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Insecticide Spraying Working Against Florida's Zika Mosquitoes: Officials

A two-pesticide punch kills insects and their larvae -- safe for people: CDC

By Steven Reinberg
HealthDay Reporter

FRIDAY, Sept. 23, 2016 (HealthDay News) -- Aerial spraying of insecticides seems to be stopping the spread of the Zika virus in south Florida, health officials said Friday.

Seventy-four confirmed cases of the mosquito-borne infection that causes devastating birth defects have been reported in the state, the only state in the nation to report any local infections.

A combination of insecticides was needed to beat back the Aedes aegypti mosquito that carries the virus, according to the U.S. Centers for Disease Control and Prevention and the Florida Department of Health.

While ground spraying was ineffective, aerial spraying with the insecticides naled and Bti (bacillus Thuringensis) dramatically reduced the mosquito population and local transmission of Zika, CDC Director Dr. Tom Frieden said during an afternoon media briefing.

"This really heralds in a new era of [mosquito] control," Frieden said. "It appears that the aerial application of the one-two punch has the ability to rapidly interrupt transmission. It doesn't mean that the area is immune from future spread, but the findings are quite striking," he added.

These pesticides kill both the insect and its larvae, preventing the birth of new mosquitoes, Frieden said.

Aerial spraying is part of a comprehensive mosquito-control program that also includes encouraging people to get rid of standing water on their property and protect themselves against mosquito bites as well as using ground spraying in hard-to-reach areas, Frieden said.

This breed of mosquito has been particularly hard to control, Frieden said. And it's impossible to know if spraying will work in the long run, he added. But after spraying, the mosquito population in the Miami area dropped significantly, as evidenced by the low numbers of insects found in mosquito traps, he said.

The initial Florida outbreak started in late June and ran through early August. In Miami's Wynwood neighborhood, 30 people were identified as having been infected with Zika virus through local mosquito-borne transmission. In Miami Beach, 44 confirmed cases have been reported so far, according to Dr. Celeste Philip, Florida's surgeon general, who also spoke at the briefing.

Transmission of the virus in Wynwood stopped quickly after aerial spraying with both chemicals, Philip said. Since early August, no new cases of locally transmitted Zika have been reported in Wynwood, the health officials said.

Any new cases of Zika infection have been among people who brought the infection with them from areas outside the United States, Philip said.

The Zika epidemic has been centered in Latin America and the Caribbean, with Brazil reporting the largest numbers of infections and the birth defect microcephaly, which causes babies to be born with extremely small heads and underdeveloped brains.

In Miami Beach, aerial spraying stopped only recently, so it's too early to know if it will be as effective as it was in Wynwood, Frieden said. However, early results appear to mirror those seen in Wynwood.

Despite concerns about the effect of these pesticides on humans, Frieden said they are safe when used as directed, and no short-term health problems have been reported.

To reduce the risk of local Zika transmission within the United States, the CDC recommends that people returning from places with ongoing infections should use mosquito repellent every day for three weeks and follow the CDC's guidelines to prevent sexual transmission of Zika.

The Zika virus doesn't pose a significant health threat to most people, except pregnant women and fetuses.

The virus can be spread by infected men and women to their sex partners. There is no vaccine or treatment for Zika.

The CDC advises that partners of pregnant women use a condom to guard against sexual transmission during pregnancy.

The results of the aerial spraying efforts were reported Sept. 23 in the CDC publication Morbidity and Mortality Weekly Report.

More information

The U.S. Centers for Disease Control and Prevention provides more information on mosquito-borne diseases.

This Q & A will tell you what you need to know about Zika.

To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.

SOURCES: Sept. 23, 2016, media briefing with: Tom Frieden, M.D., M.P.H., director, U.S. Centers for Disease Control and Prevention; and Celeste Philip, M.D., M.P.H., Florida Surgeon General and Secretary; Sept 23, 2016, Morbidity and Mortality Weekly Report

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