Previous dengue exposure may confer a protective effect against Zika virus infection, according to a paper published in.
In a prospective cohort study, researchers followed 1,453 urban residents in Salvador, Brazil, to assess the impact of the 2015 Zika virus outbreak in the region. Data on dengue immunity was available for 642 of these individuals.
Overall, 73% of the cohort were seropositive for Zika virus. However, the frequency of seropositivity varied significantly by location, from 29% in a valley in the northeastern sector of the study area to 83% in the southeast corner; the authors wrote that this was consistent with some form of acquired immunity “blunting the efficiency of transmission.”
When researchers looked at the relationship between prior immunity to the dengue virus and the risk of Zika infection, they found that each doubling of total IgG titers against dengue NS1 was associated with a 9% reduction in the risk of Zika virus infection.
Individuals in the highest tertile of dengue IgG titers showed a 44% reduction in the odds of Zika seropositivity, compared with individuals with no or low dengue IgG titers, while those in the middle tertile of dengue IgG titer had a 38% reduction.
“These findings provide empirical support for the hypothesis that accumulated immunity drove ZIKV [Zika virus] to local extinction by reducing the efficiency of transmission,” wrote, from the department of medicine at the University of California, San Francisco, and her coauthors.
Individuals who were infected with the Zika virus but had high dengue IgG titers were significantly less likely to exhibit fever with viral infection, but had the same risk of developing rash as those with low or no IgG titers.
Researchers also examined the link between a subclass of IgG antibodies that are associated with more recent exposure to dengue virus – within the prior 6 months – and the risk of Zika virus infection. In contrast, they found that the levels of this subclass of antibodies, known as IgG3, were positively associated with an increased risk of Zika virus infection. Each doubling in IgG3 levels was associated with a 23% increase in the odds of being positive for Zika.
“This positive association might reflect an immune profile, in individuals who have experienced a recent DENV [dengue virus] infection, that is associated with having a greater risk of a subsequent ZIKV infection,” the authors wrote. “Alternatively, it is also possible that higher levels of IgG3 are a proxy for frequent DENV exposure and thus greater risk of infection by Aedes aegypti–transmitted viruses.”
The study was supported by Yale University, a number of Brazilian research organizations, the Research Support Foundation for the State of São Paulo, CuraZika Foundation, Wellcome Trust, and the National Institutes of Health. Three authors are listed on a patent application related to the work, and one reported an honoraria from Sanofi-Pasteur.