Know your Zika virus facts for patients traveling in affected areas

March 08, 2016

Paul Sehdev, M.D., MS, FACP, FIDSA, medical director, Oregon Region, Medicine Program/Service line and Infectious Disease Consultants/Traveler's Clinic

In the first century, author and philosopher Pliny the Elder wrote, "There is always something new out of Africa." Today, his ancient observation still rings true. Recent decades have seen novel viral infections such as HIV, dengue and chikungunya emerge from Africa and disseminate worldwide. Zika virus is the latest virus to do so.

The Zika virus is not really new. It was first isolated in 1947 from a rhesus monkey in the Zika forest near Entebbe, Uganda (hence the name). During the next 70 years, only 14 cases and zero outbreaks of Zika virus infection were reported. Things changed in 2007 when an outbreak of more than 100 Zika cases occurred in Micronesia. Our current outbreak began in March 2015 in Brazil, and in less than a year it has spread to 30 countries in the Americas.

Zika virus is primarily transmitted through the bite of infected Aedes mosquitoes, the same mosquitoes that spread chikungunya and dengue fever. These mosquitoes are aggressive daytime biters that prefer to feed on humans. The mosquitoes are not native to Oregon. Zika also may be transmitted from a pregnant mother to her baby during pregnancy or birth. Sexual transmission of Zika virus has been reported.

Eighty percent of Zika virus infections are asymptomatic. Fever, rash, joint/muscle pain, headache and conjunctivitis are common symptoms. The incubation period (the time from exposure to symptoms) is not known but is thought to be a few days to a week. The illness most often is mild and self-limited, lasting about a week. Patients usually aren't sick enough to require hospitalization, and death from Zika is very rare. Guillain-Barré Syndrome (GBS), a disorder in which a person’s immune system targets nerve cells causing muscle weakness and paralysis, may complicate Zika virus infection.

Microcephaly is a birth defect in which a baby’s head is smaller than expected when compared to babies of the same sex and age. Babies with microcephaly often have smaller brains that may not have developed properly. In Brazil, a temporal association between mothers infected with Zika virus during pregnancy and microcephaly has been observed. However, it’s not clear if this association is one of cause and effect. While this is being investigated, pregnant women or women trying to become pregnant should avoid non-essential travel to outbreak-affected areas.

Zika infection should be considered when symptoms are present in an ill traveler returning from an affected area. PCR testing can detect the virus in blood during the first week of illness. After that, diagnosis relies on serologic tests. Test results can be difficult to interpret since cross-reacting antibodies from other flavivirus infections (e.g., dengue or West Nile) or vaccines (yellow fever or Japanese encephalitis) may cause false positive test results. The Centers for Disease Control can perform additional assays to help in determining a diagnosis.

Treatment is supportive. There are no vaccines or medicines that can prevent Zika infection. Mosquito avoidance is the key to preventing infection. Wearing long-sleeved shirts and pants, staying in places with air conditioning or window screens, and sleeping under a mosquito net are some ways to protect yourself. Use EPA-registered insect repellents such as DEET – these agents are safe and effective, even for pregnant and breast-feeding women.

The current outbreak is dynamic and changing day to day. For the latest updates, go to or For patient-specific questions, please contact Providence Traveler’s Clinic at 503-216-7000 or send your question to the Ask ID service using EPIC (phone note to P Ask ID pool).