1.   Hantavirus is contracted primarily by inhaling airborne particles from rodent droppings, urine or saliva left by infected rodents or through direct contact with infected rodents.

2.   Otherwise, you may be inhaling unburned particles.

3.   Smaller particles can be inhaled all the way into the lower lung.

4.   They may also be exposed by inhaling dirt particles or tracking dirt inside their homes, said co-researcher Kimberly Gray, a Northwestern University environmental engineer.