Name: a multi-detection assay for malaria transmitting mosquitoes
Uploaded: 2015-02-28T14:00:00
Description: Watch this Scientific Journal Video about A Multi-detection Assay for Malaria Transmitting Mosquitoes at JoVE.com

We thank Drs. Anthony Cornel and Laura Norris at UC Davis and Dr. Katharina Kreppel at the University of Glasgow for providing mosquito specimens from Tanzania. We thank Ms.&#160;Smita Das and Dr. Douglas Norris from Johns Hopkins School of Public Health for sharing mosquito samples from Zambia. We also thank Mr. Lee V. Millon at the Veterinary Genetics Laboratory for training on assay design. This work was supported by the National Institute of Health grant R01AI 078183 and R21AI062929.

1. PCR Amplification
<ol>
	<li>Mix all the PCR primers (See supplemental Table S1) in a 1.5ml microtube. Each SNP has two primers (forward and reverse). Ensure that the stock concentration of each PCR primer is kept at 100 &#956;M. Make enough primer mix for 500-1,000 reactions to reduce pipetting error and time at the bench (See supplemental Table S2). If desired, prepare aliquots for 100-200 reactions per tube and store at -20&#176;C.</li>
	<li>Prepare PCR cocktail as described in the manufacturer&#8217;s protocol (T...

The MDA is composed of five major steps: PCR amplification, shrimp alkaline phosphatase (SAP) reaction, SNP extension, extension product conditioning, and matrix-assisted laser desorption/ionization &#8211; time of flight (MALDI-TOF) mass spectrometry33-37. The first PCR amplification step amplifies DNA flanking each SNP so that enough template DNA will be available at the SNP extension step. The SAP reaction neutralizes unused dNTPs which can interfere with the following SNP extension step. SNP extension invo...

Anopheles arabiensis, Anopheles coluzzii and Anopheles gambiae are the major vectors responsible for malaria transmission in Africa1. These three species are morphologically indistinguishable2 and can only be distinguished by molecular assays3-9. In addition, there are many downstream assays routinely conducted to aid epidemiological and population genetics studies. These include (1) a genotyping assay for speciation islands10-12, (2) a genotyping assay recognizing non-synonymous SNPs in the 1014th amino acid codon position of para gene (the knock-down resistance, or kdr, SNP)13-18, (3) parasite detection PCR19-23, and (4) screening for host-specific DNA in mosquito midguts24,25.
We developed a multi-detection assay (MDA) that combines all these assays into a single multiplex reaction with the goal of analyzing epidemiologically important characteristics of malaria vectors in Africa. The MDA assay includes multiple markers for detecting (1) species (A. arabiensis, A. gambiae, A. coluzzii, or other (none of the three)), (2) insecticide resistance represented in kdr SNPs (both L1014Fand L1014S), (3) presence of two major malaria parasites, Plasmodium falciparum and P. vivax, and (4) blood source from one avian and six mammalian hosts.
Traditionally, these assays were conducted in separate polymerase chain reactions. When all these assays are done using a conventional PCR platform, it requires conducting 8-10 PCR reaction assays and accompanying gel electrophoresis steps. Each individual PCR reaction from preparation to documenting results takes 4-5 hr, while the MDA method presented here takes about 5 hr in totality. This is equivalent to a 90% savings in labor costs alone. The MDA presented here costs $5 per sample to genotype all 33 SNPs. This is considerably less expensive than the single agarose gel-based assays, which costs about $1.50 per sample. Assays detecting all the characteristics covered by the MDA would require a minimum of 8-10 separate agarose gel-based assays at a cost of $12-15 per sample. Moreover, the MDA greatly reduces the chance of generating a false positive or negative by utilizing at least three markers for each parasite or host source detection.
The platform we utilized is not limited to malaria vectors but can be used in a wide variety of applications such as medicine, veterinary medicine, and basic biology26-28. In-depth association studies or population genetics studies involving a large (in order of 100s) number of samples require cost-effective assays screening for multiple markers simultaneously. Most studies that utilize two or more separate PCR assays could implement the MDA for quicker results at a lower cost.

<table border="0" cellpadding="0" cellspacing="0" width="588">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Name of Material/ Equipment</td>
			<td style="width:87px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">MassARRAY Analyzer Compact</td>
			<td style="width:87px;">Sequenom</td>
			<td style="width:119px;">MT9</td>
			<td>MALDI-TOF mass spectrometry for genomic applications to analyze nucleic acids.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">MassARRAY Nanodispenser</td>
			<td style="width:87px;">Sequenom</td>
			<td style="width:119px;">RS1000</td>
			<td>Transfers completed iPLEX reaction products to the SpectroCHIP</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">iPLEX Gold Genotyping Reagent Set</td>
			<td style="width:87px;">Sequenom</td>
			<td style="width:119px;">10158</td>
			<td>Reagents used for iPLEX assay including SAP kit.</td>
		</tr>
	</tbody>
</table>

a multi-detection assay for malaria transmitting mosquitoes

The Anopheles gambiae species complex includes the major malaria transmitting mosquitoes in Africa. Because these species are of such medical importance, several traits are typically characterized using molecular assays to aid in epidemiological studies. These traits include species identification, insecticide resistance, parasite infection status, and host preference. Since populations of the Anopheles gambiae complex are morphologically indistinguishable, a polymerase chain reaction (PCR) is traditionally used to identify species. Once the species is known, several downstream assays are routinely performed to elucidate further characteristics. For instance, mutations known as KDR in a para gene confer resistance against DDT and pyrethroid insecticides. Additionally, enzyme-linked immunosorbent assays (ELISAs) or Plasmodium parasite DNA detection PCR assays are used to detect parasites present in mosquito tissues. Lastly, a combination of PCR and restriction enzyme digests can be used to elucidate host preference (e.g., human vs. animal blood) by screening the mosquito bloodmeal for host-specific DNA. We have developed a multi-detection assay (MDA) that combines all of the aforementioned assays into a single multiplex reaction genotyping 33SNPs for 96 or 384 samples at a time. Because the MDA includes multiple markers for species, Plasmodium detection, and host blood identification, the likelihood of generating false positives or negatives is greatly reduced from previous assays that include only one marker per trait. This robust and simple assay can detect these key mosquito traits cost-effectively and in a fraction of the time of existing assays.

Species identification: 
The following 5 SNPs together identify three species (A. arabiensis, A. coluzzii and A. gambiae) (Table 4). If a sample is not one of the three species, the three SNPs (01073-213, 04679-157 and 10313-052) fail to amplify.
kdr genotype for inferring insecticide resistance: 
The 1014th codon of the para voltage-gated sodium channel cor...

Watch this Scientific Journal Video about A Multi-detection Assay for Malaria Transmitting Mosquitoes at JoVE.com

A Multi-detection Assay for Malaria Transmitting Mosquitoes

Malaria transmitting mosquitoes have a number of epidemiologically important characteristics that can only be detected using molecular techniques. Utilizing a MALDI-TOF based SNP genotyping platform, we developed an assay for simultaneously detecting multiple key traits (species, insecticide resistance, parasite infection and host choice) of malaria vectors.

The Anopheles gambiae species complex includes the major malaria transmitting mosquitoes in Africa. Because these species are of such medical importance, ...

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