Miami-Dade mosquito-control workers scour county in fight against Zika
Mosquito control workers on the front lines of Miami-Dade’s fight against the insects that spread Zika virus rely on three sources to tell them where to spray: complaints, numbers and species of mosquitoes found in traps, and referrals from the Department of Health, which tracks all Zika cases statewide.
In other words, all of their information is provided after the fact.
But what if county workers could harness the power of data to figure out ahead of time which neighborhoods are more likely to breed large numbers of the two mosquito species known to spread Zika, Aedes aegypti and Aedes albopictus?
Mathematicians call that predictive analytics, a type of forecasting tool yet to be deployed in the fight against Zika in Miami-Dade, where at least 72 people have contracted the infectious disease while traveling outside the country, according to the health department.
University of Miami researchers are examining a variety of local databases to develop maps that could help county officials forecast where Zika is likely to strike before it actually happens. They’ve already made at least one early finding: Affluent neighborhoods are more likely to have Zika mosquitoes, though they don’t yet know why.
“We’re taking this data, and basically trying to understand risk areas from the perspective of mosquito exposure,” said Whitney Qualls, a UM entomologist.
Zika virus is transmitted primarily through the bite of infected Aedes aegypti and Aedes albopictus mosquitoes, which also spread dengue and chikungunya. They prefer to bite people, and live indoors and outdoors near people. They are aggressive daytime biters, but can also bite at night.
The team of UM researchers, funded by a grant from the Miami Clinical and Translational Science Institute, is tackling the Zika risk from different angles: the numbers and species of mosquitoes trapped by the county over the last four years, historic temperatures and rainfall counts by neighborhood, even the abundance of trees and bushes on a city block.
Chalmers Vasquez, Miami-Dade’s mosquito control manager, said the agency doesn’t currently use all that information to guide its spraying and other efforts. “But we hope that it will have some use for us,” he said.
UM researchers have studied risk maps in the past to help combat mosquito-borne illnesses, such as chikungunya, dengue and malaria, in Latin America and other parts of the world. And Qualls believes the same can be done with Zika when the inevitable happens: a local transmission.
“These have been used to predict when there may be epidemics,” she said. “Implementation of control efforts can be done prior to the predicted epidemic. So that would be the idea.”
Qualls, a former mosquito control worker in St. Johns County, said the maps will be most useful when placed in the hands of experienced county workers who know how best to eradicate the bugs that transmit Zika and other diseases.
But first, researchers need to work out some kinks in the data, like standardizing all the information and getting better reads on the two mosquito species that transmit Zika.
At least 45 mosquito species have been found in Miami-Dade, Qualls said. One limitation of the county’s data is that historically, Miami-Dade has focused its surveillance efforts on salt marsh mosquitoes, which are not known to transmit Zika but spawn by the thousands in coastal areas and create a public nuisance.
72 Miami-Dade residents confirmed to have Zika virus
Vasquez said Miami-Dade tracks mosquitoes using 29 light traps located throughout the county, mostly in the southern area. The traps can catch all species of mosquitoes, including the two that transmit Zika. But they’re designed to attract primarily salt marsh and other mosquitoes attracted to light.
The two species that spread Zika are mostly daytime biters, Qualls said, and they aren’t attracted to light but to chemical compounds emitted by mammals, such as ammonia, carbon dioxide and lactic acid.
In the four years from 2012 through 2015, the light traps caught more than 1.16 million mosquitoes representing at least 34 different species. Of the two species that spread Zika virus, there were 7,564 Aedes aegypti and 6,872 Aedes albopictus.
UM researchers plan to focus on the two Zika mosquitoes by placing different traps, designed to attract those species, around the county.
Miami-Dade already uses about six of the traps, Vasquez said, beginning in 2010, when the county reported its first locally transmitted case of dengue fever, which is primarily spread by the Aedes aegypti. The traps are used to test mosquitoes for the virus. So far, none have been found.
“Finding mosquitoes that carry viruses is like looking for a needle in a haystack,” Vasquez said.
Still, UM’s early analysis of the existing data shows that environmental and social factors, including U.S. Census information on household income and population density by block, can be used to predict the abundance of Zika-transmitting mosquitoes in Miami neighborhoods.
Finding mosquitoes that carry viruses is like looking for a needle in a haystack.
Chalmers Vasquez, Miami-Dade mosquito control
One finding, Qualls said: “Areas with a higher socioeconomic status are associated with higher populations of Aedes aegytpi and Aedes albopictus.”
It’s not clear yet why that is. She said researchers are still a month or longer away from developing their first Miami-Dade risk map for Zika mosquitoes.
But their grant has run out, and UM researchers and graduate students are still collecting data to publish their research, said Qualls, who noted that risk maps are just one of the many tools that public agencies will need to help combat the spread of Zika.
“It will translate over to better protection of public health,” she said.