More data show Zika viremia in mothers, fetal infection link

Pregnant woman
Pregnant woman

Ken Hurst / iPhoto

Spanish researchers today reported more evidence of Zika replication in the fetus or placenta, describing persistent virema lasting more than 100 days after symptom onset in a mother of a baby born with microcephaly.

In other developments, Florida reported five more local Zika cases, all involving people who were sick earlier this fall, and researchers from England who reviewed studies on the effectiveness of mosquito control methods found weak evidence for some of the common strategies.

Prolonged viremia and fetal infections

The patient in the Spanish report is a woman who contracted a Zika infection in December 2015 while visiting Colombia, her home country. The group reported the findings in a letter to the New England Journal of Medicine.

Her Zika symptoms began when she was 9 weeks pregnant, and blood tests for Zika virus were positive for 89 days—until she was 29 weeks along. The reverse-transcriptase polymerase chain reaction (RT-PCR) test was positive for 107 days after her symptom onset. Tests for Zika from urine, vaginal, and endocervical samples were negative.

Fetal brain ultrasound at 12 and 15 weeks didn't show any problems, but repeat imaging tests at 20, 24, and 29 weeks revealed bilateral mild ventriculopathy and a shortened corpus callosum, along with parenchymal calcification and severe atrophy. The Zika viral load in the mother's amniotic fluid was higher than that of the blood.

The baby was delivered at 37 weeks because of fetal growth restriction, and at birth all samples from the mother, including those from the placenta, tested negative for Zika. The baby's samples—including cerebrospinal fluid—were all negative for acute infection. Ultrasound and magnetic resonance imaging confirmed the microcephaly diagnosis.

The group noted that an earlier report described Zika RNA in a pregnant woman's blood 8 weeks after symptoms began and that the new findings support the hypothesis that persistent viremia might reflect virus replication in the fetus or placenta. The researchers added that stable blood levels, higher viral load in amniotic fluid, and negative urine findings also support virus replication in reservoirs such as the fetus or placenta.

They concluded that persistent Zika RNA in a mother's blood may be a sign of fetal infection.

US Zika developments

The Florida Department of Health (Florida Health) reported five more local Zika cases, the first since Nov 30, according to an update today.

All five involve Miami-Dade County residents, people who had symptoms in September and October. As such, the newly reported cases don't affect the lifting of three active Zika transmission zones. Investigators recently wrapped up probes of the five cases to rule out travel.

Florida now has 249 local Zika cases, plus 15 in which it's not known where the individuals were exposed to the virus. The state has 972 travel-related cases and is monitoring 180 pregnant women who have lab evidence of Zika infection.

Texas health officials said in a Zika update yesterday that the number of local cases remains at one, involving a woman from Cameron County whose illness was reported on Nov 28. The Texas Department of State Health Services (TDSHS) said it has recorded 270 travel-related Zika cases. The number includes 21 pregnant women, 2 babies infected before birth, and 2 people who had sexual contact with travelers.

In other US Zika developments, the New York City Department of Health and Mental Hygiene has recorded at least four babies born with Zika-related problems since July, prompting an alert to physicians today, the New York Times reported. Overall, five such cases have been reported.

Health officials urged doctors to remain vigilant for Zika-affected pregnancies and to warn pregnant and reproductive-age women to take precautions when traveling to areas where the virus is spreading.

Studies on mosquito control, traveler patterns

  • A meta-analysis of 13 studies on control measures against Aedes mosquitoes that spread diseases such as Zika, dengue, and yellow fever found a lack of clear evidence behind many strategies and that some may be counterproductive. A team based at the University of East Anglia reported its findings today in PLoS Neglected Tropical Diseases. Methods covered included biological controls such as adding mosquito-eating fish to water, chemical controls such as pesticides and larvicides, and educational campaigns. Biological interventions appeared to reduce mosquito numbers more than chemical methods, but the quality of evidence was poor, the authors found. They noted that chemical spraying might be counterproductive, because it builds a false sense of security, and they repeated the World Health Organization's stance that elimination of breeding sites is the most effective intervention, which requires sustained campaigns. Better studies are needed to gauge the effectiveness of current tools, and consideration of their use should factor in cost effectiveness, the authors said.

  • An analysis of US residents traveling to Zika-affected countries who were seen at Global TravEpiNet sites reveals that nearly 75% were men and women of reproductive age, and two thirds of the women traveling to the areas were of reproductive age, only a third of whom reported using prescription birth control. Researchers from Massachusetts and the US Centers for Disease Control and Prevention reported their findings today in Emerging Infectious Diseases. A quarter of the reproductive-age women were traveling for mission or service. The percentage of those traveling to visit family and relatives, at 1% of reproductive age women, was smaller than expected, suggesting a need for more efforts to reach that group with pretravel health services.

See also:

Dec 7 N Engl J Med letter

Dec 7 Florida Health statement

Dec 7 TDSHS update

Dec 7 New York Times story

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