Modified mosquitoes can cut back the danger of illness for people and animals

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A female Aedes aegypti mosquito receives a blood meal from a human host. (Photo by James Gathany / CDC)

Plans to release genetically modified mosquitoes in the Florida Keys should benefit humans and possibly animals as well.

In August, Florida Keys Mosquito Control District officials approved plans to work with biotechnology company Oxitec to drive the company’s genetically modified Aedes aegypti mosquitoes away from 2021 with the aim of reducing the population of these mosquito species and the risk of human disease from dengue fever to reduce and reduce Zika virus infection, according to a company announcement and regulatory filings. The target mosquito species feed primarily on humans, although studies have found differences in the frequency of their diet with other animals.

The mosquitoes produced by Oxitec are modified with a genetic kill switch for female larvae. These larvae survive in the presence of tetracycline but die when the drug is taken from their diet, allowing the company to maintain a breeding population and distribute an all-male population to mate with wild female mosquitoes. This emerges from the information provided by the company at the environmental protection agency.

The males are homozygous for a dominant gene that kills female offspring. Therefore, their heterozygous offspring wear the kill switch and continue to reduce the wild population over generations. Oxitec records indicate that when the company tested previous versions of the mosquitoes in Brazil, the Cayman Islands, and Panama, it found reductions in Aegypti populations.

Company spokeswoman Meredith Fensom said two years of trials in Brazil had reduced the local mosquito population by 96%.

Rhoel R. Dinglasan, PhD, is Professor of Infectious Diseases at the University of Florida, Chair of Research in the University of Infectious Diseases and Immunology College of Veterinary Medicine, and Director of the Southeastern Regional Center’s Centers for Disease Control and Prevention of Excellence in Vectors transmitted diseases. Citing an article published in Viruses magazine this April, he said that not all Aegypti populations have the same eating habits.

In that study, researchers in Texas who caught Aegypti mosquitoes near the southern border found that 50% of blood meals were from dogs and 30% from humans. However, the article notes that the study came from a region of low human density compared to wildlife and that in 18 previously published studies of A aegypti blood meal analysis, the mosquitoes were human-fed 84% of the time.

Dr. Dinglasan said the A aegypti that feed on dogs can transmit Dirofilaria immitis larvae – a risk that is increased from stray dogs in the Florida Keys – and those that feed on birds can transmit avian malaria parasites that cross affect perching birds. One of those bird malaria parasites, Plasmodium relictum, was found among sparrows in Tampa, he said.

Reducing the Aegypti population could reduce the risk of disease for dogs and birds, including migratory birds that travel through Florida’s wetlands, said Dr. Dinglasan. The intervention could have additional unidentified benefits for animals, he said.

John Beckmann, PhD, assistant professor of biotechnology at the Institute of Entomology and Plant Pathology at Auburn University, does not expect any effects on animal populations. He said that Aegypti mosquitoes are adapted to feed on humans, and that the viruses these mosquitoes carry are also adapted to humans and other primates.

When asked by JAVMA, Dr. Beckmann with his medical-veterinary entomology course on the possible effects of mosquito release and provided a video of the discussion. In the video, he said the modified mosquitoes would likely be safer and more effective than insecticides in reducing the Aegypti population, without the untargeted effects of spraying insecticides on ponds and lakes.

“I would vote to release these mosquitoes in my hometown if I was plagued by Aedes aegypti,” he said.

correction: In an earlier version of this article it was incorrectly stated that the mosquitoes were genetically engineered rather than genetically modified.

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