A beforehand unknown outbreak of the Zika virus swept throughout Cuba in 2017, a yr after the world well being emergency was declared over, scientists reported on Thursday.
Until now, the Pan American Health Organization had no document of any Zika an infection in Cuba in 2017, a lot much less an outbreak. Following inquiries by The New York Times about the new research, printed in the journal Cell, officers acknowledged that that they had didn’t tally 1,384 circumstances reported by Cuban officers that yr.
That determine is a pointy improve over the 187 circumstances confirmed in 2016 and is “in line with the estimates for 2017 from our own study,” stated Kristian Andersen, an infectious illness researcher at Scripps Research Translational Institute in La Jolla, Calif., and a co-author of the new research.
Because most circumstances of Zika go unconfirmed, Dr. Andersen added, the outbreak truly could have comprised tens of 1000’s of infections.
Cuba noticed document tourism in 2017, elevating the chance that many vacationers had been unknowingly uncovered. Some four.7 million international guests arrived that yr, a rise of 16 % over 2016. More than a million had been Canadians.
“If we want to stay ahead of communicable diseases, we need to know where they are and how many cases are occurring,” stated Jennifer Gardy of the Bill & Melinda Gates Foundation in Seattle. “For some diseases in some settings, this is pretty straightforward. For others, like Zika, it isn’t.”
Officials at P.A.H.O., an arm of the World Health Organization, blamed the failure to publish well timed knowledge on the Cuba outbreak on a “technical glitch.” The info was held in a database, they stated, however not seen on the web site. By Thursday afternoon, the web site had been updated.
Dr. Andersen and his colleagues began tracking Zika’s spread when the mosquito-borne virus first appeared in the Americas in 2015. The epidemic first came to light in Brazil, where babies of some infected mothers were born with severe brain damage. The virus spread swiftly to neighboring countries.
Dr. Andersen and his colleagues collected blood from people infected with the virus. The researchers plucked the virus’s genetic material from the samples and used mutations in the DNA to estimate the timing of Zika’s spread.
Before Zika was identified in Brazil, the scientists discovered, it had been quietly circulating in the country for over a year. “And by that time, it had spread across all the Americas,” Dr. Andersen said.
Even in Florida, where the state government keeps careful tabs on new outbreaks, Zika arrived three months before it was detected, the scientists learned.
In November 2016, the World Health Organization announced that the epidemic was no longer a global public health emergency. “But we sat here with this question,” Dr. Andersen recalled. “Is it really over?”
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The scientists continued tracking the Zika virus across the Americas. They reviewed data on local outbreaks that countries reported to P.A.H.O. They also tallied confirmed cases of Zika in travelers coming home to Florida.
Across the Americas, both sets of statistics told the same story: The number of Zika cases crashed toward the end of 2016 and remained low afterward. But there was one glaring exception in the data.
In 2016, only a few people returning to Florida from Cuba were infected with Zika. In 2017, however, Cuba accounted for 98 percent of the travel-associated Zika cases in Florida.
This was an unexpected finding. Cuba has a sophisticated public health system, and it had seemed to be winning the war against Zika, apparently avoiding the outbreaks seen on other Caribbean islands.
To see if the initial results held up, Dr. Andersen and his colleagues turned to public health data in Europe and discovered a similar pattern among visitors to Cuba. The team developed a statistical model to predict the size of a Zika outbreak in a country, based on the number of travelers who went to Cuba and came back sick.
They concluded that Cuba’s outbreak in 2017 was “the same size as on other Caribbean islands, meaning thousands of reported cases,” Dr. Andersen said. But because reported cases typically comprise about 10 percent of a given outbreak, “we’re actually talking about tens of thousands of cases.”
The researchers also examined blood samples from travelers to Cuba to learn the history of the outbreak and determined that the virus appeared in Cuba in the summer of 2016. There was no Patient Zero; instead, Zika arrived several times from other islands. Then it smoldered, as it had elsewhere, for a year.
Dr. Andersen suspects that Cuba’s aggressive mosquito control and disease surveillance held back the virus while it raged elsewhere in 2016. Other mosquito-borne viruses, such as dengue, were also surging through the Caribbean, but Cuba didn’t see many cases of those, either.
But after the global emergency was called off, Zika gained momentum in Cuba in 2017, the researchers speculated.
“It is easy to miss an outbreak,” said Dr. Ester Sabino, the director of the Institute of Tropical Medicine at the University of São Paulo in Brazil, who was not involved in the new study. Many people infected with Zika don’t feel any symptoms, while some suffer only a mild fever for a few days.
It is rare in many Latin American countries for an infection to be confirmed with a sophisticated genetic test, Dr. Sabino said. The methods used by Dr. Andersen’s team were “a smart way to do world surveillance” for diseases like Zika, she added.
Dr. Andersen said that the new study adds to the evidence that public health workers should look for signs of outbreaks earlier.
“In many of these cases, we wait until we see weird symptoms and diseases in patients, and then we realize we have an outbreak,” he said. “If we look at the mosquitoes, we could detect it much earlier.”
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