Elevated Threat from Hantavirus in Parts of Western Washington

Juvenile deer mouse. He must have been fearless or ill.
I took this with an iPhone at close range. 

Update to elevated hantavirus risk warning issued April, 5.  As of April 26, 2017, the invasion of Deer mice appears to be continuing. With the spring weather they are in their breeding season and are at least as much of a threat as they were during the period in which the three recent confirmed cases occurred. For this reason, The warning I'm extending the warning issued below until further updates. The risk will likely decline with dry, warm, summer weather, if we get that. 

A cluster of sin nombre hantavirus cases comprising at least three people has occurred in Western Washington. This, combined with observations of the local environments of these patients, makes it possible and appropriate to warn of an elevated risk of contracting hantavirus in similar areas for the near future. This warning is intended to have greater specificity than those issued by local health authorities.

Observations have confirmed that all three of these recent hantavirus patients, along with an earlier (1999) case near Monroe, lived in areas with significant populations of big leaf maple trees. These trees have recently produced very large crops of maple seeds that are a favored food for deer mice, the local reservoir species for hantavirus. This has resulted in what appears to be greater abundance of deer mice in the area.

In general, a higher population of deer mice leads to a higher portion of the deer mice contracting hantavirus, and to more of them shedding hantavirus particles in their urine and feces.

This means that it is likely that there are both a greater number of deer mice, and that they shedding a greater amount of hantavirus than is usually the case.

In addition, heavy rainfall in Western Washington has placed these deer mice under environmental stress, their food sources are now depleted and rotting and their underground burrows are often flooded. As a result, there exists an increase in the number of deer mouse intrusions into human homes, vehicles, outbuildings, garages, and vehicle cabin air handling systems.

It is probable that: In areas where big leaf maple trees grow, which includes much of the Western Washington lowland forest region, from the foothills of the Cascades to near coastal areas,

Big leaf maples trees with massive seed clusters.
 Fall, 2016.  The leaves are 10" to 12" across.

a higher abundance of deer mice shedding hantavirus particles at a greater than usual rate, combined with an increased rate of incursion into human environments, has produced an elevated risk of humans contracting hantavirus. 

If your property has big leaf maple trees, or adjoins areas that do, you should take particular care to avoid breathing in dust from mouse debris. This includes extra caution cleaning garages, outbuildings, vehicles, and other areas where these extremely common mice have intruded.

Areas without these trees may also see an increased risk because of ground water saturation driving mice from burrows and rodent spillover from adjacent areas.

The cabin air handling system in a vehicle is suspected in one of these local cases. The filters in these systems in automobiles, trucks, and tractors that have been parked in areas with big leaf maple trees should be inspected for rodent infestation and replaced as needed. Inspection should take place while wearing respirator mask and gloves.

I posted a more detailed analysis of this threat weeks ago, before the third recent local case was reported. Some of the qualifying words could be adjusted, but most of this discussion from March 17 is still correct.
http://www.hantasite.com/2017/03/are-seattles-cascade-foothills.html

For detailed directions for cleaning up deer mouse debris, look here for a CDC brochure.

The following segment from KIRO–7 news in Seattle gives an excellent summary of current developments. KIRO–7 3rd Hantavirus Case