The Zika Virus: What you need to know


This mosquito-borne virus is linked with microcephaly, but causation is still being investigated.

Concern is growing about the possibility that intrauterine transmission of a previously little-known mosquito-borne virus closely related to West Nile may lead to fetal brain abnormality. Two new case reports from Brazil about Zika virus and an editorial in NEJM underscore the need for ob/gyns to counsel pregnant women about the virus if they are planning to travel to areas where it is endemic.

Detailed guidance from the Centers for Disease Control and Prevention (CDC) on precautions for pregnant women and those trying to become pregnant who are traveling to such areas is available at CDC’s Level 2 travel alert about Zika virus was issued on January 15 and pertains to 14 countries and territories in Central and South America and the Caribbean where transmission of the virus is ongoing. On January 22, more countries were added to the list. Interim guidelines for pregnant women were issued by the CDC on January 19 and can be viewed here.

Writing in Ultrasound in Obstetrics & Gynecology, physicians from Brazil describe what may be the first 2 cases of documented intrauterine transmission of Zika virus. In one case, fetal ultrasound at 30.1 weeks’ gestation showed anomalies limited to the brain; in the second case, fetal ultrasound at 29.2 weeks’ gestation showed markedly asymmetric hemispheres and absence of the thalami; the eyes were also involved. Both mothers had symptoms of the virus but negative blood tests, whereas amniocentesis and polymerase chain reaction were positive for Zika virus.

Contemporary OB/GYN Editorial Board member Joshua A Copel, MD, said, “We don’t know the absolute risk of fetal effects if a woman contracts Zika virus in pregnancy from this report, but it certainly raises our concern for detectable prenatal effects of Zika virus in pregnancy.”

Click here to see Dr Copel's comments to NBC news

Unlike West Nile virus, Zika virus is transmitted by aedes mosquitos, and particularly Aedes aegypti. Said Gustavo Malinger, co-author of the case reports, “As shown in the map published in NEJM, until now Zika virus has been reported in countries between the Tropics. This is due to the fact that the aedes mosquito prefers a hot and humid climate. For this reason the risk of spreading of the disease to more temperate regions is, in my opinion, low. In places where Dengue fever is prevalent, cases of Zika are to be expected.”

“Particularly during the first half of pregnancy,” Dr Malinger said, “women need to be counseled regarding the danger and possible measures of prevention mosquito bites when traveling to Dengue and Zika endemic zones. According with our experience in the fetus examined and verbal reports from Brazil, the fetal Zika virus infection is expected to produce a wide range of anomalies involving not only the brain but also other systems; the expected spectrum of disease will range from mild cases to severely affected newborns and even stillbirths. Microcephaly in affected fetuses and newborns is most probably produced by a severe and widely spread insult to the whole brain."


The 2 case reports were from the state of Paraiba in Brazil and, in another area of the country, head circumference below the 10th percentile has been seen in more than 3000 children with Zika virus who were born to mothers with apparently asymptomatic disease during pregnancy. Incidence of microcephaly in Brazil increased 20-fold from 2014 to 2015, and the government has declared a state of national health emergency. In some areas of the country, the NEJM editorial says, pregnant women are being advised to “take meticulous precautions to avoid mosquito bites and even to delay pregnancy.” As Drs Fauci and Morens note, “It is critically important to confirm or dispel a causal link between Zika infection of pregnant women and the occurrence of microcephaly by doing intensive research, including careful case-control and other epidemiologic studies as well as attempts to duplicate this phenomenon in animal models.”

According to the CDC, locally transmitted Zika has not been reported in the United States except for a single case in Puerto Rico in December 2015, but it has been diagnosed in returning travelers. Symptoms are mild, with fever, rash, joint pain, and conjunctivitis that last several days.

Offering perspective to ob/gyns on the case reports, Jeanne Sheffield, Professor of Obstetrics & Gynecology and Division Director, Maternal Fetal Medicine, Johns Hopkins, said, “The association of the Zika virus and CNS abnormalities including microcephaly is concerning. The CDC has issued a travel alert for pregnant women, recommending considering postponing travel to affected areas. If travel is required, they should be advised to use appropriate preventative measures to avoid mosquito bites, including insect repellent. Recommendations for evaluation and management of women exposed to the Zika virus are forthcoming [the week of January 18] from the CDC.” 

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