A recent U.S. study published in the Journal of the American Medical Association has found that 6% of 400 babies infected with Zika virus born here had one or more related birth defects. The study pales in comparison, however, to a Brazilian study of 125 women just reported in the New England Journal of Medicine. In that study, 46% of babies had abnormalities or did not survive the pregnancy. Previous studies had shown a risk of defects of 1 to 13 per cent.
Troubling evidence has now emerged that suggests that babies may still develop issues even as they approach their first birthday. Previously, it was thought that all damage occurred while still in the womb. Now scientists are asserting that the virus may continue to destroy nervous tissue for a time after birth.
The timing of the infection seemed to have an impact, with 11% of U.S. pregnancies diagnosed with Zika in the first trimester yielding babies with birth defects, less in mid- or late-pregnancy. Although Zika virus lasts only a short time in the blood, it appears to possibly last for months in brain tissue. The overall incidence of 6% in the U.S. was the same for women who experienced symptoms of Zika illness and those who were asymptomatic.
Most cases in the continental United States were diagnosed in women who had traveled to the epidemic zone, although an epidemic of more than 30,000 locally transmitted cases was seen in Puerto Rico and a local outbreak of more than 200 cases was noted in South Florida. More recently, a case of local transmission was reported in the Brownsville area of Texas.
Zika virus is known to cause increased numbers of newborns with microcephaly, an abnormality of growth in the brain and fetal head normally seen in less than 1% of all births. In the lab, Zika has been shown to kill brain cells. Other defects in sight, hearing, joints, and elsewhere have also been detected, according to Margaret Honein, lead author of the U.S. study and head of the U.S. Centers for Disease Control and Prevention’s National Center on Birth Defects and Developmental Disabilities.
Another troubling aspect is that the Zika virus is completely asymptomatic in 80% of those infected. This means that the actual number of cases may be five times the recorded numbers. Additionally, it is unknown what developmental milestones may be delayed over the first few years of life, and whether school performance may be affected.
The best way to prevent Zika virus is still to prevent mosquito bites by wearing appropriate clothing and using repellent when in at-risk areas (or avoid travel there altogether), Pregnancies should be delayed for 8 weeks in women who have had the virus or traveled to the epidemic zone. Men shouldn’t attempt to impregnate their partner for at least 6 months.
Joe Alton, MD
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