Name: multiplexed isothermal amplification based diagnostic platform to detect zika, chikungunya, and dengue 1
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Description: Watch this Scientific Journal Video about Multiplexed Isothermal Amplification Based Diagnostic Platform to Detect Zika, Chikungunya, and Dengue 1 at JoVE.com

The work was supported in part by FDOH-7ZK15 and NIAID 1R21AI128188-01. Research reported in this publication was supported in part by the National Institutes of Allergy and Infectious Diseases, and in part by Biomedical Research Program of Florida Department of Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH or Florida Department of Health. Dynamic Combinatorial Chemistry LLC is acknowledged for their support and contribution to this project.
Dengue 1 virus (strain BOL-KW010) was kindly provided by the Florida Department of Health Bureau of Laboratories. Zika virus and the Asian lineage of chikungunya virus were graciously provided by the Centers for Disease Control and Prevention. The Indian Ocean lineage of chikungunya virus was kindly provided by Robert Tesh (World Reference Center for Emerging Viruses and Arboviruses, through the University of Texas Medical Branch in Galveston, Texas) to the UF-FMEL. We thank S. Bellamy, B. Eastmond, S. Ortiz, D. Velez, K. Wiggins, R. ZimLer, and K. Zirbel for assistance with the infection studies. We also thank M. S. Kim for providing Q-paper.

NOTE: Mosquitoes were the only animals directly used in this study. The procedures to manage chickens, whose blood was used to feed the infected mosquitoes, were approved as IACUC Protocol #201507682 by the University of Florida Institutional Animal Care and Use Committee.Virus propagation and mosquito infection studies were performed at the BSL-3 facility of the Florida Medical Entomology Laboratory in Vero Beach, FL. RT-LAMP experiments were performed in the BSL-2 laboratory shared by FfAME and Firebird Biomolecular Sc...

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Mosquito-borne viruses including Zika, chikungunya, and dengue threaten the public health and recent Zika outbreaks highlight the need for low-cost point-of-care detection alternatives for patient diagnostics, as well as for mosquito surveillance. Isothermal amplification methods were developed as affordable alternatives to PCR-based systems. Particularly, RT-LAMP-based platforms have been applied to detect a wide range of pathogens. However, the use of isothermal platforms has been mainly limited to single target detect...

Mosquito-borne virus infections, including dengue, chikungunya, and Zika viruses are on the rise and demand immediate management strategies. Dengue and chikungunya viruses are already endemic in many of the tropical regions where Zika is now spreading in the Western Hemisphere1. Zika virus, like dengue, is a member of the Flaviviridae family and is native to Africa with one Asian and two African genetic lineages2. Even though the identification of the Zika virus dates back to 1947, Zika infection in humans remained sporadic for a half century before emerging in the Pacific and the Americas. The first reported outbreak of Zika fever occurred on the island of Yap in the Federated States of Micronesia in 2007, followed by French Polynesia in 2013 and 2014. The first major outbreak in the Americas occurred in 2015 in Brazil.
Zika, chikungunya, and dengue viruses are primarily transmitted by Aedes aegypti and Aedes albopictus. However, Zika has additional downstream human-to-human transmission possibilities, likely being spread through sexual contact, mother-to-fetus interaction, and via breast-feeding3,4,5. Zika fever was first believed to cause only mild illness. However, it was later associated with Guillain-Barr&#233; syndrome in adults, microcephaly in neonates, and chronic musculoskeletal diseases that may last months to years. Diagnosis of Zika illness can be challenging, since the symptoms of a Zika infection are similar to those of other mosquito-spread viruses6. Common co-infections of these viruses make differential diagnosis even more challenging7,8. Therefore, rapid and reliable detection of the nucleic acids from Zika and other viruses is needed to understand epidemiology in real time, to initiate control and preventive measures, and to manage patient care9.
Current diagnostic tests for these viruses include serological tests, virus isolation, virus sequencing, and reverse-transcription PCR (RT-PCR). Standard serological approaches often suffer from inadequate sensitivity and results can be complicated by cross-reactivity in patients who have previously been infected by other flaviviruses.
Therefore, nucleic acid testing remains the most reliable way to detect and differentiate these viruses. Detection of Zika and other mosquito-borne viruses is usually performed using RT-PCR or real-time RT-PCR in variety of biological fluids, such as serum, urine, saliva, semen, breast milk, and cerebral fluid10,11. Urine and saliva samples are generally preferred over blood, since they exhibit less PCR-inhibition, higher viral loads, virus presence for longer periods of time, and increased ease of collection and handling12,13. RT-PCR-based diagnostic tests, however, comprise extensive sample preparation steps and expensive thermal cycling equipment, making it less optimal for the point-of-care.
Reverse transcription loop-mediated isothermal amplification (RT-LAMP) has emerged as a powerful RT-PCR alternative due to its high sensitivity and specificity14, its tolerance for inhibitory substances in biological samples15, and operation on single temperature, which significantly lowers assay complexity and associated costs, making it suitable for low resource environments. RT-LAMP, as it is classically implemented, comprises six primers that bind to eight distinct regions within the target RNA. It runs at constant temperatures between 60 &#176;C and 70 &#176;C, and uses a reverse transcriptase and a DNA polymerase with strong strand displacing activity.
During the initial stages of RT-LAMP, forward and backward internal primers (FIP and BIP, Figure 1A) along with outer forward and backward primers (F3 and B3) form a dumbbell structure, the seed structure of exponential LAMP amplification. Amplification is further accelerated by the loop forward and backward primers (LF and LB), which are designed to bind the single stranded regions of the dumbbell, and results in the formation of concatemers with multiple repeating loops16. Classical LAMP assays based on turbidity or readout by DNA intercalating dyes is not entirely suited for point-of-care detection of Zika, where some level of multiplexing is desired17,18,19. Multiplexing is not easily obtained in these systems, as they are prone to generate false-positives due to off-target amplifications.
To manage these issues, the literature adds an additional component in the form of a &#34;strand-displacing probe&#34; to the classical RT-LAMP architecture20,21,22. Each probe has a sequence-specific double-strand region and a single-stranded priming region. The probe with the single-stranded region is tagged with a 5&#39;-fluorophore, and the complementary probe is modified with a 3&#39;-end quencher. In the absence of a target, no fluorescence is observed due to hybridization of the complementary probe strands, which brings the fluorophore and quencher into close proximity. In the presence of a target, the single-stranded portion of the fluorescent probe binds to its complement on the target, and is then extended by a strand displacing polymerase. Further polymerase extension by reverse primers causes the separation of the quencher strand from its complementary fluorescently labeled strand, allowing emission of fluorescence (Figure 1B). With this design, the signal is generated after the dumbbell formation, reducing the chances of false-positive signals.
The double-stranded portion of the strand-displacing probe can be any sequence, and when multiplexing is applied, the same sequence may be used with different fluorophore-quencher pairs. With this architecture, virus-contaminated urine, serum, or mosquito samples squished on paper were directly introduced to the assay without sample preparation. Three-color fluorescence read-outs visible to human eye were generated within 30 - 45 min, and signals were visualized by a 3D-printed observation box that uses a blue LED and an orange filter. Freeze-drying the RT-LAMP reagents enabled deployment of this kit to lower resource settings without a need for refrigeration.

<table>
	<tbody>
		<tr>
			<td>SafeBlue Illuminator/ Electrophoresis System, MBE-150-PLUS</td>
			<td>Major Science</td>
			<td>MBE-150</td>
			<td>Gel electrophoresis</td>
		</tr>
		<tr>
			<td>G:BOX F3</td>
			<td>Syngene</td>
			<td>G:BOX F3</td>
			<td>Gel imaging</td>
		</tr>
		<tr>
			<td>LightCycler 480 Instrument II, 96-well</td>
			<td>Roche Applied Science</td>
			<td>05 015 278 001</td>
			<td>Real-time PCR</td>
		</tr>
		<tr>
			<td>Amicon Ultra-0.5 Centrifugal Filter Unit with Ultracel-10 membrane</td>
			<td>Millipore Sigma</td>
			<td>UFC501096</td>
			<td>ultrafiltraton membrane for dialysis</td>
		</tr>
		<tr>
			<td>Eppendorf 5417C Centrifuge</td>
			<td>Marshall Scientific</td>
			<td>EP-5417C</td>
			<td>centrifuge</td>
		</tr>
		<tr>
			<td>Myblock Mini Drybath</td>
			<td>Benchmark Scientific</td>
			<td>BSH200</td>
			<td>drybath</td>
		</tr>
		<tr>
			<td>FreeZone Plus 6 Liter Cascade Console Freeze Dry System</td>
			<td>Labconco</td>
			<td>7934020</td>
			<td>lyophilizer</td>
		</tr>
		<tr>
			<td>all priers and probes</td>
			<td>IDT</td>
			<td>custom</td>
			<td>RT-LAMP primers and probes</td>
		</tr>
		<tr>
			<td>dNTP set</td>
			<td>Bioline</td>
			<td>BIO-39049</td>
			<td></td>
		</tr>
		<tr>
			<td>Deoxyuridine Triphosphate (dUTP)</td>
			<td>Promega</td>
			<td>U1191</td>
			<td></td>
		</tr>
		<tr>
			<td>Bst&#160;2.0 WarmStart&#160;DNA Polymerase</td>
			<td>New England Biolabs</td>
			<td>M0538L</td>
			<td>enzyme</td>
		</tr>
		<tr>
			<td>WarmStart RTx Reverse Transcriptase</td>
			<td>New England Biolabs</td>
			<td>M0380L</td>
			<td>enzyme</td>
		</tr>
		<tr>
			<td>RNase Inhibitor, Murine</td>
			<td>New England Biolabs</td>
			<td>M0314L</td>
			<td>enzyme</td>
		</tr>
		<tr>
			<td>Antarctic Thermolabile UDG</td>
			<td>New England Biolabs</td>
			<td>M0372L</td>
			<td>enzyme</td>
		</tr>
		<tr>
			<td>50bp DNA Step Ladder</td>
			<td>Promega</td>
			<td>G4521</td>
			<td>marker</td>
		</tr>
		<tr>
			<td>LightCycler 480 Multiwell Plate 96, white</td>
			<td>Roche Applied Science</td>
			<td>4729692001</td>
			<td>real-time RT-LAMP analysis</td>
		</tr>
	</tbody>
</table>

multiplexed isothermal amplification based diagnostic platform to detect zika, chikungunya, and dengue 1

Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different downstream patient-to-patient transmission potentials, and require very different patient treatments. Thus, recent Zika outbreaks make it urgent to develop tools that rapidly discriminate these viruses in patients and trapped mosquitoes, to select the correct patient treatment, and to understand and manage their epidemiology in real time.
Unfortunately, current diagnostic tests, including those receiving 2016 emergency use authorizations and fast-track status, detect viral RNA by reverse transcription polymerase chain reaction (RT-PCR), which requires instrumentation, trained users, and considerable sample preparation. Thus, they must be sent to &#34;approved&#34; reference laboratories, requiring time. Indeed, in August 2016, the Center for Disease Control (CDC) was asking pregnant women who had been bitten by a mosquito and developed a Zika-indicating rash to wait an unacceptable 2 to 4 weeks before learning whether they were infected. We very much need tests that can be done on site, with few resources, and by trained but not necessarily licensed personnel.
This video demonstrates an assay that meets these specifications, working with urine or serum (for patients) or crushed mosquito carcasses (for environmental surveillance), all without much sample preparation. Mosquito carcasses are captured on paper carrying quaternary ammonium groups (Q-paper) followed by ammonia treatment to manage biohazards. These are then directly, without RNA isolation, put into assay tubes containing freeze-dried reagents that need no chain of refrigeration. A modified form of reverse transcription loop-mediated isothermal amplification with target-specific fluorescently tagged displaceable probes produces readout, in 30 min, as a three-color fluorescence signal. This is visualized with a handheld, battery-powered device with an orange filter. Forward contamination is prevented with sealed tubes, and the use of thermolabile uracil DNA glycosylase (UDG) in the presence of dUTP in the amplification mixture.

Initially, the performances of each RT-LAMP primer (Table 1) with its corresponding viral RNA substrate as well as negative controls were assessed by gel electrophoresis. RT-LAMP primers were designed to target NS5 region (RNA-dependent RNA polymerase) for Zika and Dengue 1, and nsP2 region (non-structural protein P2) for Chikungunya. Templates were total RNA extracted from viral stocks cultured in African green monkey kidney (Vero) cells. In one case, total nucleic acid ...

Watch this Scientific Journal Video about Multiplexed Isothermal Amplification Based Diagnostic Platform to Detect Zika, Chikungunya, and Dengue 1 at JoVE.com

Multiplexed Isothermal Amplification Based Diagnostic Platform to Detect Zika, Chikungunya, and Dengue 1

Current multiplexed diagnostics to detect Zika, chikungunya, and dengue viruses require complex sample preparation and expensive instrumentation, and are difficult to use in low resource environments. We show a diagnostic that uses isothermal amplification with target-specific strand displaceable probes to detect and differentiate these viruses with high sensitivity and specificity.

Zika, dengue, and chikungunya viruses are transmitted by mosquitoes, causing diseases with similar patient symptoms. However, they have different ...

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