As of Sunday afternoon, there were 34 confirmed cases of measles in Clark County, just north of Portland, Oregon, and one in King County, which includes Seattle.
"Measles is a highly contagious infectious disease that can be fatal in small children", Inslee said in the declaration.
Health officials in OR have raised concerns that the virus could easily cross the border.
Thirty-one patients had not been vaccinated against measles, and the status of four others who were infected is not known.
Children under the age of one can not be immunized.
In the Clark County cases, numerous infected folks visited hubs in the community where there are larger crowds. The first known patient sought medical care on December 31, but it isn't known if other people may have gotten sick before that and did not seek treatment.
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In the USA last year, there were 17 outbreaks and about 350 cases of measles.
On Jan. 16 health officials out of Denver alerted the public of a measles exposure in Colorado.
The Washington Military Department, the release says, is organizing resources to assist the DOH and local officials in easing the effects on people, property and infrastructure. Clark County's immunization rate for school-aged children is 78 percent, and a large majority of these cases were in children who were not vaccinated.
Before the vaccine, 400 to 500 people died from the measles each year, 50,000 people were hospitalized and 4,000 people developed brain swelling that can cause deafness, he said.
"The bottom line is, there's no surprise we're seeing this right now", Melnick said. "And then you see another generation of cases", he said. Measles was declared eliminated - defined by absence of continuous disease transmission for greater than 12 months - from the United States in 2000. The measles virus is transmitted by air very easily, and people are contagious several days before they show any symptoms.
Both Washington and OR allow vaccine exemptions for personal and philosophical reasons.
Doctors say the full vaccine is 97 per cent effective and protects you for life. Symptoms such as high fever, rash all over the body, stuffy nose and red eyes typically disappear without treatment within two or three weeks. The disease is so contagious that 90 per cent of unvaccinated people who are exposed will catch it.