Zika virus has been in the media recently and, even if your patients have not been asking about it, you might still be interested in following this developing story. Zika infections, in and of themselves, are not typically severe; however, the major concern is a proposed relationship between Zika virus infection during pregnancy and a baby born with microcephaly. So, what do we know?
Zika virus — the biology
Zika virus is a single-stranded RNA virus that is a member of the Flavivirus family. Other viruses in this family include dengue virus, West Nile virus and yellow fever virus. Transmission typically occurs through the bite of an infected mosquito; however, the virus can also be transmitted from infected women to their unborn babies, through sexual relations, via blood transfusions and from lab exposures. While theoretically possible, transmission through breast milk or organ transplantation has not been described to date.
Zika virus — the infection
About 80 percent of Zika virus infections are asymptomatic. And, while all ages can be infected, adults more often require medical attention. Most people with symptoms will have a rash (90 percent) and more than half will experience fever, arthralgia and conjunctivitis. About 4 or 5 of every 10 will have myalgia and headache. Retro-orbital pain, edema and vomiting will occur less often.
The course of disease is typically mild and rarely results in hospitalization or fatalities. Symptoms typically last about one week. While it is speculated that people infected with Zika may be more likely to get Guillain-Barré Syndrome (GBS), a causal association has yet to be proven.
Several diagnostic tests are available, but their accuracy depends on when specimens were collected relative to start of infection. These tests are currently only available at the CDC and a few state health departments. CDC is working to increase testing capacity at other locations. Serum collected within seven days of symptom onset can be tested for viral RNA by reverse transcriptase-polymerase chain reaction (RT-PCR). Serum collected four days or later after onset of illness can be tested for IgM and neutralizing antibodies. Immuno-histochemical staining for viral antigen or RT-PCR can be used for fixed tissues, such as placental tissue and umbilical cords from infants born with microcephaly, or from mothers whose testing for exposure to Zika virus during pregnancy were positive or inclusive.
Diagnosis can be complicated by the similarity of symptoms caused by dengue and chikungunya. Dengue is most important to rule out because of the importance of proper management to improve outcomes. Symptoms of dengue but not the other two conditions can include hemorrhage and shock. Zika is the only one of these three viruses that causes conjunctivitis, and rash is most common, but not limited to Zika.
Treatment is supportive; no antiviral therapy is available. Aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs) should not be prescribed until after dengue is ruled out because of the potential for hemorrhage. Any suspected cases of Zika should be reported to the health department and subsequently to the CDC as it is a nationally notifiable condition (arboviral disease).
A vaccine is not available, but several different approaches to vaccine development are being evaluated. It will likely take several years before a sufficient supply of a licensed vaccine is widely available. In the meantime, the best protection is to reduce exposure to mosquitoes. The particular mosquitoes that spread Zika, Aedes aegypti and Aedes albopictus, are active during the day, so the use of protective measures needs to go beyond evening or nighttime hours. Because the virus spreads from mosquitoes to humans to mosquitoes, attempts to interrupt transmission can include protecting infected people from mosquito exposure during the first week of illness.
Zika virus and microcephaly
Whether Zika virus infection of pregnant women is causally associated with microcephaly is still not known for certain. The hypothesis comes from a dramatic increase in the incidence of microcephaly in Brazil; however, two important pieces of information need to be considered. First, the baseline rates of microcephaly in Brazil are not known, and second, not all infants born with microcephaly have tested positive for Zika. On the other hand, Zika virus has been found in the brains of a few infants who died during gestation or shortly after birth. Other information that remains uncertain includes the full spectrum of phenotypes in affected infants, the relative timing and severity of infection related to outcomes, and the magnitude and spectrum of the possible outcomes associated with infection during pregnancy.
While studies around this concern continue, pregnant women are being advised to avoid travel to Zika-infected areas, if possible, and if travel to those areas is necessary, to take protective measures to decrease the chance of being bitten by a mosquito. Additionally, if their male partners are at risk for Zika infection, they should abstain from sexual intercourse or use condoms. Providers are being advised to be proactive in testing pregnant women and their unborn babies if Zika infection is a concern. The CDC has developed testing algorithms for both pregnant women with a history of travel to an area in which Zika virus is circulating as well as babies for whom congenital Zika virus infection is a concern. (See resources section below for links to the publications that include these algorithms.)
- CDC’s interim guidelines:
- CDC’s dedicated Web page.
- Zika Virus — What Clinicians Need to Know? Presented as a Clinical Outreach and Communication Activity (COCA) on Jan. 26, 2016 — Continuing education credits available. Slides, audio, transcript and webinar are available for convenient viewing.
- WHO information about Zika, microcephaly and GBS.
- Zika Virus Associated with Microcephaly — Case report in New England Journal of Medicine, published 2/10/16.
- Evidence of Zika Virus Infection in Brain and Placental Tissues from Two Congenitally Infected Newborns and Two Fetal Losses — Brazil, 2015, published 2/10/16, MMWR 65(6):1-2.
- Fears that Zika causes brain damage in infants sparks vaccine hunt — published 2/2/16, Science, DOI: 10.1126/science.aae0300.