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November 20, 2019
Q Fever

Mosquitoes Causing Dengue and Yellow Fever are Easily Identified With a New Analyzer

Highlights:

  • Researchers have developed a new, rapid, cost-effective and
    easy-to-use diagnostic tool that uses a smartphone camera, a small 3D-printed
    box and a simple chemical test to show whether a dead mosquito belongs to the Aedes aegypti species -the one that
    carries the Zika or yellow fever virus
  • The
    tool can also effectively detect the Wolbachia bacterial
    strain that is widely studied for possible properties to block transmission of
    viruses like chikungunya, dengue, and Zika.

Researchers have developed a new diagnostic tool that can quickly carry
out species-identification of a dead mosquito at a simple cost. The test determines
if the mosquito belongs to a viral species that
carries dangerous diseases like the Zika and dengue
.

The tool can also identify if the bug has come into contact with a
mosquito-control strategy known as Wolbachia.

‘A newly developed cellphone-read assay identifies mosquitoes carrying dangerous tropical diseases and Wolbachia bacteria, a type that keeps mosquitoes from spreading diseases.’


The research was conducted at The University of Texas at Austin and
appears in the journal PLOS Neglected Tropical Diseases.

“Many of these diseases are spreading in areas where they weren’t
common before,” said Sanchita Bhadra, a research associate in the
Department of Molecular Biosciences and first author on the paper. “Having
surveillance is important in conjunction with any kind of outbreak, and this
method allows a rapid test in the field.”

Aedes aegypti is a mosquito species that infects about 100 million people worldwide
with illnesses like dengue, Zika, chikungunya or yellow fever
. These mosquito-transmitted viruses initially affected only people in the
tropics, but have grown to become a widespread health menace due to increased
global movement and insecticide resistance. The species is the reason mosquito-borne
diseases have tripled in the United States since 2004.

In order to curb viral transmission, in countries around the
world and in 20 U.S. states where the Aedes aegypti mosquito is found, the researchers working in
public health agencies have used a strategy to infect
the disease-causing mosquitoes with a
biopesticide
called
Wolbachia, a type of bacteria that keeps mosquitoes from spreading
diseases
.

However, Aedes aegypti, do not show any
visual signs of having Wolbachia infection.
Besides, current diagnostic tests are hard to read, expensive and logistically
cumbersome.

Public health groups along with monitoring efforts trap and kill
mosquitoes routinely, but the technology that exists to extract nucleic acid
from inside mosquitoes is very complicated, requiring them to be dead for days
and starting to decay; the method turns out to be expensive and error-prone.

Hence, Sanchita Bhadra of the University of Texas in Austin,
and her colleagues developed a probe
that along with a smartphone camera can test the nuclear material of
Wolbachia, in addition to finding out
the mosquito species type
. The tool represents a significant step forward to test the
effectiveness of Wolbachia.

LAMP-OSD – Loop-mediated
isothermal amplification and oligonucleotide strand displacement

The probes termed “OSD probes” are based on
fundamentals of nucleic acid chemistry. The researchers applied the probes to
accurately read “LAMP assays” (a relatively simple nucleic acid
detection test). The OSD probe will
produce a visible signal only if it binds to the target LAMP DNA; in the
absence of specific target DNA, no signal is generated.

The new design of the tool yields an accurate Yes/No visual
readout on the smartphone and prevents a very common drawback of LAMP – false
positive results. Moreover, when using the one-pot assay, the nucleic acid does
not need to be removed and purified to analyze the crudely softened individual
or pooled mosquitoes and renders the test simple and one that can be done
anywhere.

Study

Scientists conducted a blinded test of 90 field-caught mosquitoes

  • The cellphone assay specificity was 98 percent and sensitivity was 97 percent in identifying Ae. aegypti mosquitoes, even when the samples were stored at 37 degrees Celsius without a desiccant for 3 weeks.
  • The test also readily identified the Wolbachia strain in field-collected mosquitoes without generating any false positive signals

The authors note that there is a possibility of false
positives with their assay due to Wolbachia DNA merging
with the chromosomes of an uninfected host, such as a fruit fly; however, this
problem is not isolated to this assay alone and can happen in all nucleic acid
amplification assays, including PCR.

The researchers conclude: “We are currently automating
the assays and workflow on low-cost paper and plastic devices that will not
only further streamline diagnostic application but will also provide sealed
chambers for biohazard and aerosol containment for macerating mosquitoes. Our
sample preparation and workflow not only simplify the application of molecular
diagnostics for surveillance but also reduce cost by eliminating the need for
nucleic acid extraction and complex instruments for assay incubation and
readout.”

References :

  1. Sanchita Bhadra, Timothy E. Riedel, Miguel A. Saldaña, Shivanand Hegde, Nicole Pederson, Grant L. Hughes, Andrew D. Ellington. Direct nucleic acid analysis of mosquitoes for high fidelity species identification and detection of Wolbachia using a cellphone. PLOS Neglected Tropical Diseases, 2018; 12 (8): e0006671 DOI: 10.1371/journal.pntd.0006671
  2. Sanchita Bhadra, Timothy E. Riedel, Miguel A. Saldaña, Shivanand Hegde, Nicole Pederson, Grant L. Hughes, Andrew D. Ellington., “Direct nucleic acid analysis of mosquitoes for high fidelity species identification and detection of Wolbachia using a cellphone” PLOS Neglected Tropical Disease August 30, (2018) https://doi.org/10.1371/journal.pntd.0006671

Source: Medindia

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