ID Consult

Zika virus: More questions than answers?


 

With spring break in full swing and summer vacations right around the corner, pediatricians are increasingly fielding questions from families about Zika virus.

“There are a lot of resources available online, but they’re constantly being updated, and it’s difficult to stay current,” a friend and fellow pediatrician confided. “It seems like there’s new information every day, but still as many questions as answers.”

Dr. Kristina Bryant

Dr. Kristina Bryant

A quick PubMed search validated her concern: More than 200 articles have been published about Zika virus since the beginning of the year. The Centers for Disease Control and Prevention and the World Health Organization post new information to their Zika websites regularly, if not daily, and the WHO has released a Zika app for clinicians. Understanding that the busy pediatrician may not always have time to peruse these authoritative references during the course of a day in the office, I’ve compiled some common questions and answers.

“Is Zika really as serious as the media portrays it?” asked the mother of two children as she contemplated Caribbean vacation plans. In truth, most healthy people infected with Zika virus never develop symptoms. Illness, when it occurs, is most often mild and includes low-grade fever, headache, arthralgia, myalgia, nonpurulent conjunctivitis, and a maculopapular rash. Unlike dengue, another Flavivirus carried by Aedes mosquitoes, Zika does not cause hemorrhagic fever, and death appears to be rare.

An understanding of Zika infection and neurologic complications is a work in progress. A 20-fold increase in the incidence of Guillain-Barré (GBS) cases was noted in French Polynesia during a 2013-2014 outbreak of Zika virus.

In a case-control study involving 42 patients hospitalized with GBS, 98% had anti–Zika virus IgM or IgG, and all had neutralizing antibodies against Zika virus, compared with 56% of 98 control patients (P less than .0001 ) (Lancet. 2016 Feb 29. doi: 10.1016/S0140-6736(16)00562-6).

To date, 10 countries or territories have reported GBS cases with confirmed Zika virus infection. According to the World Health Organization, “Zika virus is highly likely to be a cause of the elevated incidence of GBS in countries and territories in the Western Pacific and Americas,” but further research is needed. Zika has recently been associated with other neurologic disorders, including myelitis, and the full spectrum of disease is likely not yet known.

Most Zika virus infections are transmitted from the bite of an Aedes mosquito. What we know about Zika transmission among humans continues to evolve. Viremia can persist for 14 or more days after the onset of symptoms, during which time blood is a potential source of infection. Two possible cases of transfusion-related viral transmission are under investigation in Brazil, and during the French Polynesia outbreak, 3% of samples from asymptomatic blood donors contained detectable Zika RNA. The U.S. Food and Drug Administration has recommended that individuals who have lived in or traveled to an area with active Zika virus transmission defer blood donation for 4 weeks after departure from the area .

 CDC/James Gathany

Zika virus also has been detected in the urine and saliva of infected individuals, but these fluids have not been linked to transmission. Sexual transmission from infected men to their partners is well documented, but the period of risk remains undefined. The virus can persist in the semen long after viremia clears, and in one individual, Zika virus was detected in the semen 62 days after symptom onset.

Maternal-fetal transmission can occur as early as the first trimester and as late as at the time of delivery. Zika virus has been recovered from both amniotic fluid and placentas. The consequences of maternal-fetal transmission are less certain. Coincident with an epidemic of Zika in Brazil, that country has observed a marked increase in the incidence of microcephaly. Between Oct. 22, 2015, and March 12, 2016, 6,480 cases of microcephaly and/or central nervous system malformation were reported in Brazil, contrasting sharply with the average of 163 cases reported annually from 2001 to 2014. Zika virus has been linked to 863 cases of microcephaly investigated thus far. Proving causality takes time, but the World Health Organization says the link between microcephaly and Zika infection is “strongly suspected.”

Because of the association between Zika virus and birth defects, including abnormal brain development, eye abnormalities, and hearing deficits, the CDC currently recommends that pregnant women not travel to areas with Zika transmission, while men who have lived in or traveled to an area with Zika and who have a pregnant partner should either use condoms or not have sex for the duration of the pregnancy.

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