West Nile virus, St. Louis encephalitis found in Yuma County mosquitoes

YUMA — Just more than three weeks after West Nile virus claimed the life of the 74-year-old resident of Imperial Valley’s Bombay Beach, neighboring Yuma County has confirmed mosquitoes there have tested positive for both West Nile and Saint Louis encephalitis.

The Yuma County Pest Abatement District has reported that nine separate samples of mosquitoes collected last week from riparian areas in Yuma County have tested positive for one of the viruses, which can be transmitted to humans through mosquito bites.

The samples were taken along several locations on the Colorado River and around County 12th Street and Avenue F, and insects in those pools tested positive for Saint Louis encephalitis and West Nile virus, district manager Elene Stefanakos said.

She said the district’s monitoring, which began in March, shows mosquitoes have transmitted the viruses in riparian areas in several locations on the Colorado River, in the western part of the county around County 12th Street and Avenue F, in the Yuma Valley and in northwest Yuma.

YCPAD staff have sprayed these areas by ground-fogging trucks to eliminate infected mosquitoes.

The mosquitoes for the most recent samples were collected July 15. YCPAD has found 75 positive mosquito pools with St. Louis encephalitis this year, along with six sero-conversions in sentinel chicken flocks, which shows the virus is being transmitted to other animals in the area.

“For St. Louis, (the number) is higher, because we haven’t seen a lot of St. Louis encephalitis for a few years,” Stephanakos said. “We had some in ’16, none in ’17 and a little tiny bit at the end of ’18.”

For West Nile virus, they have found a total of 11 positive mosquito pools and 3 sero-conversions from sentinel chicken flocks. The number of West Nile cases isn’t out of the normal range, she said, but it began showing up earlier than normal.

The first positive test for St. Louis encephalitis was recorded May 6, while the first for West Nile showed up on June 7.

Six pools have tested positive for both diseases this year, the first time that’s happened in the county, Stephanakos said.

What’s also happening this year is that this month, when the mosquito population is usually in decline, positive samples are showing up regularly in the smaller samples being collected.

The nets used to collect mosquitoes usually pick up about 40 this time of year, versus 200 or more when the population is at its peak.

“It’s concerning because even though there’s a little bit of mosquitoes out now, the amount of mosquitoes that are positive for the virus is high,” Stephanakos said. “And in another month or two, we’re going to have a big increase in mosquitoes, so if we keep on going with this trend, that’s why it’s concerning.”

In Imperial County, Robert Mears, a resident of Bombay Beach became California’s first confirmed death from West Nile virus in 2019 when he succumbed to the disease on July 4 at UCSD Medical Center in San Diego.

West Nile virus is transmitted to humans and animals through a mosquito bite. Mosquitoes become infected when they feed on infected birds. Human-to-human transmission of WNV generally does not occur absent a blood transfusion or tissue donation from an infectious donor.

Severe symptoms of WNV include fever, nausea, vomiting and seizures. Most individuals who are infected with WNV will not experience any illness. Others will have only mild symptoms, such as fever, headache and body aches. However, WNV can be severe in the elderly and individuals with lowered, compromised immune systems.

The Imperial County Public Health Department said individuals can reduce their risk of mosquito-borne diseases by taking the following precautions:

• Limit time outdoors during dawn and early evening.

• When outdoors, wear loose-fitting, light-colored, long-sleeve shirts and pants when mosquitoes are most active (during dusk and dawn).

• Apply insect repellent that contains DEET, Picaridin or oil of lemon eucalyptus according to label instructions to prevent mosquito bites.

• Make sure that doors and windows have tight-fitting screens. Repair or replace screens that have tears or holes.

• Eliminate all sources of standing water on property that can support mosquito breeding by:

Draining or eliminating, old tires, buckets, plastic covers, toys, or any other container where mosquitoes can breed.

Empting and changing the water in bird baths, fountains, wading pools, rain barrels, and potted plant trays at least once a week to destroy potential mosquito habitats.

Draining or filling temporary pools of water with dirt.

Keeping swimming pool water treated and circulating.

• Contact Vector Control if there is a significant mosquito problem where you live or work.