Genomics Reveal Surprises About Florida Zika Outbreak

Damian McNamara

March 04, 2017

LA JOLLA, California — The Zika virus outbreak in the United States in 2016 was caused by multiple infected travelers arriving in South Florida, not by a single "patient zero," genomic research has revealed.

Reporting here at the 10th Future of Genomic Medicine Conference, Kristian Andersen, PhD, from Scripps Translational Science Institute in La Jolla, California, and his team identified four different "introductions" of the Zika virus during the outbreak using genomic sequencing by testing samples from 17 people.

Extrapolating this to the total number of infected people, "the number of introductions that caused the outbreak in Miami is quite substantial," maybe on the order of 30, he explained.

Genomic sequencing of the virus from mosquitos and patients also revealed that Caribbean travelers were the primary means of introduction. To find out more, the researchers analyzed travel data to South Florida during the outbreak.

"The vast majority [of infected travelers] came by cruise ship. That is not something I would have expected," said Dr Andersen. He pointed out that taking a cruise is not associated with infection; it's just the means by which most infected travelers brought the Zika virus to Florida.

Most cases of infection occurred in three zones in Miami Dade County; however, sequencing showed that viral strains in the different zones were not distinct.

Researchers also confirmed the virus was mosquito-borne by showing that decreases in the Aedes aegypti mosquito population from pesticide spraying corresponded with a subsequent drop in new reported cases of infection.

"It's what you would expect, but it's nice to see. More importantly, it tells you that if you get rid of the mosquito, you get rid of the Zika virus," said Dr Andersen.

In terms of timing, the virus likely arrived in Florida several months before the first case was identified, sometime in Spring 2016, he added. This is "earlier than we would have expected."

In addition to the influx of international travelers from infected countries, the warm Miami weather supports a yearlong population of Aedes aegypti mosquitos. "South Florida is the only place with this early season mosquito abundance and lots of visitor traffic. It's really quite unique," said Dr Andersen. Although Aedes aegypti is found in other parts of the country later in the year, including areas with a lot of summer travelers, "the risk is probably focused on Florida."

The take home message is that we need to diagnose or detect much earlier.

"The take home message is that we need to diagnose or detect much earlier," said George Mias, PhD, of Michigan State University in East Lansing.

Genomics would improve early detection of the Zika virus, and at some point, "detect with high sensitivity at the single molecule level," he told Medscape Medical News.

Dr Andersen noted that although the Zika outbreak in Florida is over, probably because the mosquito population decreased quickly, a new outbreak could occur if the virus is reintroduced. "We might expect the introductions to start in the next several months or so," he warned.

The researchers plan to monitor Zika virus activity in the Caribbean and South and Central America. "That will really inform us about what will happen next," said Dr Andersen.

Dr Andersen and Dr Mias have disclosed no relevant financial relationships.

10th Future of Genomic Medicine (FOGM) Conference. Presented March 2, 2017.


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