As an entomologist, Nathan Burkett-Cadena studies mosquitoes and why they bite the animals that they do -- whether they be people, deer, birds, bullfrogs or snakes, just to name a few.
“I have been fascinated by insects since I was a child,” said Burkett-Cadena, an assistant professor of entomology with the University of Florida Institute of Food and Agricultural Sciences. “However, it was in graduate school at Auburn University that I became enamored of mosquitoes. The more I learned about the impact that mosquitoes have on human health, I became certain that I wanted to devote my career to studying them.”
Burkett-Cadena, who conducts research at the Florida Medical Entomology Laboratory in Vero Beach, investigates how mosquitoes interact with people and other vertebrate animals.
These insects aren’t just nuisances, and they don’t just give you an itch. Some mosquito bites transmit viruses that can sicken or even kill a person, in a worst-case scenario. Burkett-Cadena is hoping to find ways to prevent the most perilous mosquito-bite scenarios.
Most recently, he and a team of colleagues published a study in the Journal of Medical Entomology in which they found that the mosquito species known as Culex erraticus may be just as important as Culiseta melanura in transmitting the Eastern Equine Encephalitis virus to humans.
Specifically, the study -- led by Thomas Unnasch, a distinguished health professor at the University of South Florida -- showed that Culiseta melanura is actually about twice as important at transmitting the EEE virus as Culex erraticus. Despite its inefficiency for carrying the virus from one animal to another in a lab setting, there are far more Culex erraticus mosquitoes in the southeastern United States. It also feeds on a wider range of animals than Culiseta melanura. Those factors pique scientists’ interest in the Culex erraticus, Burkett-Cadena said.
“Our study shows us how a mosquito that is a relatively poor transmitter of the virus can actually have a huge impact on human health, due to its overwhelming abundance,” Burkett-Cadena said.
Researchers at USF and UF/IFAS believe that Florida may serve as a reservoir for the EEE virus, and that the pathogen survives in wildlife between outbreaks. If correct, this hypothesis could explain how EEE virus is periodically reintroduced to other parts of the U.S.
The disease caused by EEE in humans is rare: Only 4 to 5 percent of people who are infected with the virus develop full-blown Eastern equine encephalitis disease, and only about five to 10 cases of the disease are reported annually to the U.S. Centers for Disease Control and Prevention. But more than one-third of the people who contract the illness die, and many who survive suffer brain damage. EEE is more dangerous to horses -- they have a mortality rate of 70 to 90 percent.
Burkett-Cadena focuses his research on preventing mosquito-borne diseases, such as dengue, chikungunya, EEE and Zika. Such diseases account for an estimated 17 percent of infectious diseases globally, according to the World Health Organization. Malaria, the most deadly mosquito-borne disease, caused an estimated 627,000 deaths in 2012.
Two years ago, Burkett-Cadena published a study that showed mosquitoes bite male birds nearly twice as often as they bite females, a finding that he said may help scientists understand how to prevent some viruses from spreading to humans.
Burkett-Cadena found mosquitoes bite male birds 64 percent of the time, compared to 36 percent for females. That marked the first step for scientists to try to determine why mosquitoes bite men more often than women in some parts of the world and vice-versa in other areas.
“Understanding why mosquitoes bite males more often than females may lead to novel strategies for interrupting disease transmission,” he said.
Now that scientists know mosquitoes suck blood from male birds more than females, they can turn their research attention globally. For example, the human malaria parasite can be found five times more often in men than women in China, according to a 2009 study. Burkett-Cadena said that researchers using his method could investigate whether mosquitoes bite men more often than women and if that is the reason Chinese men are more often infected with malaria.
“What if some behavior men are engaging in is exposing them more to mosquitoes?” he said. “It’s not that mosquitoes prefer to feed on men, but it’s probably something men are doing.”
In yet another study, published last year, Burkett-Cadena and his colleagues assessed whether low-cost materials could be combined to produce carbon dioxide gas, which is used to lure mosquitoes to monitoring traps.
Monitoring the insects is a critical step in management efforts that lessen the risk of human disease. Insect experts the world over use carbon dioxide, the same gas that humans exhale, to attract blood-feeding bugs to traps, so they can measure their abundance, test them for diseases and make decisions about whether or not to use control options. Commercial forms of carbon dioxide are readily available in the U.S., as bottled gas or dry ice, but those ingredients are very expensive in Africa, where the team conducted part of the study.
“We developed and tested inexpensive and easily reproducible methods of carbon dioxide production from the combination of acids and carbonates,” Burkett-Cadena said. “Our works shows that a variety of readily available natural carbonate materials, such as limestone, chalk, seashells and baking soda, can be combined with weak acids, like vinegar, to produce carbon dioxide.”
As for the future, Burkett-Cadena is researching several arthropod-borne diseases such as epizootic hemorrhagic disease virus, which affects deer and is carried by biting midges, also known as “no-see-ums.” He’s also continuing to study Eastern equine encephalitis and Everglades virus.