used to differentiate flocks with poor and better vaccine take. This study aimed to validate this approach for A20, another widely used ILT vaccine in Australia. In four meat chicken flocks vaccinated with A20 in water using two different water stabilization times (20 or 40 min), swabs from the trachea and choanal cleft and dust samples were collected at 0, 7, 14 and 21 dpv. ILTV GC detection in swabs and dust was highest at 7 dpv and at this time ILTV GC load in dust was strongly and positively associated with vaccine take in individual birds assessed by swab samples. Choanal cleft swabs provided significantly fewer ILTV positive results than paired tracheal swab samples but the level of ILTV GC detected was similar. Water stabilization time had only minor effects on vaccination response in favour of the shorter time. Location of dust collection had no effect on viral load measured in dust samples. Dust samples collected at 0 and 7 dpv can be used to assess the vaccination status of flocks.

Optimization and application of a high-resolution melting protocol in the characterization of avian infectious laryngotracheitis virus

A previous sequence analysis of a US5 gene fragment of infectious laryngotracheitis virus (ILTV) performed in an Argentinian epidemiological study allowed to differentiate between wild and vaccine strains. This analysis also defined five ILTV haplotypes with specific variations at positions 461, 484, 832, 878 and 894 of the US5 gene. This characterization of viral strains may also be accomplished using the High-Resolution Melting Analysis (HRMA), which has been described as an effective, fast and sensitive method to detect mutations in PCR products. In the present study, an HRM protocol was developed with the aim of characterizing the circulating ILTV strains in Argentina. The specificity of this tool was confirmed in different DNA diluents, without interference from heterologous DNA or other cellular metabolites. Additionally, the salt concentration in the elution buffer used for DNA extraction did not alter the curve profiles. Higher concentrations of DNA (Ct≅26.0) displayed well-defined curve profiles, whereas lower concentrations (Ct≅32.5) exhibited more heterogeneous curves. The HRMA showed 97.49% concordance with the reference technique, i.e., sequencing. The HRM protocol has the capability to perform DNA amplification prior to its characterization. Thus, eventually this technique may be used simultaneously as a diagnostic tool. This advantage implies a significant reduction in the time and effort involved in sample processing.

Marked differences in virulence of three Australian field isolates of infectious laryngotracheitis virus in meat and layer chickens

The objectives of this study were to compare the virulence of contemporary infectious laryngotracheitis virus (ILTV) field isolates of classes 9, 10, and 14 in meat and layer chickens, and to evaluate cloacal and oropharyngeal swabs and dust as sample types for ILTV detection. A total of 211 chickens were divided into groups and inoculated with ILTV class 9, 10, or 14, or sham-inoculated via eye drop at 15 or 22 days of age. Chickens were euthanized at 5 and 9 days post-infection. Virulence was assessed by scoring of clinical signs (conjunctivitis, dyspnoea, and demeanour), ILTV genomic copies (GC) in oropharyngeal and cloacal swabs, mortality and microscopic lesions in conjunctiva and trachea. Class 14 caused subclinical infection, while inoculation with class 9 or class 10 resulted in severe clinical signs and microscopic lesions. Compared to class 14 (2.25 ± 0.36 log₁₀ GC), higher viral load was observed in oropharyngeal swabs of classes 9 (7.86 ± 0.48) and 10 (7.53 ± 0.36), with a higher proportion of positive oropharyngeal and cloacal swabs in the latter groups (P < 0.0001). Viral detection in cloacal swabs was delayed at early stages of infection compared to oropharyngeal swabs. Dust samples from class 9- and class 10-inoculated groups showed a trend towards higher GC than that of class 14. Overall, clinical scores, mortality, viral load, and microscopic lesions were similar for classes 9 and 10, but class 9 caused more severe disease in layer chickens than meat chickens. In summary, ILTV classes 9 and 10 exhibited severe virulence, while class 14 exhibited very mild virulence. RESEARCH HIGHLIGHTS Wide variation in the virulence of three field Australian field ILTV strains. Class 9 and class 10 strains were highly virulent, while class 14 was mildly virulent. The highly virulent strains were associated with significantly higher viral genome copies in various sample types than the mildly virulent strain.

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.

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.

Characterization of an Outbreak of Infectious Coryza (Avibacterium paragallinarum) in Commercial Chickens in Central California

In 2017, the Turlock branch of the California Animal Health & Food Safety laboratory system received a significant increase in infectious coryza (IC) necropsy cases, with a total of 54 submissions originating from commercial broilers (n = 40), commercial layers (n = 11), and backyard chickens (n = 3). Layer flocks positive for IC were distributed within the adjacent counties of Merced and Stanislaus, while broiler flocks were concentrated within Merced County. The backyard flocks were located in Alameda and Sacramento counties. The clinical and pathologic presentation was consistent with IC, although septicemic lesions were also noticed. Avibacterium paragallinarum was isolated and identified by PCR from the respiratory tract as well as from extrarespiratory sites. Polymicrobial infections involving other viral (infectious bronchitis virus, infectious bursal disease virus) and bacterial (Mycoplasma spp., Escherichia coli, Ornithobacterium rhinotracheale, Gallibacterium anatis biovar haemolytica) agents were commonly reported. Thirteen selected Av. paragallinarum isolates were successfully characterized as serovar C (Page scheme) and serovar C2 (Kume scheme). They shared a unique enterobacterial repetitive intergenic consensus (ERIC) PCR, differing from the four reference strains, and showed consistent high minimum inhibitory concentration values for tetracycline, suggesting a common origin from a single clone. Based on these results, high biosecurity standards and proper immunization of susceptible, multi-age flocks should always be implemented and adjusted as needed. The importance of backyard flocks should not be underestimated due to their unique epidemiologic role.

Use of Commercial Swine Live Attenuated Vaccine to Control an Erysipelothrix rhusiopathiae Outbreak in Commercial Cage-Free Layer Chickens

Erysipelothrix rhusiopathiae septicemia was diagnosed in three cage-free commercial layer flocks from Washington State that experienced an increase in mortality and slight drop in egg production. Erysipelothrix rhusiopathiae was isolated from multiple organs and from environmental samples. An agar gel diffusion test of several E. rhusiopathiae isolates confirmed the presence of serotype 1b, and multiplex real-time PCR of the surface protective antigen (Spa) gene confirmed presence of SpaA. Bacitracin administered via the water reduced mortality minimally and only for a short period of time. Mortality was finally controlled by vaccination with a live attenuated swine E. rhusiopathiae vaccine delivered via the drinking water. This is the first report describing the use of an attenuated vaccine to control an E. rhusiopathiae outbreak in a chicken flock.

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.

Evaluation of Protective Efficacy When Combining Turkey Herpesvirus-Vector Vaccines

Turkey herpesvirus (HVT) is widely used as a vaccine against Marek's disease in chickens and recently as a vector for foreign genes from infectious bursal disease virus, Newcastle disease (ND) virus, infectious laryngotracheitis (ILT) virus, and avian influenza virus. Advantages of HVT-vector vaccines are that the vaccines do not contain live respiratory viruses or live infectious bursal disease virus able to replicate and cause disease or embryo mortality, they can be administered at hatch or in ovo, and they are relatively insensitive to interference from maternally derived antibodies. As producers have tried to combine HVT-vector vaccines to protect against additional diseases, reports have indicated that applying two vectored vaccines using the same HVT vector is reported to reduce the efficacy of one or both vaccines. To confirm this interference, we evaluated commercial vaccines from multiple companies, including products with inserts designed to protect against ND, infectious ILT, and infectious bursal disease (IBD). Using a standard dosage, we found that the ILT product was most severely affected by the addition of other vaccines, as demonstrated by a significant increase in clinical signs, significant decrease in weight gain, and increase in quantity of challenge virus observed from tracheal swabs collected from Days 3-5 postchallenge. The ND and IBD products were also affected by the addition of other vaccines, although in most cases differences compared to vaccination with the vector alone were not statistically significant. This study demonstrates the importance of following manufacturer guidelines and the need for validating alternative strategies to benefit from the high level of protection offered by vector vaccines.

A practical method for assessing infectious laryngotracheitis vaccine take in broilers following mass administration in water: Spatial and temporal variation in viral genome content of poultry dust after vaccination

Infectious laryngotracheitis is an important disease of chickens caused by infectious laryngotracheitis virus (ILTV). Outbreaks commonly occur in meat chicken flocks and mass vaccination with live attenuated vaccines, usually in water, is used to control the disease in these populations. Vaccination with live virus via water and nipple drinkers requires stringent adherence to protocols to ensure success, but vaccine administration monitoring is not currently assessed due to a lack of economically viable methods. Vaccinal ILTV has been shown to be detectable in dust in experimental studies and has potential as a method of assessing vaccination success. However, the pattern of vaccinal ILTV detection in dust following vaccination under commercial conditions has not been defined. We report the longitudinal profile of ILTV genome copies (GC) in poultry house dust collected on settle plates following vaccination of 8 flocks of commercial meat chickens on four farms. ILTV GC was enumerated using quantitative real-time polymerase chain reaction (qPCR). There was considerable variation between flocks in the levels of ILTV GC detected post vaccination and this variation was significantly associated with vaccine take measured in individual birds in a companion study. There was no effect of sampling location on ILTV GC in dust but the amount of dust collected was greater in locations closer to the exhaust fans in artificially ventilated houses. Results indicate that measurement of ILTV GC in single or pooled dust samples at 7-8 days post vaccination enables detection of poor vaccine takes and provides a practical means of monitoring ILT vaccination.

Validation of specific quantitative real-time RT-PCR assay panel for Infectious Bronchitis using synthetic DNA standards and clinical specimens

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Real-time quantitative PCR assays were developed for six different IBV types.

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Rapid detection of IBV type is important for control.

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Analytical sensitivity was evaluated using synthetic DNA standards.

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Specificity was determined using clinical and biological specimens.

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Linearity over a 5 log₁₀ dynamic range and a limit of detection of ≤10 target copies was realized.

Infectious bronchitis (IB) is a highly contagious upper respiratory tract disease of chickens caused by infectious bronchitis virus (IBV), which has various serotypes that do not cross-protect. Vaccine control strategies for this virus are only effective when designed around the currently circulating serotypes. It is essential to not only rapidly detect IBV but also to identify the type of virus causing disease. Six TaqMan™-based quantitative real-time RT-PCR assays (Universal, Ark, Mass, DE/GA98, GA07, GA08) were developed and examined the sensitivity and specificity for each assay. Assays were developed targeting the hypervariable region in the S1 gene subunit. The analytical sensitivity of TaqMan™-based quantitative real-time RT-PCR assays (qRT-PCR) assays was evaluated using synthetic DNA standards that were identical with the target sequence and specificity was further validated using clinical and biological specimens. All developed assays performed equivalently when using synthetic DNA templates as standard material, as it achieved linearity over a 5 log₁₀ dynamic range with a reproducible limit of detection of ≤10 target copies per reaction, with high calculated amplification efficiencies ranging between 90%–115%. Further validation of specificity using clinical and biological specimens was also successful.

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.

Uptake and spread of infectious laryngotracheitis vaccine virus within meat chicken flocks following drinking water vaccination

Vaccination against infectious laryngotracheitis virus (ILTV) in commercial broiler flocks in the field, which is only undertaken in the face of a local outbreak, requires mass administration techniques, usually via drinking water. This is often fraught with difficulties such as variable vaccination "reactions" and sometimes, vaccination failure. Laboratory testing of the outbreak strains however invariably shows the vaccines in use to be protective. To investigate this paradox, the dynamics of an ILT vaccine virus was examined within broiler flocks during a natural outbreak. In an initial flock, 70 birds were individually identified and had tracheal swabs collected sequentially at intervals from 1 to 26 days after vaccination and submitted for ILTV detection using qPCR. This evaluation was extended by collection of tracheal swabs from 40 to 45 random birds at 4, 7-8, 12-13 and 25-26 days post vaccination (pv) across a further 7 flocks. The results showed a very variable early uptake of vaccine virus from the drinking water (between 3% and 52% of tested birds with detectable virus in trachea at 4 days pv) and revealed that actual vaccination of the flocks relied on bird to bird transmission of the vaccine virus. In flocks with very low (<10%) initial bird uptake, successful exposure of vaccine virus to the majority of the flock can be delayed, leaving a large proportion of birds as susceptible at the likely time of possible exposure to wild virus. This may explain the cases of apparent failure of vaccination in the field. The variable bird to bird spread can be associated with reversion to virulence, this may explain the rolling vaccine reactions often observed. The variation in initial vaccine uptake may be affected by some factors involved with the administration technique and this requires further study in a larger sample size.

Molecular detection and phylogenetic tree of infectious laryngotracheitis virus in layers in Al-Diwaniyah province, Iraq

Background and Aim

Infectious laryngotracheitis (ILT) of chickens is a substantial issue to be studied in Iraq because this disease is one of the most highly contagious respiratory diseases in the world caused by a herpesvirus. However, in Iraq, the ILT virus (ILTV) infection and disease have yet not been confirmed in layers, so farm owners do not vaccinate these layers. The current study aimed to document the detection and characterization of ILTV in layer hens from Al-Diwaniyah city, for the first time in Iraq, using molecular techniques like polymerase chain reaction (PCR) and sequencing.

Materials and Methods

Four layer farms (15,000 unvaccinated layers/farm) in Al-Diwaniyah province, Iraq, suffered a severe ILT outbreak, was diagnosed and reported by clinical and PCR tests. This disease has been reported in Iraq, and more recently, it began to show outbreaks in Al-Diwaniyah city. The current work opted to investigate the ILTV using PCR and DNA sequencing techniques. The study targeted the p32 gene of ILTV using pooled tracheal swabs and organs including the trachea, lung, and kidneys which were collected from dead and clinically infected chickens.

Results

The analyses revealed that four of six suspected field samples showed positive results by PCR. The DNA sequencing results showed the homology of the amplified fragments with the studied gene.

Conclusion

This study confirmed the presence of ILTV in hens with respiratory signs during the outbreak.

Retrospective analysis of infectious laryngotracheitis in backyard chicken flocks in California, 2007-2017, and determination of strain origin by partial ICP4 sequencing

Infectious laryngotracheitis (ILT) can cause severe losses in backyard flocks (BYFs) and commercial poultry. The prevalence of ILT, the circulating strains of ILT virus (ILTV) in BYFs, and the correlation of disease in BYF and commercial operations, is largely unknown. Of 8,656 BYF submissions, 88 cases of ILT were diagnosed at the California Animal Health and Food Safety Laboratory System in 2007-2017. ILT diagnosis by year varied from 0.19% to 1.7% of the total BYF submissions, with the highest number of cases submitted from Amador and Riverside counties. Moderate tracheitis, conjunctivitis, and occluded tracheal lumen were commonly reported gross anatomic lesions. Microscopically, inflammation and edema were observed in the trachea, lung, and conjunctiva; 62 (70%) cases had intranuclear inclusion bodies (INIBs), with 10 cases containing INIBs only in conjunctival sections. To analyze the circulating ILTV strains and to differentiate between field and vaccine strains of ILTV, real-time PCR and sequencing of 996 base pairs of the infected-cell polypeptide 4 ( ICP4) gene was performed on 15 ILTV-positive tracheal samples and compared to reference field and vaccine ILTV ICP4 sequences in GenBank. Fourteen strains were identical or closely related to the chicken embryo origin live virus vaccine strains, and one strain was closely related to a Chinese isolate, the USDA reference strain, and a vaccine strain. The presence of ILT in BYFs in counties with high commercial poultry concentrations demonstrates a risk for disease transmission and emphasizes the importance of continued surveillance and improved biosecurity in BYFs.

A two-year prospective study of small poultry flocks in Ontario, Canada, part 1: prevalence of viral and bacterial pathogens

In Ontario, within the past few years, there has been a marked increase in the number of non-commercial poultry flocks (referred to as "small flocks"). Small poultry flocks may act as a reservoir of avian and zoonotic pathogens, given the flocks' limited access to veterinary services, inadequate biosecurity practices, and increased risk of contact with wild birds. Despite these potential risks, there is a scarcity of data concerning the prevalence of poultry and zoonotic pathogens among these flocks. To assess the baseline prevalence of bacterial and viral infectious pathogens, prospective surveillance of small flock postmortem submissions to the Animal Health Laboratory was conducted over a 2-y period. With the owner's consent, a postmortem examination and pre-set tests for infectious agents were conducted. A total of 160 submissions, mainly chickens (84%), were received. Among bacterial pathogens, Brachyspira spp., Mycoplasma synoviae, Campylobacter spp., Mycoplasma gallisepticum, and Salmonella spp. were detected in 37%, 36%, 35%, 23%, and 3% of tested submissions, respectively. Among viral pathogens, infectious bronchitis virus, fowl adenovirus, infectious laryngotracheitis virus, avian reovirus, and infectious bursal disease virus were detected in 39%, 35%, 15%, 4%, and 1% of submissions, respectively. We detected non-virulent avian avulavirus 1 from two chickens in a single submission, and low-pathogenic H10N8 influenza A virus from a single turkey submission. Our study provides baseline prevalence of viral and bacterial pathogens circulating in Ontario small flocks and may help animal and human health professionals to educate small flock owners about disease prevention.

Effect of Pullet Vaccination on Development and Longevity of Immunity

Avian respiratory disease causes significant economic losses in commercial poultry. Because of the need to protect long-lived poultry against respiratory tract pathogens from an early age, vaccination programs for pullets typically involve serial administration of a variety of vaccines, including infectious bronchitis virus (IBV), Newcastle disease virus (NDV), and infectious laryngotracheitis virus (ILTV). Often the interval between vaccinations is only a matter of weeks, yet it is unknown whether the development of immunity and protection against challenge when vaccines are given in short succession occurs in these birds, something known as viral interference. Our objective was to determine whether serially administered, live attenuated vaccines against IBV, NDV, and ILTV influence the development and longevity of immunity and protection against challenge in long-lived birds. Based on a typical pullet vaccination program, specific-pathogen-free white leghorns were administered multiple live attenuated vaccines against IBV, NDV, and ILTV until 16 weeks of age (WOA), after which certain groups were challenged with IBV, NDV, or ILTV at 20, 24, 28, 32, and 36 WOA. Five days post-challenge, viral load, clinical signs, ciliostasis, tracheal histopathology, and antibody titers in serum and tears were evaluated. We demonstrate that pullets serially administered live attenuated vaccines against IBV, NDV, and ILTV were protected against homologous challenge with IBV, NDV, or ILTV for at least 36 weeks, and conclude that the interval between vaccinations used in this study (at least 2 weeks) did not interfere with protection. This information is important because it shows that a typical pullet vaccination program consisting of serially administered live attenuated vaccines against multiple respiratory pathogens can result in the development of protective immunity against each disease agent.

Single Nucleotide Polymorphism Genotyping Analysis Shows That Vaccination Can Limit the Number and Diversity of Recombinant Progeny of Infectious Laryngotracheitis Viruses from the United States

Infectious laryngotracheitis (ILTV; Gallid alphaherpesvirus 1) causes mild to severe respiratory disease in poultry worldwide. Recombination in this virus under natural (field) conditions was first described in 2012 and more recently has been studied under laboratory conditions. Previous studies have revealed that natural recombination is widespread in ILTV and have also demonstrated that recombination between two attenuated ILTV vaccine strains generated highly virulent viruses that produced widespread disease within poultry flocks in Australia. In the United States, natural ILTV recombination has also been detected, but not as frequently as in Australia. To better understand recombination in ILTV strains originating from the United States, we developed a TaqMan single nucleotide polymorphism (SNP) genotyping assay to detect recombination between two virulent U.S. field strains of ILTV (63140 and 1874c5) under experimental in vivo conditions. We also tested the capacity of the Innovax-ILT vaccine (a recombinant vaccine using herpesvirus of turkeys as a vector) and the Trachivax vaccine (a conventionally attenuated chicken embryo origin vaccine) to reduce recombination. The Trachivax vaccine prevented ILTV replication, and therefore recombination, in the trachea after challenge. The Innovax-ILT vaccine allowed the challenge viruses to replicate and to recombine, but at a significantly lower rate than in an unvaccinated group of birds. Our results demonstrate that the TaqMan SNP genotyping assay is a useful tool to study recombination between these ILTV strains and also show that vaccination can limit the number and diversity of recombinant progeny viruses.IMPORTANCE Recombination allows alphaherpesviruses to evolve over time and become more virulent. Historically, characterization of viral vaccines in poultry have mainly focused on limiting clinical disease, rather than limiting virus replication, but such approaches can allow field viruses to persist and evolve in vaccinated populations. In this study, we vaccinated chickens with Gallid alphaherpesvirus 1 vaccines that are commercially available in the United States and then performed coinoculations with two field strains of virus to measure the ability of the vaccines to prevent field strains from replicating and recombining. We found that vaccination reduced viral replication, recombination, and diversity compared to those in unvaccinated chickens, although the extent to which this occurred differed between vaccines. We suggest that characterization of vaccines could include studies to examine the ability of vaccines to reduce viral recombination in order to limit the rise of new virulent field strains due to recombination, especially for those vaccines that are known not to prevent viral replication following challenge.

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.

Development of a qPCR for the detection of infectious laryngotracheitis virus (ILTV) based on the gE gene

1. Infectious laryngotracheitis is a respiratory disease that affects the poultry industry worldwide. It is common in flocks with high-bird density, causing major economic losses. 2. In this study, a SYBR® FAST polymerase chain reaction (PCR) double-strand DNA intercalating agent assay was performed for the detection of infectious laryngotracheitis virus (ILTV) in clinical samples in comparison with a conventional nested-PCR, both based on the glycoprotein E encoding gene. This assay amplified 56 bp and was capable of detecting 1⁹ to 1 copies of virus. 3. In total, 164 clinical samples were obtained from birds with respiratory problems from the period of 2009-2016. In the nested-PCR, there were 45.12% positive samples and 54.88% negative samples, while in the real-time PCR (qPCR), there were 81.1% positive samples and 18.9% negative samples. 4. In conclusion, qPCR from the DNA double-strand intercalating agent SYBR® GREEN FAST was useful for the diagnosis of ILTV because it detected samples that were negative in nested-PCR. This assay has advantages, such as a shortened processing-time, and no need for post-amplification processing (electrophoresis) with additional reagents, such as MgCl₂ and agarose. Hence, qPCR proved to be useful, rapid and low cost for use with clinical samples.

Esophagitis and Pharyngitis Associated with Avian Infectious Laryngotracheitis in Backyard Chickens: Two Cases

Infectious laryngotracheitis (ILT) is a contagious viral respiratory disease of great economic importance for the global poultry industry caused by Gallid herpesvirus 1 (GaHV-1). Lesions of the upper digestive tract caused by this virus have not been reported before. Two small flocks of backyard chickens experienced an outbreak of ILT, one in 2006 and the other in 2014. These birds had typical ILT lesions, characterized by a necrohemorrhagic laryngitis and tracheitis but were also affected by a severe erosive and necrotic esophagitis and pharyngitis. On microscopic examination of the esophagus and pharynx, numerous individual epithelial cells were degenerated or necrotic. Syncytial cells were present in the mucosa or sloughed in the overlying inflammatory crust, and some of these cells contained an amphophilic intranuclear viral inclusion. GaHV-1 was detected in tissues, from respiratory and digestive tracts, either by PCR, immunohistochemistry, or both diagnostic assays. This case stresses the importance for veterinarians, owners, and technicians to pay attention to different or atypical clinical manifestations of ILT given its highly contagious nature.

Multiple pathogen biomarker detection using an encoded bead array in droplet PCR

We present a droplet PCR workflow for detection of multiple pathogen DNA biomarkers using fluorescent color-coded Luminex® beads. This strategy enables encoding of multiple singleplex droplet PCRs using a commercially available bead set of several hundred distinguishable fluorescence codes. This workflow provides scalability beyond the limited number offered by fluorescent detection probes such as TaqMan probes, commonly used in current multiplex droplet PCRs. The workflow was validated for three different Luminex bead sets coupled to target specific capture oligos to detect hybridization of three microorganisms infecting poultry: avian influenza, infectious laryngotracheitis virus and Campylobacter jejuni. In this assay, the target DNA was amplified with fluorescently labeled primers by PCR in parallel in monodisperse picoliter droplets, to avoid amplification bias. The color codes of the Luminex detection beads allowed concurrent and accurate classification of the different bead sets used in this assay. The hybridization assay detected target DNA of all three microorganisms with high specificity, from samples with average target concentration of a single DNA template molecule per droplet. This workflow demonstrates the possibility of increasing the droplet PCR assay detection panel to detect large numbers of targets in parallel, utilizing the scalability offered by the color-coded Luminex detection beads.

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.

Comparison of SYBR green I real-time RT-PCR with conventional agarose gel-based RT-PCR for the diagnosis of infectious bronchitis virus infection in chickens in Morocco

BACKGROUND

A rapid, sensitive, and specific molecular method for the diagnosis of infectious bronchitis virus (IBV) infection is important in curbing infectious bronchitis outbreaks in Morocco and other countries.

METHODS

In this study, an easy-to-perform SYBR green I real-time reverse transcriptase polymerase chain reaction (RT-PCR) targeting the nucleocapsid gene of IBV was developed and compared with conventional agarose gel-based RT-PCR for the detection of IBV infection.

RESULTS

We found that the SYBR green I real-time RT-PCR was at least 10 times more sensitive than the agarose gel electrophoresis detection method. The assay exhibited high specificity for IBV infection. All negative controls, such as Newcastle disease virus, infectious bursal disease virus, and avian influenza virus, were not detected.

CONCLUSION

The SYBR green I real-time RT-PCR test described herein can be used to rapidly distinguish IBV from other respiratory pathogens, which is important for diagnosis and control of infectious bronchitis outbreaks in Morocco. The test is a valuable and useful method as a routine assay for diagnosis of clinical IBV infection in commercial chickens.

Newcastle disease virus (NDV) recombinants expressing infectious laryngotracheitis virus (ILTV) glycoproteins gB and gD protect chickens against ILTV and NDV challenges

Infectious laryngotracheitis (ILT) is a highly contagious acute respiratory disease of chickens caused by infectious laryngotracheitis virus (ILTV). The disease is controlled mainly through biosecurity and vaccination with live attenuated strains of ILTV and vectored vaccines based on turkey herpesvirus (HVT) and fowlpox virus (FPV). The current live attenuated vaccines (chicken embryo origin [CEO] and tissue culture origin [TCO]), although effective, can regain virulence, whereas HVT- and FPV-vectored ILTV vaccines are less efficacious than live attenuated vaccines. Therefore, there is a pressing need to develop safer and more efficacious ILTV vaccines. In the present study, we generated Newcastle disease virus (NDV) recombinants, based on the LaSota vaccine strain, expressing glycoproteins B (gB) and D (gD) of ILTV using reverse genetics technology. These recombinant viruses, rLS/ILTV-gB and rLS/ILTV-gD, were slightly attenuated in vivo yet retained growth dynamics, stability, and virus titers in vitro that were similar to those of the parental LaSota virus. Expression of ILTV gB and gD proteins in the recombinant virus-infected cells was detected by immunofluorescence assay. Vaccination of specific-pathogen-free chickens with these recombinant viruses conferred significant protection against virulent ILTV and velogenic NDV challenges. Immunization of commercial broilers with rLS/ILTV-gB provided a level of protection against clinical disease similar to that provided by the live attenuated commercial vaccines, with no decrease in body weight gains. The results of the study suggested that the rLS/ILTV-gB and -gD viruses are safe, stable, and effective bivalent vaccines that can be mass administered via aerosol or drinking water to large chicken populations.

IMPORTANCE

This paper describes the development and evaluation of novel bivalent vaccines against chicken infectious laryngotracheitis (ILT) and Newcastle disease (ND), two of the most economically important infectious diseases of poultry. The current commercial ILT vaccines are either not safe or less effective. Therefore, there is a pressing need to develop safer and more efficacious ILT vaccines. In the present study, we generated Newcastle disease virus (NDV) recombinants expressing glycoproteins B (gB) and D (gD) of infectious laryngotracheitis virus (ILTV) using reverse genetics technology. These recombinant viruses were safe, stable, and immunogenic and replicated efficiently in birds. Vaccination of chickens with these recombinant viruses conferred complete protection against ILTV and NDV challenge. These novel bivalent vaccines can be mass administered via aerosol or drinking water to large chicken populations at low cost, which will have a direct impact on poultry health, fitness, and performance.

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.

Prevalence and differentiation of diseases in Maryland backyard flocks

Several epidemiologic surveillance studies have implicated backyard flocks as a reservoir for poultry diseases; however, much debate still exists over the risk these small flocks pose. To evaluate this concern, the prevalence of Newcastle disease (ND), infectious laryngotracheitis (ILT), Mycoplasma gallisepticum (MG), and Salmonella was determined in 39 Maryland backyard flocks. Serum, tracheal, and cloacal swabs were randomly collected from 262 birds throughout nine counties in Maryland. Through PCR and ELISA analysis, disease prevalence and seroprevalence were determined in flocks, respectively, for the following: ND (0%, 23%); ILT (26%, 77%); MG (3%, 13%); and Salmonella (0%, not done). Vaccine status could not be accurately confirmed. Premise positives were further differentiated and identified by partial nucleotide sequencing. Screening of the 10 ILT premise positives showed that most were live attenuated vaccines: eight matched a tissue culture origin vaccine, one matched a chicken embryo origin (CEO) vaccine, and one was CEO related. The single MG-positive flock, also positive for the CEO-related sequence, was identified as the infectious S6 strain. The prevalence rates for these economically important poultry diseases ranged from none to relatively low, with the vast majority of sampled flocks presenting no clinical signs.

Immune responses to infectious laryngotracheitis virus

Infectious laryngotracheitis (ILT) is an upper respiratory tract disease in chickens caused by infectious laryngotracheitis virus (ILTV), an alphaherpesvirus. Despite the extensive use of attenuated, and more recently recombinant, vaccines for the control of this disease, ILT continues to affect the intensive poultry industries worldwide. Innate and cell-mediated, rather than humoral immune responses, have been identified as responsible for protection against disease. This review examines the current understandings in innate and adaptive immune responses towards ILTV, as well as the role of ILTV glycoprotein G in modulating the host immune response towards infection. Protective immunity induced by ILT vaccines is also examined. The increasing availability of tools and reagents for the characterisation of avian innate and cell-mediated immune responses are expected to further our understanding of immunity against ILTV and drive the development of new generation vaccines towards enhanced control of this disease.