Hantaviruses are a group of viruses that are transmitted by rodents through urine, droppings, and saliva. One of them, Sin Nombre virus, is found in deer mice in North America. Sin Nombre virus is the cause of Hantavirus Pulmonary Syndrome (HPS) in humans.

Hantaviruses belong to the Bunyaviridae family of viruses. There are five genera in this family: Orthobunyavirus, Nairovirus, Phlebovirus, Tospovirus, and Hantavirus. Like all members of this family, hantaviruses have a genome comprised of three negative-sense single-stranded RNA segments, and so are classified as negative sense RNA viruses.

Inhalation of dust contaminated by rodent excreta or saliva can result in transmission of these viruses to humans. Infected people will develop HPS one to six weeks after inhaling the virus. The disease begins with 2-6 days of flu-like illness including fever, muscle soreness, headache, nausea, vomiting and fatigue. As the disease progresses it causes shortness of breath due to fluid filled lungs; hospital care is then required. It is usually a serious infection and about 1 out of 3 infected patients have died.

The deer mouse (Peromyscus maniculatus) is the main carrier of hantaviruses in the western United States but other wild rodents may also be potential carriers. The deer mouse can carry and shed the virus without showing any clinical signs. In one study, it was shown that about 14% of over 1,100 deer mice in Washington State had been infected with Sin Nombre virus.

HPS is not known to be transmitted from one person to another, nor to be transmitted by farm animals, dogs, cats or rodents purchased from pet stores.