Infected travelers reveal Zika epidemic "hidden" in Cuba | Science

When the Zika virus invaded the Americas and the Caribbean in 2015 and 2016, it infected about 800,000 people and left nearly 4,000 critically injured newborns in the brain. But by the middle of 2017, the virus had virtually disappeared from the region – or so it seemed. A new analysis of travelers infected with the Zika virus who returned to the United States or Europe in 2017 or 2018 revealed that 98% of them had traveled to Cuba, which had not reported no cases to global health authorities at the time when the epidemic had apparently reached its climax.

"It was surprising," says Kristian Andersen, an epidemiologist in genomics at Scripps Research in San Diego, California, who led the work of 38 researchers from five countries. The group estimates 5707 the number of unreported cases of infection in Cuba reported in Cuba. Most of them occurred in 2017. These figures are similar to those of other Caribbean islands whose population was comparable a year ago.

In February 2016, the zika epidemic was so severe in South America and the Caribbean that the World Health Organization (WHO) took the rare step of declaring a public health emergency of scope international. But by November 2016, cases in the region had declined sharply and WHO had lifted the emergency situation.

To better understand persistent outbreaks, Andersen and colleagues examined cases of Zika among travelers registered by the Florida Department of Health and the European Center for Disease Prevention and Control. Between June 2017 and October 2018, there were 155 cases – confirmed by antibody tests or viral tests – and all but one person traveled to Cuba.

To further investigate the timing and origin of the outbreak in Cuba, researchers sequenced the Zika virus in nine infected people who returned to Florida and compared their viruses to those of other countries. of the region. As viral mutations occur at predictable speeds, the group could build a molecular clock that would reveal that the virus had appeared in Cuba about a year later than elsewhere in the Caribbean. In their study at Cell Today, the researchers also concluded that Zika had come to Cuba several times from different Caribbean islands.

Jennifer Gardy, an epidemiologist in genomics at the Bill & Melinda Gates Foundation's Global Health Program in Seattle, Washington, says viral sequence analysis of travelers can help clarify outlines epidemics that would otherwise have remained under the surveillance radar. "Surveillance is one of our best defenses against infectious diseases, but systems are rarely perfect. We can miss cases for many reasons, "says Gardy.

Andersen suggests that a combination of factors probably explains why the Cuban epidemic has been "hidden" from the rest of the world. As a result of the emergence of Zika in Brazil in May 2015, Cuba launched an aggressive program of pesticide application aimed at controlling the Aedes aegypti mosquito that transmits the virus. (Parallel to this program, cases of dengue fever, another disease transmitted by A. aegyptiZika cases also declined steadily in Latin America and the Caribbean that year, probably because the virus quickly infected large sections of the population, creating widespread immunity. When the WHO lifted its emergency declaration, it has eased the obligations of member countries with regard to the notification of zika cases. By the end of 2016, Cuba had confirmed only 187 cases of Zika and had stopped recording the numbers in 2017. He reported no cases of Zika-related brain injury in babies.

Contributing to the difficulty of reporting, the virus is "exceptionally difficult" to diagnose in infected people, notes Andersen. The antibodies against Zika virus and dengue virus are similar and the tests can confuse the two. Patients infected with Zika virus rarely show symptoms and virus levels in the blood drop rapidly, further complicating the confirmation of the infection.

Andersen hopes that his team's approach will be applied to a wide range of diseases among returning travelers. "This [work] establishes a framework to further investigate infectious diseases, "he says. "This is a very important new tool for monitoring infectious diseases around the world."

Michael Worobey, an evolutionary biologist who analyzed viral antecedents in his laboratory at the University of Arizona at Tucson, says the new study reminds him of the time he was working as a hunter of forest. People posted on forest towers followed lightning. The next day, they would fly over the forest areas struck by lightning. "If you saw smoke, you would send teams before there was a conflagration," says Worobey. "This new work is a demonstration of something we missed. If we improve our surveillance the next time, we will tackle it sooner and knowing that an epidemic like Zika is spreading may have an impact on its control. "