Hantavirus Pulmonary Syndrome (HPS) is a severe illness caused from exposure to the droppings or urine of deer mice that carry the virus. About 1- 5 hantavirus cases are reported each year in Washington State and about one third of the cases have been fatal.antavirus Pulmonary Syndrome (HPS) is a severe illness caused from exposure to the droppings or urine of deer mice that carry the virus. About 1- 5 hantavirus cases are reported each year in Washington State and about one third of the cases have been fatal.