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August 27, 2025
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Jackson County Vector Control District finds Aedes aegypti mosquitoes second year in a row
County’s August 2024 discovery of species was Oregon’s first
PORTLAND, Ore.—Aedes aegypti (Ae. Aegypti) mosquitoes have been discovered again in Jackson County, a year after Oregon Health Authority (OHA) and the county announced the species had been found for the first time in the state.
OHA, Jackson County Vector Control and Jackson County Public Health confirmed the identification of Ae. aegypti as part of routine mosquito surveillance.
Emilio DeBess, D.V.M., state public health veterinarian in OHA’s Public Health Division, said the repeat appearance of Ae. aegypti in Oregon is a concern because the species has been more common in much warmer climates of the United States, Southeast Asia, Africa and the Pacific Islands.
“These mosquitoes have been known carry and transmit diseases that are more typical to warmer climates, such as Zika virus, chikungunya, dengue and yellow fever,” DeBess said. These viruses spread to humans through the bite of an infected Ae. aegypti mosquito, he said.
The mosquitoes become infected when they bite and feed on someone who is infected with the virus. They primarily feed in the daytime and prefer to feed on humans.
However, DeBess emphasized that the risk of these infections to local residents is low. “Acquiring these diseases depends on the presence or arrival of someone who is currently infected with one of the diseases after infection outside the United States,” DeBess said. “As was the case when Ae. aegypti mosquitoes were first found in Oregon in 2024, there have been no reports of anyone having acquired viruses associated with Ae. aegypti from within the state.”
Routine mosquito surveillance monitors different mosquito populations in the county and tests for diseases such as West Nile virus and Western equine encephalitis that are common to the Culex mosquito genus. It also gives Jackson County Vector Control the ability to determine human risk and implement strategies to control these insects and prevent disease spread.
Adult Ae. aegypti mosquitoes are relatively small and have a black-and-white pattern due to the presence of white/silver scale patches against a black background on the legs and other parts of the body. Ae. aegypti mosquitoes most likely originated in Africa. Since then, the species has been transported globally throughout tropical and subtropical regions, and parts of the temperate world, through global trade and shipping activities.
Ae. aegypti cannot fly far—only about 500 feet. These mosquitoes prefer warm and wet weather, and to live in or near homes or in neighboring woods. Changes in climate are allowing Ae. aegypti mosquitoes to expand their range to the western United States.
Prevention
Invasive Ae. aegypti mosquitoes need only a quarter inch of water to complete their life cycle. The key to preventing these mosquitoes from becoming an established vector in Jackson County will be to eliminate standing water, even small amounts, and moisture from yards and gardens. Common mosquito breeding sources include flowerpot saucers, tires, kiddie pools, rooted plants in water, containers/buckets, and pet water bowls.
“Many prevention methods that work for other types of mosquitoes apply to Aedes aegypti,” said Geoff Taylor, manager of Jackson County Vector Control.
Those methods include:
- Dumping or draining any standing water around the home.
- Removing containers or objects that can hold water from your yard, such as water saucers from under plants, old tires, tarps, buckets, containers, toys, and other equipment.
- Repairing leaky outdoor faucets.
- Keeping rain gutters cleared.
- Covering, screening, or removing rain barrels, trashcans, bins, buckets, or tubs.
- Wearing mosquito repellent outside. Repellents containing DEET, picaridin, IR3535, some lemon eucalyptus, and para-menthane-diol products are most effective at preventing mosquito bites.
- Sleeping under a mosquito net when outside or in a room without screens.
DeBess explained that identification of Ae. aegypti demonstrates why mosquito trapping by local vector control agencies is so important. It allows for tracking and monitoring of different types of mosquitoes, and it gives state and local agencies advanced warning on the potential spread of a species so they can take steps to reduce health risks in the population.
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