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Brazil Sprays for Mosquitoes As Zika Fears Threaten Carnival

Image: Workers greet passengers at Recife airport with Zika information on Feb. 4

Workers greet passengers at Recife airport with Zika information on Feb. 4. Huge crowds are poring into city for Carnival. Jane Derenowski / NBC News

Health department workers are spending the week spraying insecticide up and down the streets of Brazil's major cities, including Recife, the city at the epicenter of the country's fast-spreading outbreak of Zika virus.

They're trying to kill as many mosquitoes as possible before Carnival, the giant festival of parades, music and dancing that attracts millions of visitors from around the world.

Zika Virus Outbreak Casts Shadow on Carnival Celebrations in Brazil 2:15

As crowds pour into Recife airport, they're met with bands and warnings. Staffers in mosquito-decorated T-shirts offer information about the Aedes aegypti mosquito that's spreading the virus across Latin America and the Caribbean.

"In a couple of days we will have about 1.5 million people on these streets during Carnival," said Jailson Correia, health secretary for the northeastern coastal metropolis.

The concerns are mostly for pregnant women. Recife's also the epicenter of what looks like a surge in cases of microcephaly, a serious birth defect in which a baby's brain is underdeveloped. There are hints of other types of brain damage to babies, as well.

Image: Brazil Group Workers
Workers prepare to spray insecticide to combat the spread of the Zika virus in Recife, Brazil, on Feb. 3, ahead of Carnival. The city expects more than a million visitors for the celebration. Jane Derenowski / NBC News

Researchers are also checking reports of an unusually high number of cases of Guillain-Barre syndrome, a serious neurological condition that sometimes develops after an infection.

Doctors say most people never know they've been infected with Zika, which causes mild symptoms at the worst — mostly a rash and fever.

Brazil's president Dilma Rousseff said she'd deploy 220,000 troops to help eradicate the mosquitoes, which bite during the day and breed inside and around homes.

"What we are doing is going house to house in this area, doing the mechanical removal or the elimination of any breeding sites," Correia said.

"Part of our job is actually to provide education to show people how can they do the job themselves to find the places where the mosquito tends to find as a breeding site in the households." Aedes mosquitoes are notorious for their ability to breed in small pots of water and even discarded bottle caps.

The preparations are a practice run for the Olympics, scheduled for August in Rio de Janeiro. That's winter in Brazil, and officials say they hope the mosquitoes will be less active then.

Brazil once eradicated Aedes aegypti mosquitoes, 50 years or so ago. But the insects crept back when eradication efforts ended. Now the mosquitoes, which prefer densely populated urban spaces and which bite during the day, spread dengue virus and Chikungunya as well as Zika. They carry yellow fever virus, also, but there's a vaccine against that one. There is no vaccine against Zika.

The World Health Organization declared the rapid spread of Zika and its feared link with microcephaly to be a global health emergency. The mosquitoes live in hot zones as far north as Florida, and spraying efforts are under way in Miami, also.

The Centers for Disease Control and Prevention says it is unlikely Zika will take hold in the U.S. in the way it has further south. Travelers will bring the virus on occasion and if there are Aedes aegypti mosquitos circulating in an area, there could be small outbreaks, CDC predicts.

But with 12 travel-associated cases in the state of Florida, Governor Rick Scott declared a public health emergency in the four counties affected.

"Although Florida's current nine Zika cases were travel-related, we have to ensure Florida is prepared and stays ahead of the spread of the Zika virus in our state," Scott said.

"We know that we must be prepared for the worst even as we hope for the best."

Florida Expands State of Emergency Over Zika Virus Fears 1:15

Dallas officials say they confirmed one case of local transmission of Zika this week and said it was almost certainly through sexual contact. One patient had recently traveled from Venezuela, where Zika is spreading, and a sexual partner who was also infected had not traveled.

But CDC and other health experts say avoiding mosquito bites is the best way to prevent infection. They recommend using insect repellents and wearing long sleeves.

Consumer Reports shared its latest rating of mosquito repellents on Thursday: No. 1 is Sawyer Fisherman's Formula Picardin, which contains a chemical the CDC says is especially effective. No. 2 is Repel Lemon Eucalyptus which contains oil of lemon eucalyptus, as well as menthoglycol. Other top-rated products contain DEET or picardin.