Many hantaviruses are known to cause hantavirus pulmonary syndrome (HPS). Each virus has a single primary host. The most important hantavirus in the US is the Sin Nombre virus, hosted by the deer mouse.
Local enzootic transmission of hantaviruses occurs at low levels during periods of unfavorable environmental conditions.
Favorable environmental conditions such as mild winters and summer rainfall may cause dramatic increases in rodent populations. More rodents become infected under crowded conditions. Deer mice may enter human structures in rural areas. Humans may become infected when they inhale airborne virus or come into direct contact with infected rodents or their urine, feces, or nests. Other mammal species (cats, dogs, coyotes) may be infected through contact with rodent hosts, but they are not known to transmit the virus.
The virus is maintained and transmitted by host reservoir rodents by horizontal transmission (aggressive behavior, biting).