Like an invader spotting a weakness in a castle’s defenses, Zika targets specific white blood cells in a pregnant woman’s immune system, enabling the virus to spread and increasing the chances of harm to unborn babies, according to a new study by researchers at the University of Southern California’s Keck School of Medicine.
Because pregnant women are more prone to immune suppression — a natural occurrence that prevents the body from rejecting the fetus — Zika exploits that weakness to infect and replicate, stifling a body’s natural defenses in a way that resembles HIV, the study authors said.
The mosquito-borne virus that emerged in Miami last year has been mostly absent in Florida this year, with fewer infections and no local cases as of Monday. The Florida Department of Health has reported a total of 151 Zika cases, with all but one — a sexually acquired case in Pinellas County — contracted by Floridians while traveling outside the country.
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The USC study, published in the journal Nature Microbiology, is the first to report that Zika targets certain white blood cells and converts those cells into immune system suppressors.
Researchers tested African and Asian Zika strains by infecting blood samples taken from men and women, including some who were pregnant, and then analyzing them at peak infection. They found that Zika made a beeline for white blood cells that help fight infections.
The Asian Zika strain pushed those white blood cells to transform into a different type of cell that tells the immune system to stand down because the threat is over, according to the study. The false signal stifles the immune system, allowing Zika to replicate.
Pregnant women have higher levels of the immune-suppressing cells, researchers said, which provides an opening for the Asian Zika virus to do more damage.
Previous clinical studies have found that Zika infection during the first and second trimesters of pregnancy increases the chances of delivering a baby with a birth defect or other abnormality. USC researchers found that the Asian Zika virus also is more harmful during a woman’s first and second trimester.