Researchers at Yale, Scripps Research Institute and Florida Gulf Coast University detected an outbreak of the Zika virus in Cuba in 2017 that had not been previously reported, by only studying the data collected from travelers to Cuba. Zika fever is a mosquito-borne disease which typically causes asymptomatic or mild infection (fever and rash) in humans. Zika virus is transmitted to people primarily through the bite of an infected Aedes species mosquito.
Yale Daily News reported that incidence rates of Zika among travelers to Cuba were used to estimate the incidence rates among Cuban locals. After comparing Zika incidence rates in travelers and locals in Puerto Rico, Jamaica, the Dominican Republic and other countries, the researchers were able to use Zika incidence rates of travelers to Cuba to estimate the number of local Zika cases in Cuba.
Nathan Grubaugh, an epidemiology professor at the Yale School of Public Health and corresponding author of the study said, “While the methods we used have been used before, the combination of methods that we used made this study the first to have reconstructed an outbreak without any data from local sources.”
The team of researchers at the Florida Department of Health has been following since Zika outbreak struck Florida in 2016. These follow-ups were intended to check whether people traveling from the United States were still getting infected with the virus. While health authorities in Brazil and Puerto Rico reported Zika virus outbreaks, the researchers felt that it was odd that no such outbreak was reported in Cuba.
The researchers heavily relied on virus evolution to paint a bigger picture of an unreported outbreak in a unique situation where data from local sources were unavailable.
“If we have viruses with a certain amount of genetic diversity at a certain point in time, we can use that to figure out when the outbreak started,” Grubaugh said.
The scientists also looked at the transmission of the dengue virus in airline travel to figure out why the outbreak was delayed — the Florida cases happened in 2017, whereas the worldwide Zika epidemic struck in 2016. While the researchers are not completely sure, they suspect that Cuba stopped its mosquito control program in 2017 after the epidemic died down. The virus still remained in Cuba, however, and it was enough to start an outbreak the next year.
According to Grubaugh, this is an important conclusion because it highlights that even the best mosquito control efforts are not always enough to fight such epidemics — in Cuba, prevention measures simply delayed the outbreak. Stronger efforts such as vaccines for the virus could have successfully prevented the outbreak from happening, he added.
He noted that the team is now planning to use the travel data to better understand the intricacies and the effectiveness of local surveillance programs in an attempt to make recommendations that would bring other hidden outbreaks to life.