Zika virus epidemic: Should the United States be worried?

Unless you’ve been living under a rock, chances are you’ve heard of the Zika virus: a mosquito-borne pathogen which can also be transferred through sexual contact with an infected person.

According to the US Centers for Disease Control and Prevention (CDC), Zika is primarily spread through the bite of an infected Aedes species mosquito (Ae. aegypti and/or Ae. albopictus). While those mosquitoes were once exclusive to tropical or subtropical regions of the world, they can be found in most regions these days, thanks in part to human activity.

Zika infection is rarely fatal, and in fact, most people who contract the virus don’t even get sick enough to go to the hospital. However, the virus can also be transmitted from a pregnant mother to her unborn fetus, resulting in birth defects including microcephaly, a defect which causes the child to have a smaller-than-expected head and a poorly-developed brain.

Much of the concern regarding the Zika virus has centered around microcephaly, and while the CDC reports that (as of June 29) there have been approximately 3,000 reported cases of the virus in US states and territories, there is not currently concern of a major outbreak in the US. But could there be?

Understanding how Zika can (and can’t) be transmitted

We tend to view Zika transmission as such: a mosquito bites a person who is infected with the virus, then bites other individuals, thus transmitting the disease to them. However, as Dr. Alfred Scott Lea, director of the Infectious Diseases Clinic at the University of Texas Medical Branch, told redOrbit via email, this explanation is “perhaps a bit simplistic.”

“Mosquitoes can also transmit the virus transovarially to their eggs, which become larvae and then mature into adult mosquitoes,” he explained. “These adult offspring can then  transmit the virus contracted from its mother. Just exactly how much transmission is accomplished by each route of exposure is unknown… [but] to date, there is no vaccine or effective treatment.”

In addition to contracting the virus through mosquito bites, the CDC warns that the Zika can be passed from a pregnant woman to her fetus during the pregnancy or around the time of birth, but that there have not yet been any reports of an infant contracting the virus through breastfeeding. Infected males can also pass the virus sexually to their partners, and the virus can even be spread before the man begins experiencing symptoms, and after said symptoms pass.

As of February 1, there had been no confirmed cases of Zika being transmitted through a blood transfusion in the US, although several such instances have been reported in Brazil, according to the CDC. Those claims are being investigated. As of June 15, there has been one instance of the disease being contracted by a scientist who had been working in a US-based laboratory.

So, what are the odds of a Zika epidemic in the continental US?

We know that the virus has already crossed the border into our country –  and has already killed an unidentified elderly Salt Lake City woman who contracted the disease while traveling – but could mosquitoes turn a few isolated cases into a full blown national epidemic?

In June, the New York Times reported that the CDC was working on a blueprint to deal with just such an event, and they had drafted a 60-page blueprint laying out how to deal with domestic cases of Zika infection. As the CDC’s deputy director, Dr. Anne Schuchat, told the newspaper, “We know that Zika is a completely unprecedented problem and the front-line response is going to be crucial. The summer is starting, and the mosquitoes are coming.”

Recent reports reveal multiple cases of the virus appearing to spread through mosquitoes in Florida, leading researchers to believe that the virus has spread to mosquito populations in the United States.

mosquito biting skin zika virus

Recent Florida-based reports suggest that the virus could exist in US mosquito populations (Credit: Thinkstock)

However, health experts added that they do not anticipate widespread transmission of the virus in the states because most homes in the US are air-conditioned and people don’t leave their windows open without using screens.

Most of the US is less densely populated than Brazil, so it’s tougher for the short-lived mosquitoes to spread the disease. Ae. aegypti usually only flies about one city block before dying.

Nonetheless, Dr. Lea said that “most experts expect that we will see cases in the USA sometime in the near future,” and Dr. Peter J. Hotez, dean of the National School of Tropical Medicine at the Baylor College of Medicine, told Fox News that “all of the conditions where they’re present in Latin America and the Caribbean are also present in Texas and other Gulf Coast states.”

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center in Nashville, disagrees “I don’t think Zika will become widespread in the United States like it has in South America and the Caribbean,” he told WKRN-TV during an interview in May. “We could have some local introduction with a little bit of spread, but that shouldn’t alarm us because the response will be fast.”

“Many areas in the continental US, primarily in the Southeast and Gulf Coast regions, have mosquitoes that can become infected with and spread Zika virus, so it is possible that these imported cases could result in local spread of the virus in some areas,” the Department of Health and Human Services website said. “Limited local transmission may occur in the mainland United States, but we believe it is unlikely that we will see widespread transmission of Zika.”

How can Americans protect themselves, domestically and abroad?

There are currently no vaccines that can prevent Zika infection, and Dr. Schaffner told WKRN –TV that while “a large number of drug manufacturers… are working on a vaccine,” they are “not close.” In fact, he noted, such a vaccine is “a good year or more away.” So how can residents of the US protect themselves, both at home and when traveling to other parts of the world?

To avoid possible infection with the Zika virus, both Dr. Lea and Dr. Schaffner recommended wearing long-sleeved shirts and pants instead of shorts, and applying mosquito repellant exposed skin. Spend the night in enclosed, air-conditioned environments when possible, and sleep under  mosquito netting when that isn’t an option, they added.

Also, take steps to eliminate places around your home that could act as breeding grounds for mosquitoes. “An individual can practice basic environmental control by eliminating standing water in their immediate environment – like in birdbaths and old tires in the yard,” Dr. Lea told redOrbit.

Mosquito net preventing zika infected mosquito

Mosquito netting is an effective way to keep yourself safe if you can’t sleep with the windows closed. (Credit: Thinkstock)

“Sexually active women need to be very careful about achieving pregnancy if their partner has been to South or Central America where an exposure may have occurred,” he added. “The CDC recommends condom use during any and all forms of sexual activity for the entire duration of the activity for prevention.”

Tests can determine whether or not a person has either contracted to been exposed to Zika. These examinations are provided primarily by the CDC, some local health departments and laboratories. However, scientists at the University of Pennsylvania are developing an inexpensive test which could quickly and accurately determine if you came into contact with the virus.


Image credit: Thinkstock