Name: vector competence analyses on aedes aegypti mosquitoes using zika virus
Uploaded: 2020-05-31T14:00:00
Description: Watch this Scientific Journal Video about Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus at JoVE.com

We acknowledge the staff of the World Reference Center for Emerging Viruses and Arboviruses (WRCEVA): Dr. Robert Tesh, Hilda Guzman, Dr. Kenneth Plante, Dr. Jessica Plante, Dionna Scharton, and Divya Mirchandani, for their tireless work in curating and providing many of the viral strains used for our and other groups&#8217; vector competence experiments. The presented work was funded by the McLaughlin Fellowship Fund (SRA) and NIH grants AI120942 and AI121452.

All procedures performed in these protocols were performed in full compliance with protocols approved&#160;by the Institutional Biosafety Committee and the Institutional Animal Care and Use Committee of the University of Texas Medical Branch at Galveston.
1. Amplify ZIKV in Vero cells
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	<li>Grow Vero cells (CCL-81 or VeroE6) in Dulbecco&#8217;s modification of Eagle&#8217;s minimal essential medium (DMEM) supplemented with 10% v/v heat-inactivated fetal bovine serum (FBS), and 1% (v/v) p...

<ol>
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K., 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=Colonized+Sabethes+cyaneus,+a+Sylvatic+New+World+Mosquito+Species,+Shows+a+Low+Vector+Competence+for+Zika+Virus+Relative+to+Aedes+aegypti.">Colonized Sabethes cyaneus, a Sylvatic New World Mosquito Species, Shows a Low Vector Competence for Zika Virus Relative to Aedes aegypti.</a> Viruses. 10 (8), 434 (2018).</li><li>Roundy, C. 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=Variation+in+Aedes+aegypti+Mosquito+Competence+for+Zika+Virus+Transmission.">Variation in Aedes aegypti Mosquito Competence for Zika Virus Transmission.</a> Emerging Infectious Diseases. 23 (4), 625-632 (2017).</li><li>Wilson, A. J., Harrup, L. 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The methods described here provide a generalized workflow to conduct vector competence analyses. As a general framework, many of these methodologies are conserved throughout the literature. However, there is substantial room for modifications (reviewed in Azar and Weaver1). Virus (e.g., viral lineage, storage of challenge virus, viral passage history), entomology (e.g., laboratory colonization of mosquito populations, innate immunity, the mosquito microbiome/virome), and experimental variables (e....

Vector competence is defined as the ability at the level of species, population, and even an individual, of a given arthropod such as a mosquito, tick, or phlebotomine sand fly, to acquire and transmit an agent biologically with replication or development in the arthropod1,2. With respect to mosquitoes and arthropod-borne viruses (i.e., arboviruses), the agent is imbibed from a viremic host by a female mosquito. Following ingestion, the virus must productively infect one of a small population of midgut epithelial cells3, overcoming various physiological obstacles such as proteolytic degradation by digestive enzymes, the presence of the microbiota (midgut infection barrier, or MIB), and the secreted peritrophic matrix. Infection of the midgut epithelium must be followed by replication of the virus and eventual escape from the midgut into the mosquito&#8217;s open circulatory system, or hemolymph, which represents the onset of a disseminated infection overcoming the midgut escape barrier (MEB). At this point the virus can establish infections of secondary tissues (e.g., nerves, muscles, and fat bodies) and continue to replicate, although such secondary replication may not be strictly necessary for the virus to infect the acinar cells of the salivary glands (overcoming the salivary gland infection barrier). Egress from the salivary gland acinar cells into their apical cavities and then movement into the salivary duct enables inoculation of the virus into subsequent hosts on biting, and completes the transmission cycle1,2,4,5,6,7.
Given this well-characterized and generally conserved mechanism of spread within a mosquito vector, laboratory vector competence assessments are often methodologically similar, although differences in protocols do exist1,2. Generally, after oral virus exposure, mosquitoes are dissected so that individual tissues such as the midgut, legs, ovaries, or salivary glands can be assayed for viral infection, disseminated infection, disseminated infection/potential transovarial transmission, and disseminated infection/potential transmission competence, respectively8. The mere presence of a virus in the salivary glands, however, is not definitive evidence of transmission capability, given evidence of a salivary gland escape/egress barrier (SGEB) in some vector/virus combinations1,2,4,5,7,9. The standard method to prove transmission competence remains mosquito transmission to a susceptible animal10,11,12. However, given that for many arboviruses this necessitates the use of immunocompromised murine models13,14,15,16, this method is often cost-prohibitive. A commonly used alternative is the collection of the mosquito saliva, which can be analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or an infectious assay to demonstrate the presence of the viral genome or infectious particles, respectively. It is worth noting that such in vitro saliva collection methods may overestimate12 or underestimate17 the amount of virus deposited during in vivo feeding, indicating that such data must be interpreted with caution. Nonetheless, the in vitro method is highly valuable when analyzed from the perspective of the mere presence of virus in the saliva, indicating transmission potential.
Two major approaches exist for determining the role of mosquito vectors in arboviral disease outbreaks. The first method involves field surveillance, in which mosquitoes are collected in the context of active transmission18,19,20,21,22,23,24. However, given that infection rates are typically quite low (e.g., the estimated 0.061% infection rate of mosquitoes in areas of active Zika virus (ZIKV) circulation in the United States21), incrimination of potential vector species can be heavily biased by trapping methodology25,26 and random chance (e.g., sampling one infected individual out of 1,600 uninfected)21. Taking this into account, a given study may not acquire sufficient mosquitoes in both raw numbers or species diversity to accurately sample mosquitoes involved in transmission. In contrast, vector competence analyses are undertaken in a laboratory setting, allowing for strict control of parameters such as oral dose. Although not fully capable of representing the true complexity of mosquito infection and transmission capability in a field setting, these laboratory assessments remain powerful tools in the field of arbovirology.
Based on various vector competence analyses with ZIKV in several mosquito species, populations, and methods27,28,29,30,31,32, as well as a recent review of vector competence assessments1, we describe here several of the protocols associated with a typical vector competence workflow. In these experiments, three Ae. aegypti populations from the Americas (the city of Salvador, Brazil; the Dominican Republic; and the lower Rio Grande Valley, TX, USA) were exposed to a single strain of ZIKV (Mex 1-7, GenBank Accession: KX247632.1) at 4, 5, or 6 log10 focus-forming units (FFU)/mL doses by way of artificial bloodmeals. Subsequently, they were analyzed for evidence of infection, disseminated infection, and transmission competence after various times of extrinsic incubation (2, 4, 7, 10, and 14 days) by means of dissection and a cell culture-based infectious assay. Although the present workflow/protocols are optimized for ZIKV, many elements are directly translatable to other mosquito-borne arboviruses in arthropod containment and biosafety levels 2 and 3 (ACL/BSL2 or ACL/BSL3).

<table>
	<tbody>
		<tr>
			<td>3mL Standard Reservoir</td>
			<td>R37P30</td>
			<td>Hemotek Ltd</td>
			<td>Insectary Equipment</td>
		</tr>
		<tr>
			<td>7/32&#34; Stainless Steel 440 Grade C Balls</td>
			<td>4RJH9</td>
			<td>Grainger</td>
			<td>Grinding Media</td>
		</tr>
		<tr>
			<td>Acetone, Histological Grade, Fisher Chemicals, Poly Bottle, 4L, 4/Case</td>
			<td>A16-P4</td>
			<td>FisherScientific</td>
			<td>Fixative</td>
		</tr>
		<tr>
			<td>Adenosine 5&#39;-triphospate disodium salt hydrat, microbial, BioReagent, suitable for cell culture</td>
			<td>A6419-1G</td>
			<td>MilliporeSigma</td>
			<td>Reagent</td>
		</tr>
		<tr>
			<td>Anti-Flavivirus Group Antigen Antibody, clone D1-4G2-4-15</td>
			<td>MAB10216</td>
			<td>MilliporeSigma</td>
			<td>Primary Antibody for focus forming assay</td>
		</tr>
		<tr>
			<td>Anti-Mouse IgG (H+L) Antibody, Human Serum Adsorbed and Peroxidase-Labeled, 1.0mL/Bottle</td>
			<td>5450-0011</td>
			<td>KPL/Seracare</td>
			<td>Secondary Antibody for focus forming assay</td>
		</tr>
		<tr>
			<td>Bleach</td>
			<td>NC0427256</td>
			<td>FisherScientific</td>
			<td>Decontamination</td>
		</tr>
		<tr>
			<td>Corning, Cell Culture Treated Flasks, 150cm2, Vented Cap, Case of 50</td>
			<td>10-126-34</td>
			<td>FisherScientific</td>
			<td>Cell culture consumable</td>
		</tr>
		<tr>
			<td>Costar Cell Culture Plates, 24-well, 5/bag, 100/case, Corning</td>
			<td>07-200-740</td>
			<td>FisherScientific</td>
			<td>Cell culture consumable</td>
		</tr>
		<tr>
			<td>Costar Cell Culture Plates, 96-well, 5/bag, 100/case, Corning</td>
			<td>07-200-91</td>
			<td>FisherScientific</td>
			<td>Cell culture consumable</td>
		</tr>
		<tr>
			<td>Crystal Violet</td>
			<td>C0775-100G</td>
			<td>MilliporeSigma</td>
			<td>Stain</td>
		</tr>
		<tr>
			<td>Eppendorf Snap Cap Microcentrifuge Safe-Lock 2mL Tubes, 500/Case</td>
			<td>05-402-7</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon 15mL Conical Centrigue Tubes</td>
			<td>14-959-70C</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon 50mL Conical Centrigue Tubes</td>
			<td>14-959-49A</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon Disposable Polystyrene Serological 10mL Pipets, 200/Case</td>
			<td>13-675-20</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon Disposable Polystyrene Serological 1mL Pipets, 1000/Case</td>
			<td>13-675-15B</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon Disposable Polystyrene Serological 25mL Pipets, 200/Case</td>
			<td>13-675-30</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon Disposable Polystyrene Serological 5mL Pipets, 200/Case</td>
			<td>13-675-22</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Falcon Standard Tissue Culture Dishes</td>
			<td>08-772B</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum-Premium, 500mL</td>
			<td>S11150</td>
			<td>Atlanta Biologicals</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Fisherbrand Economy Plain Glass Microscope Slides</td>
			<td>12-550-A3</td>
			<td>FisherScientific</td>
			<td>Immobilization of Mosquitos</td>
		</tr>
		<tr>
			<td>FU1 Feeder</td>
			<td>FU1-0</td>
			<td>Hemotek Ltd</td>
			<td>Insectary Equipment; feeding units</td>
		</tr>
		<tr>
			<td>Gibco DPBS with Calcium and Magnesium, 10 x 500mL Bottles</td>
			<td>140-040-182</td>
			<td>FisherScientific</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Gibco Fungizone, Amphotericin B, 250&#956;g/mL, 50mL/Bottle</td>
			<td>15-290-026</td>
			<td>Fisher Scientific</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Gibco Penicillin-Streptomycin (10,000 U/mL), 100mL/Bottle, 20 Bottles/Case</td>
			<td>15-140-163</td>
			<td>FisherScientific</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Gibco, Tryptsin-EDTA (.25%), Phenol red, 20 x 100mL Bottles</td>
			<td>25-200-114</td>
			<td>FisherScientific</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Gibcom DMEM, High Glucose, 10 x 500mL Bottles</td>
			<td>11-965-118</td>
			<td>FisherScientific</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Human Blood, Unspecified Gender, Na-Citrate, 1 Unit</td>
			<td>7203706</td>
			<td>Lampire</td>
			<td>Bloodmeal preparation</td>
		</tr>
		<tr>
			<td>InsectaVac Aspirator</td>
			<td>2809B</td>
			<td>Bioquip</td>
			<td>Insectary Equipment</td>
		</tr>
		<tr>
			<td>Methanol, Certified ACS, Fisher Chemicals, Amber Glass Bottle, 4L, 4/Case</td>
			<td>A412-4</td>
			<td>FisherScientific</td>
			<td>Fixative</td>
		</tr>
		<tr>
			<td>Methyl cellulose, viscosity: 3,500-5,600 cP, 2 % in water(20 &#176;C), 250g/Bottle</td>
			<td>M0512-250G</td>
			<td>MilliporeSigma</td>
			<td>Cell culture reagent</td>
		</tr>
		<tr>
			<td>Micro-chem Plus Disinfectant Detergent</td>
			<td>C849T34</td>
			<td>Thomas Scientific</td>
			<td>Decontamination; working dilution of dual quaternary ammonium</td>
		</tr>
		<tr>
			<td>Mineral Oil, BioReagent, for molecular biology</td>
			<td>M5904-5X5ML</td>
			<td>MilliporeSigma</td>
			<td>Immobilization of Mosquitos</td>
		</tr>
		<tr>
			<td>O-rings</td>
			<td>OR37-25</td>
			<td>Hemotek Ltd</td>
			<td>Insectary Equipment</td>
		</tr>
		<tr>
			<td>Plastic Plugs</td>
			<td>PP5-250</td>
			<td>Hemotek Ltd</td>
			<td>Insectary Equipment</td>
		</tr>
		<tr>
			<td>PS6 Power Unit (110-120V)</td>
			<td>PS6120</td>
			<td>Hemotek Ltd</td>
			<td>Insectary Equipment; power source</td>
		</tr>
		<tr>
			<td>Rubis Forceps, Offset blades, superfine points</td>
			<td>4525</td>
			<td>Bioquip</td>
			<td>Insectary Equipment</td>
		</tr>
		<tr>
			<td>Sarstedt Inc, 2mL Screw Cap Microtube, Conical Bottom, O-ring Cap, Sterile, 1000/Case</td>
			<td>50-809-242</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>Sucrose, BioUltra, for molecular biology</td>
			<td>84097-250G</td>
			<td>MilliporeSigma</td>
			<td>Reagent</td>
		</tr>
		<tr>
			<td>ThermoScientific, ART Barrier Low Retention 1000&#956;L Pipette Tips, 100 tips/Rack, 8 Racks/Pack, 4 Packs/Case</td>
			<td>21-402-487</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>ThermoScientific, ART Barrier Low Retention 200&#956;L Pipette Tips, 96 tips/Rack, 10 Racks/Pack, 5 Packs/Case</td>
			<td>21-402-486</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>ThermoScientific, ART Barrier Low Retention 20&#956;L Pipette Tips, 96 tips/Rack, 10 Racks/Pack, 5 Packs/Case</td>
			<td>21-402-484</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>ThermoScientific, ART Barrier Low Retention, Extended Reach 10&#956;L Pipette Tips, 96 tips/Rack, 10 Racks/Pack, 5 Packs/Case</td>
			<td>21-402-482</td>
			<td>FisherScientific</td>
			<td>Plastic consumable</td>
		</tr>
		<tr>
			<td>TissueLyser II</td>
			<td>85300</td>
			<td>QIAGEN</td>
			<td>Homogenization</td>
		</tr>
		<tr>
			<td>TrueBlue Peroxidase Substrate Kit, 200mL</td>
			<td>5510-0030</td>
			<td>Seracare</td>
			<td>Developing solution for focus forming assay</td>
		</tr>
		<tr>
			<td>Vero</td>
			<td>CCL-81</td>
			<td>American Type Culture Collection</td>
			<td>Mammalian cell line to amplify virus and conduct infectious assay</td>
		</tr>
		<tr>
			<td>Vero C1008 [Vero 76, clone E6, Vero E6]</td>
			<td>CRL-1586</td>
			<td>American Type Culture Collection</td>
			<td>Mammalian cell line to amplify virus and conduct infectious assay</td>
		</tr>
	</tbody>
</table>

vector competence analyses on aedes aegypti mosquitoes using zika virus

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine the rate of infection, disseminated infection, and potential transmission of the virus in the mosquito population in question. These procedures are widely utilized with various modifications in vector competence evaluations globally. They are important in determining the potential role that a given mosquito (i.e., species, population, individual) may play in the transmission of a given agent.

Three populations of Ae. aegypti from the Americas (Salvador, Brazil; the Dominican Republic; and the Rio Grande Valley, TX, USA) were exposed to an outbreak strain of ZIKV from the Americas (ZIKV Mex 1-7, Chiapas State, Mexico, 2015) over a range of bloodmeal titers (4, 5, and 6 log10 FFU/mL) presented in a washed human erythrocyte-based artificial bloodmeal. At days 2, 4, 7, 10, and 14 postinfection, subsets of mosquitoes were processed to determine infection, dissemination, and potential transmissi...

Watch this Scientific Journal Video about Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus at JoVE.com

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The presented protocol can determine the vector competence of Aedes aegypti mosquito populations for a given virus, such as Zika, in a containment setting.

Vector Competence Analyses on Aedes aegypti Mosquitoes using Zika Virus

The procedures presented describe a generalized methodology to infect Aedes aegypti mosquitoes with Zika virus under laboratory conditions to determine ...

An aprox mediated by arbovirus, as countermeasures are largely limited to abatement of mosquitoes. So vector competence analyses are critical prevention strategies because they determine what populations and species of mosquitoes can serve as vectors for a given arbovirus, and therefore should be targeted. So one of the most important components in our toolbox for assessing the role of mosquitoes, and other vectors in transmitting infectious diseases, is the vector competence study.These are experiments where we can very precisely control, not only the species of mosquito, or tick, for example, but also geographic strains, as well as very specific strains of a different virus or other infectious organism to get very precise and well-controlled data on the risk of different species for transmitting different agents in very specific parts of the world. Working with infected mosquitoes requires dedicated facilities, training, experience, and careful planning to minimize the risks to the experimenter, as well as the risks of an escaped, infected mosquito. It's therefore quite important for new individuals in these facilities to take the time to work with uninfected blood mosquitoes to familiarize themselves with the techniques and workflow.On the day of exposure, turn on the power source in an Arthropod containment facility to preheat the feeding units. Combine freshly harvested citrated or heparinized human blood with a viral stock at a one to one volume ratio, and overlay a standard three milliliter reservoir unit with the skin of a naive uninfected mouse. Place the covered reservoir on white paper towels, and add about two milliliters of infectious blood to the reservoir one milliliter at a time.Then, inspect the paper towels to confirm that there is no leakage. 24 hours prior to performing the infectious assay, prepare 24-well cell culture plates with Vero cells, and label each well with the identity of the mosquito and sample. On the morning that the mosquitoes will be exposed to the infectious blood meal, remove the water saturated cotton balls, and attach reservoirs with the artificial blood meals to the feeding unit leads with a clear plastic containment glove box.Place the cardboard carton with the starved mosquitoes into the glove box underneath the feeding unit. Upon completion of feeding, remove the reservoir, and immerse it in freshly prepared 10%bleach. Within the glove box, pour cold anesthetized mosquitoes into a Petri dish on ice, and sort the engorged from the un-engorged mosquitoes.Pour the engorged mosquitoes back into the cardboard carton, quickly covering it with a screen and lid. Trim the excess screen mesh off of the carton, and secure the lid with tape. Add a cotton ball saturated with sterile filtered 10%sucrose to the screen, and place the carton in a large plastic secondary container with a damp sponge to maintain humidity.Incubate the secondary container at 27 degrees celsius, allowing mosquitoes ad libitum access to the sucrose until completion of experiments. Use a mechanical aspirator to acquire a predetermined number of incubated mosquitoes from the carton, capping the collection tube with a cotton round when finished. Working within the glove box, pour cold anesthetized mosquitoes into a Petri dish on ice.Remove all six of each mosquitoes legs, and place them in a pre-labeled two milliliter micro centrifuge tube with a sterilized stainless steel ball bearing and 500 microliters of mosquito collection media, or MCM. Gently place the mosquito onto a drop of mineral oil, taking care that the oil does not contact the mosquito's head or proboscis. Insert the proboscis into a micro pipette tip filled with 10 microliters of heat inactivated FBS, and allow the mosquito to salivate for 30 minutes.Eject the pipette tip with the saliva into a micro centrifuge tube with 100 microliters of MCM, and place the carcass into a separate two millimeter tube with the sterilized steel ball bearing and 500 microliters of MCM. Transport the tubes to a bead milling tissue homogenization device within a bio safety cabinet, and triturate all body and leg samples at 26 hertz for five minutes to liberate viral particles into the supernatant. Clarify all samples by centrifugation at 200 times G for five minutes to pelite cellular debris.Immediately before inoculation with samples, remove the media from the previously prepare Vero cells. Carefully aliquot 100 microliters of clarified supernatants from the bodies or legs into each well, taking care not to disturb the mosquito cell debris from the pelite. Then, incubate the plates for one hour.After the incubation, add one milliliter of methylcellulose overlay to each well, and put the plates back in the incubator for three to seven days. Remove overlay plates from the incubator, and bring them to a bio safety cabinet. Discard the methylcellulose overlay into a tray pan containing 10%bleach, and wash each well twice with PBS, discarding each wash into the tray pan.Remove the PBS, and add one milliliter of methanol-acetone per well, and allow the cells to fix onto the plate for 30 minutes. Then, discard the fixative, and leave the plates to dry. Wash each well three times with non-sterile PBS on an orbital plate rocker for 15 minutes per wash, then add one milliliter of blocking solution to each well, and rock the plate for another 15 minutes.Add 100 microliters of anti Zika Virus, or anti flavivirus primary antibody to each well, and incubate the plate with rocking overnight. On the next day, remove the primary antibody, and repeat the washes with PBS. After the last wash, add 100 microliters of secondary antibodies, and incubate the plate while rocking for one hour.Repeat the washes with PBS, then add 100 microliters of substrate development reagent per well, and rock the plate for 15 minutes. When the foci or plaques develop, halt the reaction by rinsing the plate with tap water. Pour off the tap water, and allow the plates to air dry, then quantify the viral foci to determine the number of focus forming units present in the given sample.Three mosquito populations were exposed to an outbreak strain of Zika Virus over a range of blood meal titers. Over the following two weeks, subsets of mosquitoes were processed to determine infection, dissemination, and potential transmission rate. At the lower blood meal titers, the mosquitoes from Salvador, Brazil were infected after 4, 10, and 14 days of extrinsic incubation, with no evidence of disseminated infection observed in the assayed legs.At the highest titer, the virus was detected in the legs of the mosquitoes, but not in the saliva. The mosquitoes from the Dominican Republic proved to be the most susceptible to infection, and the most transmission competent at all tested blood meal titers. Mosquitoes fed all three doses demonstrated dissemination by seven days, and transmission competence at 14 days post infection.Mosquitoes from the Rio Grande Valley in Texas, exposed to lower blood meal titers, were infected as early as four days post infection, while disseminated infections were found after 14 days. In the cohort exposed to the highest titer, infection was observed beginning from the second day post infection, and reached peaks at 4, 10, and 14 days. Disseminated infections were observed at seven days, and only a single mosquito was transmission capable at 10 days.When attempting this protocol, it's important to work safely, as opposed to quickly. So always handle infected or potentially infected mosquitoes within the confines of a glove box or a bio safety cabinet, until they've had their legs or wings removed. The basic vector competence workflow can be adapted to produce infected mosquitoes for downstream analyses, such as transmission studies, as well as to examine the interactions between mosquitoes, the virus, and the microbiome.Vector competence has been a really important tool for understanding the role of mosquitoes in transmitting viruses during epidemics of viral disease, and this has been true for many decades. But it's also a method that's evolved over the years to include new information, as we learn it, about the interactions between these viruses and the mosquito vectors. Just by way of two examples, the genetic population of the virus, the complexity of the population within the mosquito turns out the be very important for its ability to transmit, and we can now include that in vector competence studies with new methods for sequencing the viral population.We also now know that the population of bacteria and other organisms that live in the gastrointestinal tract of the mosquito can also have a major impact on their ability to transmit, and we can also evaluate that population now with new methods in sequencing. So vector competence is a method that has evolved and continues to evolve as we learn more about these complex interactions.

vector-competence-analyses-on-aedes-aegypti-mosquitoes-using-zika

Research

JoVE Journal

Immunology and Infection

A Calcium Bioluminescence Assay for Functional Analysis of Mosquito (Aedes aegypti) and Tick (Rhipicephalus microplus) G Protein-coupled Receptors

Arthropod hormone receptors are potential targets for novel pesticides as they regulate many essential physiological and behavioral processes. The majority of them belong to the superfamily of G protein-coupled receptors (GPCRs). We have focused on characterizing arthropod kinin receptors from the tick and mosquito. Arthropod kinins are multifunctional neuropeptides with myotropic, diuretic, and neurotransmitter function. Here, a method for systematic analyses of structure-activity relationships of insect kinins on two heterologous kinin receptor-expressing systems is described. We provide important information relevant to the development of biostable kinin analogs with the potential to disrupt the diuretic, myotropic, and/or digestive processes in ticks and mosquitoes.
The kinin receptors from the southern cattle tick, Boophilus microplus (Canestrini), and the mosquito Aedes aegypti (Linnaeus), were stably expressed in the mammalian cell line CHO-K1. Functional analyses of these receptors were completed using a calcium bioluminescence plate assay that measures intracellular bioluminescence to determine cytoplasmic calcium levels upon peptide application to these recombinant cells. This method takes advantage of the aequorin protein, a photoprotein isolated from luminescent jellyfish. We transiently transfected the aequorin plasmid (mtAEQ/pcDNA1) in cell lines that stably expressed the kinin receptors. These cells were then treated with the cofactor coelenterazine, which complexes with intracellular aequorin. This bond breaks in the presence of calcium, emitting luminescence levels indicative of the calcium concentration. As the kinin receptor signals through the release of intracellular calcium, the intensity of the signal is related to the potency of the peptide.
This protocol is a synthesis of several previously described protocols with modifications; it presents step-by-step instructions for the stable expression of GPCRs in a mammalian cell line through functional plate assays (Staubly et al., 2002 and Stables et al., 1997). Using this methodology, we were able to establish stable cell lines expressing the mosquito and the tick kinin receptors, compare the potency of three mosquito kinins, identify critical amino acid positions for the ligand-receptor interaction, and perform semi-throughput screening of a peptide library. Because insect kinins are susceptible to fast enzymatic degradation by endogenous peptidases, they are severely limited in use as tools for pest control or endocrinological studies. Therefore, we also tested kinin analogs containing amino isobutyric acid (Aib) to enhance their potency and biostability. This peptidase-resistant analog represents an important lead in the development of biostable insect kinin analogs and may aid in the development of neuropeptide-based arthropod control strategies.

A Calcium Bioluminescence Assay for Functional Analysis of Mosquito Aedes aegypti and Tick Rhipicephalus microplus G Protein-coupled Receptors

This protocol provides instructions for clonal-cell line selection and a calcium bioluminescence assay to analyze the structure-activity relationships of synthesized arthropod neuropeptides on their cognate GPCRs. This assay can be used for receptor deorphanization and structure-activity relationship studies for synthetic analog design and peptide/drug-lead discovery.

Arthropod hormone receptors are potential targets for novel pesticides as they regulate many essential physiological and behavioral processes.  The ...

A Protocol for Collecting and Staining Hemocytes from the Yellow Fever Mosquito Aedes aegypti

Mosquitoes are vectors for a number of disease-causing pathogens such as the yellow fever virus, malaria parasites and filarial worms. Laboratories are investigating anti-pathogen components of the innate immune system in disease vector species in the hopes of generating transgenic mosquitoes that are refractory to such pathogens1, 2. The innate immune system of mosquitoes consists of several lines of defense 3. Pathogens that manage to escape the barrier imposed by the epithelium-lined mosquito midgut 4 enter the hemolymph and encounter circulating hemocytes, important cellular components that encapsulate and engulf pathogens 5, 6. Researchers have not found evidence for hematopoietic tissues in mosquitoes and current evidence suggests that the number of hemocytes is fixed at adult emergence and numbers may actually decline as the mosquito ages 7. The ability to properly collect and identify hemocytes from medically important insects is an essential step for studies in cellular immunity. However, the small size of mosquitoes and the limited volume of hemolymph pose a challenge to collecting immune cells. 
Two established methods for collecting mosquito hemocytes include expulsion of hemolymph from a cut proboscis 8, and volume displacement (perfusion), in which saline is injected into the membranous necklike region between the head and thorax (i.e., cervix) and the perfused hemolymph is collected from a torn opening in a distal region of the abdomen 9, 10. These techniques, however, are limited by low recovery of hemocytes and possible contamination by fat body cells, respectively 11. More recently a method referred to as high injection/recovery improved recovery of immunocytes by use of anticoagulant buffers while reducing levels of contaminating scales and internal tissues 11. While that method allows for an improved method of collecting and maintaining hemocytes for primary culture, it entails a number of injection and collecting steps that are not necessary if the downstream goal is to collect, fix and stain hemocytes for diagnostics. Here, we demonstrate our method of collecting mosquito hemolymph that combines the simplicity of perfusion, using anticoagulant buffers in place of saline solution, with the accuracy of high injection techniques to isolate clean preparations of hemocytes in Aedes mosquitoes.

A Protocol for Collecting and Staining Hemocytes from the Yellow Fever Mosquito Aedes aegypti

A simplified yet accurate method to collect and stain mosquito hemocytes is described. Our method combines the simplicity of perfusion with the accuracy of high injection techniques to isolate clean preparations of hemocytes in Aedes mosquitoes. This method facilitates studies requiring knowledge of the types of hemocytes and their abundance.

 Mosquitoes are vectors for a number  of disease-causing pathogens such as the yellow fever virus, malaria parasites  and filarial worms. Laboratories are ...

Detection of Infectious Virus from Field-collected Mosquitoes by Vero Cell Culture Assay

Mosquitoes transmit a number of distinct viruses including important human pathogens such as West Nile virus, dengue virus, and chickungunya virus. Many of these viruses have intensified in their endemic ranges and expanded to new territories, necessitating effective surveillance and control programs to respond to these threats. One strategy to monitor virus activity involves collecting large numbers of mosquitoes from endemic sites and testing them for viral infection. In this article, we describe how to handle, process, and screen field-collected mosquitoes for infectious virus by Vero cell culture assay. Mosquitoes are sorted by trap location and species, and grouped into pools containing &le;50 individuals. Pooled specimens are homogenized in buffered saline using a mixer-mill and the aqueous phase is inoculated onto confluent Vero cell cultures (Clone E6). Cell cultures are monitored for cytopathic effect from days 3-7 post-inoculation and any viruses grown in cell culture are identified by the appropriate diagnostic assays. By utilizing this approach, we have isolated 9 different viruses from mosquitoes collected in Connecticut, USA, and among these, 5 are known to cause human disease. Three of these viruses (West Nile virus, Potosi virus, and La Crosse virus) represent new records for North America or the New England region since 1999. The ability to detect a wide diversity of viruses is critical to monitoring both established and newly emerging viruses in the mosquito population.

We describe a method to process and screen field-collected mosquitoes for a diversity of viruses by Vero cell culture assay. By employing this technique, we have detected 9 different viruses from 4 taxonomic families in mosquitoes collected in Connecticut.

Mosquitoes transmit a number of distinct viruses including important human pathogens such as West Nile virus, dengue virus, and chickungunya virus. Many ...

Hybridization in situ of Salivary Glands, Ovaries, and Embryos of Vector Mosquitoes

Mosquitoes are vectors for a diverse set of pathogens including arboviruses, protozoan parasites and nematodes. Investigation of transcripts and gene regulators that are expressed in tissues in which the mosquito host and pathogen interact, and in organs involved in reproduction are of great interest for strategies to reduce mosquito-borne disease transmission and disrupt egg development. A number of tools have been employed to study and validate the temporal and tissue-specific regulation of gene expression. Here, we describe protocols that have been developed to obtain spatial information, which enhances our understanding of where specific genes are expressed and their products accumulate. The protocol described has been used to validate expression and determine accumulation patterns of transcripts in tissues related to mosquito-borne pathogen transmission, such as female salivary glands, as well as subcellular compartments of ovaries and embryos, which relate to mosquito reproduction and development. 
 The following procedures represent an optimized methodology that improves the efficiency of various steps in the protocol without loss of target-specific hybridization signals. Guidelines for RNA probe preparation, dissection of soft tissues and the general procedure for fixation and hybridization are described in Part A, while steps specific for the collection, fixation, pre-hybridization and hybridization of mosquito embryos are detailed in Part B.

Hybridization in situ of Salivary Glands, Ovaries, and Embryos of Vector Mosquitoes

Temporal and spatial gene expression analyses have a crucial role in functional genomics. Whole-mount hybridization in situ is useful for determining the localization of transcripts within tissues and subcellular compartments. Here we outline a hybridization in situ protocol with modifications for specific target tissues in mosquitoes.

Mosquitoes are vectors for a diverse set of pathogens including arboviruses, protozoan parasites and nematodes.  Investigation of transcripts and gene ...

Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons

Zika Virus (ZIKV) is an emerging pathogen that is linked to fetal developmental abnormalities such as microcephaly, eye defects, and impaired growth. ZIKV is an RNA virus of the Flaviviridae family. ZIKV is mainly transmitted by mosquitoes, but can also be spread by maternal to fetal vertical transmission as well as sexual contact. To date, there are no reliable treatment or vaccine options available to protect those infected by the virus. The development of a reproducible, effective Zika virus infectious cell culture system is critical for studying the molecular mechanisms of ZIKV replication as well as drug and vaccine development. In this regard, a protocol describing a mammalian cell-based in vitro Zika virus culture system for viral production and growth analysis is reported here. Details on the formation of plaques by Zika virus on a cell monolayer and plaque assay for measuring viral titer are presented. Viral genome replication kinetics and double-stranded RNA genome replicatory intermediates are determined. This culture platform was utilized to screen against a library of a small set of cytokines resulting in the identification of interferon-&#945; (IFN-&#945;), IFN-&#946; and IFN-&#947; as potent inhibitors of Zika viral growth. In summary, an in vitro infectious Zika viral culture system and various virological assays are demonstrated in this study, which has the potential to greatly benefit the research community in elucidating further the mechanisms of viral pathogenesis and the evolution of viral virulence. Antiviral IFN-alpha can further be evaluated as a prophylactic, post-exposure prophylactic, and treatment option for Zika virus infections in high-risk populations, including infected pregnant women.

Zika Virus Infectious Cell Culture System and the In Vitro Prophylactic Effect of Interferons

Zika Virus (ZIKV), an emerging pathogen, is linked to fetal developmental abnormalities and microcephaly. The establishment of an effective infectious cell culture system is crucial for studies of ZIKV replication as well as vaccine and drug development. In this study, various virological assays pertaining to ZIKV are illustrated and discussed.

Zika Virus (ZIKV) is an emerging pathogen that is linked to fetal developmental abnormalities such as microcephaly, eye defects, and impaired growth. ZIKV ...

Rescue and Characterization of Recombinant Virus from a New World Zika Virus Infectious Clone

Infectious cDNA clones allow for genetic manipulation of a virus, thus facilitating work on vaccines, pathogenesis, replication, transmission and viral evolution. Here we describe the construction of an infectious clone for Zika virus (ZIKV), which is currently causing an explosive outbreak in the Americas. To prevent toxicity to bacteria that is commonly observed with flavivirus-derived plasmids, we generated a two-plasmid system which separates the genome at the NS1 gene and is more stable than full-length constructs that could not be successfully recovered without mutations. After digestion and ligation to join the two fragments, full-length viral RNA can be generated by in vitro transcription with T7 RNA polymerase. Following electroporation of transcribed RNA into cells, virus was recovered that exhibited similar in vitro growth kinetics and in vivo virulence and infection phenotypes in mice and mosquitoes, respectively.

This protocol describes the recovery of infectious Zika virus from a two-plasmid infectious cDNA clone.

Infectious cDNA clones allow for genetic manipulation of a virus, thus facilitating work on vaccines, pathogenesis, replication, transmission and viral ...

Zika Virus Specific Diagnostic Epitope Discovery

High-density peptide microarrays allow screening of more than six thousand peptides on a single standard microscopy slide. This method can be applied for drug discovery, therapeutic target identification, and developing of diagnostics. Here, we present a protocol to discover specific Zika virus (ZIKV) diagnostic peptides using a high-density peptide microarray. A human serum sample validated for ZIKV infection was incubated with a high-density peptide microarray containing the entire ZIKV protein translated into 3,423 unique 15 linear amino acid (aa) residues with a 14-aa residue overlap printed in duplicate. Staining with different secondary antibodies within the same array, we detected peptides that bind to Immunoglobulin M (IgM) and Immunoglobulin G (IgG) antibodies present in serum. These peptides were selected for further validation experiments. In this protocol, we describe the strategy followed to design, process, and analyze a high-density peptide microarray.

In this protocol, we describe a technique to discover Zika virus specific diagnostic peptides using a high-density peptide microarray. This protocol can readly be adapted for other emerging infectious diseases.

High-density peptide microarrays allow screening of more than six thousand peptides on a single standard microscopy slide. This method can be applied for ...

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity of antibodies or serum to enhance infection in impermissible cell lines have relied on using viral output in the media followed by plaque assays to quantify infection. More recently, these assays have examined Dengue virus (DENV) infection in the cell lines using fluorescently labeled antibodies. Both these approaches have limitations that restrict the widespread use of these techniques. Here, we describe a simple in vitro assay using Dengue virus reporter viral particles (RVPs) that express green fluorescent protein and K562 cells to examine antibody dependent enhancement (ADE) of DENV infection using serum that was obtained from rhesus macaques 16 weeks after infection with Zika virus (ZIKV). This technique is reliable, involves minimal manipulation of cells, does not involve the use of live replication competent virus, and can be performed in a high throughput format to get a quantitative readout using flow cytometry. Additionally, this assay can be easily adapted to examine antibody dependent enhancement (ADE) of other flavivirus infections such as Yellow Fever virus (YFV), Japanese Equine Encephalitis virus (JEEV), West Nile virus (WNV) etc. where RVPs are available. The ease of setting up the assay, analyzing the data, and interpreting results makes it highly amenable to most laboratory settings.

A Simple Flow Cytometry Based Assay to Determine In Vitro Antibody Dependent Enhancement of Dengue Virus Using Zika Virus Convalescent Serum

We describe a simple and easy protocol for measuring antibody dependent enhancement of infection by Zika virus convalescent serum using Dengue virus Reporter Viral Particles.

Antibody dependent enhancement of infection has been shown to play a major role in Dengue viral pathogenesis. Traditional assays that measure the capacity ...

Evaluation of Zika Virus-specific T-cell Responses in Immunoprivileged Organs of Infected Ifnar1-/- Mice

The Zika virus (ZIKV) can induce inflammation in immunoprivileged organs (e.g., the brain and testis), leading to the Guillain-Barr&#233; syndrome and damaging the testes. During an infection with the ZIKV, immune cells have been shown to infiltrate into the tissues. However, the cellular mechanisms that define the protection and/or immunopathogenesis of these immune cells during a ZIKV infection are still largely unknown. Herein, we describe methods to evaluate the virus-specific T-cell functionality in these immunoprivileged organs of ZIKV-infected mice. These methods include a) a ZIKV infection and vaccine inoculation in Ifnar1-/- mice; b) histopathology, immunofluorescence, and immunohistochemistry assays to detect the virus infection and inflammation in the brain, testes, and spleen; c) the preparation of a tetramer of ZIKV-derived T-cell epitopes; d) the detection of ZIKV-specific T cells in the monocytes isolated from the brain, testes, and spleen. Using these approaches, it is possible to detect the antigen-specific T cells that have infiltrated into the immunoprivileged organs and to evaluate the functions of these T cells during the infection: potential immune protection via virus clearance and/or immunopathogenesis to exacerbate the inflammation. These findings may also help to clarify the contribution of T cells induced by the immunization against ZIKV.

Evaluation of Zika Virus-specific T-cell Responses in Immunoprivileged Organs of Infected Ifnar1-/- Mice

A protocol to evaluate antigen-specific T-cell responses in the immunoprivileged organs of the Ifnar1-/- murine model for the Zika virus (ZIKV) infection is described. This method is pivotal for investigating the cellular mechanisms of the protection and immunopathogenesis of ZIKV vaccines and is also valuable for their efficacy evaluation.

The Zika virus (ZIKV) can induce inflammation in immunoprivileged organs (e.g., the brain and testis), leading to the Guillain-Barr&#233; syndrome and ...

Rescue of Recombinant Zika Virus from a Bacterial Artificial Chromosome cDNA Clone

The association of Zika virus (ZIKV) infection with neurological complications during the recent worldwide outbreak and the lack of approved vaccines and/or antivirals have underscored the urgent need to develop ZIKV reverse genetic systems to facilitate the study of ZIKV biology and the development of therapeutic and/or prophylactic approaches. However, like with other flaviviruses, the generation of ZIKV full-length infectious cDNA clones has been hampered due to the toxicity of viral sequences during its amplification in bacteria. To overcome this problem, we have developed a nontraditional approach based on the use of bacterial artificial chromosomes (BACs). Using this approach, the full-length cDNA copy of the ZIKV strain Rio Grande do Norte Natal (ZIKV-RGN) is generated from four synthetic DNA fragments and assembled into the single-copy pBeloBAC11 plasmid under the control of the human cytomegalovirus (CMV) immediate-early promoter. The assembled BAC cDNA clone is stable during propagation in bacteria, and infectious recombinant (r)ZIKV is recovered in Vero cells after transfection of the BAC cDNA clone. The protocol described here provides a powerful technique for the generation of infectious clones of flaviviruses, including ZIKV, and other positive-strand RNA viruses, particularly those with large genomes that have stability problems during bacterial&#160;propagation.

The recent epidemic of Zika virus highlights the importance of establishing reverse genetic approaches to develop vaccines and/or therapeutic strategies. Here, we describe the protocol to rescue an infectious recombinant Zika virus from a full-length cDNA clone assembled in a bacterial artificial chromosome under the control of the human cytomegalovirus immediate-early promoter.

The association of Zika virus (ZIKV) infection with neurological complications during the recent worldwide outbreak and the lack of approved vaccines ...