Local Transmission of Zika Likely Occurring in Florida


July 29, 2016

UPDATED August 1, 2016 // Mosquitos probably are spreading the Zika virus in southern Florida, the state's health department announced today.

The Florida Department of Health (DPH) said there is a "high likelihood" that four individuals with the virus probably acquired it through mosquito bites in an area of active transmission north of downtown Miami. These cases — representing three men and one woman — are the first known instances of local transmission of the virus, which causes microcephaly and other birth defects, in the continental United States.

In contrast, the 1658 cases of Zika infection reported by the US Centers for Disease Control and Prevention (CDC) as of July 28, with one exception, resulted from a person becoming infected while visiting a country where the virus was spreading locally, or having sex with such a traveler. In a single case, someone became infected in a laboratory.

US territories, such as Puerto Rico, are a different story. All but 21 of the 4750 cases in US territories as of July 28 resulted from local transmission; the rest were travel related, according to a running tally onthe CDC's website.

As of July 21, 13 women infected with Zika in the United States have delivered babies with birth defects. For another six women with the virus, a pregnancy was lost with evidence of birth defects.

The DPH acknowledged that no trapped mosquitos in Florida have yet to test positive for the virus. However, it's ruled out the possibility that the four individuals had become infected on account of foreign travel or having sex with an infected person.

In a news briefing today, CDC Director Tom Frieden, MD, MPH, downplayed the importance of finding an infected mosquito to confirm local transmission, saying the task was like searching for a needle in a haystack.

"As we anticipated, Zika is now here," Dr Frieden told reporters. "Everything we've seen so far indicates this is a mosquito-borne transmission."

The CDC, he said, continues to recommend that everyone in areas where the virus-bearing Aedes aegypti mosquitos are present take precautions against getting bit. He underlined the importance of that advice for pregnant women.

The CDC said that it expects to see more cases of locally transmitted Zika infections in the continental United States. The agency has sent a medical epidemiologist to Florida to help the state investigate its outbreak.

Funding Controversy Comes to the Fore

The news conference took a political turn when a reporter asked Dr Frieden about his agency's ability to finance its campaign to prevent the spread of Zika. President Barack Obama has asked Congress to appropriate $1.9 billion to fight the virus, but the Republican-controlled Congress adjourned for the summer without passing any sort of funding bill.

"We are doing the best we can with the resources we have available to us," said Dr Frieden. "If we had more resources, we would be able to mount a more robust response."

The Florida outbreak illustrates the importance of creating an infectious-disease rapid response fund, something both houses of Congress and both parties support, he said.

A reporter from the New York Times asked Dr Frieden why the CDC hasn't issued a travel advisory cautioning Americans about visiting the Miami neighborhood suspected in the Zika outbreak, although it has issued travel advisories about Latin America and the Caribbean. "This does not seem consistent," the reporter said. "It looks like bowing to pressure from the Florida tourism industry."

The agency has been consistent, countered Dr Frieden. He said the travel advisories for south of the border reflected widespread local transmission of the Zika virus, which hasn't happened here, and which the CDC does not expect to happen. But if it does, he said, the agency would issue travel advice.

Discouraging News From Puerto Rico

On the same day that Florida officials announced that Zika was spreading locally, the CDC issued a distress call for Puerto Rico. According to an article published online today in the agency's MMWR Morbidity and Mortality Weekly Report, the Zika outbreak that is occurring there is both widespread and accelerating. The US territory reported 2612 new confirmed and presumptive Zika cases in June, almost eight times as many as in February. Among pregnant women exhibiting Zika symptoms, the percentage with confirmed or presumptive infections rose from 8% to 41% during that time.

In all, Zika has been diagnosed in 5582 people, including 672 pregnant women, in Puerto Rico as of July 7. The MMWR article cites a higher number of cases than the CDC does (4684) in its running tally because it relies on Puerto Rico's arboviral surveillance system, not the CDC's.

In a news release, the CDC noted that the number of pregnant women infected with Zika in Puerto Rico probably far exceeds 672 because roughly 80% of people who get infected have no symptoms and therefore may not seek medical care and testing. The agency recommended that all pregnant women in Puerto Rico and other Zika zones be routinely tested as part of their prenatal care whether or not they experience symptoms.

Lyle Petersen, MD, MPH, the incident manager for the CDC's Zika response team, warned that the country's epidemic could result in hundreds of newborns with birth defects in the coming year. "We must do all we can to protect pregnant women from Zika and to prepare to care for infants born with microcephaly," Dr Petersen said in the news release.

Promising Discovery for Vaccine Development

In an encouraging development, a study published online today in Cell Reports said that a Zika vaccine incorporating one strain of the virus should work against all other strains.

Zika viruses fall into two genetic lineages — the African one, discovered in 1947, and an Asiatic counterpart that recently made its way to Latin America and the Caribbean. In the study, serum samples were taken from people infected with Asiatic strains circulating in South America and mixed with a grab bag of strains in the laboratory. Antibodies in the sera neutralized viruses in both the Asiatic and African families. Likewise, antibody-containing sera from mice infected with either African or Asiatic strains effectively neutralized Zika viruses from either lineage.

These findings indicate that the two lineages, though genetically distinct, have identical surface antigens, making them the same serotype. The study's authors said that the ability of a single strain to elicit broadly neutralizing antibodies against multiple strains provides "a direct path for the development of an effective vaccine."

The study was conducted by investigators from the National Institute of Allergy and Infectious Diseases, Washington University in St Louis, Missouri. and Emory University, in Atlanta, Georgia.

Follow Robert Lowes on Twitter @LowesRobert


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