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Mosquitoes That Spread Zika are Becoming Resistant to the Pesticides Targeting Them

An Aedes-Aegypti Mosquito
European Centre for Disease Prevention and Control
An Aedes-Aegypti Mosquito

Researchers are seeing that the species of mosquito that spreads Zika virus is growing resistant to pesticides.

The Zika virus came to light in Florida five years ago, with a South Florida outbreak of 224 reported cases, according the Centers for Disease Control (CDC).

Zika can have a devastating effect on pregnancies, newborns, and family planning. The disease carries an increased risk of neurological complications in adults and children.

And it all starts with a bug: namely, a mosquito that carries the virus. And those disease-carrying pests have shown resistance to insecticides specifically developed to prevent the spread of the disease, say University of Florida scientists at the Institute of Food and Agricultural Sciences (UF/IFAS). Their published study examines a specific species of mosquito responsible for transmitting the Zika virus that is resistant to chemicals designed to kill them.

“Here we demonstrate a causative link between the development of insecticide resistance in a mosquito and how it interacts with a pathogen it transmits,” said Barry Alto, a co-author in the study and an associate professor at UF/IFAS Florida Medical Entomology Laboratory in Vero Beach.

The chemicals, known as pyrethroids, have been used in mosquito control and residential products since the early 1960s, the researchers say. In Florida, these chemicals make up about 90% of insecticides currently deployed via ground application for mosquito control. Casey Parker-Crocket, Ph.D., lead author of the recent study in the Journal of Medical Entomology, now works in the mosquito control industry. The study indicates a need to consider insecticide resistance and “to implement insecticide-resistance management and mitigation strategies in mosquito-control programs,” she says.

The study utilized Aedes aegypti, a species widely distributed throughout the state and commonly known as the “yellow fever mosquito.” Parker-Crocket says this particular species is exceptionally difficult to control.

“Our research is telling us that insecticide-resistant mosquitoes are replacing susceptible mosquitoes, both capable of transmitting the Zika virus,” she says.

Researchers learned that mosquitoes resistant to this major group of pyrethroids were also more likely to have an advanced infection of the Zika virus, a critical factor for further investigation.

“What we found is that more mosquitoes are making it to the stage of infection where they have the opportunity to transmit the virus to a human through blood feeding,” said Parker-Crockett. “This finding is important to the public health professionals … and to the general public who have even more of a reason to protect themselves from mosquito bites.”

Equally concerning is that the Zika virus is a risk for travelers in parts of the world where outbreaks are common. In 2016, there were 4,897 travel-related cases throughout the United States. The following year, the CDC reported seven locally transmitted cases and 437 travel-related cases in the U.S.

While the numbers have decreased, Zika is still a threat due to travel-related cases that are spread upon U.S. entry.