Being immune to a virus is a good thing, until it’s not. That’s the lesson from a study that sought to understand the severity of the Zika outbreak in Brazil. Experiments in cells and mice suggest that a previous exposure to dengue or West Nile can make a Zika virus infection worse.
“Antibodies you generate from the first infection … can facilitate entry of the Zika virus into susceptible cells, exacerbating the disease outcome,” says virologist Jean K. Lim. Lim and colleagues report the results online March 30 in Science.
The study is the first to demonstrate this effect in mice, as well as the first to implicate West Nile virus, notes Sharon Isern, a molecular virologist at Florida Gulf Coast University in Fort Myers.
Zika is similar to other members of its viral family, the flaviviruses. It shares about 60 percent of its genetic information with dengue virus and West Nile virus. Dengue outbreaks are common in South and Central America, and dengue as well as West Nile are endemic to the United States.
Exposure to a virus spurs the body to create antibodies, which prevent illness when a subsequent infection with the virus occurs. But a peculiar phenomenon called antibody-dependent enhancement has been described in dengue patients (SN: 6/25/16, p. 22). The dengue virus has four different versions. When a person with immunity to one dengue type becomes sick with another type, the illness is worse the second time. The antibodies from the previous dengue exposure actually help the subsequent dengue virus infect cells, rather than blocking them.
Outcomes of Zika infections for mice depended on whether certain viral antibodies were present in their systems….
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