Zika fever

The Zika Epidemic Began Long Before Anyone Noticed

Zika virus
Researchers used genetic information from Zika virus (illustrated) to follow its spread among affected regions in South and Central America and the Caribbean.

ON THE MOVE

The Zika virus probably arrived in the Western Hemisphere from somewhere in the Pacific more than a year before it was detected, a new genetic analysis of the epidemic shows. Researchers also found that as Zika fanned outward from Brazil, it entered neighboring countries and South Florida multiple times without being noticed.

Although Zika quietly took root in northeastern Brazil in late 2013 or early 2014, many months passed before Brazilian health authorities received reports of unexplained fever and skin rashes. Zika was finally confirmed as the culprit in April 2015.

The World Health Organization did not declare the epidemic a public health emergency until February 2016, after babies of Zika-infected mothers began to be born with severe neurological problems. Zika, which is carried by mosquitoes, infected an estimated 1 million people in Brazil alone in 2015, and is now thought to be transmitted in 84 countries worldwide.

Although Zika’s path was documented starting in 2015 through records of human cases, less was known about how the virus spread so silently before detection, or how outbreaks in different parts of Central and South America were connected. Now two groups working independently, reporting online May 24 in Nature, have compared samples from different times and locations to read the history recorded in random mutations of the virus’s 10 genes.

One team, led by scientists in the United Kingdom and Brazil, drove more than 1,200 miles across Brazil — “a Top Gear–style road trip,” one scientist quipped — with a portable device that could produce a complete catalog of the virus’s genes in less than a day. A second team, led by researchers at the Broad Institute of MIT and Harvard, analyzed more than 100 Zika genomes from infected patients and mosquitoes in nine countries and Puerto Rico. Based on where the cases originated, and the…

Getting dengue first may make Zika infection much worse

dengue antibody and dengue virus
FRIEND OR FOE A dengue antibody (blue, shown bound to a dengue virus protein, red, in this molecular model) can ease Zika’s entry into cells, a new study finds.

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….