Texas A&M Entomology Research Network

mosquito

AgriLife Research team makes strides in fight against Zika

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by Steve Byrns, Texas A&M AgriLife Communications

Dr. Kevin Myles, Texas A&M AgriLife Research scientist at Texas A&M University, discusses research notes with AgriLife Research associate scientist Glady “Hazitha” Samuel. (Texas A&M AgriLife Extension Service photo by Rob Williams)
Dr. Kevin Myles, Texas A&M AgriLife Research scientist at Texas A&M University, discusses research notes with AgriLife Research associate scientist Glady “Hazitha” Samuel. (Texas A&M AgriLife Extension Service photo by Rob Williams)

COLLEGE STATION – There’s a war raging on a tiny battlefield and the outcome could well touch millions of people worldwide threatened by Zika and related viruses. The key ally unlocking the mystery surrounding this conflict is the long-dreaded yellow fever virus.

Dr. Kevin Myles, Glady “Hazitha” Samuel and Dr. Zach Adelman are Texas A&M AgriLife Research scientists at Texas A&M University, College Station, who published “Yellow fever virus capsid protein is a potent suppressor of RNA silencing that binds double-stranded RNA.”

The paper appears in the Proceedings of the National Academy of Sciences. Go to http://bit.ly/2eYsyIQ.

The mystery has been how these viruses get around the insect’s immune response, and the answer is the virus makes a protein that suppresses the immune response, Myles said.

“When mosquitoes are infected with these viruses, there’s a signal that lets the mosquito’s cells know that they are infected, resulting in targeting of the virus by the mosquito’s immune response.

“Something similar occurs in our bodies when we’re infected with these viruses; there are signals our cells detect that let our immune system know all is not well,” he said.

The AgriLife Research team found a protein that is produced by yellow fever virus, as well as Zika virus, West Nile virus and dengue virus, that suppresses the immune response of the mosquito.

“While the mosquito doesn’t want the virus in its body any more than we want it in ours, and is trying to get rid of it, the virus isn’t defenseless,” Myles said. “It’s fighting back and deploying its own countermeasures. Basically this is what’s known as an evolutionary arms race. The survival of this group of viruses depends on their ability to stay one step ahead of the mosquito’s immune response.”

Aedes aegypti mosquito. (Texas A&M AgriLife Research photo by Gabriel Hamer)
Aedes aegypti mosquito. (Texas A&M AgriLife Research photo by Gabriel Hamer)

Now that the scientists know this, there are a couple of options. By using gene drive, a method targeting specific genes, they could go in and tip the scale in the mosquito’s favor. Alternatively, they could give the nod to the virus. In the latter, the virus would actually make the mosquito sick preventing transmission to humans.

“It will also be interesting to see if this protein interferes with the human immune response,” Myles said. “Certainly similar types of proteins have been found in other viruses that are not transmitted by mosquitoes but do infect people, influenza viruses for example.

“If it does interfere with our immune response, it could become a target for vaccine development, not only for Zika virus, but possibly other viruses as well.

“More research is needed before we reach that point though, but as ironic as it may seem, we are using the yellow fever virus, once arguably the most feared pestilence in the Western Hemisphere, to help us defeat the Zika virus and quite possibly others as well.”

Myles and Adelman joined the department of entomology at Texas A&M on Aug.1. The scientists were previously at Virginia Tech and now lead AgriLife Research’s efforts to stop Zika.

Myles is working to understand the basic biology of how viruses such as Zika replicate in mosquitoes, and Adelman’s projects involve creating mosquitoes resistant to viruses such as Zika.

For more information, contact Myles at 979-458-3110, mylesk@tamu.edu .

New discovery may improve future mosquito control

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AgriLife Research scientist’s paper outlines a new mechanism of sugar feeding aversion

By: Steve Byrns, Texas A&M AgriLife Communications

Aedes aegypti females reject the sucrose solution containing the synthetic peptide. The sugary solution contained a blue dye to trace the meal in their gut. (Photo courtesy Dr. Patricia Pietrantonio, Texas A&M AgriLife Research Fellow)
Aedes aegypti females reject the sucrose solution containing the synthetic peptide. The sugary solution contained a blue dye to trace the meal in their gut. (Photo courtesy Dr. Patricia Pietrantonio, Texas A&M AgriLife Research Fellow)

COLLEGE STATION – Major rainfall across most of Texas triggering hordes of mosquitoes coupled with seemingly constant mosquito-related Zika virus media reports from around the globe may have set the stage perfectly for what one researcher deems as a very significant discovery in man’s war against earth’s leading human disease carrier.

Dr. David Ragsdale, head of the entomology department at Texas A&M University, College Station, credits Dr. Patricia Pietrantonio, a Texas A&M AgriLife Research Fellow in the entomology department at College Station, along with her students and colleagues from other institutions, with discovering a receptor on the legs of mosquitoes that when activated, keeps female mosquitoes from taking a sugar meal and makes them fly away.

“This finding could lead to novel mosquito repellents,” Ragsdale said. “This is really a big deal, a major achievement.”

Ragsdale said Pietrantonio has just had the article, “Leucokinin mimetic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron,” on the work published in the Proceedings of the National Academy of Sciences. To view the work and its authors go to http://www.pnas.org/content/early/2016/06/01/1520404113.abstract.

“What makes this even more compelling is the work was with Aedes aegypti, the mosquito species responsible for spreading Zika, dengue, yellow fever and Chikungunya viruses,” Ragsdale said. “This work is the culmination of over five years of study by Dr. Pietrantonio, her students and collaborators. With Zika a looming threat, this is a timely discovery.”

Pietrantonio said after mating, Aedes aegypti females immediately search for a blood meal from a human host.

“They are highly anthropophilic, meaning they are attracted to humans,” Pietrantonio said. “They may even follow people indoors. If female mosquitoes are infected with viruses they may transmit them to humans when they acquire a blood meal.”

The blood meal supplies the protein source female mosquitoes require to produce eggs, she said.

“However, in the field, if human hosts are not present, females will feed on sucrose solutions such as nectar from flowers, though they prefer a blood meal to a sugar meal but male mosquitoes feed only on nectar. Certainly sugar feeding is one of the two feeding modalities for adults of this species.”

“We found that a synthetic peptide that was designed to mimic a peptide naturally present in mosquitoes triggers an aversive fly away, walk away or jump away behavior in female mosquitoes.”

If the same aversion could be tied to a blood meal, she said a totally new and effective mosquito feeding deterrent may be in the offing, one that perhaps would cause the mosquito to pass up the required blood meal needed to lay eggs. Doing so would either disrupt the life cycle and/or reduce disease transmission.

However, this is far from being accomplished, she said.

“One of our team designed a peptide mimetic of the kinin peptides, which are diuretic hormones in mosquitoes, to be resistant to enzymatic degradation,” Pietrantonio said. “These mimetics are more potent than those found naturally, because they take longer to be degraded by the insect. These diuretic hormones make mosquitoes lose water after a blood meal, but we also found the peptidomimetic blocked sugar perception. This is a completely new and unexpected discovery.”

The research team localized these receptors in the feet and mouthparts of mosquitoes. What is really new, they said, is that this type of receptor proteins known as GPCRs, were not previously considered to be important for “taste” in insects and further, contact with the peptidomimetic made the mosquitoes fly away.

“In sum, we unequivocally verified this kinin receptor is present in the taste organs of the legs and labella, the pair of lobes at the tip of the proboscis.”

Pietrantonio said their observation that the peptide blocks sugar perception is interesting because the peptide is insect-specific, therefore, the receptor represents a target for further applied research to find ways to diminish the ability of female mosquitoes to feed. Doing so would likely reduce their lifespan or reproductive capacity.

“We had a lot of fun doing this research within the frame of an international, multi-institutional and multidisciplinary collaboration,” she said.

Institutions involved along with Texas A&M were the U.S. Department of Agriculture-Agriculture Research Service, Iowa State University and Université Paris-Saclay, France.

Pietrantonio said the team will continue to study the system in the hope of developing an effective mosquito feeding deterrent in order to stop what is arguably the greatest foe to mankind on earth.

 

AgriLife Extension experts inform Texans on protecting from Zika, other mosquito-borne diseases

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By: Paul Schattenberg and Steve Byrns, Texas A&M AgriLife Communications

SAN ANTONIO – Texas A&M AgriLife Extension Service entomologists are informing Texans on how to protect themselves from the mosquito vectors that spread Zika and other diseases.

The Aedes aegypti mosquito has been identified as the primary vector for transmission of the Zika virus. (Texas A&M AgriLife Extension Service photo)
The Aedes aegypti mosquito has been identified as the primary vector for transmission of the Zika virus. (Texas A&M AgriLife Extension Service photo)

“The ongoing outbreak of the Zika virus has spread throughout most of South America, Central America and the Caribbean,” said Sonja Swiger, AgriLife Extension entomologist, Stephenville. “The effects this virus will have on the United States are not entirely known, but experts are concerned about the possibilities.”

According to health officials, more than 350 travel-associated cases of Zika have been confirmed in the U.S., with 27 to date being in Texas. All of these cases occurred when the affected individual traveled to an endemic location and was bitten by an infected mosquito.

“The primary means of contracting Zika virus is through the bite of an infected mosquito, but it can also be transmitted sexually through semen,” Swiger noted.

The Centers for Disease Control and Prevention officially confirmed Zika virus as the cause of the increased cases of microcephaly in newborns that have been occurring in Brazil and other countries since fall 2015.

“Microcephaly is a condition affecting unborn children where the baby’s head is much smaller than expected,” said Swiger, who recently coordinated the North Texas Mosquito Education Conference in Grapevine and is conducting workshops throughout Texas.

“This occurs due to the decreased development of the baby’s brain while infected with the virus. Microcephaly can occur under other conditions but a significant increase of cases has been seen in Brazil since fall of 2015 and new cases are now being reported in Columbia.”

Swiger said the CDC is instructing pregnant women or women who plan to become pregnant to not travel to endemic outbreak areas at this time. The CDC’s website also has tips for men who plan to visit endemic areas at http://wwwnc.cdc.gov/travel/page/zika-travel-information.

“Thus far, Zika is not here in the Texas mosquito populations, but what the future holds for Zika in the U.S. is not entirely known,” Swiger said.

Previous diseases have entered the U.S. by means of travelers bringing them in, but have failed to infect the local mosquito populations long term, she said.

“The Aedes aegypti mosquito is the main vector of the Zika virus, as well as dengue and chikungunya,” said Molly Keck, AgriLife Extension entomologist, Bexar County. Keck recently presented mosquito education programs in Bexar, Comal and Atascosa counties.

“Health professionals have established a strong connection between the Zika virus and Guillain-Barré syndrome and microcephaly, as well as an autoimmune disease with neurological symptoms similar to multiple sclerosis,” Keck said. “And while media reports tend to emphasize the risk to pregnant women, the virus holds potential dangers for people of all ages.”

The National Center for Atmospheric Research has mapped the U.S. cities which it has determined have the highest risk for Zika. (Graphic courtesy of NCAR)
The National Center for Atmospheric Research has mapped the U.S. cities which it has determined have the highest risk for Zika. (Graphic courtesy of NCAR)

Houston, Dallas, San Antonio and Brownsville have been identified by the National Center for Atmospheric Research as some of the highest-risk cities in Texas for Zika. According to public health officials, if it does enter Texas it will likely begin as small “pockets” of locally acquired human cases that are the result of infected travelers returning from countries where the disease is endemic.

“Currently the chances are slim for anyone in Texas to get a disease such as Zika or chikungunya, but there is a possibility these could become endemic through transmission by the Aedes aegypti, which is prevalent in this state,” Keck said.

She explained chikungunya was recently brought to the U.S. by travelers returning from places where the disease is endemic. Its symptoms include fever and joint pain, headache, muscle pain and swelling.

Keck also noted the hundreds of cases of another mosquito-borne disease — West Nile virus — in Texas during recent years. According to the Centers for Disease Control and Prevention, in 2013 there were 183 human cases of West Nile in Texas. In 2014, there were 379 cases, and in 2015 there were 252 cases.

“The common denominator in each of these diseases is there is a mosquito vector that transmits them,” she said.

There are various locations in the typical backyard that can serve as a breeding ground for mosquitoes. (Texas A&M AgriLife Extension Service graphic)
There are various locations in the typical backyard that can serve as a breeding ground for mosquitoes. (Texas A&M AgriLife Extension Service graphic)

Both Keck and Swiger said the best means to defend against any mosquito-borne illness is to eliminate the vector or, if that is not possible, to defend against it using what they call the “four Ds.”

The Ds are to dress in long, loose-fitting, light-colored pants and shirts; drain any standing water from containers, ponds, tires, gutters, etc. around the home; reduce outdoor activity during dusk and dawn;  and defend using a U.S. Environmental Protection Agency or CDC-approved insect repellent.

Keck recommended homeowners “attack the mosquitoes at the larval stage” by removing standing water and using mosquito dunks in areas where they might breed.

“Homeowners should apply their efforts to draining and removing the items that might make for a good mosquito breeding ground and/or putting mosquito dunks into any pools of standing or stagnant water,” she said. “A mosquito dunk is a small, brown donut-looking object that floats on water and slowly dissolves, releasing a bacterium that kills mosquito larvae.”

Keck said generally it’s a waste of time, money and effort for the average homeowner to try and control mosquitoes at the adult stage.

“The best you can do when they’re at the adult stage is try to avoid them. If that’s not practical, be sure to wear a good repellent when outdoors.”

Additional information on Zika can be found at these websites of the Texas A&M University System: http://preventingzika.org and https://vitalrecord.tamhsc.edu/zika360.

For more information about mosquito types, biology and control, go to http://mosquitosafari.tamu.edu/.

AIBS to Convene Expert Panel Webinar on Science of Zika, Potential for Genetic Control

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Washington, DC – The Zika virus is the most recent example of a virus spreading rapidly around the world with the assistance of an animal vector – in this case the mosquito Aedes.

On March 15, 2016, the American Institute of Biological Sciences will convene a meeting of scientific experts to discuss the epidemiology of Zika, the potential for genetic control of the mosquito species that transmit it, and the ethical issues associated with the use of this new biotechnology. This webinar program is free and open to the public, but space is limited and pre-registration is required.

The extraordinarily fast spread of the Zika virus has prompted international concern because of its apparent link to birth defects, including microcephaly, in infants born to infected women. The virus may also be linked to cases of Guillain-Barré syndrome, an immune disorder. The World Health Organization has declared the Zika outbreak an international health emergency.

“The control of this disease, among other emerging diseases, is a challenge as people routinely travel around the world, global commerce provides increased opportunities for animal vectors to move into new environments, and climate change allows species to invade new habitats, often exposing the people in the colonized area to new pathogens,” said Dr. Robert Gropp, AIBS Interim Co-Executive Director.

The plants, microbes, and animals with which we share the planet provide us with life sustaining benefits every day. Periodically, however, some of them threaten our well being, such as in the case of Aedes and the Zika virus.

A way to slow the spread of Zika is to control or eliminate Aedes, which is also responsible for the transmission of dengue and chikungunya virus, among other pathogens.

“One line of research to suppress Aedes populations involves a “gene drive,” a genetic construct that once introduced into wild populations is expected to spread rapidly. Such an approach could be designed to bring about a population crash, for example, by distorting the sex ratio in mosquito populations,” said Gropp.

Despite the promise, using gene drives to control wild species raises ethical questions, some of which will be considered in this program. The webinar will also explore aspects of Zika epidemiology and biology.

Speakers are:

  • Davidson H. Hamer, MD, Boston University School of Public Health, Center for Global Health and Development
    Dr. Hamer is a board-certified specialist in infectious diseases, with a particular interest in tropical infectious diseases, and has twenty years of field experience in neonatal and child survival research including studies of micronutrient interventions, maternal and neonatal health, malaria, pneumonia, and diarrheal diseases. He is currently the Principal Investigator for the GeoSentinel Surveillance Network, which performs active surveillance for emerging infections such as Zika using returning travelers, migrants, and refugees as sentinels of disease transmission.
  • Zach N. Adelman, PhD, Virginia Tech, Department of Entomology
    Among Dr. Adelman’s research interests are genetics, gene control, and mosquito-pathogen interactions. Little is known about how mosquitoes defend themselves against foreign DNA elements. What are the effects of transgene insertions on chromosome structure? Will the mosquito recognize and shut down a transgene over time? And what effect will this have on the potential for genetic control? The answers to these questions are of vital importance to the implementation of a successful genetic control strategy.
  • Sahotra Sarkar, PhD, University of Texas, Austin, Department of Philosophy
    Dr. Sarkar specializes in the history and philosophy of science, conservation biology, and disease ecology. He is Professor in the Departments of Integrative Biology and Philosophy at the University of Texas at Austin. He is the author of  Genetics and Reductionism: A Primer (Cambridge, 1998), Molecular Models of Life (MIT, 2004), Biodiversity and Environmental Philosophy (Cambridge, 2005), Systematic Conservation Planning (with Chris Margules; Cambridge, 2007); “Doubting Darwin? Creationist Designs on Evolution” (Blackwell, 2007); and “Environmental Philosophy” (Wiley, 2012). He is the editor of fifteen works in the philosophy of science and the author of more than 200 scientific and philosophical articles.

To register for this program, please visit https://www.aibs.org/events/leadership/using-gene-drives-to-counter-zika.html .

The American Institute of Biological Sciences is a non-profit scientific organization working to provide decision-makers with timely, reliable, and vetted information. The organization does this independently and in partnership with its membership and business partners. To learn more about AIBS and its programmatic initiatives in science policy, education, scientific publishing, and scientific peer advisory and review services, please visit www.aibs.org.

Entomologists Discover New Way For Humans to Avoid Being Bitten By Mosquitoes

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Michael Sanders - 1 - Smaller
Michael Sanders stands with the mosquito cage used in the experiments. Photo by Rob Williams.

Summer is usually a time for get-togethers, barbecues, and spending time outdoors. It also means a time where mosquitoes are the most active.

A group of scientists, led by Dr. Jeff Tomberlin, is looking at a possible way of making humans unattractive to these biting insects by outsmarting mosquitoes simply by using the chemical communications systems bacteria on the skin.

Tomberlin, along with Drs. Craig Coates, Tawni Crippen from USDA and Tom Wood from Pennsylvania State University, and former TAMU graduate student researcher Ms. Xinyang Zhang have discovered that they can disrupt mosquito attraction to a potential blood-meal by manipulating microbial communication (aka, quorum sensing).

Quorum sensing is a communications system between bacterial cells that allows cells to communicate amongst each other for various functions. The cell-to-cell communication is used in controlling or preventing such processes such as swarming or reproducing. To communicate, bacteria produce compounds that contain specific biochemical messages. The more these compounds are made, the more concentrated the chemical message becomes until it creates a group response, thus creating a behavior. The behaviors are likely to occur when the chemical messages are very concentrated, which makes it easy for other organisms to listen to the “conversation”.

Tomberlin said that this had derived from his previous research in forensics that determine why blow flies were attracted to dead animals. Like with blow flies, Tomberlin said that mosquitoes are influenced by several factors. For mosquitoes, these include, but are not limited to, the volume of carbon dioxide exhaled, our body temperature, and body odor including those odors associated with the microbes on our skin. He also said that the insects use chemoreceptors on their antennae to “listen in” to various communications systems of microbes on our skin.

He said that this “quorum sensing” of microbes ability has always occurred in nature, and the mosquitoes have evolved the ability to perceive these pathways via natural selection over time. The mosquitoes benefit from this ability by selecting a blood host based on the information received by the bacteria.

Tomberlin noted that if they can find the right code that the bacteria are producing to signal unattractiveness, this could be used to keep mosquitoes from biting us.

During the experiments, the group used a mutant form of bacteria that could be found on our skin (Staphylococcus epidermidis) and removed the genetic mechanism that encodes quorum sensing. They then carried out several experiments using blood feeder containers covered either with the silenced or unmodified wild-type bacteria to test how attractive the feeders were to the female Aedes Aegypti, which is known to be the main vector for yellow fever, he said.

Tomberlin said that each of the feeders was fitted with a paraffin film containing a millimeter of rabbit blood that was injected between the flask and the film. The feeders were then kept at average body temperature via warm water pumped through the flask and placed in mosquito cages containing 50 mosquitoes each for 15 minutes.

Some of the different scenarios tested included placing each of the feeders in separate cages, then putting both types in the same cage at the same time. Based on the results, Tomberlin said that they believe that inhibiting bacterial communications could lead to newer, safer methods for deterring mosquitoes than conventional methods that include DEET.

Tomberlin also said that this discovery of manipulating bacterial conversations has other applications, including blocking communications between bacteria in the lungs of patients with cystic fibrosis that lead to new treatments and helping to reduce pipeline corrosion that could be caused by microorganisms.