After the recent discovery in Washington, D.C. of mosquitoes capable of carrying and transmitting the Zika virus, worry over the disease — which can lead to severe birth defects — possibly spreading across the continental United States has grown. According to David Severson, a professor in the department of biological sciences, this panic over is not grounded in the reality of the situation.
Severson said his primary research areas include entomology, evolutionary biology, genetics and genomics and infectious and vector-born diseases. Though Severson does not work directly with the Zika virus, he has studied the mosquitoes that transmit the virus.
“People’s paranoia about Zika, in some ways is overdone. Some of these other viruses are much more of a threat when you go to these places,” Severson said.
Those more threatening viruses include the dengue virus and yellow fever virus, both of which are of the Flaviviridae family along with the Zika virus. Additionally, the chikungunya virus, though of a different family, is carried through the same type of mosquito. All four related viruses are found in the “new world tropics,” Severson said, though none of the viruses are endemic, but rather were brought over from Africa and southeast Asia during colonialism.
“We’re in a global society,” Severson said, “In most cases, with all four viruses, you may never realize you’re infected. So … the virus is circulating in your system, but you either hardly get sick at all, or you might feel like you have a slight cold, something like that.”
Severson also said despite the recent discovery of mosquitoes that are capable of carrying the Zika virus in Washington, D.C., “there’s little transmission in the continental U.S., although there is certainly potential for transmission.”
“As far as we know, there is no virus, there has been no active transmission in the Washington, D.C. area,” Severson said, “But it’s at least five years that that population has been there … so if you have active breeding during the summer, and you have someone come in from Brazil that lives in that neighborhood, you have the potential for a short term, seasonal outbreak of these viruses.
“We have had dengue virus endemic transmission in southern Florida for probably the last three or four years, probably a little longer,” Severson said, “So we certainly have the potential for this coming in to the southern warmer areas around the east coast, then around the gulf and then along the Texas-Arizona-California-Mexican border.”
If the Zika virus were to be transmitted widely across the United States, Severson said, “it probably won’t be as severe” as in Central and South America.
“In the U.S. we have different standards of living: we tend to like air conditioning, we like screens on our windows, so we have everything closed up,” Severson said. “So we have limited contact compared to … [for instance] Brazil, you might not even have screens, people like to have the breeze blow through, so there’s a lot more opportunity for exposure to being bitten by a mosquito. And there’s a lot of opportunity for breeding sites, these things will breed in any little container that holds water for a couple weeks … and people don’t tend to have dependable municipal water in some places, so they’ll tend to hoard water in gallon drums or big plastic tanks … and those are the prime breeding grounds oftentimes.
“So in the U.S., I suspect we’ll likely have some transmission. It’s the dry season in the new world tropics right now, so mosquito breeding is at the lowest point of the whole year, disease transmission is at the lowest point of the whole year. Rainy season will start in early June and ramp up, and that’s when the mosquito breeding will start, and shortly after that there will be a rapid spike in disease transmission.”
Though there is no cure or treatment for the Zika, dengue or chikungunya viruses yet, Severson said that curbing outbreaks would begin with combatting insecticide resistance.
“Right now with all those viruses, the only one for which there is a good vaccine is yellow fever,” Severson said, “There is no good vaccine for the other three. And there are no drug treatments. If you get sick, you have to power through it and get better. So right now the only way to deal with outbreaks of this or to try to prevent outbreaks is to try to control the mosquito population. So there’s massive insecticide use throughout the tropics to try to control the mosquito population, and you get pretty strong genetic resistance to those. People are looking at different ideas on how to deal with this.”
Severson said his recent research with the mosquitoes that carry the dengue and Zika viruses has focused on “understand(ing) various pathways, what genes are up or down and regulated.”
“We may be able to identify chemicals and drugs that you could take so if you were infected … you wouldn’t transmit it through the mosquito to another human host, so you could break the cycle that way,” he said.
Severson said he hopes that his research with mosquitoes could lead to possible vaccination developments in the future, as well as species-specific pesticides that would cut back on the use of pesticides that “blanket kill every insect that’s out there.”
“If we understand what makes a mosquito genetically competent to transmit this pathogen, then perhaps we can engineer a genetically modified mosquito that’s no longer capable … [of transmitting] that virus,” Severson said, “Then look into actually releasing those into the environment. So there’s a whole host of things that people have talked about, and some of those are actually in practice.”
According to Severson, the Zika virus can only be transmitted from person to person in two ways. The first is through a blood transfusion, if the blood donor happens to be viremic. Severson said if a person goes to donate blood and finds that he or she is carrying the virus, however, “they might just say come back in a couple weeks and then you can donate blood.”
Zika virus can also be sexually transmitted, Severson said, although this is “completely unusual,” noting there have only been two documented cases of sexual transmission.
“The point to remember with Zika is that this virus has been around for a long, long time,” Severson said. “And usually it’s been most people, probably 90-plus percent of people, either don’t know they’ve had it or they get some mild (symptom), a cold, a flu or they just don’t feel well. … Microcephaly in Brazil, that’s brand new, and outside of that, if you’re not a young woman in a child-bearing age where you have the potential to get pregnant, it’s generally a benign problem.”
As far as taking precautions against these viruses, Severson said it is important to note the time of day in which mosquitoes transmitting Zika virus bite.
“These mosquitoes are day biters, they bite people during the daylight hours,” Severson said, “You hear about malaria and people sleeping under bed nets, but they won’t stop Zika virus. The mosquitoes that transmit malaria are night biters. So right now if you go to Brazil, for example, it does absolutely zero good at preventing Zika or dengue or chikungunya to sleep under a bed net. The mosquitoes that transmit these viruses are most active right at dawn and right near dusk. … That coincides when people are the most active, getting up to go to school or go to work, you’re coming home … especially in the tropics.”
Severson said U.S. citizens planning on traveling to Brazil and other areas in which Zika outbreaks have been prevalent shouldn’t worry too much about the dangers of that virus, but should focus on avoiding the dengue virus.
“Globally, there are about half a million hemorrhagic fever forms of (dengue) virus per year where you get internal hemorrhaging, and if you don’t get adequate healthcare, you could actually die from it,” Severson said, “So for people going to [tropical areas], dengue is a much greater threat. And that’s another one where you get infected and in most people you get a mild illness. The same thing with chikungunya. It doesn’t tend to cause [fatality], but habitual neuropathy in some people. … So of all the other things that are out there, outside of microcephaly coming through pregnant women, Zika is a pretty benign virus.”
