Name: detection of plasmodium sporozoites in anopheles mosquitoes using an enzyme-linked immunosorbent assay
Uploaded: 2021-09-30T15:00:00
Description: Watch this Scientific Journal Video about Detection of Plasmodium Sporozoites in Anopheles Mosquitoes using an Enzyme-linked Immunosorbent Assay at JoVE.com

We thank Mr. Kirakorn Kiatibutr, MVRU, for training and guidance. We also thank Mrs. Pinyapat Kongngen, MVRU, for her technical assistance in preparing Figure 2. This work was supported by a grant from the National Institute for Allergy and Infectious Diseases and the National Institute of Health (U19 AI089672).

1. Preparation of reagents
NOTE: Refer to the Table of Materials for a list of equipment, reagents, and other consumables used in this protocol and to Table 1 for a list of solutions and their composition.
<ol>
	<li>Capture and peroxidase-conjugated mAbs
	<ol>
		<li>To reconstitute the mAb, resuspend the lyophilized mAb in a 1:1 mixture of distilled water:glycerol at 0.5 mg/mL. Make aliquots as needed to avoid repeated freeze-thawing, and st...

<ol>
	<li>Bray, R. S., Garnham, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+life-cycle+of+primate+malaria+parasites.">The life-cycle of primate malaria parasites.</a> British Medical Bulletin. 38 (2), 117-122 (1982).</li><li>Held, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primate+malaria.">Primate malaria.</a> Annals of the New York Academy of Sciences. 162 (1), 587-593 (1969).</li><li>World Health Organization. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Division+of+Malaria+and+Other+Parasitic+Diseases.+Manual+on+practical+entomology+in+Malaria,+Part+I+and+Part+II.">Division of Malaria and Other Parasitic Diseases. Manual on practical entomology in Malaria, Part I and Part II.</a> World Health Organization. , (1975).</li><li>Robert, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+of+the+distribution+of+circumsporozoite+antigen+in+Anopheles+gambiae+infected+with+Plasmodium+falciparum,+using+the+enzyme-linked+immunosorbent+assay.">Study of the distribution of circumsporozoite antigen in Anopheles gambiae infected with Plasmodium falciparum, using the enzyme-linked immunosorbent assay.</a> Transactions of the Royal Society of Tropical Medicine and Hygiene. 82 (3), 389-391 (1988).</li><li>Fontenille, D., Meunier, J. Y., Nkondjio, C. A., Tchuinkam, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+circumsporozoite+protein+enzyme-linked+immunosorbent+assay+compared+with+microscopic+examination+of+salivary+glands+for+calculation+of+malaria+infectivity+rates+in+mosquitoes+(Diptera:+Culicidae)+from+Cameroon.">Use of circumsporozoite protein enzyme-linked immunosorbent assay compared with microscopic examination of salivary glands for calculation of malaria infectivity rates in mosquitoes (Diptera: Culicidae) from Cameroon.</a> Journal of Medical Entomology. 38 (3), 451-454 (2001).</li><li>Echeverry, D. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+and+robust+single+PCR+for+Plasmodium+sporozoite+detection+in+mosquitoes+using+the+cytochrome+oxidase+I+gene.">Fast and robust single PCR for Plasmodium sporozoite detection in mosquitoes using the cytochrome oxidase I gene.</a> Malaria Journal. 16 (1), 230 (2017).</li><li>Singh, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+genus-+and+species-specific+nested+polymerase+chain+reaction+malaria+detection+assay+for+epidemiologic+studies.">A genus- and species-specific nested polymerase chain reaction malaria detection assay for epidemiologic studies.</a> American Journal of Tropical Medicine and Hygiene. 60 (4), 687-692 (1999).</li><li>Snounou, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genotyping+of+Plasmodium+spp.+Nested+PCR.">Genotyping of Plasmodium spp. Nested PCR.</a> Methods in Molecular Medicine. 72, 103-116 (2002).</li><li>Snounou, G., Singh, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nested+PCR+analysis+of+Plasmodium+parasites.">Nested PCR analysis of Plasmodium parasites.</a> Methods in Molecular Medicine. 72, 189-203 (2002).</li><li>Snounou, G., Viriyakosol, S., Jarra, W., Thaithong, S., Brown, K. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+the+four+human+malaria+parasite+species+in+field+samples+by+the+polymerase+chain+reaction+and+detection+of+a+high+prevalence+of+mixed+infections.">Identification of the four human malaria parasite species in field samples by the polymerase chain reaction and detection of a high prevalence of mixed infections.</a> Molecular and Biochemical Parasitology. 58 (2), 283-292 (1993).</li><li>Wirtz, R. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+Plasmodium+vivax+sporozoites+in+mosquitoes+using+an+enzyme-linked+immunosorbent+assay.">Identification of Plasmodium vivax sporozoites in mosquitoes using an enzyme-linked immunosorbent assay.</a> American Journal of Tropical Medicine and Hygiene. 34 (6), 1048-1054 (1985).</li><li>Wirtz, R. A., Burkot, T. R., Graves, P. M., Andre, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Field+evaluation+of+enzyme-linked+immunosorbent+assays+for+Plasmodium+falciparum+and+Plasmodium+vivax+sporozoites+in+mosquitoes+(Diptera:+Culicidae)+from+Papua+New+Guinea.">Field evaluation of enzyme-linked immunosorbent assays for Plasmodium falciparum and Plasmodium vivax sporozoites in mosquitoes (Diptera: Culicidae) from Papua New Guinea.</a> Journal of Medical Entomology. 24 (4), 433-437 (1987).</li><li>Wirtz, R. A., Sattabongkot, J., Hall, T., Burkot, T. R., Rosenberg, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+and+evaluation+of+an+enzyme-linked+immunosorbent+assay+for+Plasmodium+vivax-VK247+sporozoites.">Development and evaluation of an enzyme-linked immunosorbent assay for Plasmodium vivax-VK247 sporozoites.</a> Journal of Medical Entomology. 29 (5), 854-857 (1992).</li><li>Burkot, T. R., Williams, J. L., Schneider, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+Plasmodium+falciparum-infected+mosquitoes+by+a+double+antibody+enzyme-linked+immunosorbent+assay.">Identification of Plasmodium falciparum-infected mosquitoes by a double antibody enzyme-linked immunosorbent assay.</a> American Journal of Tropical Medicine and Hygiene. 33 (5), 783-788 (1984).</li><li>Rosenberg, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Circumsporozoite+protein+heterogeneity+in+the+human+malaria+parasite+Plasmodium+vivax.">Circumsporozoite protein heterogeneity in the human malaria parasite Plasmodium vivax.</a> Science. 245 (4921), 973-976 (1989).</li><li>Marie, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+a+real-time+quantitative+PCR+to+measure+the+wild+Plasmodium+falciparum+infectivity+rate+in+salivary+glands+of+Anopheles+gambiae.">Evaluation of a real-time quantitative PCR to measure the wild Plasmodium falciparum infectivity rate in salivary glands of Anopheles gambiae.</a> Malaria Journal. 12, 224 (2013).</li><li>Arevalo-Herrera, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunoreactivity+of+sera+from+low+to+moderate+malaria-eEndemic+areas+against+Plasmodium+vivax+rPvs48/45+proteins+produced+in+Escherichia+coli+and+chinese+hamster+ovary+systems.">Immunoreactivity of sera from low to moderate malaria-eEndemic areas against Plasmodium vivax rPvs48/45 proteins produced in Escherichia coli and chinese hamster ovary systems.</a> Frontiers in Immunology. 12, 634738 (2021).</li><li>Balkew, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+update+on+the+distribution,+bionomics,+and+insecticide+susceptibility+of+Anopheles+stephensi+in+Ethiopia,+2018-2020.">An update on the distribution, bionomics, and insecticide susceptibility of Anopheles stephensi in Ethiopia, 2018-2020.</a> Malaria Journal. 20 (1), 263 (2021).</li><li>Wirtz, R. A., Avery, M., Benedict, M., Sutcliffe, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasmodium+sporozoite+ELISA.">Plasmodium sporozoite ELISA.</a> Methods in Anopheles Research. , 333-343 (2016).</li><li>Durnez, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=False+positive+circumsporozoite+protein+ELISA:+a+challenge+for+the+estimation+of+the+entomological+inoculation+rate+of+malaria+and+for+vector+incrimination.">False positive circumsporozoite protein ELISA: a challenge for the estimation of the entomological inoculation rate of malaria and for vector incrimination.</a> Malaria Journal. 10, 195 (2011).</li></ol>

The CSP-ELISA provides a highly specific and cost-effective method to detect Plasmodium CSP. It allows discrimination between P. falciparum and P. vivax sporozoites as well as between the two subtypes, VK210 and VK247, of P vivax11,13,14,15. Certain critical points should be considered to obtain reliable and reproducible results. All solutions should be kept ...

Plasmodium sporozoites are the infectious stage of the malaria parasites in the mosquitoes. The sporozoites are delivered to humans via mosquito bites. In the mosquito, the sporozoites first form inside the oocysts on the midgut wall. Once ready, they are released into the hemocoel and travel to the mosquito salivary glands. There, they mature and become ready for transmission to humans during blood feeding. In humans, the sporozoites are deposited in the dermis. Then, they enter the blood vessel and travel along the blood circulation to reach the liver to establish infection in the hepatocytes1,2.
Three different methods have been used to determine sporozoite infection of the mosquito salivary glands. The first method is the dissection of the salivary glands followed by direct examination of sporozoites under a light microscope. This method is the gold standard to detect and quantify sporozoites in Anopheles mosquito salivary glands3. However, it requires a technician well trained in both dissection and microscopic examination. Moreover, it cannot be used to determine Plasmodium species and CSP subtyping (for P. vivax)4,5. The second method uses polymerase chain reaction (PCR) to detect Plasmodium DNA in the upper part of the mosquito body6. Given the specificity of PCR, both species and subtyping of the parasite are possible7,8,9,10. Although PCR is increasingly used, it requires relatively expensive equipment and well-trained staff. The last method, the ELISA to detect the Plasmodium specific circumsporozoite protein (CSP), has been the mainstay for three decades11,12,13. CSP is present in both oocyst sporozoites and salivary gland sporozoites12,14. Using specific antibodies, this method allows Plasmodium species identification and CSP subtyping of P. vivax sporozoites. The rationale for this assay is the requirement of a simple high-throughput assay to examine a large number of wild mosquitoes to understand malaria transmission (i.e., determine the sporozoite infection rate).
The ELISA method has two key advantages over microscopic examination. First, it allows researchers to keep mosquito samples until they are ready for sample processing. Second, the ELISA method can be used to differentiate Plasmodium species through species-specific monoclonal antibodies. In addition, ELISA can accommodate a larger number of mosquito specimens, permitting a much higher throughput15. Compared to PCR, which detects sporozoite DNA, the ELISA procedure takes more time but costs less16. The ELISA assay described here was developed to determine the mosquito infectivity and separately detect CSP of P. falciparum and each of the two CSP variants of P. vivax, VK210 and VK247. This ELISA method has been used in many studies to determine the seasonal dynamics of mosquito infection and identify the species of the major malaria vectors in the field12,13,17,18. To perform this assay, a standard laboratory equipped with an ELISA plate reader is sufficient.
The overall approach is summarized in Figure 1. In this sandwich ELISA, the primary (capture) monoclonal antibody (mAb) specific for each Plasmodium species/subtype is first used to coat the ELISA plate. Each plate is coated with a single capture mAb. The function of the mAb is to capture the corresponding CSP antigen in the mosquito homogenates. After antigen capture and plate washes, a second CSP-specific antibody labeled with peroxidase is used to detect the presence of CSP bound to the capture mAb. The chemical reaction catalyzed by peroxidase results in color development in wells positive for CSP.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ELISA plate reader</td>
			<td>BioTek Instrument, Inc.</td>
			<td>Synergy H1</td>
			<td>Absorbance is measured using UV-VIS absorbance detection mode</td>
		</tr>
		<tr>
			<td>Grinder pestle</td>
			<td>Axygen</td>
			<td>PES-15-B-SI</td>
			<td>For homogenizing the mosquito head/thorax</td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ABTS substrate 2-component</td>
			<td>KPL</td>
			<td>50-62-00</td>
			<td>For peroxidase driven detection</td>
		</tr>
		<tr>
			<td>Blocking buffer (BB)</td>
			<td></td>
			<td></td>
			<td>Note: solution</td>
		</tr>
		<tr>
			<td>Capture and peroxidase-conjugated monoclonal antibodies (mAbs)</td>
			<td></td>
			<td></td>
			<td>Note: mAbs can be obtained in the lyophilized form as part of the Sporozoite ELISA Reagent Kits (MRA-890 for P. falciparum and MRA-1028K for P. vivax) from BEI Resources (https://www.beiresources.org.)</td>
		</tr>
		<tr>
			<td>Casein</td>
			<td>Sigma aldrich</td>
			<td>9000-71-9</td>
			<td>For blocking buffer preparation</td>
		</tr>
		<tr>
			<td>Grinding buffer (GB)</td>
			<td></td>
			<td></td>
			<td>Note: solution</td>
		</tr>
		<tr>
			<td>Igepal CA-630</td>
			<td>Sigma aldrich</td>
			<td>9002-93-1</td>
			<td>For grinding buffer preparation</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Sigma aldrich</td>
			<td>7447-40-7</td>
			<td>For phosphate buffer saline preparation</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Sigma aldrich</td>
			<td>7778-77-0</td>
			<td>For phosphate buffer saline preparation</td>
		</tr>
		<tr>
			<td>Na2HPO4</td>
			<td>Sigma aldrich</td>
			<td>7558-79-4</td>
			<td>For phosphate buffer saline preparation</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Sigma aldrich</td>
			<td>7647-14-5</td>
			<td>For phosphate buffer saline preparation</td>
		</tr>
		<tr>
			<td>NaOH</td>
			<td>Sigma aldrich</td>
			<td>1310-73-2</td>
			<td>For blocking buffer preparation</td>
		</tr>
		<tr>
			<td>PBS-Tween</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Pf capture mAb</td>
			<td>CDC</td>
			<td>Pf-CAP</td>
			<td>For capturing Pf circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pf peroxidase mAb</td>
			<td>CDC</td>
			<td>Pf-HRP</td>
			<td>For detecting Pf circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pf positive control</td>
			<td>CDC</td>
			<td>Pf-PC</td>
			<td>Pf positive control</td>
		</tr>
		<tr>
			<td>Phenol red</td>
			<td>Sigma aldrich</td>
			<td>143-74-8</td>
			<td>For blocking buffer preparation</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (PBS)</td>
			<td></td>
			<td></td>
			<td>Note: solution</td>
		</tr>
		<tr>
			<td>Positive controls</td>
			<td></td>
			<td></td>
			<td>Note: solution</td>
		</tr>
		<tr>
			<td>Pv210 capture mAb</td>
			<td>CDC</td>
			<td>Pv210-CAP</td>
			<td>For capturing Pv210 circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pv210 peroxidase mAb</td>
			<td>CDC</td>
			<td>Pv210-HRP</td>
			<td>For detecting Pv210 circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pv210 positive control</td>
			<td>CDC</td>
			<td>Pv210-PC</td>
			<td>Pv210 positive control</td>
		</tr>
		<tr>
			<td>Pv247 capture mAb</td>
			<td>CDC</td>
			<td>Pv247-CAP</td>
			<td>For capturing Pv247 circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pv247 peroxidase mAb</td>
			<td>CDC</td>
			<td>Pv247-HRP</td>
			<td>For detecting Pv247 circumsporozoite protein</td>
		</tr>
		<tr>
			<td>Pv247 positive control</td>
			<td>CDC</td>
			<td>Pv247-PC</td>
			<td>Pv247 positive control</td>
		</tr>
		<tr>
			<td>Tween20</td>
			<td>Sigma aldrich</td>
			<td>9005-64-5</td>
			<td>For PBS-Tween preparation</td>
		</tr>
		<tr>
			<td>Consumables</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable pipetting reservoirs</td>
			<td>Generic</td>
			<td></td>
			<td>For working reagents</td>
		</tr>
		<tr>
			<td>ELISA plates: 96 well clear round bottom PVS</td>
			<td>Corning Life Science</td>
			<td>2797</td>
			<td>For ELISA</td>
		</tr>
		<tr>
			<td>Gloves: disposable gloves and freezer gloves</td>
			<td>Generic</td>
			<td></td>
			<td>For personal protection</td>
		</tr>
		<tr>
			<td>Lab gown</td>
			<td>Generic</td>
			<td></td>
			<td>for personal protection</td>
		</tr>
		<tr>
			<td>Multichannel Pipette P30-300</td>
			<td>Generic</td>
			<td></td>
			<td>For solution transfer</td>
		</tr>
		<tr>
			<td>Pipette set, P2, P20, P200, and P1000</td>
			<td>Generic</td>
			<td></td>
			<td>For solution transfer</td>
		</tr>
		<tr>
			<td>Pipette tips 10 &#181;L, 200 &#181;L, and 1000 &#181;L</td>
			<td>Generic</td>
			<td></td>
			<td>For solution transfer</td>
		</tr>
		<tr>
			<td>Serological pipettes 5 mL, 10 mL</td>
			<td>Generic</td>
			<td></td>
			<td>For solution transfer</td>
		</tr>
		<tr>
			<td>Transfer pipettes</td>
			<td>Generic</td>
			<td></td>
			<td>For solution transfer</td>
		</tr>
	</tbody>
</table>

detection of plasmodium sporozoites in anopheles mosquitoes using an enzyme-linked immunosorbent assay

Plasmodium sporozoites are the infective stage of malaria parasites that infect humans. The sporozoites residing in the salivary glands of female Anopheles mosquitoes are transmitted to humans via mosquito bites during blood feeding. The presence of sporozoites in the mosquito salivary glands thus defines mosquito infectiousness. To determine whether an Anopheles mosquito carries Plasmodium sporozoites, the enzyme-linked immunosorbent assay (ELISA) method has been the standard tool to detect the Plasmodium circumsporozoite protein (CSP), the major surface protein of the sporozoites. In this method, the head along with the thorax of each mosquito is separated from the abdomen, homogenized, and subjected to a sandwich ELISA to detect the presence of CSP specific to Plasmodium falciparum and each of the two subtypes, VK210 and VK247, of Plasmodium vivax.This method has been used to study malaria transmission, including the seasonal dynamics of mosquito infection and the species of the major malaria vectors in the study sites.

Representative ELISA results are shown in Figure 2. In this experiment, the P. falciparum ELISA detected sporozoite infection in well A7. The positive well could be visually detected by its faint green color (Figure 2A). The absorbance value of this well was above the cut-off threshold (twice the mean value of the four negative control wells) (Figure 2B). The distribution of the absorbance values of all 80 unknown wells is ...

Watch this Scientific Journal Video about Detection of Plasmodium Sporozoites in Anopheles Mosquitoes using an Enzyme-linked Immunosorbent Assay at JoVE.com

Detection of Plasmodium Sporozoites in Anopheles Mosquitoes using an Enzyme-linked Immunosorbent Assay

This protocol describes a sandwich enzyme-linked immunosorbent assay to detect salivary gland sporozoites in mosquitoes. Using easily available monoclonal antibodies, the method enables cost-effective, high-throughput detection of mosquitoes carrying Plasmodium falciparum or Plasmodium vivax. The method is suitable for malaria transmission research, including vector surveys.

Detection of Plasmodium Sporozoites in Anopheles Mosquitoes using an Enzyme-linked Immunosorbent Assay

Plasmodium sporozoites are the infective stage of malaria parasites that infect humans. The sporozoites residing in the salivary glands of female ...

ELISA technique is really useful for detecting malaria parasite in the mosquito vector with high sensitivity and specificity, and able to process lot of sample at the same time. This technique allow researchers to keep mosquito samples until they are ready for sample processing, and it can be performed to differentiate Plasmodium species using species-specific monoclonal antibodies. Prepare the sample by separating the head and thorax of the mosquitoes from the abdomen, and place them in a pre-labeled 1.5 milliliter centrifuge grinding tube.Add 50 microliters of grinding buffer to each tube, and homogenize the sample with a pestle. Rinse the pestle with 250 microliters of grinding buffer, and add the solution to the tube to bring the final volume up to 300 microliters. Prepare an ELISA plate for circumsporozoite protein, and fill out the sporozoite ELISA worksheet.Prepare the antibody solution in PBS, and add five milliliters of the solution per plate. Pipette 50 microliters of the antibody solution into each well of the ELISA plate. Place a lid on the plate, and incubate for 30 minutes or overnight at room temperature.Aspirate the solution in the well, and tap the plate on a paper towel five times to remove the liquid. Add 200 microliters of blocking buffer in the well plates, and cover with a lid. Incubate for one hour at room temperature, and aspirate the well content.Again tap the plate on a paper towel to remove the liquid. Add 50 microliters of positive control to the H one and H two wells. Then add 50 microliters of blocking buffer into the wells in columns one and two of rows C to G.Add 50 microliters of the positive control into the G one and G two wells.Serially dilute the positive control starting from G one and G two, followed by F one and F two until C one and C two. Add 50 microliters of the negative control to wells A one, A two, B one, and B two. Extract 50 microliters of the homogenate solution, and add it to an unknown well.Cover the plate and incubate it at room temperature for two hours. Prepare the substrate solution by mixing substrate A and B at a ratio of one to one. Determine the required volume based on adding five milliliters of working conjugate antibody solution to each plate.Evaluate the peroxidase activity by adding five microliters of the peroxidase labeled antibody solution to 100 microliters of the substrate solution in a 1.5 milliliter tube. Aspirate the well content, and remove the liquid by putting the plate upside down on a paper towel. Wash the wells two times with 200 microliters of PBS Tween.Aspirate the well contents, and tap the plate five times. Add 50 microliters of peroxidase labeled antibody solution to each well. Then incubate in the dark for one hour at room temperature.Aspirate the well content, and tap the plate on a paper towel five times. Wash the wells with 200 microliters of PBS Tween three times, aspirate the contents, and tap the plate five times. Add 100 microliters of the substrate solution to each well.Cover the plate, and incubate in the dark for 30 minutes at room temperature. After the incubation, read the absorbance at 405 to 414 nanometers using an ELISA plate reader. Label the samples having absorbance with a value above the cutoff as positive, and determine the CSP concentration in the sample using the standard.Plot the absorbance values versus solution concentration to generate a standard curve. Determine the best fit using the linear regression method. Solve the equation of each absorbance value for a positive sample to determine the CSP concentration.After 30 minutes of performing ELISA with ABTS, sporozoite infection could be detected by the appearance of a faint green color in the well. The positive control did not show any color change in the well. The absorbance values for the negative and positive wells were determined.The positive well exhibited an absorbance value that was above the cutoff threshold, while the negative controls demonstrated significantly lower values. Furthermore, the absorbance values of the other 80 unknown wells were also obtained. The solid line represents the mean absorbance of the negative control wells, and dashed line represents the positivity threshold.Using the standard curve, the CSP concentration in well A seven was determined to be 0.35 picograms per microliter This step of ELISA processing should be performed quickly to prevent nonspecific vector. In addition, all samples and solution should be kept in the refrigerator to prevent the microbial growth. Researchers are recommended to confirm the positive detections by other methods such as PCR.This will significantly improve the confidence, especially when the only reading is valued above the threshold. This technique has allowed researchers to conduct larger scale surveys of possible infection in the mosquitoes, which is important for identifying the main vector.

Research

JoVE Journal

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