So far, in the United States 258 people have shown up at hospitals with the Zika virus – the mosquito-borne disease that has spread frighteningly quick through much of Latin America.
None of them acquired the illness from a bug bite in the U.S., the Centers for Disease Control and Prevention reports. But that may only be a matter of time.
Fresno is in a recent study that lists 50 U.S. cities where the six-legged, blood-sucking transmitter of the virus – the mosquito Aedes aegypti – would be able to survive in the upcoming summer months. Four California cities join Fresno on the list: Sacramento, Bakersfield, Los Angeles and San Diego. All five could have a “low abundance” of the virus-carrying mosquitoes by July, says the study, published by PLOS Currents: Outbreaks.
The Fresno County Department of Public Health has tested six people for Zika this year. Four of those tested were women – three were pregnant and one had recently delivered. The four women all tested negative for Zika. Results for the two men are pending, said Dr. Kenneth Bird, the health officer for Fresno County.
The Aedes aegypti mosquito can spread other infections, and since the beginning of 2014, the Fresno health department has reported nine cases of chikungunya and three dengue cases. All were from travel exposure, Bird said.
“It is extremely important that individuals protect themselves from mosquito bites when traveling to areas where there is active transmission of these illnesses,” Bird said. “Pregnant women, women planning pregnancy, and male partners of these women should avoid travel to areas where Zika is active, but discuss it with their health care provider if they do. A last caution is to take extra steps to avoid mosquito bites back here at home, at least for two weeks, when returning from these areas.”
California has had 21 travel-associated confirmed cases of Zika since 2013, and 12 of the cases have been reported this year. Contra Costa, Los Angeles, Orange, San Bernardino, San Diego, San Francisco, San Joaquin and Yolo counties have had cases in 2016, according to the California Department of Public Health.
The Aedes aegypti has established itself in the central San Joaquin Valley in the past three years, said Steve Mulligan, manager of Consolidated Mosquito Control District, which handles mosquito abatement for Clovis.
The mosquito thrives in backyards, and Mulligan said small containers can be breeding grounds. “With the rain that we’ve had, people need to check around their homes, their yards and eliminate any containers that would hold water,” he said.
The district has tried innovative methods to control the mosquito, and this summer it could try a new strategy of releasing male mosquitoes infected with Wolbachia, a bacterium. When the infected males mate with female mosquitoes, the embryos will not develop, Mulligan said. But the Aedes aegypti is a backyard problem that makes it difficult for vector control districts to access.
Study: 9 cities could have ‘high abundance’
Nine U.S. cities, home to an estimated total of 14 million people, could have a “high abundance” of the mosquito, the new study says. They are Miami, Orlando, Tallahassee, Tampa and Jacksonville, Florida; Charleston, South Carolina; New Orleans; Savannah, Georgia; and Mobile, Alabama.
That doesn’t necessarily mean the U.S. will see a sudden explosion in Zika cases. The finding is just a simulation, based on climate data and other information from the past 10 years. It’s not clear how far north the Aedes aegypti will get, as warmer, wetter weather makes the U.S. more hospitable to the insect, and scientists still are figuring out how exactly the bugs transmit the disease.
It also doesn’t account for vector control practices that could be developed before the situation gets too bad – things like installing window screens or developing an insecticide to which the pests aren’t already resistant.
But the study provides a “baseline risk” level for the country, the researchers write, especially as public health officials gear up for the mosquitoes’ likely arrival. It gives a sense of where and when we should start to be worried.
The cold, dry weather of U.S. winters means that, until now, the potential abundance of Aedes aegypti is relatively low, and the mosquito is likely confined to a few very Southern cities. But that probably will change in the coming months.
To figure out which cities were most at risk of a summer outbreak, the authors examined a few factors: The estimated abundance of the bugs based on the weather conditions and their life cycles, the number of people arriving from Latin America who could carry the virus with them, the past presence of Aedes aegypti as well as cases of locally transmitted dengue and chikungunya, two other diseases that also are transmitted by the mosquito.
Poverty associated with risk
They also looked at the percentage of households living under the poverty line. Poverty is associated with decreased access to things like sanitation, air conditioning and safe housing; the first is important because it limits the amount of standing water in which the bugs can breed, the latter two because they make it less likely that mosquitoes can get into people’s homes.
By July, conditions are suitable across the entire southern half of the U.S. for Aedes aegypti to thrive, particularly in the Southeast. Some of the identified cities never have seen the disease-carrying mosquito before, but it already has been observed along the U.S.-Mexico border and up the East Coast to New York. (The study didn’t include non-contiguous U.S. states and territories – places like Puerto Rico and Hawaii already have been identified as likely hot spots for an outbreak.)
The Zika virus has been linked to a range of birth defects, including microcephaly, which causes children to be born with abnormally small heads and underdeveloped brains. It’s almost certainly the cause of an increase in cases of Guillain-Barr syndrome, which can lead to paralysis. But researchers still are scrambling to figure out who is most vulnerable to infection, how the disease should be treated and whether the mosquito that carries it can be stopped.
“There is nothing about Zika control that is quick or easy,” Thomas Frieden, director of the CDC, said earlier this month during a conference call with reporters. “The only thing quick is the mosquito bite that can give it to you.”
Bee staff writer Barbara Anderson contributed to this report.