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The more a person is immunized against the dengue virus, the lower the risk of infection with Zika virus, reports an international team of scientists led by the University of Pittsburgh School of Public Health, School Yale Public Health and the University of Florida.
The study, which followed nearly 1,500 people living in a poor neighborhood at the heart of the Zika epidemic in Brazil in 2015, also shows that the Zika epidemic in Brazil is largely endangered because enough people have acquired immunity to reduce the efficiency of transmission.
"Take that with a grain of salt, however," said lead co-author Ernesto TA Marques, MD, PhD, badociate professor in the Department of Infectious Diseases and Microbiology of Public Health at Pitt and a public health researcher at Fundação Oswaldo Cruz in Brazil. "Our study focused on a very small urban area and it is likely that in other parts of Brazil, even in different neighborhoods of the same city, people remain likely to be infected with the Zika virus."
The discovery was based on dengue and Zika tests developed by Marques and his team and patented by Pitt. Brands is scientific director of Cura Zika, an international alliance aimed at boosting research on Zika, microcephaly and other conbad diseases that it causes in babies.
The research team relied on a lengthy study of the health of urban slum dwellers in Salvador, a city in northeastern Brazil, led by lead author Albert Ko, MD, director of epidemiology at the Yale School of Public Health. Study participants gave several blood samples before, during and after the Zika outbreak. The samples collected in October 2014 and March 2015 were almost entirely negative for Zika, but as of October 2015, 63% had shown signs of Zika infection.
Before the Zika epidemic, a subset of 642 participants had also been tested for prior dengue infection and 86% were positive. Specifically, the test evaluated the level of antibodies contained in participants' blood against dengue fever. The team found that each doubling of dengue antibody levels corresponds to a 9% reduction in the risk of Zika.
"This means that dengue provides some cross-protective antibodies against Zika," Marques said. "A future study might be warranted to determine whether new dengue vaccines could be helpful in preventing Zika infection."
Paradoxically, the computer models of the lead author, Derek AT Cummings, PhD, a professor of biology at the University of Florida, revealed that participants with a very recent dengue infection were actually more vulnerable to zika.
Scientists suspect several possible explanations: it is possible that protective antibodies have not yet developed or that the immune system of these people has an impact on the risk of contracting Zika. And the mosquitoes that transmit dengue also transmit the Zika virus. Thus, a recent dengue infection might simply mean that they are in a place where the transmission of Zika virus is also active.
Additional studies are also needed to determine how these findings might be of value to clinicians, Marques said.
Developing reliable and commercially available tests for women of childbearing age, in order to badess their previous exposure to dengue and Zika, is an immediate concern, as well as evaluating recommendations to that clinicians know what to do with this information, noted Brands. The tests could help clinicians determine whether women's immunization against dengue could protect them from Zika during pregnancy. This would also provide a baseline, so that obstetricians would know how closely to monitor the fetus of a pregnant woman for microcephaly, depending on her susceptibility to Zika.
Studies are also under way on babies born to women who contracted Zika virus during pregnancy to evaluate the effect of maternal dengue immunity on the degree of ZIK-related conbad injury in infants. .
The co-authors of this research are Eduardo J.M. Nascimento, PhD, Pitt Vaccine Research Center; Isabel Rodriguez-Barraquer, MD, Ph.D., University of California at San Francisco; and Federico Costa, PhD, Yale.
The other institutions that participated in this research are the Universidade Federal da Bahía in Brazil; Universidade de Pernambuco in Brazil; University of Texas; Institute of Sustainable Sciences in Nicaragua; Ministry of Health in Nicaragua; University of California, Berkeley; and Faculdade de Medicina of São José do Rio Preto in Brazil.
Source: Health Sciences at the University of Pittsburgh
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