HHS Officials: No Evidence of Larvicide Link to Microcephaly

Alicia Ault

February 18, 2016

It can't be ruled out, but it is not likely that larvicide used to kill mosquitos in drinking water in Brazil is tied to the uptick in microcephaly seen in that country, said Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), in a conference call with reporters.

An Argentinian group, Physicians in the Crop-Sprayed Villages, first made the allegation that the larvicide pyriproxyfen was the likely cause of the increase in birth defects in a paper that has ricocheted through social media.

"It's a theory that's difficult to disprove at this time," said Dr Fauci. But, he added, "you still have to explain the mounting evidence of virus in the brains of stillborn babies."

Tom Frieden, MD, director of the Centers for Disease Control and Prevention (CDC), said that federal officials "don't yet consider [Zika] a definitive causal link" to microcephaly, but that epidemiological and laboratory data "strongly suggest a link between microcephaly and Zika in pregnancy."

The final determination will come "by doing careful case-controlled studies," said Dr Fauci. Those studies have begun in Brazil and "will tell us whether or not there is a connection, and what the magnitude of the connection is," he said, adding that he expects answers in a few months.

"Urgent Action"

Both NIAID and the CDC are currently shifting money away from other programs to fund Zika efforts such as assisting Brazilian researchers. President Obama has requested $1.8 billion in emergency appropriations to combat Zika, including for mosquito control, vaccine development, diagnostic testing, epidemiologic studies, and helping overseas partners, but Congress has yet to act.

"The sooner Congress acts, the better," said Dr Frieden, noting that the CDC has 500 staff members working on Zika.

Several dozen are in Puerto Rico, which has had local transmission and needs "urgent action," said Dr Frieden. Eighty to ninety percent of adults on the island are infected with dengue, and 25% have been infected with chikungunya in the past year, he said. Both of those viral diseases are spread by the Aedes aegypti mosquito, which also transmits Zika.

There's "a concern there could be rapid and widespread introduction of Zika," said Dr Frieden, who called aegypti "the cockroach of mosquitos," because of the difficulty in killing it.

The CDC is also preparing for "hundreds if not thousands of returning travelers with Zika," said Dr Frieden. Each year, 40 million Americans travel to and from the countries and territories where Zika has been identified.

Dr Frieden would not say whether there might ultimately be any travel restrictions, as had been discussed during the Ebola outbreak in 2014.

He and Dr Fauci said that the Ebola crisis had taught the world the importance of maintaining sentinel systems to find and contain such diseases. "The lesson of Ebola is don't let something get ahead of you," Dr Fauci said.

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