Dengue may bring out the worst in Zika

Mice infused with either dengue or West Nile virus became far more susceptible to disease and death from Zika virus, a new study published online in Science shows. The mice, engineered to cripple an immune gene that normally helps suppress Zika virus, of course may not represent what happens in humans. But antibody-dependent enhancement (ADE) is a well-known phenomenon with dengue, which has four “serotypes” that infect humans. Infection with one dengue serotype typically causes little harm, but the antibodies produced against it can set people up for severe and even deadly disease if they subsequently become infected by a different serotype. Dengue, West Nile, and Zika are all from the flavivirus family and the researchers warn that a vaccine against one could put a person at risk for ADE from a relative. Dengue is closest to Zika, and indeed the mouse experiment showed that dengue antibodies led to the most severe Zika disease. ADE also led to high levels of virus in mouse testes and spinal cords, which may help explain sexual transmission of Zika in humans and central nervous system diseases like microcephaly in babies and Guillain-Barre Syndrome in adults.