Researchers at the Yale School of Public Health (YSPH) have detected a large unreported Zika outbreak that occurred in Cuba during 2017, a year after Zika outbreaks peaked throughout the Americas.
Unreported outbreaks present a risk of silently spreading viruses to other parts of the world. They also highlight the need for alternative detection methods when there is a lack of access to reliable local case reporting, the researchers said.
The study, published online today in the journal Cell, was a large collaborative effort with Scripps Research, Florida Gulf Coast University, the Florida Department of Health, and other institutions.
Towards the end of 2016, as the Zika epidemic in the Americas appeared to be waning, lead author Nathan Grubaugh, an assistant professor of epidemiology, and other researchers involved in the study became interested in whether hidden outbreaks were occurring.
"Accurate case detection is not always possible in many places for a variety of biological and socioeconomic reasons," said Grubaugh. "So, we constructed a framework using infections diagnosed from travelers, travel patterns, and virus genomics to detect outbreaks in the absence of local data." Virus genomics sequences the genetic code of a virus, which helped scientists determine how the viruses in Cuba were related to those appearing throughout the Americas.
Using travel-related Zika cases reported by the Florida Department of Health, the team discovered a spike in cases from people returning from Cuba in 2017. They estimated that the outbreak in Cuba should have resulted in 1,000 to 20,000 Zika cases, even though only 187 cases were reported in 2016 and none in 2017.
"A big question was: Why did the outbreak in Cuba occur a year after others in the region?" said Chantal Vogels, a postdoctoral fellow at YSPH. "We investigated virus genomics, travel patterns, and models of mosquito transmission, and found that the outbreak in Cuba may have been delayed by an effective mosquito control campaign."
The Cuban government launched a large mosquito control campaign to prevent local Zika virus transmission as outbreaks peaked in the Americas. Researchers believe that while that initial effort was effective, local control eventually waned, leading to the delayed Zika outbreak in Cuba reported in the current study.
With Zika virus transmission still occurring in countries such as Angola, Thailand, and India, the analytical approach used by the research team to identify the Cuban outbreak may help uncover other unreported outbreaks around the world.
"While this study was about Zika, the analytical framework we developed can easily be applied to help identify hidden outbreaks of other diseases that are hard to detect under existing local surveillance systems," said Grubaugh.
Zika virus first made headlines in 2015 when it was detected in Salvador, Brazil and was associated with severe birth defects, such as microcephaly. As the health impacts of Zika are still not fully understood, monitoring where outbreaks are occurring is paramount, researchers noted.
Other authors include Sharada Saraf, Karthik Gangavarapu, Alexander Watts, Amanda L. Tan, Rachel J. Oidtman, Jason T. Ladner, Glenn Oliveira, Nathaniel L. Matteson, Moritz U.G. Kraemer, Chantal B.F. Vogels, Aaron Hentoff, Deepit Bhatia, Danielle Stanek, Blake Scott, Vanessa Landis, Ian Stryker, Marshall R. Cone, Edgar W. Kopp IV, Andrew C. Cannons, Lea Heberlein-Larson, Stephen White, Leah D. Gillis, Michael J. Ricciardi, Jaclyn Kwal, Paola K. Lichtenberger, Diogo M. Magnani, David I. Watkins, Gustavo Palacios, Davidson H. Hamer, GeoSentinel Surveillance Network, Lauren M. Gardner, T. Alex Perkins, Guy Baele, Kamran Khan, Andrea Morrison, Sharon Isern, Scott F. Michael, and Kristian G. Andersen.
This work was supported by The Pew Charitable Trusts, The Ray Thomas Foundation, and grants from NIH NCATS CTSA UL1TR002550, NIAID R21AI137690, and NIAID U19AI135995.