Zika, dengue, and West Nile viruses are all related - literally. They are all part of the flavivirus family, and similar viral protein structures shared by all three may explain why some populations in South America were hit so hard by the Zika virus outbreak in 2015.
Dengue and West Nile viruses are endemic in the same places as Zika, including Puerto Rico and other United States territories. Visible trends show people with a history of dengue, West Nile, or both viral infections at an increased risk for Zika virus infection.
For the first time, in a study published in Science, researchers from the Icahn School of Medicine at Mount Sinai completed a large-scale analysis of the effect of preexisting antibodies from dengue or West Nile viruses on Zika virus infection.
First, researchers collected blood samples from people infected with either dengue or West Nile virus. In cell cultures, antibodies from the plasma in these blood samples enhanced Zika virus growth.
Next, they injected the same plasma into mice genetically altered to be particularly susceptible to Zika virus infection. Researchers saw increased mortality, morbidity, and Zika viral loads in the mice. However, this effect was only visible when low concentrations of dengue or West Nile virus antibodies were administered; high concentrations of the same antibodies actually had a protective effect against Zika infection for the mice.
Researchers from Mount Sinai believe that this dose-dependent connection is responsible for recent Zika outbreaks. Co-author Jean Lim, PhD says that this study “highlights the need for great caution when designing vaccines for Zika and other flaviviruses.” The present study is just the beginning to fully understanding the relationship between pre-existing flavivirus immunity and effective vaccine development.
Currently, Zika virus is endemic to multiple U.S. territories, meaning the virus is regularly found in these areas. However, active transmission has also occurred in U.S. states Florida and Texas. Combined with Zika’s tendency to persist for long periods of time in the body tissues, the virus’s association with microcephaly and other neurological disorders, a connection that is yet to be completely understood, puts Zika virus at a high priority for scientists developing vaccines and other preventative and therapeutic drugs.