KENNEWICK — Two people, in addition to two horses, have been recently sickened with West Nile virus in Eastern Washington.
The Washington state Department of Health announced late Monday afternoon that the virus had been confirmed in a Franklin County resident and a Walla Walla County resident.
Both had been diagnosed with the mosquito-borne virus within the past week, and each were likely infected in the county where they lived.
The Department of Health announcement followed one earlier in the day by the Washington state Department of Agriculture, which said cases had been confirmed in a horse in Franklin County and a horse in Grant County.
They were the first four cases of the mosquito-borne illness confirmed in Washington state people or horses this year, other than a case in a person believed to have been infected while out of state.
The Benton County Mosquito Control District said in August that it was seeing the worst year for West Nile virus since 2009.
Eighty samples of mosquitoes collected this year in the state have been positive for West Nile virus. There were 19 in Benton County, 29 in Grant County, 32 in Yakima County and none elsewhere in the state.
In 2022 just six samples collected statewide were positive for West Nile virus.
The state Department of Health on Monday urged the public to avoid mosquito bites and urged health care providers and veterinarians to consider West Nile virus if symptoms were present.
“Most cases of West Nile virus are mild,” said Dr. Amy Person, a Department of Health regional medical officer. “However, serious illness and death are also possible. That’s why we urge people to take precautions to avoid mosquito bites and to contact their healthcare provider if they develop symptoms.”
Most people and animals who are bitten by mosquitoes infected with West Nile virus develop no symptoms.
About 1 in 5 people who are infected will develop fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash.
Most people recover completely, but fatigue and weakness can last for weeks or months.
Serious illness occurs in fewer than 1 in 100 people infected with West Nile virus. The risk of severe infection is highest among people 60 or older and people with certain medical conditions such as cancer, diabetes, hypertension and kidney disease.
The last death of a person reported from the virus in the Tri-Cities was a woman in her 70s in 2016.
There is no vaccination against the virus for people, but horses can be vaccinated.
2 cases in horses
The two horses infected were either unvaccinated or not fully vaccinated, according to the Washington state Department of Agriculture.
“We have seen a decline in Washington state in recent years of this virus in horses, and we believe that is due to horse owners taking action before the season with vaccination,” said Amber Itle, the state veterinarian.
The disease is fatal in about a third of cases in which horses develop symptoms.
However, both horses infected this month are recovering.
Most horses that are infected do not become ill. Those that do can lose coordination and appetite and have confusion, fever, stiffness and muscle weakness in their hindquarters.
Vaccination for horses is recommended in the spring, with an annual booster shot also in the spring. But horses can benefit from a vaccination or booster any time of the year, according to the Department of Agriculture.
The West Nile virus is spread by mosquitoes that have fed on infected birds and does not spread directly from horses to people or other animals.
Preventing West Nile virus
In addition to vaccinating horses, their owners can limit exposure to mosquitoes.
They can eliminate stagnant water, stable horses at dawn and dusk when mosquitoes are most active, use mosquito repellents approved for horses, place fans in barns and stalls to keep air moving, and avoid using incandescent bulbs inside stables at night.
The best way for people to prevent the disease is to take steps to lessen the chance of a mosquito bite until the first hard frost of the year.
The Benton Franklin Health District recommends:
- Drain sources of standing water around your home each week so mosquitoes do not hatch. The mosquitoes most likely to spread West Nile virus prefer to breed in water found in containers, tires, buckets and other small sources of stagnant water. One female mosquito can lay 250 eggs in a batch that can turn into 250 adults within a week.
- If possible, stay indoors during prime mosquito-biting times — dusk and dawn.
- If you go outside at those times use a mosquito repellent with ingredients approved by the Environmental Protection Agency, including DEET, picaridin, PMD, IR3535 or oil of lemon eucalyptus
- Make sure doors and windows have tight-fitting screens. Windows and doors without screens should be kept shut, especially at night.
- Dress with long sleeves, pants, and a hat when mosquitoes are present.