West Nile virus activity hits ‘record’ high in some parts of Sacramento area. Here’s where
Mosquito control officials reported “record” levels of West Nile virus in some portions of the Sacramento region this week, as ongoing hot weather in Northern California continues to hatch large populations spawned due to heavy winter rainfall.
The Placer County Mosquito and Vector Control District on Wednesday said it has tallied 66 mosquito samples and 10 dead birds testing positive for the virus this year, less than a month after Placer’s first cases were detected in late June. The district said the latest mosquito total is a record high for the county.
“Under these conditions, West Nile virus transmission risk from a mosquito bite is very high,” Placer County district officials said in a news release.
Aerial- and ground-based mosquito control measures have been underway for about a month, with the district spraying for both adult and larval populations in parts of Placer County including Roseville.
The Sacramento-Yolo Mosquito and Vector Control District in a separate news release Wednesday said already-high levels of West Nile activity have “intensified” in recent days in parts of those two counties.
“Virus activity continues to be widespread and very intense,” Gary Goodman, the manager for the Sacramento-Yolo district, said in a statement.
Officials in 2023 have detected 83 mosquito samples and 46 dead birds in Sacramento County, up from 69 and 43, respectively, last week. In Yolo County, 14 more mosquito samples were found, bringing the 2023 total to 47 from 33; the dead bird total did not change.
The district said it has “intensified ground mosquito control efforts conducting treatments in urban and agricultural areas where mosquitoes have been found to be breeding” in Sacramento and Yolo counties.
The two districts say particular areas of concern include the South Natomas, Tahoe Park and Elder Creek areas within the city of Sacramento; Davis and Woodland in Yolo County; and west Roseville, Lincoln and Newcastle in Placer County, as well as rural parts of western Placer.
State and local mosquito control officials urge residents to drain standing water to limit mosquito breeding; wear insect repellent that contains DEET, picaridin, oil of lemon eucalyptus or IR3535; secure doors and window screens in good working condition; avoid being outdoors at dawn and dusk if possible; and wear long sleeves and pants when outside.
California’s hot weather contributes to West Nile
The California Department of Public Health issued a warning in late June noting that record rain totals this past winter have led to increases in mosquito populations.
Extreme heat also exacerbates West Nile activity by speeding up the hatching of mosquitoes, officials say.
The Sacramento region is forecast to reach high temperatures above 100 degrees Thursday through Saturday, according to the National Weather Service, and to hit 99 degrees Sunday.
CDPH as of last Friday reported 533 cases of West Nile virus in mosquito samples and 90 in dead birds so far in 2023 – increases of 250 mosquitoes and 25 birds compared to one week earlier. The state has reported 50% more cases in mosquitoes to date than in 2022, and nearly four times as many in dead birds.
No human cases have been reported by state health officials in 2023 as of Thursday. Last year, California detected 216 human cases including 15 fatalities.
What are West Nile virus symptoms in humans?
West Nile virus in humans often results in mild or no symptoms, but in severe cases the disease can be deadly. Many people can recover from West Nile virus at home, but about 20% of those bitten develop symptoms of West Nile fever.
Roughly one out of every 150 people bitten by an infected mosquito gets the most severe form of the disease, West Nile encephalitis.
Symptoms of severe West Nile virus include sudden onset of high fever, severe headache, nausea, vomiting, sore throat, backache, joint pain, aches and weakness in prominent muscles, prolonged fatigue and swollen lymph nodes. Those with West Nile fever may also get a rash.
