Another Reason to Hate Mosquitoes

A USF research project finds that the “flying syringes” are packing a multitude of viruses.


By Vickie Chachere

USF News


ST. PETERSBURG (June 9, 2011) – Mosquitoes are undeniably nasty little creatures. They carry horrendous diseases such as malaria and yellow and dengue fevers and devastating illnesses like Eastern equine and St. Louis encephalitis.


As if this global scourge needed one more reason to make it unpopular, a new USF project now finds the pests laden with a wide variety of viruses, including those related to herpes, pox and human papillomaviruses. Mosquitoes - said virus hunters Terry Fei Fan Ng, a recent USF PhD graduate, and  Mya Breitbart, an assistant professor in USF’s College of Marine Science - are “flying syringes” that their research shows can be exploited for virus surveillance.


The most surprising discovery in their study is that the majority of DNA viruses found in mosquitoes had not been seen before, the researchers said.


“When I look at the data, nine out of 10 of the viral sequence is novel,” Ng said. “This means that even after decades of research, we still only know a fraction of all the viruses out there.


“Since animal and human viruses are often interlinked, one of the biggest questions in science is what animal viruses are out there. The challenge of characterizing viruses in animals is that you have to collect samples from enough individuals – this can take a tremendous effort considering the number of animal species out there.”


Their findings were published Monday in the journal, PLoS One. The study was conducted in collaboration with researchers at San Diego State University, the Genome Institute of Singapore and the Wildlife Disease Labs at the San Diego Zoo’s Institute for Conservation Research.


While recent programs such as One Health and Global Viral Initiative have begun to investigate viruses in animals one species at a time, the new study funded by the Canadian Institute for Advanced Research and the National Science Foundation took on a different approach. It took advantage of the feeding behaviors of mosquitoes, specifically culex erythrothorax, a species known to feed on humans and a wide range of animals.


By investigating the viruses found in the mosquito, the researchers were able to take a snapshot of DNA viruses representing hundreds of human and animal hosts. The researchers used a technique developed by Breitbart, a biological oceanographer, which allows DNA to be extracted from viruses, sequenced and compared against databases of known viruses. The technique allows researchers to more rapidly identify viruses not known to exist.


 “Most studies of viruses in mosquitoes search for specific, well-known pathogens,” Breitbart said. “Our study is fundamentally different because it uses metagenomic sequencing to provide an overview of the diversity of the total viral community – including viruses that infect the many hosts the mosquitoes feed upon, as well as those viruses that infect the mosquitoes themselves.”


The study makes no conclusions on whether or how mosquitoes might transmit some of those viruses, but breaks new ground in understanding the wide variety of viruses that are present in mosquitoes.


The lab’s ability to sequence and identify never-before-seen viruses has recently shed new light in a series of recently published papers on insects – including whiteflies and dragonflies – carrying a diverse range of viruses. The latest study is the first time a plant virus has been identified in mosquitoes, they said.


Using a procedure called vector-enabled metagenomics – which allows the scientists to identify a wide range of viruses quickly through DNA analysis – the project provides a snapshot of the diversity of DNA viruses present in mosquitoes.


The project specifically looked at three different species of mosquitoes captured at three different times and places in San Diego County in a trap baited with dry ice; the viruses were extracted from the mosquitoes’ bodies, purified, sequenced and then compared to known virus DNA sequences.


The scientists found a series of animal viruses, including those related to herpes viruses and pox viruses;   papillomaviruses was found in one mosquito. The researchers believe the mosquito picked up the papillomaviruses from the host’s skin during feeding – some 80 percent of normal human skin harbors papillomaviruses but the virus has never before been detected in mosquitoes.


The researchers cautioned that their work did not explore whether humans can contract those viruses from mosquitoes and concludes only that the virus is present. However, now that a range of viruses has been uncovered in mosquitoes, the information can be used to develop specific tests to determine if these viruses are being transmitted by the pests, the scientists said.


 “Many, many viruses can be drawn from humans to mosquito, but only a few are proven to be spread by mosquitoes,” Ng said. “For mosquitoes to spread a virus like dengue fever, the virus has to evolve and be able to replicate itself in mosquitoes, transfer itself to the salivary gland, and then be injected into humans.”


Vickie Chachere can be reached at 813-974-6251.