Health Care

Miami-Dade considers new weapon in Zika fight: disease-fighting bacteria

Vector biologist Katherine Ramirez with the Consolidated Mosquito Abatement District in Fresno County, California releases non-biting sterile male Aedes aegypti mosquitoes infected with Wolbachia in June 2016. Miami-Dade officials are considering using the same method to help reduce the numbers of mosquitoes that spread Zika.
Vector biologist Katherine Ramirez with the Consolidated Mosquito Abatement District in Fresno County, California releases non-biting sterile male Aedes aegypti mosquitoes infected with Wolbachia in June 2016. Miami-Dade officials are considering using the same method to help reduce the numbers of mosquitoes that spread Zika. ezamora@fresnobee.com

As the only county in the nation grappling with a local outbreak of Zika, Miami-Dade has emerged as something of an open laboratory for experimenting with new technologies in mosquito control.

First, county officials said they are considering the release of genetically engineered mosquitoes to help stop the virus’ spread in Miami Beach and Miami’s Little River neighborhood. Now, they also are looking at another approach: using mosquitoes infected with a naturally occurring bacteria called Wolbachia that stops the insects from transmitting viruses.

Wolbachia doesn’t typically infect Aedes egypti mosquitoes, a species commonly found in South Florida and the most capable of spreading Zika and other diseases, including dengue and chikungunya. But infecting the mosquitoes with the bacteria could be key to halting the spread of those diseases — not only in Miami-Dade, but also in Latin America, Australia and Southeast Asia.

In a letter to State Surgeon General Celeste Philip detailing local plans for combating Zika, Miami-Dade Mayor Carlos Gimenez said mosquito control officials had contacted the University of Kentucky’s Department of Entomology to explore the possibility of using its Wolbachia-infected mosquitoes.

“During the upcoming mosquito season,” Gimenez wrote, “the county intends to conduct open trials in areas with high mosquito populations.”

The Environmental Protection Agency approved the experimental use of UK’s Wolbachia-infected Aedes aegypti mosquitoes this year for limited tests in Monroe County, which encompasses the Florida Keys, and in California, where officials in Fresno County have released thousands of non-biting males dusted with the bacteria into the wild, where they produced offspring that never matured.

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The mosquitoes have not been tested yet in Florida. But while the UK technology, marketed as MosquitoMate, largely aims to reduce the numbers of mosquitoes in an area by releasing sterile males, others are using Wolbachia to focus solely on preventing the insects’ ability to spread disease.

The Eliminate Dengue Program, a not-for-profit international collaboration led from Australia’s Monash University, uses the bacteria to stop disease-causing viruses from replicating inside the mosquito and being transmitted between people.

During the upcoming mosquito season, the county intends to conduct open trials in areas with high mosquito populations.

Miami-Dade Mayor Carlos Gimenez, on use of Wolbachia mosquitoes to combat Zika

Phil Lounibos, a professor at the Florida Medical Entomology Laboratory at the University of Florida, said Eliminate Dengue’s approach has been proven effective in Australia and Indonesia — not necessarily as a mosquito control program, but as a mosquito “replacement program” that produced generations of Wolbachia-infected mosquitoes incapable of transmitting viruses to people.

Of the two approaches to using Wolbachia in mosquitoes, Lounibos said he prefers the Eliminate Dengue model.

“It’s ecologically sounder,” he said, adding that both methods may help reduce spread of disease, but only one will require repeated releases of sterile male mosquitoes, which could mean long-term expense for local taxpayers.

Lounibos cited as an example the biotechnology company Oxitec, which has been collaborating with the Florida Keys Mosquito Control District for a potential trial release of genetically engineered mosquitoes. In a straw poll this week, voters in Monroe County said they agreed with the idea.

“It’s unrealistic to think that you can just eliminate a mosquito species as simply as one of these sterile-male control programs wants to do,” he said.

He said Oxitec’s model will require repeated releases. “We don’t know how long they’ll be effective or if they’ll be able to reduce Aedes aegypti there, but certainly it’s not indefinite.”

Mike Hernandez, a spokesman for Miami-Dade’s mayor, said that county officials are aware of both Wolbachia technologies, and that they are consulting with the Centers for Disease Control and Prevention for “expert advice” on the best approach for South Florida.

“We’re in the middle of the process of fact-finding,” Hernandez said.

640,000 Male mosquitoes infected with Wolbachia released in Clovis, California, in June

While the MosquitoMate approach undergoes testing in California and eventually Florida, the Eliminate Dengue program has been spreading to more countries. An international coalition of organizations including the Bill and Melinda Gates Foundation, the U.S. and British governments and the Wellcome Trust, a biomedical research charity, announced in October that it would invest $18 million in an Eleminate Dengue experiment in Latin America to see if Wolbachia can effectively cut disease transmission.

In the experiment, researchers will ask local residents in areas of Brazil and Colombia to release mosquitoes infected with Wolbachia, which will be passed to any offspring who then can spread the bacteria into the population without requiring repeated releases of the insects.

Organizers of the experiment have even helped Colombians to create a “Amigos Wolbachia” program, where children raise the mosquitoes and release them. A similar program for children in Australia is called “Wolbachia Warriors”.

Researchers had been testing Wolbachia to prevent the spread of dengue when they learned the bacteria also seemed to stop Zika from spreading. The Gates Foundation has been funding research into dengue transmission as part of its Grand Challenges In Global Health Initiative in 2003.

Steven Kern, deputy director of quantitative sciences at the Gates Foundation, said that judging from the results of earlier experiments with Wolbachia-infected mosquitoes, such as in Australia, the technique has advantages that compared favorably to other types of mosquito control.

“Once you get it established, it hasn’t receded,” he said. “You don’t have to go back and release more.”

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A previous version of this story stated the wrong country for the “Wolbachia Warriors” program.

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