Previous infections with dengue virus may have protected some people in an urban slum in Brazil from getting Zika.
In a study of more than 1,400 people in the Pau da Lima area of Salvador, those with higher levels of antibodies against a particular dengue virus protein were at lower risk of contracting Zika, researchers report in the Feb. 8 Science. “The higher the antibody, the higher the protection,” says Albert Ko, an infectious disease physician and epidemiologist at the Yale School of Public Health.
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That finding contrasts with previous studies in mice and in cells grown in lab dishes, in which antibodies against dengue seemed to make Zika worse (SN: 5/29/17, p. 14).
Ko and other researchers had been tracking a rat-borne bacterial illness in the poverty-stricken neighborhood for two years when the Zika outbreak hit in 2015. “We were at the epicenter of the pandemic,” Ko says. Blood samples taken every six months enabled researchers to track people there before, during and after the outbreak.
Zika infected an estimated 73 percent of people in the slum but “it really, really varied geographically,” says Isabel Rodriguez-Barraquer, an epidemiologist at the University of California, San Francisco. In some areas of the 0.17-square-kilometer community, 83 percent of people were infected. In other pockets, just 29 percent were.
Blood tests showed that many of the residents had contracted dengue in the past and had protective antibodies that could ward off Zika, or lessen its ability to cause fever. But “this protection was not absolute,” Ko says. People with a type of antibody, called IgG3 antibodies, indicating recent dengue infection were at higher risk of getting Zika. It’s puzzling why recent, but not older, dengue infections affect Zika risk differently, but that doesn’t necessarily mean that new dengue antibodies directly aid Zika infection, the researchers say. The finding may just mean people who get bitten often by mosquitoes are at higher risk of getting both dengue and Zika.