The Zika Virus: Update on an Epidemic

Living up to its description as a “public health emergency of international concern” by the World Health Organization (WHO), the Zika virus continues to spread rapidly across Brazil and Latin America.

While the WHO, the Centers for Disease Control and Prevention (CDC), and national ministries of health have launched significant and coordinated efforts to better understand, track and contain the mosquito-borne epidemic, it remains a public health threat—primarily to pregnant women through its association with severe birth defects.

To date, local transmission of Zika has been reported in 41 countries (since 2015). In the U.S., more than 150 travel-associated cases of the virus have been documented across 30 states. New Hampshire joined that list last week, announcing its first case of Zika infection. More information about Zika can be found here.

Elizabeth Talbot, MD, an associate professor of medicine at Geisel School of Medicine, who specializes in infectious disease and international health at Dartmouth-Hitchcock and also serves as New Hampshire’s deputy state epidemiologist, talks about what the scientific and medical communities are learning about Zika, its implications, and what people can do to protect themselves.

Elizabeth Talbot, MD
Elizabeth Talbot, MD

Q: How do people get the Zika virus?

Talbot: The virus is primarily spread by the Aedes aegypti mosquito, which can be found anywhere in the Americas, from Argentina to the southern U.S. It’s a very competent vector, that is, it’s a mosquito that can carry a lot of different diseases, including dengue, chikungunya, and yellow fever. Many U.S. health officials are concerned that these mosquitos in the southern U.S. will become infected (if they bite an ill return traveler who has virus in their blood) and transmit the virus person-to-person.

We also now know, through a growing number of proven cases, that the virus can be transmitted through sexual contact, which was not recognized during the previous decades of Zika transmission in Africa or Asia. No one saw this coming.

The risk of Zika is predominantly to women who are pregnant, because this virus has a unique ability to cross from mother to baby and cause severe birth defects like microcephaly—a condition which causes babies to be born with unusually small heads, and in many cases damaged brains.

Q: Has a causal link been established between Zika and microcephaly?

Talbot: I don’t think there’s very much doubt anymore that this virus causes these defects, as well as Guillain-Barre syndrome, an autoimmune disorder that we often associate with viral infections. There are many different levels of evidence that make these associations seem extremely likely. As we speak, the CDC and other stakeholders are conducting case control research in the epicenter area of Brazil to try to pinpoint the causes and provide more definitive answers about the risks.

Q: What can people do to protect themselves?

Talbot: First and foremost, pregnant women should avoid traveling to Brazil or any area where Zika is known to be circulating. They should also avoid unprotected sex with any male traveler to these regions.

In general, anyone traveling to the tropics should be fastidious about preventing mosquito bites—that’s the best protection. Using insect repellant (applying DEET according to the manufacturer), using permethrin in your clothing and covering as much of your body as possible, and using bed nets when you’re sleeping are all highly effective methods of preventing Zika and other mosquito-borne diseases.

We’re challenged by the fact that about 80 percent of Zika infections are asymptomatic, so a man who travels into these regions cannot be sure whether or not he has had disease based on his symptom history. The rare person who actually has symptoms is likely to experience body aches, fever, rash, joint pain, and also may have conjunctivitis or red eye.

Q: Are there misconceptions you’re hearing locally that you’d like to address?

Talbot: Yes. The first is that Zika is transmissible from person-to-person in our region. That is not the case, except through this rare sexual transmission from a male traveler to his partner. The mosquitos that transmit Zika are not found in New Hampshire.

The second is that the virus can affect long-term pregnancy safety. For women who are not pregnant or planning pregnancy in the immediate future, who travel to an affected area and get the virus, there’s no evidence that it will persist in their body for a long period of time.

The incubation period, which is the time between when an infected mosquito bites to the time the virus shows up in a person’s blood, is two weeks or less. It’s then active for only 4 or 5 days, so the window of time that the virus can do damage is fairly narrow.

Q: Looking ahead, what are the projections for Zika?

Talbot: The WHO estimates there will be up to 4 million cases this year in the Western Hemisphere. It’s important to note that we still have much to learn about Zika and how we can contain it—our efforts in this regard won’t be a sprint, but a marathon.

The priority the WHO has given this is an important first step. It facilitates the kind of resource allocation and mobilization of technological support we need for mosquito control efforts, and to develop diagnostics, vaccine, and treatment.