After simmering for years in Africa, Asia, and Micronesia, 2016 marked the year that the Zika virus stormed onto the world’s stage. While the Brazilian outbreak began last year, a surge in cases preceded the country’s hosting of the 2016 Olympics. Fearing that spectators would take the virus home with them—sparking a global pandemic—public health officials, researchers, and doctors raced to study the disease in hopes of finding a way to stop it.
The virus was first isolated by entomologist Alexander Haddow from a sample taken in 1947 in the Zika forest in Uganda. (Decades later, his grandson, Andrew, would be among the first to sound the warning about Zika’s potential to spread.) Over the years, the mosquito-borne illness traveled from Africa through Asia and on to the Pacific islands of Micronesia in 2007. From there, epidemiologists think it made the jump to Brazil, which has plenty of habitat for the virus’s two mosquito vectors.
At first, the disease was thought to cause only mild, flu-like symptoms. But during an outbreak in French Polynesia in 2013, researchers noticed an uptick in birth defects and neurological problems in babies born to infected women.
In Brazil, the virus found a large and susceptible population, and doctors soon reported a rash of cases of microcephaly, in which babies are born with smaller than normal brains and skulls. The defect may be caused by the particular cells in developing fetuses that the virus infects. These cranial neural crest cells are related to skull formation and, when hijacked by Zika, appear to release molecules that damage the neural progenitor cells that give rise to different types of brain cells.
Since the Brazilian outbreak started, scientists confirmed that the virus can be transmitted sexually andnonsexually in addition to the usual mosquito vector, making it an outlier among arboviruses. The disease may cause lasting damage in adults, too.
Virologists have been working overtime to develop vaccines and treatments for the disease. While progress has been slow, one company recently reported positive results in a small, 40-person study of a vaccine. It will likely be many more months or years before the vaccine is ready for wide use. In the meantime, the virus continues to spread.