First Cases of Mosquito-Borne Zika Transmission Identified in the U.S.

By John Henry Dreyfuss, staff.

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  • Four cases of Zika direct human infection in Miami are highly likely to have been caused by infected mosquitoes.
  • The Florida Department of Health has documented the first instances of local transmission in the continental U.S.
  • The four cases involve three men and one woman who are called “very likely” to have contracted the disease locally from Zika infected mosquitoes.


Figure 1. Aedes aegypti, the yellow fever mosquito, is known to carry the Zika virus,
as well as dengue fever, chiungunya, and other diseases.
(Sources: Wikipedia/By Muhammad Mahdi Karim (
Facebook Youtube - Own work
, GFDL 1.2/Creative Commons.)

Four cases of Zika infection in Miami are highly likely to have been caused by infected mosquitoes, according to the Florida Department of Health. These would be the first documented instances of local transmission within the continental U.S.

This news has been widely reported in the U.S. by The New York Times, The Washington Post,,, and other major news outlets.

"The cases are likely the first known occurrence of local mosquito-borne
Zika virus transmission in the continental United States."
—Centers for Disease Control and Prevention

The New York Times

“Officials believe that the area of active transmission is limited to a one-square mile area just north of downtown Miami. No mosquitoes tested have been found to be carrying the Zika virus, and the department is going door to door in the neighborhood collecting urine samples to test residents.

“Miami-Dade County is one of the biggest ports of entry into the United States from countries where the Zika virus is circulating, and experts have long described it as one of the areas most at risk for the spread of the disease.

“Governor Rick Scott said in a statement that the four cases involve three men and one woman. The statement did not indicate if the woman was pregnant.”

“The cases mark a new stage in the life of the virus in the United States. There are more than 1,300 Zika cases in the continental United States, but until the Florida announcement, all of them had been a result of travel abroad — contracted either by a mosquito bite elsewhere or by sexual intercourse with someone who had traveled to a Zika-infected area.”


Figure 2. The larva of the Aedes aegypti can be found growing and maturing
in any body of standing water. Preventing the spread of Zika includes
emptying all standing water containers around the house.
(Sources: Wikipedia/By Econt - Own work/Creative Commons.)

“Four individuals in Miami-Dade and Broward counties have been infected with the Zika virus by local mosquitoes, Florida health officials said Friday.

These are the first known cases of the virus being transmitted by mosquitoes in the continental United States.

"While no mosquitoes trapped tested positive for the Zika virus, the department believes these cases were likely transmitted through infected mosquitoes in this area," according to a statement from the Florida Department of Health.

“To date, there have been 386 cases of Zika in the state of Florida, including 55 pregnant women. The counties with the highest number of cases are Miami-Dade with 99 and Broward with 55.”

“Blood donation centers in the two affected counties have stopped accepting blood from donors in the affected ZIP code until officials implement measures to screen donated blood or institute a process to deactivate the virus in blood.”

“At least 13 infants have been born with Zika-related birth defects in the continental U.S. and Hawaii, and there have been six sudden or voluntary Zika-related pregnancy losses reported. There are more than 400 pregnant women with the virus in the United States.

In February, the World Health Organization declared a "public health emergency of international concern" because of an alarming increase in cases of microcephaly linked to the virus.”


Figure 3. Aedes aegypti mosquito distribution in the U.S. 2016.
(Sources: Wikipedia/By U.S. Centers for Disease Control and Prevention/Public Domain.)

The Washington Post

Florida officials on Friday announced the first local spread of the Zika virus through infected mosquitoes in the continental United States.

Gov. Rick Scott made the announcement during a press conference Friday after a health department investigation into four suspected cases in Miami-Dade and Broward counties. He said transmission was confined to a small neighborhood just north of Miami.

“We learned today that four people in our state likely have the Zika virus as a result of a mosquito bite," he said. "All four of these people live in Miami-Dade and Broward Counties, and the Florida Department of Health believes that active transmissions of this virus could be occurring in one small area in Miami."

The Centers for Disease Control and Prevention, which has been closely coordinating with Florida and sent a medical epidemiologist at the state's request, said in a statement Friday: "The cases are likely the first known occurrence of local mosquito-borne Zika virus transmission in the continental United States."


Figure 4. Aedes albopictus, also known as the Asian tiger mosquito, is one of two mosquito
species known to carry the Zika virus and West Nile virus with the potential to infect humans.
(Sources: Wikipedia/By James Gathany - CDC Public Health Image Library/Public Domain.)

“An outbreak of the Zika virus has been confirmed in Florida, marking the first time the virus has been found to be transmitted via infected mosquitoes within the continental U.S.

“The outbreak has infected at least four people, three men and one woman, through local transmission, Florida officials said today.

“’This means Florida has become the first state in our nation to have local transmission of the Zika virus,’ Florida Gov. Rick Scott said.

“Scott said a small area in northern Miami that is about a square mile in size is the only area where the Zika virus is being transmitted from mosquitoes to people.

“’We’re being very aggressive at testing people there we are testing the mosquitoes there and we spraying to make sure it’s contained,’ Scott said. He said health officials do not think that the transmission was ongoing.”


Figure 5. Global map of the predicted distribution of Aedes albopictus in 2015.
The map depicts the probability of occurrence (from 0 blue to 1 red)
at a spatial resolution of 5 km × 5 km.
(Sources: Wikipedia/By Moritz UG Kraemer, Marianne E Sinka, Kirsten A Duda,
Adrian QN Mylne, et al./Public Domain – Creative Commons

Local Transmission within the U.S. Had Been Widely Predicted

“You will start to see Zika cases transmitted by mosquitoes in the southern United States,” Nitin S. Damle, MD, MS, predicted earlier this summer. It could travel as far north as Maine. It is not exclusive to the south. Physician’s discussions about prevention are crucially important.”

Dr. Damle is President of the American College of Physicians and a member of the clinical faculty in the Alpert Medical School of Brown University. He is also a founding and managing partner at South County Internal Medicine Inc. in Wakefield, Rhode Island.