SAN JUAN, Puerto Rico (AP) — As many as 50 pregnant women in Puerto Rico are becoming infected with Zika every day, top US health officials said Wednesday as they urged the US territory to strongly consider aerial spraying to prevent further spread of the mosquito-borne virus.

The warning came as Puerto Rico debates whether to fumigate with the insecticide Naled, a proposal that has sparked protests in the US territory over concerns about its impact on human health and wildlife.

Dr Tom Frieden, director of the US Centres for Disease Control and Prevention, told The Associated Press that aerial spraying is the island’s best defense to fight a virus that can cause microcephaly, a rare defect in which babies are born with abnormally small heads and brain damage.

He said the island lacks an integrated mosquito control program.

“If any part of the continental US had the kind of spread of Zika that Puerto Rico has now, they would have sprayed months ago,” he said. “This is more a question of neglect than anything else. … If we wait until children with microcephaly are born, it will be too late. That’s the problem.”

Puerto Rico government officials are still debating the issue, with legislators holding public hearings amid a growing number of protests. Some health officials have warned of the dangers of Naled, with Puerto Rico’s health secretary saying pregnant women and asthmatics should remain indoors if it is sprayed. Puerto Rico has one of the highest asthma rates in the world.

Ultimately, it is up to Puerto Rico’s governor to decide whether to implement aerial spraying, which would be run and paid for by the US government.

In May, Puerto Rico reported the first microcephaly case acquired on US soil. It involved a foetus that a woman turned over to US health officials who found it tested positive for Zika.

A total of 339 pregnant women in Puerto Rico have been diagnosed with Zika, and Frieden said it is only a matter of time before one of them gives birth to a child with microcephaly.

Overall, Puerto Rico has reported nearly 2,400 Zika cases, 44 hospitalizations and one death. In addition, 16 people have been diagnosed with a temporary paralysis condition known as Guillain-Barre that has been linked to Zika infections.

The CDC estimates more than 20 percent of Puerto Rico’s 3.5 million people could be infected with Zika in an outbreak expected to peak by this summer. Local health officials have dismissed that number as being exaggerated.

Frieden said the spread of Zika is not that apparent because eight of 10 people infected show no symptoms and many others have only mild symptoms.

“It’s really something of a silent epidemic now,” he said. “The data is extremely clear that it’s spreading rapidly in many parts of Puerto Rico. …This is in line with what we feared would happen.”

Gina McCarthy, administrator for the US Environmental Protection Agency, told the AP that Puerto Rico needs to seriously consider aerial spraying.

“It can be done safely and effectively and is perhaps the most important tool we can use right now to change the trajectory,” she said.

The EPA notes on its website that people sensitive to chemicals could experience skin, eye and nose irritation. In addition, it says Naled poses some risk to aquatic invertebrates and wildlife, noting that applications made between dusk and dawn can reduce exposure to honey bees.

Frieden said less than two tablespoons of Naled would be used per acre. He said the product was used last year on 6 million acres in Florida, including Miami. He also said it was used in New York and there was no increase in the number of asthma cases there.

US officials said aerial spraying would be done several times a week and then weekly, depending on its effect on mosquitoes.

“We know how to do this,” McCarthy said. “We are more than willing and anxious to do this.”