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Q+A: Is Zika Virus a Threat to the United States?


Aedes aegypti is a species of mosquito that can spread Zika virus, yellow fever, dengue and West Nile virus. (James Gathany / CDC)

A mosquito-borne illness that has spread throughout South America, Central America and the Caribbean adds fuel to growing fears about where viruses could strike next, infectious disease experts say.

The Zika virus, previously restricted to the Eastern Hemisphere and thought to be pretty harmless, began to spread west last spring. Now it is causing alarm after scientists linked the virus to a sharp rise in babies born with microcephaly in Brazil. Microcephaly is a congenital brain defect in which an infant’s head is abnormally small.

Last Friday, the Centers for Disease Control and Prevention (CDC) issued an advisory for pregnant women, recommending that they avoid traveling to any of the countries experiencing high rates of Zika infection.

So far, the dozen cases of Zika virus that have shown up in the United States have come from travelers who have brought it back to the country. But with warmer climates, increased travel and urban crowding, are Zika and other once-ignored viruses now threats to States?

Two professors from Drexel’s College of Medicine weighed in about the threat of disease spread and what it means for humans living in an increasingly globalized world.

Akhil Vaidya, PhD, is a professor and director of the Center for Molecular Parasitology in the Department of Microbiology and Immunology. He studies malaria.

Why do mosquitoes spread so many diseases?
Female mosquitoes — which are the only ones that bite, by the way — need to take a blood meal in order to reproduce. They can bite any vertebrate — birds, pigs, even reptiles, and, of course, humans. And since they are so mobile, they easily spread disease from one host to another. They act as syringes for transmitting viruses. What is happening now with the Zika virus, is what is happening among many other arboviruses, like dengue, West Nile and chikungunya: They all seem to be spreading westwards. And we’re undergoing a pandemic.

Why are people so worried about Zika?
The scary part of the infection is the birth defects that it is causing. In an adult, the infection itself is not that complicated, but the effects for a fetus seem to be really drastic. There have been thousands of cases of suspected microcephaly in Brazil since October, and there is a strong suspicion that is caused by Zika.

Why have birth defects not been linked to Zika in the past?
We don’t know anything about the biology of the virus. To cause birth defects, the virus would have to cross the placental barrier and make its way to the fetus. There have not been any reports of that happening before what happened in Brazil. Is it a new property that the virus has acquired? No one knows.

Does the rapid spread of the virus in Latin America mean that a larger outbreak could happen in the United States or other nations?
We know Zika is spread by species of Aedes mosquitoes. But under that genus of mosquitoes, there are all different species prevalent in different parts of the world. If the virus adapts to transmission by a species more commonly found in the United States, then it could cause an outbreak in the United States, yes.

Why should we be concerned about the spread of Zika and other infectious diseases?New and emerging diseases are a real problem. We exist in a buggy world. Viruses are lurking out there, and they jump, and they find new ecological niches. It’s what happened with Ebola. HIV is another great example. The virus jumped from primates to humans, adapted to humans, and then caused a pandemic. We are in the middle of all of these pandemics. The viruses may have always existed with us, and we figured out how to live with them, but now they are getting to us in new ways and causing new problems.

What is the solution?
The solution is more research and vigilance, finding out new ways to detect them and prevent them from spreading, so they can be contained and nipped in the bud.

Hans Schlecht, MD, is a clinical associate professor in the Division of Infectious Diseases and HIV Medicine. He heads the Drexel Medicine Travel Health clinic. 

Is it surprising that the virus spread like it did?
International travel by millions of people is going to spread disease. This is just another example of a disease traveling outside of its home range, similar to West Nile virus and chikungunya. Now it’s been able to enter a population that has mosquito hosts that are flying around everywhere, and so the virus spread like wildfire.

What are symptoms of Zika?
Most people don’t even know that they have the infection. Maybe they’ll have some aches and pains, but no big symptoms beyond that. But a fetus is pretty sensitive to a lot of things, whether it’s chemicals, toxins in foods, etc. and it definitely seems like the outbreak of microcephaly cases is related to the virus making its way to Brazil. But scientists are hesitant to jump to conclusions.

How will scientists be able to definitively link the birth defect cases to the Zika virus?
It’s really tough to study this. They are probably going to take the mothers of newborns who have microcephaly and test the placenta for X, Y and Z. For a live birth, they’ll want pathology on the placenta, they want frozen tissue to be tested, and I imagine they’ll also check for dengue to make sure these aren’t women who are co-infected. Maybe if you get infected with dengue and Zika at the same time, your risk goes up. And maybe they’re not picking up that signal. There may be more to the story than just Zika. Maybe there is something to the environment that can’t be explained.

What advice would you offer to travelers going abroad?
No one should worry about going to Canada. It depends where you’re going. Use the CDC travel website, and do your research. You can look at the country you’re going to, read travel notices and find out exactly what vaccinations you will need to travel. Your primary care physician can offer basic vaccinations, but if you need something like a Typhoid vaccination, you’ll have to book an appointment with a travel health clinic.

Members of the news media interested in talking to Vaidya or Schlecht should contact Lauren Ingeno at 215-895-2614 or

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