Use of polymerase chain reaction (PCR) for the detection of vaccine contamination by infectious laryngotracheitis virus

Molecular Detection of Infectious Laryngotracheitis Virus in Chickens with a Microfluidic Chip

Simple Summary

Infectious laryngotracheitis (ILT) presents a major risk to the chicken industry. Rapid, specific, simple, and point-of-need molecular detection of the virus is crucial to enable chicken farms to take timely action and contain the spread of infection. The current study describes an isothermal amplification assay for infectious laryngotracheitis virus (ILTV) infection and the implementation of this assay in a microfluidic chip suitable for molecular detection and quasi-quantification of ILTV in diagnostic veterinary laboratories with low resources and poultry farms. Our assay performance was compared and favorably agreed with quantitative PCR (qPCR). Clinical tests of our assay and chip with samples from diseased chickens demonstrated good concordance with the gold-standard benchtop qPCR assay.

Abstract

Infectious laryngotracheitis (ILT) is a viral disease of chickens’ respiratory system that imposes considerable financial burdens on the chicken industry. Rapid, simple, and specific detection of this virus is crucial to enable proper control measures. Polymerase chain reaction (PCR)-based molecular tests require relatively expensive instruments and skilled personnel, confining their application to centralized laboratories. To enable chicken farms to take timely action and contain the spread of infection, we describe a rapid, simple, semi-quantitative benchtop isothermal amplification (LAMP) assay, and a field-deployable microfluidic device for the diagnosis of ILTV infection in chickens. Our assay performance was compared and favorably agreed with quantitative PCR (qPCR). The sensitivity of our real-time LAMP test is 250 genomic copies/reaction. Clinical performance of our microfluidic device using samples from diseased chickens showed 100% specificity and 100% sensitivity in comparison with benchtop LAMP assay and the gold-standard qPCR. Our method facilitates simple, specific, and rapid molecular ILTV detection in low-resource veterinary diagnostic laboratories and can be used for field molecular diagnosis of suspected ILT cases.

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.

Two stage, nested isothermal amplification in a single tube

Sensitive, specific and rapid molecular diagnosis of respiratory diseases in animals and humans is critical to facilitate appropriate control measures and treatment. Conventional polymerase chain reaction (PCR)-based molecular diagnostics requires relatively expensive equipment and trained staff, restricting its use to centralized laboratories with significant delays between sample collection and test results. Herein, we report a highly sensitive, rapid, point-of-need, two-stage-molecular test that requires minimal instrumentation and training. Our test, dubbed Penn-RAMP, combines recombinase polymerase amplification (RPA, 38 °C) and loop-mediated isothermal amplification (LAMP, 63 °C) in one tube, enabling nested, two-stage isothermal amplification. We demonstrate Penn-RAMP's efficacy by testing for two common viral respiratory diseases of chickens: infectious laryngotracheitis (ILT) and infectious bronchitis (IB) that impose great economic burden worldwide. Test results of clinical samples with our closed-tube Penn-RAMP assays concord with the gold standard quantitative PCR (qPCR) assay; with 10-fold better limit of detection than LAMP and qPCR. Our closed-tube Penn-RAMP assays have the potential to greatly reduce false negatives while requiring minimal instrumentation and training.

Application of recombinase polymerase amplification method for rapid detection of infectious laryngotracheitis virus

Infectious laryngotracheitis is a significant respiratory disease of chickens that causes huge economic losses due to high morbidity and mortality and reduced egg production. A real-time recombinase polymerase amplification (RPA) assay was developed to accurately detect ILTV. The specific probe and primer sets were carefully designed and screened. The real-time RPA assay was carried out at 39 °C for 30 min, and results were obtained within 15 min. The results of the specificity assay showed no fluorescence signals with other avian-related viruses. The sensitivity of the assay was 1 × 10² copies/μL. The low CV value showed that the assay was reproducible. A total of 115 clinical samples were tested using the real-time RPA assay and the real-time PCR assay in parallel; the coincidence rates of the two detection methods were 100%. The results indicated that the real-time RPA assay is a specific, sensitive, rapid, and useful tool for epidemiological studies and clinical diagnosis, especially in the field and in resource-poor areas.

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

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

Molecular 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.

Avian leukosis virus subgroup - J as a contaminant in live commercially available poultry vaccines distributed in Nigeria

Globally, vaccines are used to prevent and control the menace of infectious diseases in livestock with some reported to be inadvertently contaminated with extraneous agents (EAs). With the aim of screening and characterizing for some selected EAs, 44 live viral poultry vaccines were randomly selected based on availability. The vaccines comprised 14 manufacturers in 10 different countries including Nigeria were screened by Polymerase Chain Reaction. In 9% (4/44) of the vaccines, contamination with only avian leukosis virus (ALV) subgroup J (ALV-J) was recorded. Other exogenous ALV subgroups, chicken infectious anemia and infectious laryngotracheitis viruses were absent. The EAs was found in infectious bursal disease (n = 1), Fowlpox (n = 2) and Mareks disease (n = 1) vaccines. Phylogenetic analysis of the ALV-J env gene showed clustering with contemporary group I and II. The result underscores the importance of screening vaccines to avoid the introduction and spread of EAs that could pose a threat to poultry production.

Detection of infectious laryngotracheitis virus by real-time PCR in naturally and experimentally infected chickens

Infectious laryngotracheitis (ILT) is an acute, highly contagious upper-respiratory infectious disease of chickens. In this study, a real-time PCR method was developed for fast and accurate detection and quantitation of ILTV DNA of chickens experimentally infected with ILTV strain LJS09 and naturally infected chickens. The detection lower limit of the assay was 10 copies of DNA. There were no cross reactions with the DNA and RNA of infectious bursal disease virus, chicken anemia virus, reticuloendotheliosis virus, avian reovirus, Newcastle disease virus, and Marek's disease virus. The real-time PCR was reproducible as the coefficients of variation of reproducibility of the intra-assay and the inter-assay were less than 2%. The real-time PCR was used to detect the levels of the ILTV DNA in the tissues of specific pathogen free (SPF) chickens infected with ILTV at different times post infection. ILTV DNA was detected by real-time PCR in the heart, liver, spleen, lung, kidney, larynx, tongue, thymus, glandular stomach, duodenum, pancreatic gland, small intestine, large intestine, cecum, cecal tonsil, bursa of Fabricius, and brain of chickens in the infection group and the contact-exposure group. The sensitivity, specificity, and reproducibility of the ILTV real-time PCR assay revealed its suitability for detection and quantitation of ILTV in the samples from clinically and experimentally ILTV infected chickens.

Development and comparison of a Primer-Probe Energy Transfer based assay and a 5' conjugated Minor Groove Binder assay for sensitive real-time PCR detection of infectious laryngotracheitis virus

In this study the design and development of two real-time PCR assays for the rapid, sensitive and specific detection of infectious laryngotracheitis virus (ILTV) DNA is described. A Primer-Probe Energy Transfer (PriProET) assay and 5' conjugated Minor Groove Binder (MGB) method are compared and contrasted. Both have been designed to target the thymidine kinase gene of the ILTV genome. Both PriProET and MGB assays are capable of detecting 20 copies of a DNA standard per reaction and are linear from 2×10(8) to 2×10(2)copies/μl. Neither PriProET, nor MGB reacted with heterologous herpesviruses, indicating a high specificity of the two methods as novel tools for virus detection and identification. This study demonstrates the suitability of PriProET and 5' conjugated MGB probes as real-time PCR chemistries for the diagnosis of respiratory diseases caused by ILTV.

An Optimized Polymerase Chain Reaction Assay to Identify Avian Virus Vaccine Contamination with Chicken Anemia Virus

The use of embryonating chicken eggs in preparation of avian virus vaccines is the principle cause for contamination with Chicken anemia virus (CAV). Identification of CAV in contaminated vaccines relies on the expensive, tedious, and time-consuming practice of virus isolation in lymphoblastoid cell lines. The experience of the last 2 decades indicates that polymerase chain reaction is extending to replace most of the classic methods for detection of infectious agents. In the present report, a simple, rapid, and accurate polymerase chain reaction method for detection of CAV in poultry vaccines is described. Oligonucleotide primers homologous to highly conserved sequences of the VP1 gene were used to amplify a fragment of 676 bp. The developed assay was specific for detecting CAV from different sources, with no cross reactivity with many avian viruses. No inter- and intra-assay variations were observed. The analytical sensitivity of the test was high enough to detect 5 TCID50 (50% tissue culture infective dose) of the virus per reaction; however, different factors related to the vaccine matrix showed considerable effects on the detection limit. In conclusion, this method may represent a suitable alternative to virus isolation for identification of CAV contamination of poultry virus vaccines.

Rapid detection and characterization from field cases of infectious laryngotracheitis virus by real-time polymerase chain reaction and restriction fragment length polymorphism

A real-time polymerase chain reaction (PCR) assay was developed to specifically amplify infectious laryngotracheitis virus (ILTV) DNA from field samples. The 222-base-pair PCR fragment was amplified using primers located in a conserved region of the infected cell protein 4 gene that was demonstrated in this work to encompass a single nucleotide polymorphism. Subsequent restriction fragment length polymorphism (RFLP) analysis of real-time PCR amplified fragments from a range of ILTV isolates using the restriction endonuclease MspI enabled differentiation between older ILTV isolates that were prevalent in the 1960s prior to the availability of vaccine strains and more recent isolates that predominantly are identical to vaccine strains. The assay, using real-time PCR, RFLP and sequence analysis, was used to characterize two recent field cases of infectious laryngotracheitis from Northern Ireland. One of the field cases was demonstrated to be similar to older "wild-type" isolates, while the other field case was identified to have a concurrent ILTV infection of both "wild-type" and vaccinal type origin. The assay described here using real-time PCR and RFLP provides a rapid, specific method that enables detection and characterization of ILTV directly from field cases.

Application of RT-PCR for the detection of avian reovirus contamination in avian viral vaccines

An efficient procedure for the detection of avian reovirus (ARV)-specific RNA sequences in veterinary immunological medicinal products using reverse transcriptase polymerase chain reaction (RT-PCR) is described. Four ARV vaccine strains (1133, 1733, 2408 and Olson WVU2937), two ATCC strains (VR826 and VR856) as well as several ARV field isolates obtained from domestic, wild and pet birds could be easily detected with S2- and S4-specific primers. The identity of the amplified fragments was confirmed by restriction endonuclease analysis and sequence analysis. Furthermore, not only the starting substrates used for the production of a vaccine, but also additives and the manufacturing process (matrix effects) can influence the results. These RT-PCRs have been useful for screening poultry vaccines for extraneous ARV in the quality control of biologicals used in veterinary medicine.

Detection of porcine circovirus type 1 in commercial pig vaccines using polymerase chain reaction

The absence of extraneous viruses is a requirement in the quality control of vaccines for veterinary use in the European Pharmacopoeia. A polymerase chain reaction (PCR) assay for the detection of porcine circovirus type 1 (PCV1) and type 2 (PCV2) was evaluated in 18 commercial porcine vaccines. Since vaccine components may contain PCR enhancers or inhibitors, 13 of the studied vaccines (used as diluents) were subsequently spiked with different dilutions of PCV2 and tested by PCR. Although PCV2 DNA was not detected in any of the vaccines tested, PCV1 was detected in 2/18 vaccines (11%). Eleven out of 13 PCV2 spiked vaccines showed a positive PCR result. The lack of amplification observed in two spiked vaccines suggested that use of the PCR assay to detect PCV2 could depend on vaccine composition. The results of this exploratory study have demonstrated that PCR is a rapid and fairly sensitive method for the detection of porcine circoviruses as extraneous agents in vaccine products and can be used in the quality control of pig vaccines. The study has also indicated the need for optimising the sensitivity of PCR methods for PCV genome detection in vaccine products.