- A team at University of Texas Austin has developed a new method for identifying whether a mosquito is of the Aedes aegypti species, which is responsible for transmitting Zika, dengue and other deadly diseases.
- The method can easily be conducted while out in the field and does not need much more than a cell phone, a 3D-printed box and a few chemical solutions.
- This toolkit can also determine whether a mosquito has been exposed to the Wolbachia bacteria, which infects mosquitoes and prevents them from transmitting dangerous pathogens.
- Although portable tools and “biopesticides” such as Wolbachia are currently effective, adaptive dengue and Zika viruses will likely evolve past these tactics just as they have for countless other methods. Constant attention and funding is needed to stay ahead of such pathogens in this ever-lasting battle.
A team at University of Texas Austin has developed a new method for identifying whether a mosquito is of the Aedes aegypti species, which is responsible for transmitting Zika, dengue and other deadly diseases.
The method can easily be conducted while out in the field and does not need much more than a cell phone, a 3D-printed box and a few chemical solutions.
This toolkit can also determine whether a mosquito has been exposed to the Wolbachia bacteria, which infects mosquitoes and prevents them from transmitting dangerous pathogens.
Although portable tools and “biopesticides” such as Wolbachia are currently effective, adaptive dengue and Zika viruses will likely evolve past these tactics just as they have for countless other methods. Constant attention and funding is needed to stay ahead of such pathogens in this ever-lasting battle.
Biologists and doctors alike have sought creative methods to track, analyze, and prevent infectious diseases spread by mosquitoes. Some of the approaches taken may appear unconventional and yet are highly effective. For instance, what better way to fight off a mosquito-borne microbe other than to use another microbe?
DIY Diagnostics, a team of researchers based at University of Texas at Austin, has been investigating how the Wolbachia bacterium can be used to suppress the load of dangerous viruses transmitted to humans by one of the most notorious mosquito species, Aedes aegypti. The Wolbachia bacterium prevents the reproduction and spread of diseases that live inside Ae. aegypti, such as dengue, Zika and yellow fever, and has already caught on as an effective approach to combating such infectious diseases.
The UT Austin team’s recent study describes their new, portable method for identifying Ae. aegypti mosquitoes and whether a mosquito has come in contact with Wolbachia bacteria. Combining a 3D-printed box, a smartphone camera, and a simple chemical test, they designed a pocket-sized toolbox that can accurately determine if a captured mosquito is Ae. aegypti and whether it has been rendered harmless by Wolbachia.
Thirteen years ago, the first successful transfer of Wolbachia into an Ae. aegypti mosquito population was a big jump for epidemiologists, but the laboratory protocols for identifying both Ae. aegypti and Wolbachia were tedious. Now, this toolkit may allow researchers to bring that functionality out of the lab and into the field.
Mosquito in, genetic results out
After capturing a mosquito, the user mashes up the insect, which exposes more genetic material, and places the remains within two capsules in the test kit’s 3D-printed toolbox. In each of these capsules, a particular chemical compound is added that responds to the presence of a gene: one compound looks for the coi gene, which is both unique to and prevalent in Ae. aegypti, and the other identifies the wsp gene, found in Wolbachia bacteria. If coi is present in the mosquito smoothie, the first capsule will glow; if Wolbachia is present too, the second capsule also glows. The user can then slip a cellphone into a holster and snap a photo of the toolbox’s contents, thereby recording the results.
This method works even when the user hastily or crudely crushes the mosquito, as may be the case when a scientist is away from a controlled lab setting and in a remote field location.
“A low-cost, portable, and accurate tool like ours, which is easy to use and interpret, will facilitate access to testing and more widespread and/or frequent [mosquito] surveillance, especially in austere settings,” Dr. Sanchita Bhadra, lead author of the study, told Mongabay. “Better surveillance of [mosquito] species, and prevalence and stability of the biocontrol agent, Wolbachia, are essential for effective [mosquito] control and pre-emption of disease outbreaks.”
When a researcher is in the field, identifying mosquito species is exceedingly difficult, due to the small size of the insects and how few visual distinctions exist between some species. DIY Diagnostics’ method can successfully identify the Ae. aegypti mosquito without the support of additional lab equipment, and for a minimal cost: the materials used to make the toolbox cost around $5, and the chemical cues needed only $1.50 per test. The combination of easy and cheap use makes this toolbox a potentially valuable asset for research on Ae. aegypti, which occurs throughout the global tropics and into subtropics, such as the southern United States.
Other species of tropical primates also suffer from diseases transmitted by this mosquito, namely yellow fever. Early detection of Ae. aegypti by use of this toolbox may also protect primates from succumbing to the disease or, as has been the recent case with endangered golden lion tamarins in Brazil, to slaughter by misinformed people.
This study has not been the first creative approach to identifying mosquitoes in the field. Last year, a Stanford University team designed and implemented a method to distinguish mosquitoes by recording the buzz of their wings with only the use of a cellphone. They have packaged the method into a smartphone app so that anyone can identify a mosquito, provided one has enough patience to successfully record the insect. Such efforts enable non-scientists to monitor mosquito distributions or signal sudden outbreaks, which helps build big datasets that inform large-scale mapping efforts.
As of late, infectious diseases have been spreading not only among people locally, but also to entirely new regions. Scientists have known for decades that with a warming global climate, the heat-loving Ae. aegypti mosquito will creep to higher latitudes than its historical range in the tropics, bringing along its suite of deadly diseases. As new dengue outbreaks confirm model predictions from years ago, for example, the global health community still scrambles to stay in front of the disease.
“Many of these diseases are spreading in areas where they weren’t common before,” Bhadra said. “Having surveillance is important [to combat] any kind of outbreak, and [our] method allows a rapid test in the field.”
An endless cycle of fighting fire with fire
Application of the Wolbachia bacterium has presented an opportunity to combat the spread of dengue, Zika and other viral diseases on a global scale. Wolbachia bacteria occur naturally in many insects but are not found in wild Ae. aegypti. When introduced into Ae. aegypti mosquitoes, the bacterial “biopesticide” outcompetes viruses such as dengue for crucial resources within the insect’s gut. As a result, the virus cannot multiply and does not spread into a human bitten by the mosquito.
Furthermore, when a Wolbachia-infected female mosquito reproduces, she passes the bacteria to her offspring, which then also cannot spread dengue to humans. The hope is that gradually, Wolbachia-infected mosquitoes will increase in prevalence until they completely replace non-Wolbachia mosquitoes, rendering the insect’s inflictions to not much more than itchy bites.
But there may be a limit to the success of the Wolbachia method. As has been the case in attempts to combat infectious disease with antibacterial drugs or soap, the disease fights back.
When a biological tactic is used to suppress a virus or bacteria, those individual microbes susceptible to the tactic will be removed from the population, either because they perish or cannot reproduce. Microbes that may have some genetic mutation that provides resistance to the bio-weapon will persist and then pass the mutation to their progeny. As a result, the effectiveness of the biological tactic will wane, and the remaining microbe population will rebound into a prominent threat. In turn, scientists must work out a new solution to combat the pathogen.
This evolutionary arms race, in which researchers and microbes iteratively overtake each other, is commonplace in research on infectious disease. Use of Wolbachia bacteria to reduce the threat of Zika and other diseases is both novel and effective, but only for now. Eventually, fast-reproducing resistant microbes will likely overpower this tactic, and a new method will need to be developed.
So, what will be our next battle plan? Scientists have taken to arms on all fronts of the war with mosquito-transmitted pathogens. A team at Iowa State University has weaponized natural repellants from plants to create a novel class of mosquito sprays. Another group has analyzed the most effective tactics for responding to and containing sudden outbreaks of mosquito-borne pathogens. Perhaps the next battle will be won right at the source, as some scientists seek to understand–and therefore, manipulate–how viruses like dengue infect and change the body functions of Ae. aegypti.
For now, the effectiveness of the Wolbachia bacterium, paired with low-cost and accurate mosquito surveillance through means such as the DIY toolbox, can still save many lives from deadly pathogens. DIY Diagnostics plans to package their kit into disposable, field-ready devices and to develop a smartphone app that can read image results and send them to public health agencies, with the hope that non-specialists can soon help authorities track potential disease outbreaks.
The marathon race against infectious pathogens may someday have a winner: us, or a formidable disease. With progressive technology, inspired application, and citizen involvement, however, we can manage to stay one step ahead.
Bhadra, S., Riedel, T. E., Saldaña, M. A., Hegde, S., Pederson, N., Hughes, G. L., & Ellington, A. D. (2018). Direct nucleic acid analysis of mosquitoes for high fidelity species identification and detection of Wolbachia using a cellphone. bioRxiv, 291849. https://doi.org/10.1371/journal.pntd.0006671
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