Wednesday, April 17

ZIKA-Infected Mosquitoes Can Harbor Insecticide-Resistance, UF Study Shows

Female Yellow fever mosquito, Aedes aegypti. Photo taken 03/14/16.

Boca Raton, FL – When a disease-carrying mosquito begins to show resistance to insecticides that were developed specifically to prevent the spread of the disease, the threat to public health becomes a critical issue. 

University of Florida scientists at the Institute of Food and Agricultural Sciences (UF/IFAS) have published a study that looks at the resistance to commonly used insecticide chemicals designed to kill a specific species of mosquito responsible for transmitting the Zika virus. 

“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 public health mosquito control and residential products since the early 1960s, according to researchers. To date, only two other studies have explored the impact of insecticide resistance in infected mosquitoes that spread West Nile and dengue viruses to humans by biting them. In Florida, these chemicals make up approximately 90% of insecticides currently deployed via ground application for mosquito control.

“We have to be better stewards of insecticide use,” said Casey Parker-Crocket, lead author of the study published today in the Journal of Medical Entomology and a recent UF/IFAS PhD graduate who now works in the mosquito control industry. “Our findings support the need to consider the status of insecticide resistance during times of virus transmission, and to implement insecticide-resistance management and mitigation strategies in mosquito-control programs.” 

The study utilized Aedes aegypti, a species widely distributed throughout the state and commonly known as the yellow fever mosquito, as the subject of the experiment conducted in the center’s biosafety lab. 

“This is a species that is a source of frustration for mosquito control professionals because it is exceptionally difficult to control,” said Parker-Crocket. “These mosquitoes are ubiquitously distributed throughout the state and our research is telling us that insecticide-resistant mosquitoes are replacing susceptible mosquitoes, both capable of transmitting the Zika virus.”

Researchers learned that mosquito resistance to this major group of pyrethroids were also more likely to have an advanced infection of the Zika virus as well – a key to explore in future research. 

To get to the heart of the matter, UF/IFAS researchers pondered whether mosquitoes that are resistant to insecticides are any better (or worse) at transmitting the Zika virus compared to their counterparts that are not resistant to insecticide? 

When mosquitoes ingest virus infected blood, the virus goes through an infection process throughout the mosquito’s body before it reaches the salivary glands where they can transmit the virus, explained Parker-Crockett. Through that process, there are barriers to infection in the gut and salivary glands  that the virus must overcome before the mosquito becomes infectious and capable of transmitting virus by bite. If the virus cannot overcome those barriers, the mosquito is never able to transmit the virus.

For the experiment, there were 507 female Aedes aegypti mosquitoes used that represented two separate colonies – a colony selectively-bred to be insecticide-resistant and a colony susceptible to insecticides. The colonies were bred from two existing groups colonized by the USDA as early as the 1950s.  

“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 that we entrust with protecting us from vector-borne disease and to the general public who have even more of a reason to protect themselves from mosquito bites.”

The Zika disease can have a devastating effect on pregnancies, newborns, and couples looking to conceive. An increased risk of neurologic complications is also associated with the virus infection in adults and children. Equally concerning is that the Zika virus is a risk for travelers in parts of the world where outbreaks continue to exist. 

Zika virus came into light for the first time in Florida in 2016, when an outbreak occurred in South Florida with 224 reported cases according the Centers for Disease Control (CDC). Meanwhile, there were 4,897 travel-related cases throughout the United States that same year. 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.

Co-authors of this paper are Blair Siegfried, Department Chair for UF’s Entomology and Nematology Department, and Roxanne Connelly, who was a member of the faculty at the UF/IFAS Florida Medical Entomology Lab and is now the Chief Entomologist at the Centers for Disease Control in Fort Collins, CO. 

The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human, and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries and all Florida residents.  |  @UF_IFAS

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