Health officials in Florida are investigating whether the Zika infection of a woman in the Miami area could be the first transmission of the virus from a mosquito bite in the continental United States.
Lab tests confirmed the Zika infection, according to statements from the U.S. Centers for Disease Control and Prevention and Florida’s Department of Health.
Health officials said the case had no apparent links to recent travel outside the country. They did not immediately respond Wednesday to questions about ruling out other methods of transmission, such as sex.
The patient is an adult woman who lives in Miami-Dade County, according to a health official familiar with the case who wasn’t authorized to reveal details beyond the statements of the agencies involved, and thus spoke on condition of anonymity.
No other details about her case were released.
More than 1,300 Zika infections have been reported in the U.S., none involving bites from local mosquitoes; 14 of these were sexually transmitted and one lab worker was stuck with a contaminated needle.
Miami-Dade County has the most confirmed infections in Florida – 89, but so far all have involved someone who traveled outside the U.S. mainland to areas with Zika outbreaks, such as Latin America and the Caribbean.
Health officials predicted the virus would reach U.S. mosquitoes this summer and have mobilized to keep Zika from spreading beyond isolated clusters of cases.
According to a CDC response plan, health officials would want to see more than just one unexplained case before declaring that someone has been infected by a mosquito bite in the continental United States.
The plan suggests there should be two or more cases within a 1-mile area, in people who do not live together, who did not have sex with Zika-infected people, and who did not recently travel to countries with Zika outbreaks.
Evidence of the virus in mosquitoes captured in the same areas also might help investigators declare Zika is spreading, but short of that, it might be difficult to determine with certainty that mosquito transmission has occurred.
Mosquito control inspectors in Miami have been going door-to-door in the area under investigation since health authorities alerted them late last week, spraying to kill mosquitoes and emptying containers of the water they need to breed. If the virus is there, they want to keep it from spreading through more mosquito bites.
“We’re constantly in the area. We’re doing hand-held spraying, and we’ll do more truck spraying Thursday,” said Gayle Love, a spokeswoman for Miami-Dade County Solid Waste Management.
Zika prevention kits and mosquito repellent – strongly recommended for women who are pregnant or planning to be – are being distributed in the area and can be picked up at the health department as well.
Crews in Utah, meanwhile, are setting traps in old tires and junkyards and dumping mosquito-eating fish into ponds and abandoned pools after a man who cared for his dying father was infected with Zika as well. Since that case doesn’t involve travel or sex, it has raised more questions about how the virus might spread.
“Our best option is to try find these mosquitoes quickly so that way we can eliminate them prior to their establishment,” said Ary Faraji, manager of the Salt Lake City Mosquito Abatement District. “Once they become established, it is extremely difficult to get rid of those species.
There is no vaccine for Zika. The main defense is to avoid mosquito bites. Zika also can spread through unprotected sex with someone who is infected.
In most people, Zika causes only a mild and brief illness, at worst. But it can cause fetal death and severe brain defects in the children of women infected during pregnancy.