Development of loop-mediated isothermal amplification assays for rapid and easy detection of Coxiella Burnetii

Q Fever: A troubling disease and a challenging diagnosis

Q fever is a disease caused by the bacterial pathogen Coxiella burnetii. This hardy organism can easily spread long distances in the wind, and only a few infectious aerosolized particles are necessary to cause serious illness. Presentations of Q fever disease can be wide-ranging, allowing it to masquerade as other illnesses and highlight the importance of laboratory testing for diagnosis and treatment. This review summarizes Q fever's epidemiology and clinical presentations and presents classical laboratory diagnostic assays and novel approaches to detecting this troubling disease.

Development of a Rapid and Sensitive Colorimetric Loop-Mediated Isothermal Amplification Assay: A Novel Technology for the Detection of Coxiella burnetii From Minimally Processed Clinical Samples

Q fever is an important zoonotic disease caused by the bacterium Coxiella burnetii. The agent is considered as a potential agent for bioterrorism because of its low infectious dose, aerial route of transmission, resistance to drying, and many commonly used disinfectants. Humans are largely infected by the inhalation of aerosols that are contaminated with parturition products of infected animals as well as by the consumption of unpasteurized milk products. Thus, rapid and accurate detection of C. burnetii in shedders, especially those that are asymptomatic, is important for early warning, which allows controlling its spread among animals and animal-to-human transmission. In the present study, a colorimetric loop-mediated isothermal amplification (LAMP) assay was developed to confirm the presence of IS1111a gene of C. burnetii in sheep vaginal swabs. The sensitivity of this assay was found to be very comparable to the quantitative PCR (qPCR) assay, which could detect three copies of the gene, which corresponds to a single cell of C. burnetii. The applicability of the colorimetric LAMP assay in the disease diagnosis was assessed by evaluating 145 vaginal swab samples collected from the sheep breeding farms with a history of stillbirth and repeated abortions. Compared to qPCR, colorimetric LAMP had a sensitivity of 93.75% (CI, 69.77–99.84%) and specificity of 100% (CI, 97.20–100%), with a positive (PPV) and negative predictive value (NPV) of 100 and 99.24%, respectively. A very high level of agreement was observed between both colorimetric LAMP and reference qPCR assay. The colorimetric LAMP assay reported here is a rapid and simple test without extensive sample preparation and has a short turnaround time of <45 min. To the best of our understanding, it is the very first study describing the use of colorimetric LAMP assay that detects C. burnetii in vaginal swab samples with minimal sample processing for DNA extraction.

Loop-mediated isothermal amplification assay for detection of Coxiella burnetii targeting the com1 gene

We developed the com1 gene based loop-mediated isothermal amplification (LAMP) assay for the detection of Coxiella burnetii and validated it by screening DNA isolated from serum samples collected from animals and humans. The detection of Coxiella by LAMP assay was comparable with the com1 based-PCR.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

A rapid bio-optical sensor for diagnosing Q fever in clinical specimens

Recent zoonotic outbreaks, such as Zika, Middle East respiratory syndrome and Ebola, have highlighted the need for rapid and accurate diagnostic assays that can be used to aid pathogen control. Q fever is a zoonotic disease caused by the transmission of Coxiella burnetii that can cause serious illness in humans through aerosols and is considered a potential bioterrorism agent. However, the existing assays are not suitable for the detection of this pathogen due to its low levels in real samples. We here describe a rapid bio-optical sensor for the accurate detection of Q fever and validate its clinical utility. By combining a bio-optical sensor, that transduces the presence of the target DNA based on binding-induced changes in the refractive index on the waveguide surface in a label-free and real-time manner, with isothermal DNA amplification, this new diagnostic tool offers a rapid (<20 min), 1-step DNA amplification/detection method. We confirmed the clinical sensitivity (>90%) of the bio-optical sensor by detecting C. burnetii in 11 formalin-fixed, paraffin-embedded liver biopsy samples from acute Q fever hepatitis patients and in 16 blood plasma samples from patients in which Q fever is the cause of fever of unknown origin.

Evaluation of the stability of lyophilized loop-mediated isothermal amplification reagents for the detection of Coxiella burnetii

Coxiella burnetii, the causative pathogen for Q fever, is an obligate intracellular bacterium and designated as a biosafety level 3 agent. Detection and quantification of the bacteria with conventional culturing methods is time-consuming and poses significant health risks. Polymerase chain reaction (PCR)-based assays have been developed for detecting C. burnetii and could provide rapid diagnosis. However, they require specialized equipment, including a cold chain for PCR reagents that maintains their stability during storage and transport. These requirements limit the advantage of PCR-based methods, especially in resource-limited areas.

Previously, we had developed a lyophilized loop-mediated isothermal amplification (LAMP) assay to detect the presence of C. burnetii. To simplify and improve this assay, the reagents for the LAMP assay and the detecting reagent, SYBR green, were lyophilized together. The stability of the lyophilized reagents was evaluated by measuring changes in detection limit for plasmid DNA encoding a C. burnetii gene upon storage at 4 °C, 25 °C, or 37 °C. Our data indicate that the lyophilized reagents remain stable for 24 months when stored at 4 °C, 28 days at 25 °C, and 2 days at 37 °C. This improved LAMP assay can be easily performed in a simple water bath or heating block. The stability at ambient temperature, the simplicity of assay procedure, and the availability of low cost equipment make this method ideal for use in resource-limited settings where Q fever is endemic.

Clinical and epidemiological use of nested PCR targeting the repetitive element IS1111 associated with the transposase gene from Coxiella burnetii

Q fever is a worldwide zoonosis caused by Coxiella burnetii-a small obligate intracellular Gram-negative bacterium found in a variety of animals. It is transmitted to humans by inhalation of contaminated aerosols from urine, feces, milk, amniotic fluid, placenta, abortion products, wool, and rarely by ingestion of raw milk from infected animals. Nested PCR can improve the sensitivity and specificity of testing while offering a suitable amplicon size for sequencing. Serial dilutions were performed tenfold to test the limit of detection, and the result was 10× detection of C. burnetti DNA with internal nested PCR primers relative to trans-PCR. Different biological samples were tested and identified only in nested PCR. This demonstrates the efficiency and effectiveness of the primers. Of the 19 samples, which amplify the partial sequence of C. burnetii, 12 were positive by conventional PCR and nested PCR. Seven samples-five spleen tissue samples from rodents and two tick samples-were only positive in nested PCR. With these new internal primers for trans-PCR, we demonstrate that our nested PCR assay for C. burnetii can achieve better results than conventional PCR.

The Development of Lyophilized Loop-mediated Isothermal Amplification Reagents for the Detection of Coxiella burnetii

Coxiella burnetii, the agent causing Q fever, is an obligate intracellular bacterium. PCR based diagnostic assays have been developed for detecting C. burnetii DNA in cell cultures and clinical samples. PCR requires specialized equipment and extensive end user training, and therefore, it is not suitable for routine work especially in a resource-constrained area. We have developed a loop-mediated isothermal amplification (LAMP) assay to detect the presence of C. burnetii in patient samples. This method is performed at a single temperature around 60 °C in a water bath or heating block. The sensitivity of this LAMP assay is very similar to PCR with a detection limit of about 25 copies per reaction. This report describes the preparation of the reaction using lyophilized reagents and visualization of results using hydroxynaphthol blue (HNB) or a UV lamp with fluorescent intercalating dye in the reaction. The LAMP reagents were lyophilized and stored at room temperature (RT) for one month without loss of detection sensitivity. This LAMP assay is particularly robust because the reaction mixture preparation does not involve complex steps. This method is ideal for use in resource-limited settings where Q fever is endemic.

Usefulness of the early molecular diagnosis of Q fever and rickettsial diseases in patients with fever of intermediate duration

Most cases of fever of intermediate duration (FDI) in Spain are associated with infectious diseases (mainly Q fever and rickettsia infections). In clinical practice, the causal diagnosis of these entities is based on immunodiagnostic techniques, which are of little help in the early stages. Therefore, the aim of this study was to evaluate the usefulness of molecular techniques for the early diagnosis of Q fever and rickettsia diseases in patients with FDI. A PCR method was used to detect the presence of genetic material of Coxiella burnetii and Rickettsia spp. in blood specimens from 271 patients with FDI. The specificity of both techniques is high, allowing diagnosis in cases undiagnosed by specific antibodies detection. These data suggest that the use of molecular techniques, with proper selection of the study specimen, and using appropriate primers is a useful tool in the early diagnosis of the main causes of FDI, especially if serology is negative or inconclusive.

Development of loop-mediated isothermal amplification test for the diagnosis of contagious agalactia in goats

Contagious agalactia is a highly infectious disease affecting sheep and goats, mainly caused by Mycoplasma agalactiae. Although various tests are available for diagnosis of contagious agalactia, none of them is credited with the capacity to provide rapid and cost-effective diagnosis. This article reports the development of loop-mediated isothermal amplification (LAMP) test targeting the p40 gene of M. agalactiae, for the diagnosis of classical contagious agalactia. Optimum amplification was obtained at 58 °C in 70 min. The developed test was found to be 100-fold more sensitive than PCR and detected up to 20-fg level of DNA. The test was also superior to conventional PCR in detecting from artificially contaminated milk, i.e. 10(4)-fold more sensitive. The developed LAMP test could detect up to 10 cfu/ml of artificially contaminated milk, indicating its potential for being developed as a field test for rapid and sensitive diagnosis.