Aerial spraying of the insecticide naled, followed by a product that targets mosquitoes when they are in the larval stage, may be responsible for a sharp drop in Aedes aegypti mosquitoes in a part of Miami where local transmission of the Zika virus was first found, the Centers for Disease Control and Prevention reported Friday.
CDC Director Dr. Tom Frieden said the apparent success of the combination in the Miami neighborhood of Wynwood may represent a new standard for control of Aedes aegypti mosquitoes.
“It appears that the aerial application of this one-two punch has the ability to rapidly interrupt transmission,” Frieden said during a media conference Friday.
“The findings are quite striking,” he added. “Those who’ve worked in the field of arbovirology and control of diseases spread by Aedes aegypti and have looked carefully at this data are struck that we haven’t seen similar control in other diseases spread by this particular mosquito species.”
Aedes aegypti mosquitoes are extremely difficult to control. The females, which need a blood meal to procreate, prefer to bite humans. As a result, they live close to people, in or around homes. They need only small amounts of water to lay their eggs—as little as the amount that a discarded bottle cap could hold—which adds to the difficulty of getting rid of this species.
The bugs are resistant to some of the chemicals that have been used against them in the past, which is why public health officials turned to the combination of naled and a biological product called Bacillus thuringiensis subspecies israelensis—Bti—that kills larvae.
Naled alone didn’t appear to knock down the mosquito populations as successfully, Frieden said. It was tried in a different part of the city.
The CDC’s report noted that local hospital admission records were checked to see if people came in complaining of respiratory problems or skin rashes followed spraying of the chemicals. There was no evidence that happened.
A number of protesters in Miami objected to the spraying. And earlier, Puerto Rico dropped a plan to use this approach there over public objections.
Duane Gubler, an expert in mosquito transmitted diseases, was cautious about interpreting the results, saying several methods of mosquito control were used in the Wynwood neighborhood, and it’s not clear the drop in mosquitoes can be attributed to the aerial spraying.
A former head of the CDC’s dengue branch in Puerto Rico, Gubler had been skeptical of the aerial spraying plan before the work was undertaken.