Zika virus: More questions than answers?
"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."
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-Barre syndrome (GBS) cases was noted in French Polynesia during a 2013-2014 outbreak of Zika virus.
In a case-controlled 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/S00140-6736(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.
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.
The good news for nonpregnant women who contract Zika infection is that the infection is not thought to pose any risk to future pregnancies. Currently, there is no evidence that a fetus conceived after maternal viremia has resolved would be at risk for infection. Still, many unanswered questions remain about Zika infection during pregnancy. For example, it's currently unknown how often infection is transmitted from an infected mother to her fetus, or if infection is more severe at a particular point in gestation.
Although Zika virus has been isolated from breast milk, no infections have been linked to breastfeeding, and mothers are encouraged to continue to nurse, even in areas with widespread transmission. Infection with Zika at the time of birth or later in childhood has not been linked to microcephaly. Beyond that, the long-term health outcomes of infants and children with Zika virus infection are unknown.
"How far north do you think the virus will spread?" one mom asked me. "Do I need to be worried?"
For public health officials, that's the $64,000 question. To date, there have been no cases acquired as a result of a mosquito bite in the United States, but the edge of the outbreak continues to creep north. Local transmission of the virus was reported in Cuba on March 14.
As of March 16, 2016, 258 travel-associated Zika virus cases have been diagnosed in the United States, including 18 in pregnant women. Six of these were sexually transmitted. Theoretically, "onward transmission" from one of these cases could occur if the right kind of mosquito bites an infected person during the period of active viremia and then bites someone else, transferring a tiny amount of the virus-contaminated blood.
According to CDC experts, "Texas, Florida, and Hawaii are likely to be the U.S. states with the highest risk of experiencing local transmission of Zika virus by mosquitoes." Although this estimate is based on prior experience with similar viruses, the principal vector of Zika, Aedes aegypti, has been identified as far west as California and in a number of states across the South, including my home state of Kentucky. Aedes albopictus mosquitoes also have been proven competent vectors for Zika virus transmission and are more widely distributed throughout the continental United States.
In a thoughtful review published in JAMA Pediatrics, "What Pediatricians and Other Clinicians Should Know About Zika Virus," Dr. Mark W Kline and Dr. Gordon E. Schutze noted that up to two-thirds of the U.S. population live in an area where Aedes mosquitoes are present at least part of the year (JAMA Pediatr. 2016 Feb 18. doi: 10.1001/jamapediatrics.2016.0429). Fortunately, transmission of dengue and chikungunya, two other viruses carried by the same insect, is still very uncommon. Public health experts are urging individuals with Zika virus infection to avoid mosquito bites during the first week of illness, to protect others.
We should start now counseling our patients and families to avoid mosquito bites at home and abroad. Besides Zika virus, mosquitoes transmit several pathogens in the United States each year, including West Nile virus, LaCrosse encephalitis virus, St. Louis encephalitis virus, and dengue.
Any collections of standing water should be eliminated, as these can be mosquito breeding grounds. These include flower pots, buckets, barrels, and discarded tires. The water in bird baths and pet dishes should be changed at least weekly, and children's wading pools should be drained and stored on their side after use.
To the extent practical, exposed skin should be covered with long-sleeved shirts, long pants, and socks when individuals are in areas with mosquito activity. To enhance protection, clothing can be treated with permethrin, or pretreated clothing can be worn. An FDA-registered insect repellent should be applied to exposed skin, especially during hours of highest mosquito activity. Zika-carrying mosquitoes bite during the day, or dawn to dusk. Effective repellents include DEET, picaridin, IR3535, and oil of lemon eucalyptus, although families should read labels carefully as instructions for use vary, as does the recommended time period of reapplication. Combination sunscreen/insect repellent products are not recommended as repellent usually does not need to be reapplied as often as sunscreen. Parents also should be reminded not to use oil of lemon eucalyptus-containing products on children under 3 years of age.
"We're going to get a lot more questions as the weather turns warmer," said a colleague of mine. "I'm just waiting for the first call about a child who develops fever and a rash after a mosquito bite. Parents will wonder if it could be Zika."
It is going to be an interesting summer. Stay tuned.
BY KRISTINA BRYANT, M.D.
Dr. Bryant is a pediatrician specializing in infectious diseases at the University of Louisville (Ky.) and Kosair Children's Hospital, also in Louisville. She had no relevant financial disclosures.
Caption: Most Zika virus infections are transmitted from the bite of an Aedes mosquito. Sexual transmission from infected men to their partners is well documented, but the period of risk remains undefined.
Please note: Illustration(s) are not available due to copyright restrictions.
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|Title Annotation:||ID CONSULT|
|Date:||Apr 1, 2016|
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