After the wettest spring in 81 years, high water has settled into stagnant pools across Multnomah County, creating a breeding ground for the largest mosquito outbreak since at least 2010. And the worst is yet to come.
Multnomah County Vector Control, the team that conducts mosquito surveillance and control, inspects breeding habitats for mosquitos and monitors for the presence of mosquito-borne disease. Each year, May-September, the team sets traps in 150 locations and subsequently sends batches to Oregon State University for testing. To date this year the team has trapped over four times the total for all of 2021.
Multnomah County’s batches have never yet returned positive results for West Nile virus. But samples from other parts of Oregon routinely come back positive. Last year, ecologists identified West Nile virus in 75 batches of mosquito samples taken across eastern and southern Oregon.
To limit West Nile and other diseases, Multnomah County uses an integrated mosquito management approach designed to keep mosquito populations at a safe level, not eliminate them. Emilio DeBess, public health veterinarian for the Oregon Health Authority said, “A lot of people say there are no mosquitoes in Multnomah County. That’s because Vector Control does an amazing job of controlling mosquitoes.”
However, since there are still some of those annoying mosquitoes buzzing around, the community is urged to do their part to prevent the mosquito population from growing by dumping standing water around their homes. Mosquitoes can breed in as little as an inch of water. Dumping or regularly changing standing water in kiddie pools, buckets and dog bowls can prevent their reproduction.
Taking protective measures like repairing damaged window and door screens, wearing long sleeves, using bug spray when around mosquitoes and minimizing time spent outside during dawn and dusk when mosquitoes are at their worst, will reduce the chance of being bitten.
In addition to producing itchy bumps or welts, mosquito bites can also transmit West Nile Virus. The illness is mild in most people but in rare cases it can be fatal. Often if West Nile is in an area, crows will start dying before mosquitoes or humans test positive. Report newly-dead crows (within 24 hours of death). Do not report crows that have clearly been hit by a vehicle or electrocuted (hint: look for burned -off feet).
Mosquito facts: a female mosquito can lay up to 300 eggs at a time; it takes just 10 days for an egg to become a blood-sucking adult; mosquitoes hunt us by sensing the carbon dioxide we exhale up to 30 feet away and gauge proximity using our body temperature; mosquitoes can travel up to 20 miles, the equivalent of flying from downtown Portland to Vancouver and back again.
Photo by Multnomah County