Both the Cayman Islands and its neighbor to the north, Florida, are fighting the Aedes aegypti mosquitoes that can infect people with the Zika virus, in similar ways – up to a point.
The Cayman Islands Mosquito Research and Control Unit, which has long instituted measures to eradicate the Aedes aegypti mosquitoes, immediately stepped up its efforts once it learned of the emergence of the virus in other countries this year – now numbering around 70. After a public education campaign, aerial and ground-level fogging and a trial run of releasing genetically modified mosquitoes, Cayman to date reports just five locally transmitted cases.
Meanwhile, the most recent figures for the state of Florida indicate a total of 46 locally transmitted cases statewide, with at least 29 linked to Miami’s artsy Wynwood neighborhood, the Miami Herald reports. Since then, the newspaper states, additional locally transmitted cases have been reported in the Miami Beach area, across the bay from Wynwood.
In each case, leaders in those jurisdictions, working with state and national public health leaders, including from the Florida Department of Health and the U.S. Centers for Disease Control and Prevention, have positioned their communities on a kind of sudden war footing against an emergent epidemic of Zika virus cases.
“Controlling this epidemic absolutely depends on our determining one of those sources of infection for each new case,” said Diana Martinez, a medical technologist in Miami/Dade County.
When the time came to ramp up Cayman’s control effort, MRCU Director William Petrie was ready with a three-pronged approach. Step one was to remind citizens how serious the epidemic is and begin educating them about ways to discourage mosquito breeding by cleaning up puddles and removing scrap and debris that could hold stagnant water, as mosquito eggs and pupae thrive in standing fresh water. Adult mosquitoes emerge from their pupal stage in one to three days.
An old coffee can full of water might release hundreds of mosquitoes a week. A discarded damp tarpaulin in a vacant lot could produce tens of thousands, the MRCU says.
The second step was to provide information on protection, by covering up as much as possible with long sleeves, pants and hats, and using insect repellant containing DEET.
“You have to repeat those messages over and over in fresh ways for them to stick,” Dr. Petrie said.
The third step is eradication. For the MRCU’s part, they:
Walk the turf where reports of infestation are the highest, collecting or destroying anything that can hold water.
Break up and spread bundles of organic waste – tree limbs, leaves, piles of mown grass and weeds – that could get damp and enable mosquito-friendly pools to develop.
Spray dense foliage and swampy areas as well as garbage cans, using backpack insecticide dispensers.
Drive the streets and alleys in motorized vehicles carrying industrial-sized sprayers trailing a fog of poison.
Releasing all the insecticides onto street-level neighborhoods is not the most effective way of protecting the community, Petrie knows. It’s hard to predict what effect the fogs and sprays might have on people and the environment in the long term.
So far, the Miami/Dade approach seems to mirror the traditional mosquito-control methods of Cayman’s MRCU – with a couple of differences. One is that South Florida is using aerial spraying more extensively, as of course it must over a greater landmass.
“It’s a necessity,” according to a manager in the Solid Waste Management Department. “Dade is a huge county in terms of area. And consider that a big part of it is in the Everglades. A swamp.”
Dade Waste Management also reflects Dr. Petrie’s vigorous public information approach, and the department’s website offers plain talk: “Miami-Dade County is currently working to combat the Zika virus. Florida Gov. Rick Scott declared a public health emergency in February 2016, and the County is working with the Florida Department of Health to address the issue.”
Role of Oxitec
Above and beyond the traditional public health standards, the MRCU has partnered with Oxitec, a British biotech company that has developed a way to control mosquitoes by using genetically modified mosquitoes.
The company is releasing hundreds of thousands of GM mosquitoes each week through a small defined area in West Bay.
Oxitec’s Tali Cohen and Heidi Groves were out in a modified van last month to release the GM modified male mosquitoes in hopes that the insects will mate with female Aedes aegypti mosquitoes. When a female mates with a GM male mosquito, the next generation is unable to survive to adulthood, and the hope is that this will kill off the population of mosquitoes responsible for spreading Zika and other viruses.
The World Health Organization has been monitoring Oxitec’s field trials, including extensive efforts in the Cayman Islands, hoping to determine whether the selective release of male mosquitoes bred so that they pass down a fatal gene to their offspring will substantially wipe out insect colonies.
Oxitec’s approach relies upon what decades of basic research has shown about these species, including that males do not bite. Releasing hundreds of thousands of GM males to an existing regional populations means that females will breed, but the offspring of the GM bugs will get the genetic poison pill and die. Repeat the process over and over again, as Oxitec has done in Cayman and other test venues, and the total number of mosquitoes can decline by as much as 90 percent.
In Florida, “Oxitec’s efforts to test and bring its ‘mutant’ insects to the U.S. to fight the Zika virus have been blocked by opposition in the Florida Keys. The issue is now headed to the November ballot for voters to decide,” U.S. news outlets, including National Public Radio, reported last week.
But the U.S. Food and Drug Administration ruled in the closing days of August that a field trial in the Keys is permissible. The FDA said a fresh study “will not have significant impacts on the environment.”
The company is working with the Florida Keys Mosquito Control District on the project and has a lab in the Marathon, Florida, office of the agency. Oxitec and the agency have been working together since a dengue fever outbreak in 2010, according to a report in the Tampa Bay Times.
Fight the disease or control its transmission?
The greatest concern about the Zika virus is that when it infects pregnant women, it can cause severe birth defects, including underdeveloped skulls and crippling brain damage.
Dr. Lyle R. Petersen, the CDC’s Zika Response Manager, said, “This could lead to hundreds of infants being born with microcephaly or other birth defects in the coming year. We must do all we can to protect pregnant women from Zika and to prepare to care for infants born with microcephaly.”
Zika can also be transmitted sexually.
Dr. Samuel Williams-Rodriguez, Cayman’s head of public health, said in a statement last month that he is confident that with the MRCU, government and the public working together, “a large outbreak of the [Zika virus] disease will be prevented” on island.