Rapid detection of infectious laryngotracheitis virus isolates by loop-mediated isothermal amplification

Point-of-Care Diagnostic Test for Rapid Detection of Infectious Laryngotracheitis Virus by Loop-Mediated Isothermal Amplification and Nanoprobes

Infectious laryngotracheitis virus (ILTV), a DNA virus classified as Gallid alphaherpesvirus 1, causes a highly contagious respiratory disease in chickens, leading to significant economic losses and health risks for the poultry industry. The rapid detection of ILTV is essential to control its spread and prevent outbreaks. Traditional diagnostic methods like PCR are costly, require specialized personnel, and delay response efforts. To address this, we developed a point-of-care diagnostic test combining loop-mediated isothermal amplification (LAMP) with DNA nanoprobes on respiratory swabs. LAMP targets the ILTV-glycoprotein E (gE) gene, enabling rapid nucleic acid amplification at 65 °C without extraction, making it suitable for on-site detection. DNA nanoprobes provide a colorimetric readout visible to the naked eye. Gold nanoparticles drive this readout, as their red color, based on localized surface plasmon resonance, persists in the presence of ILTV DNA through DNA-DNA hybridization, ensuring reliable detection. The assay achieved 100% sensitivity and specificity for ILTV-gE, with a detection limit of 200 copies per reaction, allowing for the early identification of infections. The results are available within 45 min, enabling prompt measures to control ILTV spread. Cost-effective and user-friendly, this method enhances disease management and biosecurity in poultry farms.

Molecular Detection of Respiratory Tract Viruses in Chickens at the Point of Need by Loop-Mediated Isothermal Amplification (LAMP)

Accurate and timely molecular diagnosis of respiratory diseases in chickens is essential for implementing effective control measures, preventing the spread of diseases within poultry flocks, minimizing economic loss, and guarding food security. Traditional molecular diagnostic methods like polymerase chain reaction (PCR) require expensive equipment and trained personnel, limiting their use to centralized labs with a significant delay between sample collection and results. Loop-mediated isothermal amplification (LAMP) of nucleic acids offers an attractive alternative for detecting respiratory viruses in broiler chickens with sensitivity comparable to that of PCR. LAMP's main advantages over PCR are its constant incubation temperature (∼65 °C), high amplification efficiency, and contaminant tolerance, which reduce equipment complexity, cost, and power consumption and enable instrument-free tests. This review highlights effective LAMP methods and variants that have been developed for detecting respiratory viruses in chickens at the point of need.

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.

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.

Rapid Detection of Avian Infectious Bronchitis Virus by Reverse Transcriptase-Loop Mediated Isothermal Amplification

A reverse-transcription loop mediated isothermal amplification (RT-LAMP) was developed for rapid diagnosis of infectious bronchitis (IB) in poultry by targeting the spike protein 2 gene (S2). RT-LAMP primers were designed for IBV-S2 targets and optimized to run at 60 °C for 45 min. As compared with RT-PCR, RT-LAMP was 100 times more sensitive for IBV-S2 gene. RT-LAMP showed specific amplification with IB viral genome but not with other avian respiratory pathogens due to their mismatching with IBV-S2-RT-LAMP primers. RT-LAMP reaction products were visually detected by the addition of propidium iodide stain. Out of 102 field samples tested for detection of IBV, RT-LAMP detected IBV in 12 samples for S2 gene whereas RT-PCR detected IBV in six samples for S2 gene. The sensitivity of the RT-LAMP was 100 % and the specificity was 94 % for S2 gene. Since the developed RT-LAMP to detect IBV is simple, rapid, sensitive and specific, it can be a useful diagnostic tool for detection of IB in poultry in less equipped laboratories and in field conditions.

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.

Rapid Detection of Viruses Using Loop-Mediated Isothermal Amplification (LAMP): A Review

Most of the diseases caused by viral infection are found to be fatal, and the diagnosis is difficult due to confusion with other causative agents. So, a highly efficient molecular-based advance detection technique, i.e., loop-mediated isothermal amplification (LAMP) method, is developed for diagnosis of viral infections by various workers. It is based on amplification of DNA at very low level under isothermal conditions, using a set of four specifically designed primers and a DNA polymerase with strand displacement activity. This technique is found to be superior than most of the molecular techniques like PCR, RT-PCR, and real-time PCR due to its high specificity, sensitivity, and rapidity. Major advantage of LAMP method is its cost-effectiveness as it can be done simply by using water bath or dry bath. Here, in this review information regarding almost all the effective LAMP techniques which is developed so far for diagnosis of numerous viral pathogens is presented.

Development of a loop-mediated isothermal amplification assay for rapid detection of bovine parvovirus

A loop-mediated isothermal amplification (LAMP) assay was developed for detection of bovine parvovirus (BPV) DNA. Four primers were designed to recognize six distinct regions on the target DNA based on a highly conserved sequence in the VP2 region of the BPV genome. The optimized LAMP reaction conditions were 8 mM Mg²⁺, 1.2 mM betaine, and an incubation at 63°C for 45 min. After amplification the products were detected either by observing a ladder pattern following gel electrophoresis, observation of turbidity, or a color change with the addition of SYBR Green I to the reaction tube. The detection limit of the LAMP assay was 9 copies of BPV-DNA and was 100 times more sensitive than conventional PCR. A ladder pattern of bands after gel electrophoresis was observed for only BPV isolates and showed that the BPV LAMP assay was highly specific without any cross-reactivity with other related viruses. The LAMP assay was evaluated further using 59 field samples and the results were comparable to conventional PCR. The LAMP assay is a simple, rapid and economic detection method; it can provide a useful technique suitable for detection of BPV infection in both field conditions and laboratory settings.

Rapid detection of the Marek's disease viral genome in chicken feathers by loop-mediated isothermal amplification

A loop-mediated isothermal amplification (LAMP) method for the rapid detection of serotype 1 Marek's disease virus (MDV) was developed. The method used a set of three pairs of primers to amplify the MEQ gene for detecting serotype 1 MDV. The MDV LAMP method did not cross-react with serotype 2 and serotype 3, nor did the LAMP primers have binding sites for the common avian DNA viruses (reticuloendotheliosis virus, chicken anemia virus, subgroup J of the avian leukosis virus). Additionally, the assay could detect up to 10 copies of the MEQ gene in the MD viral genome, and it had 10 times higher sensitivity than the traditional PCR methods. The LAMP master mix was stable for 90 days at -20°C. Furthermore, the efficiency of LAMP for detection of serotype 1 MDV in clinical samples was comparable to those of PCR and viral isolation. The LAMP procedure is simple and does not rely on any special equipment. The detection of serotype 1 MDV by LAMP will be useful for detecting and controlling oncogenic Marek's disease.

Visual detection of turkey coronavirus RNA in tissues and feces by reverse-transcription loop-mediated isothermal amplification (RT-LAMP) with hydroxynaphthol blue dye

A sensitive reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay was developed for the rapid visual detection of turkey coronavirus (TCoV) infection. The reaction is performed in one step in a single tube at 65 °C for 45 min, with hydroxynaphthol blue (HNB) dye added prior to amplification. The detection limit of the RT-LAMP assay was approximately 10² EID_50/50 μl TCoV genome, and no cross-reaction with other avian viruses was observed. The assay was evaluated further in tissue suspensions prepared from the ileum and ileum–caecal junctions of infected turkey embryos; 100% of these samples were positive in the RT-LAMP assay. All individual feces samples collected in the field were considered positive by both conventional RT-PCR and RT-LAMP. In conclusion, RT-LAMP with HNB dye was shown to be a sensitive, simple assay for the rapid diagnosis of TCoV infection, either directly from feces or in association with virus isolation methods.